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Dead DT50 repair fun

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So last week at rehearsal my DT50 112 insisted on pleading the 5th - I couldn't get a sound out of it.  Fortunately I have my HD500, so I was able to run direct as a workaround (that sure is nice!).  Neither the L6 link nor the front input jacks worked.  So I brought it back home for some debug.  Symptoms:  no output, faint hum, no hiss.  All front panel switches/controls were functional.  No fuses blown.

 

I am lucky enough to have a DT50 212 at home, so I figured I could do some A/B comparisons to see where the problem lie (btw, I'm a hardware design engineer and have been working on electronics and amps most of my life).  I wanted to avoid a) the long drive to the nearest authorized service center, b) the cost of a repair, and c) the dreaded 3 month wait time, so I decided to roll up the sleeves and dig in.  Both amps are out of warranty, so what do I have to lose?

 

First thing I did was eliminate the problem down to a board assembly.  The DT50 has 2 main boards, one is digital and one analog.  Since I could hear a faint hum and some pops when changing topologies, I figured the power amp stage was working.  So the first thing I did was swap digital boards.  Sure enough, the problem did not follow the digital board.  OK, either the analog board or a transformer is the problem.  Next step, swap analog boards.  Sure enough, problem followed the analog board, so that eliminated the transformers.

 

On the analog board, I noticed that V3, the 12AX7 buffer, was not glowing.  V4, the 12AX7 phase inverted was glowing nicely.  I swapped the two tubes and the problem remained on V3, so the tube wasn't the problem.  After some probing around (all I had was a DMM), I found that V4 has an 13V AC heater voltage, while V3 has a diode rectifier that converts the 13V down to 5-6V DC.  So I think the tube wasn't glowing as brightly as V4 due to the lower voltage rather than there being a problem with it.  So this turned into a rabbit trail.

 

So while looking at this, I noticed a relay near V3 whose switching coil pins measured differently from the working amp.  There is a 14 pin connector from the digital board that controls this relay and several others.  It appears that these relays are used to switch in and out the different analog components for the different topologies.  I was able to find that something like 9 pins of the connector control 11 or so relays throughout the board.  Comparing each of the relay controls, I found that there were 3 differences from the working amp.

 

So after hours of poking and pondering and at the point of giving up, I stumbled across one of the relays having a short across the control coil.  Turns out there is a diode that sits across the 2 input pins and the diode was shorted out, preventing the relay from switching.  Fortunately for me, the diode was a 1N4148, a pretty common diode, and I actually had a few sitting in my Nerd Box from college EE labs.  So I swapped out the bad for the good, put everything back together, and sure enough it worked like a champ!  I could not believe it.

 

I wanted to share the experience in case it is helpful to others.

 

Thanks,

Randy

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Nice to know. thanks for sharing your success story. Do you have a picture handy of the relay and diode in the chassis? Would be nice in case I run into it, LOL.

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VERY nice, and competent, diagnostics - I doff my hat to a master.

 

One of the "hats" I wear is in the commercial swimming pool biz - considered something of an expert at a national level.  And on any given day I may be challenged in diagnosing this-or-that issue - equipment, hydraulics, chemistry, control systems - and I've been forced to admit over the years that calm, linear, logical thinking seems to be a dying art.  So in a way (admittedly geeky and kinda weird) I enjoyed your post - gives me hope for the breed...

 

Nicely done!

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Well done Randy! I just read your post and your methodology was perfection! Replies like yours are so helpful and passing the information along will help us amateurs tremendously should we run into the same problem. Nothing worse than waiting to get your amp fixed (correctly if you're lucky) and dishing out hard earned money. I applaud you and all of those on this forum for sharing and making this such a great community.

 

Cheers!!

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So last week at rehearsal my DT50 112 insisted on pleading the 5th...

 

I wanted to share the experience in case it is helpful to others.

 

Thanks,

Randy

 

What a totally awesome post!  Am I weird for enjoying the read?  (I've got an AA in ET, so maybe that explains it?) 

 

You're right--you are lucky to have 2 DT50's!  And while most of us won't be able to simply swap boards like you did, it's good to know that bad diodes can cause stuff like this.  

 

THANKS!!!!  This is good stuff to be able to access when my warranty runs out!!!!

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Thanks everyone for the kind comments.  Funny, I was hesitant to post this thinking it wouldn't be of interest to anyone, but I was certainly wrong!

 

My amp is still acting flaky after this fun repair.  For years now, randomly, the sound will gradually fade out to nothing, and most of the time, fade back in to full volume.  Usually it happens once about 15 minutes after powering up.  Last weekend, it happened 3 times within a 5 minute period, and one of the times it wouldn't come back up.  So I rebooted it and it worked, only to fade again the 3rd time.  I hoped that this problem would disappear when I fixed the diode.  All of this to say that, once again, I think I'm going to be digging in for another attempted repair job.  Only this time will be tough because the problem rarely occurs.

 

Oh, and this is with a brand new set of EH tubes (had JJs, but after the recent threads on tubes, went back to EHs).

 

I'm curious if anyone else has run into this with their amps?

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I'm curious if anyone else has run into this with their amps?

 

I love a post that gets technical, but it's those flakey things that happen to this amp that leads me to believe the intricate parts of this amp may've been made a bit too intricate. I've read quite few threads over the years about issues with this amp and the reliabilty factor being cut down, wheather it be tubes, tranformers or quality of tubes.

 

Don't get me wrong. I love the sound of my new DT50 Head but I can't say it's super reliable yet. I've got high hopes that this amp will be more reliable but I'm not going to get sucidle over it, lol.

 

I hope you find out why you've got this volume swing issue, maybe it's a simple thing.

 

The only thing I can say is before my amp went south the first time. When I powered it up it made a weird noise when I switched the stby and the volume fizzled out, so I powered down, waited a few minutes and powered it back up and was seemingly good until I noticed Topo III was noisier at idle. I used it for a few months off and on at home and it went silent only to find the tubes were cold and the 3 fuses I could check easily where fine. I thought tubes so I bought a matched set of the recommended tubes, installed them, biased them to the recommended setting and the amp was back up but only for a short period of time (around 4 hrs) when this time it went silent while playing. This time I shut it off and waited for it to completely cool down, powered it back it up and it worked good for about 15 minutes and the tubes went cold again. I repeated that cool down thing one more time.

 

I also tried both power tubes from the dead DT in my Picovalve tube amp and they worked fine for hours. This may not be a good test and I'm no expert. I did it out of curiosity.

 

After the second failure it went in for warranty. They said replaced the main board, did tsb 059, and replaced the power tubes. It worked fine for about 12 hours and the next time I powered it up it was silent and the tubes were cold so I proceeded to do another support ticket and it's now at Line 6, hopefully it gets fixed. I know they're good people and trying to fix it for me so I've got faith in them.

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OK guys, after what, almost 2 months, I finally solved my amp problem and learned a ton in the process.  I want to share my experience and learning with everyone.

So my symptoms started with a slow fade-out of sound after 5-10 minutes of playing.  Most of the time the sound would fade back in and be fine, but eventually it just went out completely.  Since I have 2 DT50's, I was able to swap out the analog board between them and verify that the analog board itself had the problem.  Digital board fine, transformers fine, tubes fine.  I called fullcompass.com and asked them about a replacement.  After some digging, they quoted me about $275 and 4-6 weeks lead time.  Since I wanted to spend my money on the new HD500 model packs, I decided to go ahead and debug my board as time permitted.  Why not, if I can always buy a replacement?

 

First, I got a feel for the signal flow.  There's a lot on the board, and I'm not an analog guy, so I did what I could.  I found first that the signal arrives from the effects return board on the back of the amp and runs first into TI TL074C quad op amp and a Microchip Technology MCP4241-503E digital potentiometer.  I suspect this is the circuit that allows you to control the volume remotely over MIDI - who knows.  It then goes to V3, the first 12AX7 tube, which seems to only use 1 of the two triodes to buffer or pre-amp the signal before running over to V4, the phase inverter, and then on to the power tubes.

 

After poking around a bit, I concluded that from the output of V3, the pre-amp tube, everything was working fine.  I could touch pin 1 of the 12AX7 and get a very loud pop out of the speaker.  This told me that the problem was before or at the first tube.  So I started on my first dead-end rabbit trail by comparing the resistance values of various pins and components surrounding the op-amp and digital pot circuit between my working amp and the failing amp.  First I thought maybe the digital potentiometer was bad, crushing the output signal.  Nope, this wasn’t the problem.  Then I thought maybe the op-amp was bad.  No, that wasn’t it either.  I actually found a cool debug tool on this guy’s website:

http://billmaudio.com/wp/?page_id=1254

This is a probe that allows you to trace the audio signal through the circuit.  This helped me determine that the signal was getting to V3 properly.  So after hours of poking and prodding, I realized I was on a rabbit trail.  So now the focus was on V3.  Maybe the tube was bad afterall?  No, I realized it was fine after swapping V3 and V4, then swapping the pair with the tubes from my good amp.  Well what the heck is the problem then?  I was getting very frustrated.  By now I had something like 12 hours into this project over about 2 weeks.  And I was getting obsessed!

 

Next rabbit trail – from my old board design & debug days, I used an old trick to find cracked solder joints.  I took a pencil and started pressing down in different areas of the board while running a test signal into the amp.  I noticed that pressing near the op-amp and digital pot area of the board would cause some big time static, cracks, and pops.  This indicated to me either a bad solder joint or fractured PCB traces.  So out the board came yet again from the chassis to reflow the solder joints.  I reflowed everything on that half of the board, just to be sure.  I popped it back in and wow, the static problem disappeared!  I played at room volume for about 5 minutes and thought, viola, the problem is solved!  But then – pop!  It went out again!  This time it went it quickly, no fade.  Dang!  I give up!  So I set it aside for a few days and pondered.  I’m thinking now that there really was something else going on that was in fact solved by reflowing the joints, since the static when pressing the board is gone, but it didn’t solve my first problem.  Incidentally, if I count the bad diode above, this problem, and the fade-out problem, that totals 3 different issues with this one board!  Sheesh, I think I got a lemon or something.

 

Over the next several days, I kept thinking about it.  Then it hit me – maybe the B+ voltage to the tubes was going out.  That would definitely explain the problem I was experiencing.  Maybe a bad cap?  So I probed the B+ voltage around V3 and V4.  After some time I was able to probe while working properly and while exhibiting the fade-out, and wouldn’t you know, the B+ voltage was constant the whole time.  Time to bang my head against the wall, cuz I’m giving up again.

For some reason, I decided to probe the heater voltage of V3, out of curiousity.  I mentioned in my first post above that there is a full wave rectifier diode bridge that provides about 5VDC to V3.  So when I probed in the failing state, I found that there was almost 0V.  I almost jumped for joy.  I almost couldn’t believe what I was seeing.  So I probed again, and again 0V.  I pressed a bit harder to make sure the probes were cutting through the solder flux, and pop!  The amp started making noise and I registered about 5VDC.  Bingo!  I found my problem, but I could not figure out why the problem was occurring.

 

After studying this circuit and comparing schematics on the internet, I determined that the 6.5VAC connector from the power transformer provides voltage to 4 1N4007 diodes forming the full wave rectifier.  Each diode has a forward voltage drop of about 1V, so that should leave between 4.5V to 5VDC at the heater pins of V3.  There is also a 1000uF, 35V cap soldered directly under V3.  So I figured it must be one of the diodes flaking out, or the cap.  After measuring the diodes over and over again, I became confident that they weren’t the problem.  On to the cap.  I probed the heater voltage of V3 and sorta wiggled the cap around and noticed that the voltage would cut out (I think, or maybe my probe was intermittently making contact while I was wiggling).  That was enough for me.  Time to replace the cap.

 

I found a local Radio Shack that carried this cap in stock.  Sweet!  They also had the diodes, so I bought all of them for about $5.00.  The V3 socket is soldered on the backside of the board, covering the solder pads of the cap, so I had to remove the socket first, then the cap.  I went ahead and replaced the diodes too, just to be safe (I’m about sick of disassembling this amp!).  After putting everything back together, I fired it up and pow, it works.  I played at loud room volume for about 15 minutes so far, which is much longer than I was able before.  Works like a champ.  Let’s hope I’m not back on this post to say it still fails in a few days!  Incidentally, after replacing the diodes and cap, my heater voltage now measures 5.6V, 1V more than before.

 

Now, some background for you techies out there.  I did a bunch of circuit tracing and learned a few things that might be interesting.

  1. As mentioned above, only ½ of the 12AX7 tube is used – the other half seems to be no-connected.  The functional half is there to amplify the signal from the effects return.
  2. The 12 in 12AX7 means that the heater voltage is meant to be 12V.  Since there are 2 heaters, one for each triode, that would be 6.3V for each, totaling 12V.  Cool!
  3. This amp only supplies 5VDC to each heater, less than the 6.3V.  Not sure why.  I saw some posts on various forums indicating that lower heater voltages can emulate the variac effect used to get Eddy Van Halen’s brown sound.  Others claim it is for better tube reliability.  Not sure why Line 6/Bogner does this.
  4. The V3 tube uses a DC heater voltage, while the remaining tubes use AC voltages.  The V4 phase inverter voltage is 6.3VAC * 2 = 12VAC.  I read somewhere that the pre-amp tube must have a DC heater voltage to reduce hiss/hum.  I read somewhere else that using DC voltages on all the tubes’ heaters further reduces noise.  I’m not bold enough to try that experiment!  Incidentally, I also read that the SLO100 uses AC voltages on all its tubes, so who knows.
  5. The V4 phase inverter circuit follows what is called a “Long Tail Pairâ€, which apparently was used by Marshall and Fender amps.  Note that this circuit greatly amplifies the signal in addition to splitting the phase.
  6. While in topology #1, the B+ voltage on my amp reads 340V.  In topology #2 and #4, it reads 440V.  And in topology #3, it reads 270V.  At least one of the relays on the board is used to switch in a pair of large wattage resistors to reduce the B+ voltage.  These resistors are easy to spot because they are soldered on the back side of the board, likely because they ended up being larger than the footprint provided for them on top side of the PCB.  Perhaps Line 6 realized they underspecified the wattage of the resistors they originally intended to use.

Well I hope this is helpful to someone someday.  Let me know if you have any questions or anything, I hope I can help.

 

Thanks,

Randy

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Wow! Thanks so much for all the detail and description of your debugging.

 

What do you think is the root cause of the issues?  Do you think the failed cap caused the failed diode? Or vice versa?  Or perhaps intermittent signal problems from the cracked solder at the knobs caused the components to fail?

 

Perhaps we should treat the knobs with more care since apparently they aren't supported enough and therefore cause board failure?

 

Given the price on Musician's Friend/GC, I'm considering getting a DT50 112.... So thanks for all this info.  And of course I've only got an HD-Bean, so I'll have to pick up a 500(X), too...

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That was a great post Randy. Thanks a million for taking the time to do all that diagnosing and posting your findings. I've some issues with my DT50 too, although Line 6 has been doing their part in trying to help me. Information like this is what helps make me more knowledgeable. Please let us know later how it's working in the long run.

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Thanks guys.  I've been spending quite a bit of time jamming in stereo with my 2 DT-50s, and I've had absolutely no problem with the one since the repair.  I've got probably 15 hours of use on it now - used to drop out after 5-10 minutes (if it was working at all).  And no more crackling/popping when flexing the analog board.

 

@FlyingsCool - I really don't know whether any of the components I replaced were faulty.  My first hunch is that there was a bad connection with the electrolytic cap, either at the solder joints or in the body of the cap itself.  My second hunch is that the cap was bad, but it didn't measure as shorted out when tested with my meter.  Who knows.  Something strange was definitely going on.  I wasn't intent on finding the root cause as much as I just wanted to get it working properly again, so I just replaced all 4 diodes and the cap (all in the same circuit).  Bottom line is I love these amps and I highly recommend getting one!

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I'm glad your having luck with your DT's Randy. You always have such interesting posts. I'm sad to report that my amp is not working. I received my DT50 about a month ago and I powered it up for the first time to play Mom some music for Mothers Day and not a peep out it. I looked at the power tubes and they're not even lit up. Very disappointing since sitting a little over a month in an air conditioned room shouldn't be a problem. I'm back at square one. I sure hope Line 6 helps me.

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Brazzy, that is awful, so sorry to hear that.  Hey, if you're up to it and feel capable of digging in, we can try to debug here on this forum!  Judging by the symptoms, it should actually be fairly straightforward to troubleshoot.  You'll need a Digital Multimeter (DMM) in order to do some basic debugging.

 

So first off, assuming the tubes themselves are good - when you say the tubes aren't lit up, do you mean all 4 of them?  Like even the power tubes?  Do the front panel lights come on?  Do you hear relays clicking after a few seconds of powering on?  What should happen is when you turn on the power switch, the heater circuits should fire up to warm up the tubes.  Also, the digital board gets full power and starts booting up.  The tube B+ voltage remains off until the Standby switch is turned on.  If none of the tubes light up, it sounds like a fuse problem, a power transformer problem, or some analog board circuit problem (like I had).  As far as fuses, there are 3 I know of.  One on the input AC connector on the back panel, another just to the right also on the back panel, and one on the analog board right next to the heater voltage connector H2.  So you'll want to see if any of these are blown, and if so, we'll have to figure out why.

 

If the fuses all look good, you'll want to try to measure them with the DMM to make sure they measure 0 ohms.  Sometimes a fuse may look good, but actually be an open circuit.

 

If the fuses all check out, then the next culprit would be the power transformer.  H2 is the connector that accepts the 6.5VAC used for the heater circuits.  If there is no voltage available, the transformer could be bad.  You can get new transformers on fullcompass.com for like $70USD.  They are very easy to replace.

 

If the transformer checks out, there could be a circuit problem on the board.

 

So, what do you think?

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I think that sounds great Randy. I think I should wait to see what Line 6 has to say first before I get deep with you. Everything you say always makes sense to me as I too have some experience with electronics.

 

When I powered it up all the lights on the front panel lit up normally, after 5 maybe 10 seconds I heard the relays clicking. After that I waited for the tubes to warm up giving the amp a minute before taking standby off at which point not one peep with settings that I know would produce a pleasant sound. Then I looked back at the Power Tubes and they were unlit. The 12AX7's looked dark also but I must admit it's harder to see if they're lit unless you're in a somewhat dark room. I didn't check any of the fuses yet as I think Line 6 needs to take a look at it.

 

I appreciate your help and will stay in touch with you on this. I'll also be getting my DMM and other tools ready in case I have to take the bull by horns in the very near future.

 

Your help is much appreciated Randy. Have a Great Day!

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Great plan.  Either way, we WILL get this working for you.  You can't sell it broken.  Parts are available.  Future's so bright, we gotta wear shades!

 

So tell me again (haven't read all the details on the other posting), Line 6 did repair work for you.  So the tubes are new?  And did they replace the power transformer?  Did they replace the analog board or anything else?  Trying to figure out what else we can eliminate as culprits in case you have a blown fuse.

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Your positive attitude is refreshing to say the least :). Sounds great and I really don't have plans to sell it I'm kind of stubborn when it come admitting failure by selling something, lol.

 

Line 6 recently had it twice. I had to call them to get details on repairs since the paper work they gave me didn't tell much. The first time it they said they replaced the power tubes, the main board and the transformer fuse I thought they also said TSB 059, don't hold me to the latter. The second time I don't know what they did since I haven't called them to find out.

 

I just got a response from Line 6 and they asked me to call them to see if they can troubleshoot with me. I'm going to do that in about 20 minutes or so.

 

Thanks Again!

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Hey Randy, Line 6 is going to call tag this amp and try to fix it once and for all. The only other options I had was to exchange this one and in return get a U.S. DT25 HD or a DT50 HD from Europe in which case they would make sure the power supply was changed so I could use it in the U.S. . So this one I have looks like a lemon but maybe they can fix it and get it right.

 

To answer the question of what they did the second time is they replaced the main board and power tubes.

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Well I hope this is helpful to someone someday.  Let me know if you have any questions or anything, I hope I can help.

 

Thanks,

Randy

 

Randy, thanks again for the INFORMATIVE post(s)!

 

!)  Do you have a schematic, and if so, where can I get one?

 

2)  How's the noise floors in your amps?  I play at a level akin to cranking your stereo about halfway, and the noise in my DT50-112 has been bothering me tremendously.  I have white noise and ground buzz.  I had it in the shop but the noise is still there.  I've now bought 5 tubes, the most recent being a mesa spax7 for the inverter, and this seemed to take the edge off just enough that I could forget about the noise when playing.  I've compared my amp to a DT25, a Spider Valve, MKII, a Blackstar HT40, and a Marshall DSL40C, and all of them are SO much more quiet than mine!  I've never heard an amp so noisey, although to be fair, If I turn up the volume the noise does not increase in this amp the way it did in the Marshall, so the noise can be drowned out in a band situation (I think/hope).  Recently I seemed to have developed the fizzys (as if I haven't suffered enough already).  So just wondering, when you turn on your amps and nothing is plugged in and your volumes and gains are at zero, do the amps sound like really loud fans or even quiet air conditioners?

 

THANKS!

 

Mike

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Hey Ronnie, great to hear, but sad that you'll be without the amp for a while again.  Very frustrating, but it sounds like Line 6 wants to do you right.

 

Hey Mike, I don't have a schematic, but I'd love to get one.  That'll never happen though.  So I have some notes and diagrams I drew up by hand while debugging my amp.  Mostly the op-amp circuit connections, some of the pre-amp tube connections, and some of the phase inverter tube connections.  Not a whole lot.  I found that what I was probing matched quite closely to most of the Fender/Marshall schematics you can find on the internet, especially with the phase inverter and power tubes.

 

As for noise, I get an annoying hiss while in topology 3 like most people.  I find that the noise grows in this topology order (no guitar connected):  topo 1=quietest, topo 4=same amount of hiss, slightly more hum, topo 2=more hiss and more hum than both 1 and 4, and topo 3=most hiss and hum.

 

I just downloaded the free Sound Meter app for my Galaxy S5 and did some measurements on my 112 (the one I repaired).  I don't know how to calibrate it yet, so consider the relative differences of my measurements:  topo 1=46dB; topo 2=66dB; topo 3=80dB; topo 4=67dB; standby mode=26dB.  All measurements done 12" from my 112 combo speaker, Pentode, default class.

 

On the 212:  topo 1=34dB; topo 2=56dB; topo 3=77dB; topo 4=64dB.  So this one is a bit quieter than my 112.  Perhaps the tubes make the difference.

 

Hope this helps!

Randy

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Oh, and forgot to mention, I have a little Honeywell fan from Home Depot that measures around 76dB.  So yes, my topo 3 on both amps is actually louder than my fan!

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Hey Ronnie, great to hear, but sad that you'll be without the amp for a while again.  Very frustrating, but it sounds like Line 6 wants to do you right.

 

Hey Mike, I don't have a schematic, but I'd love to get one.  That'll never happen though.  So I have some notes and diagrams I drew up by hand while debugging my amp.  Mostly the op-amp circuit connections, some of the pre-amp tube connections, and some of the phase inverter tube connections.  Not a whole lot.  I found that what I was probing matched quite closely to most of the Fender/Marshall schematics you can find on the internet, especially with the phase inverter and power tubes.

 

As for noise, I get an annoying hiss while in topology 3 like most people.  I find that the noise grows in this topology order (no guitar connected):  topo 1=quietest, topo 4=same amount of hiss, slightly more hum, topo 2=more hiss and more hum than both 1 and 4, and topo 3=most hiss and hum.

 

I just downloaded the free Sound Meter app for my Galaxy S5 and did some measurements on my 112 (the one I repaired).  I don't know how to calibrate it yet, so consider the relative differences of my measurements:  topo 1=46dB; topo 2=66dB; topo 3=80dB; topo 4=67dB; standby mode=26dB.  All measurements done 12" from my 112 combo speaker, Pentode, default class.

 

On the 212:  topo 1=34dB; topo 2=56dB; topo 3=77dB; topo 4=64dB.  So this one is a bit quieter than my 112.  Perhaps the tubes make the difference.

 

Hope this helps!

Randy

 

Thanks, Randy!  I'm gonna hafta get me a dB meter!  

 

Well, those readings would seem to be to be quite loud for an amp with no guitar plugged in, but you haven't calibrated...  In my amp it follows that same pattern but I'd guess my dB's in voice I are double or more what I've got in standby.  Voice I has also gotten worse during my 3 months of ownership.  Voice 4 has more hiss than 1 and just slightly less than 2, with more buzz than either.  voice 3 is crazy.

 

When I tried my 212 Fender Bandmaster bottom the noise dropped too, so I'm thinking that's what you're hearing--the noise split between 2 speakers.  From 20 feet it would be the same for either cab, but at 1 ft you're only picking up 1 cone in the 212 (I'm thinking).

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Oh, and forgot to mention, I have a little Honeywell fan from Home Depot that measures around 76dB.  So yes, my topo 3 on both amps is actually louder than my fan!

 

Hmmm, well then maybe we are in the same ballpark.  I don't know if my fan is louder than yours or not, but it's just about totally drowned out by topo 3.  If I turn the fan off or on I can still hear the difference, but the amp is definitely louder than the fan.  If this is normal--and I'm not necessarily agreeing to that yet--ya gotta wonder why Line 6 didn't correct it with an internal noise gate or some filter caps or whatever.  I've yet to find an amp so noisey.  And mine, even with new tubes, seems to rather break up than deliver smooth crunch.  Of course, I'm not playing at the intended volume (although my ears do ring when I'm done from standing in the cone blast).  Maybe I should sneak it into work this saturday and crank the sh*t outta it?  Or go audition somewhere...

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Good point about the 212 noise level - you're probably right, I had the mic closer to 1 speaker than the other.

 

When I use my 112 at church, I typically stay away from the topo 3 setting since it is so loud when idle - the sound guys pick it up for sure since I'm mic'ed.  So I usually try to find a topo 1 amp, one of the Fenders, to get a more chimey tone to substitute.  I suppose they could put a gate on it.  I'm going to try the new Fawn Normal during Wednesday's rehearsal - we'll see if the sound guys notice the idle noise level.  This will also be my first out-of-the-house test of my 112 since fixing it (fingers crossed!).

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Reading through this tread scared the heck out of me  :lol:

There's too many things goin' on inside (analog/digital boards relay and gremlins)  DT amps and the chances of failing (hauling the amp in a car or van constantly) on a gig are very likely!  now I'm scared of buying one   :unsure:

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Reading through this tread scared the heck out of me  :lol:

There's too many things goin' on inside (analog/digital boards relay and gremlins)  DT amps and the chances of failing (hauling the amp in a car or van constantly) on a gig are very likely!  now I'm scared of buying one   :unsure:

 

Speaking for myself here. Before I bought a DT50 I read about them having issues and some people were unhappy about it and some were very happy. Some people were very upset and made that clear on many forums. Even after that I still wanted one, hopeing I wouldn't get one that was bunk. Even after all that hope I got one that was a problem. I still don't regret getting one and Line 6 is trying to make good on it. I still don't have a working DT50 and I'm looking forward to what happens next. Even after all the issues I've had I still don't regret it, mainly 'cause I have back up amps. Also, I'm not a gigging musician ......yet, meaning I don't move the amp around much at all.

 

So far in my experience the DT50 has excellent sonic capability.

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... How's the noise floors in your amps?  I play at a level akin to cranking your stereo about halfway, and the noise in my DT50-112 has been bothering me tremendously.  I have white noise and ground buzz. ... Recently I seemed to have developed the fizzys ... So just wondering, when you turn on your amps and nothing is plugged in and your volumes and gains are at zero, do the amps sound like really loud fans or even quiet air conditioners?

As for noise, I get an annoying hiss while in topology 3 like most people.  I find that the noise grows in this topology order (no guitar connected):  topo 1=quietest, topo 4=same amount of hiss, slightly more hum, topo 2=more hiss and more hum than both 1 and 4, and topo 3=most hiss and hum.

 

I just downloaded the free Sound Meter app for my Galaxy S5 and did some measurements on my 112 (the one I repaired).  I don't know how to calibrate it yet, so consider the relative differences of my measurements:  topo 1=46dB; topo 2=66dB; topo 3=80dB; topo 4=67dB; standby mode=26dB.  All measurements done 12" from my 112 combo speaker, Pentode, default class.

 

On the 212:  topo 1=34dB; topo 2=56dB; topo 3=77dB; topo 4=64dB.  So this one is a bit quieter than my 112.  Perhaps the tubes make the difference.

 

Hi Mike and Randy,

 

I just got a new DT50 head, which I have plugged into a Jet City 333 4x12 cab, and was thinking about what you guys were saying here. So, I powered up and with nothing plugged in, this amp/cab gives me these readings with the free (not calibrated) Sound Meter app (ver. 1.6.1 by Smart Tools) for my Galaxy S5:

 

The ambient room measurement in standby mode hovers around 30dB. With the phone touching the cover cloth I get these readings directly in front of the the top left speaker:

 

I = 58

II = 65

III = 79

IV = 68

 

One foot away, directly in front of the the top left speaker, I get these readings:

 

I = 48

II = 58

III = 74

IV = 62

 

Looks pretty similar. 

 

One additional question for either of you guys: In a thread called "DT50 question", some folks were wondering about the "PIV HI/LOW and TIGHT/SMOOTH switches" found using DTEdit. I quoted you Randy (I hope I quoted you correctly, post #16 in that thread) about the PIV circuit but I have not found any information about the TIGHT/SMOOTH switch. Do you guys have any insight as to how this switch actually works and how they are intended to be perceived? 

 

Thanks

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Hi CipherHost,

   On the analog board, there are 10 relay units, 6 of which appearing to affect the power tube section and 4 of which appearing to affect the phase inverter section.  From what I can tell, these relays switch in and out some resistors and caps.  Maybe the PIV HI/LOW setting changes one of the 4 relay settings near the phase inverter section.  I have no idea on the TIGHT/SMOOTH setting.  Perhaps you could try changing these settings and listen for a click of one of the relays.  If the relays do switch, I'd guess they are switching in and out some filtering circuitry.  If no clicking, maybe the settings only affect the digital realm before the signal reaches the analog board.  With a setting called PIV HI/LOW, sure sounds like a real circuitry change though, eh?

 

I wish I had more time, I could experiment with things like this on my amp to see what's really going on :-).

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When I use my 112 at church, I typically stay away from the topo 3 setting since it is so loud when idle - the sound guys pick it up for sure since I'm mic'ed.  So I usually try to find a topo 1 amp, one of the Fenders, to get a more chimey tone to substitute.  I suppose they could put a gate on it.  I'm going to try the new Fawn Normal during Wednesday's rehearsal - we'll see if the sound guys notice the idle noise level.  This will also be my first out-of-the-house test of my 112 since fixing it (fingers crossed!).

 

Okay, I can totally related to this!  With my amp I've been contemplating the question "Is this amp, by design, normally so noisey that guitarists need to either switch to standby or voice/topo 1 between songs?  You just answered the question "yes."  At this point I am ready to conclude that my amp isn't defective or malfunctioning, a question that's nagged me since 2 days after I bought it (3 months ago).

 

THANKS!!!

 

One thing that might not be known--that I didn'T know until 3 days ago--is that switching to "triode" reduces the noise.  It also reduces power by 50%.  When I first got the amp I immediately discarded the notion of ever using anything other than pentode, but after recent experimenting, I've found that this helps with some tones.  In triode function you lose attack, headroom, power, and the amp seems less lively.  But for crunchy tones at a lower volume, it seems to dramatically reduce the fizzies, it allows for more sustain and saturation, and it even mellows lower string riffs and stuff while somehow making them stand out better.  So I'm thinking I'll go pentode for voice 1 and triode for most patches using voices 2-4.

 

Another surprise was that low power mode can really alter how the gain setting interacts with the tone.  I was in voice 1 with LPM off and the gain up to 2:00, and I turned LMP on and all of a sudden I got crunch and saturation (after turning up the master, natch).

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Reading through this tread scared the heck out of me  :lol:

There's too many things goin' on inside (analog/digital boards relay and gremlins)  DT amps and the chances of failing (hauling the amp in a car or van constantly) on a gig are very likely!  now I'm scared of buying one   :unsure:

 

Sorry to hear that!  Does the DT have more breakdowns than other amps?  I can't say--I have no opinion due to limited exposure.  As one person noted elsewhere, you're going to see more people with problems in a support forum, cuz that's why they have them--to solve problems.  

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Hi CipherHost,

   On the analog board, there are 10 relay units, 6 of which appearing to affect the power tube section and 4 of which appearing to affect the phase inverter section.  From what I can tell, these relays switch in and out some resistors and caps.  Maybe the PIV HI/LOW setting changes one of the 4 relay settings near the phase inverter section.  I have no idea on the TIGHT/SMOOTH setting.  Perhaps you could try changing these settings and listen for a click of one of the relays.  If the relays do switch, I'd guess they are switching in and out some filtering circuitry.  If no clicking, maybe the settings only affect the digital realm before the signal reaches the analog board.  With a setting called PIV HI/LOW, sure sounds like a real circuitry change though, eh?

 

I wish I had more time, I could experiment with things like this on my amp to see what's really going on :-).

 

Thanks for the feedback. I'll be doing a little digging this weekend and I will post anything that might be of benefit to know. Once again, I really appreciated your original post. 

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As for noise, I get an annoying hiss while in topology 3 like most people.  I find that the noise grows in this topology order (no guitar connected):  topo 1=quietest, topo 4=same amount of hiss, slightly more hum, topo 2=more hiss and more hum than both 1 and 4, and topo 3=most hiss and hum.

 

I just downloaded the free Sound Meter app for my Galaxy S5 and did some measurements on my 112 (the one I repaired).  I don't know how to calibrate it yet, so consider the relative differences of my measurements:  topo 1=46dB; topo 2=66dB; topo 3=80dB; topo 4=67dB; standby mode=26dB.  All measurements done 12" from my 112 combo speaker, Pentode, default class.

 

On the 212:  topo 1=34dB; topo 2=56dB; topo 3=77dB; topo 4=64dB.  So this one is a bit quieter than my 112.  Perhaps the tubes make the difference.

 

The ambient room measurement in standby mode hovers around 30dB. With the phone touching the cover cloth I get these readings directly in front of the the top left speaker:

 

I = 58

II = 65

III = 79

IV = 68

 

One foot away, directly in front of the the top left speaker, I get these readings:

 

I = 48

II = 58

III = 74

IV = 62

 

Looks pretty similar. 

 

One additional question for either of you guys: In a thread called "DT50 question", some folks were wondering about the "PIV HI/LOW and TIGHT/SMOOTH switches" found using DTEdit. I quoted you Randy (I hope I quoted you correctly, post #16 in that thread) about the PIV circuit but I have not found any information about the TIGHT/SMOOTH switch. Do you guys have any insight as to how this switch actually works and how they are intended to be perceived? 

 

Thanks

 

Thanks, Randy!  I'm gonna hafta get me a dB meter!  

 

Well, those readings would seem to be to be quite loud for an amp with no guitar plugged in, but you haven't calibrated...  In my amp it follows that same pattern but I'd guess my dB's in voice I are double or more what I've got in standby.  Voice I has also gotten worse during my 3 months of ownership.  Voice 4 has more hiss than 1 and just slightly less than 2, with more buzz than either.  voice 3 is crazy.

 

When I tried my 212 Fender Bandmaster bottom the noise dropped too, so I'm thinking that's what you're hearing--the noise split between 2 speakers.  From 20 feet it would be the same for either cab, but at 1 ft you're only picking up 1 cone in the 212 (I'm thinking).

 

In reference to your findings concerning the idle db levels I agree with your results as being normal for this amp. I haven't measured the db level with a device, just my ears, and the numbers make sense to me. Topo III was always the noisiest.

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Hi Mike,

   Just found this (you probably already knew this though):  http://www.sweetwater.com/insync/pentodetriode-switch

 

So it looks like 2 of the 3 grids are disabled in triode mode.  Sounds like it would be akin to shutting off 4 cylinders of a V8.

 

After messing with the Fawn Brt amp, I've decided a) I didn't like the tone, and b) topo 3 is still too noisy for me, so I replaced it with the Tweed Bassman and used the 212 Silver Bell speaker model.  Sounds great to me for what I'm trying to do and has much less hiss/hum.  I'll be trying it out at tonight's rehearsal.

 

I'm a bit embarrassed to say that I almost always use LVM because I love the modeled power-stage distortion since I play at bedroom volumes most of the time (even at church).  Until I have the opportunity to crank full mode up past 12 o'clock (which may be in the summer when we have an outdoor gig), I'll continue to use LVM.  I'll have to give triode mode a try for kicks.

 

Thanks!

Randy

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Happy to say that hurray, the amp performed flawlessly during rehearsal tonight.  So nice to have my amp troubles behind me, knock on wood.

 

And I really love the Fender Bassman with the 212 Silver Bell combination as a substitute for the noisier Vox AC30TB.  I put a Blue Comp Treb compressor in front and it sounds great. 

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Happy to say that hurray, the amp performed flawlessly during rehearsal tonight. So nice to have my amp troubles behind me, knock on wood.

 

And I really love the Fender Bassman with the 212 Silver Bell combination as a substitute for the noisier Vox AC30TB. I put a Blue Comp Treb compressor in front and it sounds great.

Sounds like confidence is back. Glad to hear it Randy. How long did you have the amp on for rehearsal? Thanks for sharing. Here's to your success, Hip Hip Hurray!! :).

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Hi Ronnie, I had the amp on for almost 3 hours.  That brings me up to > 20 hours now, no glitches.  Rock solid!  Woohoo!

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Hi Ronnie, I had the amp on for almost 3 hours.  That brings me up to > 20 hours now, no glitches.  Rock solid!  Woohoo!

 

Good Going Randy, Thanks for the update. Thumbs Up to ya!

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Hi Mike,

   Just found this (you probably already knew this though):  http://www.sweetwater.com/insync/pentodetriode-switch

 

So it looks like 2 of the 3 grids are disabled in triode mode.  Sounds like it would be akin to shutting off 4 cylinders of a V8.

 

After messing with the Fawn Brt amp, I've decided a) I didn't like the tone, and B) topo 3 is still too noisy for me, so I replaced it with the Tweed Bassman and used the 212 Silver Bell speaker model.  Sounds great to me for what I'm trying to do and has much less hiss/hum.  I'll be trying it out at tonight's rehearsal.

 

I'm a bit embarrassed to say that I almost always use LVM because I love the modeled power-stage distortion since I play at bedroom volumes most of the time (even at church).  Until I have the opportunity to crank full mode up past 12 o'clock (which may be in the summer when we have an outdoor gig), I'll continue to use LVM.  I'll have to give triode mode a try for kicks.

 

Thanks!

Randy

 

Randy, nothing to be embarrassed about there (or should I just say you're not alone, me too, +1...)  LVM changes things, and IMO usually for the better in lower volumes.  I've been liking voice IV, though, and that seems better with LVM off.

 

I'm gonna hafta try that tweed with the silver bells.  I've always used pre's with no cab with my DT50--am I missing out?

 

Say, you've got the 112 and the 212, right?  Could you help me out and weigh in on my new thread?  it's here:

 

http://line6.com/support/topic/13889-celestion-g12h90-vs-vintage-30/

 

Thanks!

 

Mike

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