Dt-25 Effects Loop Bypassed When Using Xlr Out?

[tankaviator]

I'm having to send my HD 500 into the shop (broken USB port) and I am hooking up a few of my stand alone pedals to my DT-25. I noticed that the effects loop sounds fine coming out of the speaker, but the XLR out seems to be tapped before the effects loop, so isn't sending the post-processed signal to my mixer. I have checked in both standby mode (LVM) as well as with the power amp on and the behavior is the same. I have seen 1 other mention of this in regards to a DT-50, and it sounds like the newest firmware update changed the behavior of the XLR out to be tapped pre-effects loop. Can anyone verify whether or not the XLR out should be tapped pre- or post-effects loop?

 

Thanks,

Mike

[boyce89976]

If I'm not mistaken, and it's likely I am... it seems like I read somewhere that the XLR out on the DT's tap off the preamp, which would be before the effects loop.  

 

I'd like to know this too, as I wanted to experiment with different connections to FOH, and if true, this rules out tapping off the XLR out of the DT.  

[tankaviator]

What would be the point of tapping before the effects loop? It either means that the XLR out is useless (when using the effects loop), or the effects loop is useless (when sending the signal to FOH). I don't really understand what the usefulness is then?

[phil_m]

In standby mode, yes, the effects loop is bypassed, and the direct out gives you just the signal from the preamp. If you have standby off, whatever you have in the effects loop should be present in the XLR out.

[radatats]

From the DT25 Pilot's Guide:

 

Serial Effect Loop – Use the effect loop to send your audio signal to external effects processors and stomp boxes such as modulations, delays & reverbs. Note: Signal path is in series. When using the SEND, audio will not pass through to the poweramp without a connection back to the RETURN.

 

Cabinet Simulated Direct Out – Provides a transformer-tapped direct output with cabinet simulation for studio recording or live performance without mic’ing your amplifier. The ground lift switch can be used to eliminate hum or buzz.

 

From the DT Series L6 LINKâ„¢ Connectivity Guide:

 

Direct Out

The DT amplifier’s DIRECT OUT continues to function as an analog output with L6 LINK in use. Use of this XLR output is recommended to feed your “fully baked†POD HD + DT amp tone to an external recorder, mixing console, etc. Since the audio signal fed to the DT amp via L6 LINK is a mono signal, this Direct Out is a mono signal as well. Note that the Direct Out functionality differs based on the DT amp’s LOW VOLUME MODE (see page 4•3) and STANDBY switch settings:

• Low Volume Mode Off, Amp in Standby = The DT amp’s Direct Out is disabled.

• Low Volume Mode On, Amp in Standby = Direct Out signal consists of the “Full†(preamp + power amp) Amp Model with no analog amp.

• Low Volume Mode Off, Amp On (not in Standby) = Direct Out signal consists of the “Preamp†Amp Model with the analog amp.

• Low Volume Mode On, Amp On (not in Standby)= Direct Out signal consists of the “Full†Amp Model and the analog amp.

 

Based on all the above:

- serial FX loop is between preamp and analog power section.  XLR out is (power section output) transformer tapped to give you the "fully baked" signal for the PA or recording.

- seems safe to say that the only time it "may" bypass the FX loop is in LVM Standby.

 

Can you confirm all your settings when this discrepancy occurs?  

Have you tried bypassing the preamp completely and just going straight in to the FX return to see if you get a signal?

[boyce89976]

 

From the DT25 Pilot's Guide:

 

Serial Effect Loop – Use the effect loop to send your audio signal to external effects processors and stomp boxes such as modulations, delays & reverbs. Note: Signal path is in series. When using the SEND, audio will not pass through to the poweramp without a connection back to the RETURN.

 

Cabinet Simulated Direct Out – Provides a transformer-tapped direct output with cabinet simulation for studio recording or live performance without mic’ing your amplifier. The ground lift switch can be used to eliminate hum or buzz.

 

From the DT Series L6 LINKâ„¢ Connectivity Guide:

 

Direct Out

The DT amplifier’s DIRECT OUT continues to function as an analog output with L6 LINK in use. Use of this XLR output is recommended to feed your “fully baked†POD HD + DT amp tone to an external recorder, mixing console, etc. Since the audio signal fed to the DT amp via L6 LINK is a mono signal, this Direct Out is a mono signal as well. Note that the Direct Out functionality differs based on the DT amp’s LOW VOLUME MODE (see page 4•3) and STANDBY switch settings:

• Low Volume Mode Off, Amp in Standby = The DT amp’s Direct Out is disabled.

• Low Volume Mode On, Amp in Standby = Direct Out signal consists of the “Full†(preamp + power amp) Amp Model with no analog amp.

• Low Volume Mode Off, Amp On (not in Standby) = Direct Out signal consists of the “Preamp†Amp Model with the analog amp.

• Low Volume Mode On, Amp On (not in Standby)= Direct Out signal consists of the “Full†Amp Model and the analog amp.

 

Based on all the above:

- serial FX loop is between preamp and analog power section.  XLR out is (power section output) transformer tapped to give you the "fully baked" signal for the PA or recording.

- seems safe to say that the only time it "may" bypass the FX loop is in LVM Standby.

 

Can you confirm all your settings when this discrepancy occurs?  

Have you tried bypassing the preamp completely and just going straight in to the FX return to see if you get a signal?

 

 

Great info, rad.  I looked for this in the .pdf manuals I have, but I guess I don't have the L6 Link guide... will have to download that.  I'm going to play with this output at my next rehearsal.  

[innovine]

just to confirm:

 

Low Volume mode OFF:

Amp On (not in standby):   FX Loop heard on direct out

Amp Off (in standby):  Nothing

 

Low Volume Mode ON:

Amp On (not in standby): FX Loop NOT present on direct out

Amp Off (in standby); FX Loop NOT present on direct out

 

 

So the only time it works is when the amp is fully on.

 

 

I noticed another odd thing while trying this (I've no wish to repeat this experiment) is that the fx return seems to come in AFTER the Master vol.. does that make sense?? I had the master fully down but could still hear the fx loop return. I should NOT have used my re-20 space echo in self oscillation mode for this test! I got extremely loud feedback :O

[phil_m]

I noticed another odd thing while trying this (I've no wish to repeat this experiment) is that the fx return seems to come in AFTER the Master vol.. does that make sense?? I had the master fully down but could still hear the fx loop return. I should NOT have used my re-20 space echo in self oscillation mode for this test! I got extremely loud feedback :o

 

That makes sense. The master volume is essentially the volume control for the preamp section.

[innovine]

I thought that was the channel volume?

[boyce89976]

I thought that was the channel volume?

 

Everyday, I'm learning I know less and less about this thing.   :wacko:

[MartinDorr]

I think what it was called on the HD does not matter for the DT.

The important part is to recognize that the Master Volume control on the DT happens before the effects loop send.

Just like reverb is applied before the effects loop send (which seems a little odd to me)

It all makes sense from a minimal HW design investment though.

One would want to do all the DSP work before some final DA stage.

If the effects loop would be in the middle of the signal path like on the HD the DT would need an additional AD/DA conversion and associated HW.

[radatats]

absolutely disagree.  the master volume is for the analog power section. doesn't even make any kind of sense otherwise.  I agree it needs more investigation but it definitely doesn't come before the FX loop and doesn't affect the digital signal.  Other wise you would need the power section to be driven full blast at all times and simply be varying the strength of the preamp signal being applied.  Doesn't work that way...

[phil_m]

absolutely disagree.  the master volume is for the analog power section. doesn't even make any kind of sense otherwise.  I agree it needs more investigation but it definitely doesn't come before the FX loop and doesn't affect the digital signal.  Other wise you would need the power section to be driven full blast at all times and simply be varying the strength of the preamp signal being applied.  Doesn't work that way...

 

It does work that way... The master volume has no effect on the power section output. It's easy to prove. Simply plug something into the effects return. The master volume knob doesn't do anything when you do that. So going into the effects return plugs you into the power amp with the power amp full open. The master volume attenuates the input going into the power amp. This is the same way the Spider Valve amps work. The channel volume is simply that. It controls the volume of each channel in the preamp. The master volume is the overall preamp volume.

[radatats]

that totally lollipop sucks balls... so the DT master does the same thing as the POD master, just controls the signal level  being applied to  the power section...  What about with the POD hooked up by L6 link?  you mean to tell me we are just adding 2 master volumes to the same signal before it hits the power section?  So its just a fixed level tube power amp being driven by a variable preamp signal...  totally lollipops with my understanding of how this beast works...  I am not a happy camper right now...  WTF did they bother unlocking the POD master for with the last firmware update?  Doesn't make sense...

[innovine]

Now would be an excellent time for a 'I told you so!' :)

And my personal favorite annoying quote 'if it sounds good it is goood!'

 

As you pointed out, post preamp effects benefit from the ability to attenuate.

[phil_m]

Fwiw, having the master volume before the effects loop isn't all that uncommon. I used to have an Egnater Tweaker and I still have an Egnater Renegade, and both of them are like this, too. I also think it's common in Fender amps with effects loops. The preamp is there to regulate the volume into the power section. I think guitarists are taught to think that the drive or gain control is the preamp volume and the master volume is the power amp volume. In practice, that's not a bad way to think about it, but the reality is, I believe, that tube power sections are always running at full open. How hard they are pushed depends on how hot the signal is going into them.

 

As far as why Line 6 "unlocked" the master volume on the HD500 in the latest update, it was purely for convenience. It just gave people a way to adjust the volume on the HD500 instead of walking back to the amp.

[radatats]

so I guess I have wasted a lot of time on this bulloney...  I might as well just go from the left 1/4 out into the FX return and out to my PA speakers in Studio Direct and not have to worry about making different patches for the DT.  All that lollipop about setting the DT master and the POD master to get power amp distortion a total waste of time... not to mention I no longer believe half of what I read so I am going to stop trying to give advice or help.  All you Line 6 Experts can step up to the plate...

 

Really Line 6, publish the block diagrams and signal flow so we can stop trying to figure it out...  :angry:

[phil_m]

so I guess I have wasted a lot of time on this bulloney...  I might as well just go from the left 1/4 out into the FX return and out to my PA speakers in Studio Direct and not have to worry about making different patches for the DT.  All that lollipop about setting the DT master and the POD master to get power amp distortion a total waste of time... not to mention I no longer believe half of what I read so I am going to stop trying to give advice or help.  All you Line 6 Experts can step up to the plate...

 

Really Line 6, publish the block diagrams and signal flow so we can stop trying to figure it out...  :angry:

 

Well, if you have a POD connected via L6 Link going straight from the 1/4" out won't sound right because the POD won't be in Studio Direct mode. It will be in one of the Front modes.

 

I guess I don't completely see what you're upset about. I do agree that block diagrams would be useful. But the location of the master volume doesn't change the fact that in full volume mode, the signal going to the XLR out is tapped off of the output transformer, so it does benefit from the power amp being pushed.

[radatats]

For a long time after the last firmware update we were all I was under the impression that unlocking the POD master in L6 link freed us up to jack the DT master and load the power section while we decreased the pre section output.  In reality all that jerking off was a waste of time since both masters attenuate the pre section out before hitting the power section.  Might just as well leave either one maxed and control with the other.  We are not changing the power section one bit, only the signal being applied to it.

 

As far as the other thought, obviously not connecting with L6 link, just going from the left 1/4 out into the FX return and staying in Studio Direct.  Basically just gives me a straight tube power amp.  I can use the switches to set it up the way I want and just use all the FRFR patches without having to make special DT ones.

 

I am just really tired of trying to figure out how this thing is really working, having to jump back and forth between multiple manuals for snippets of info that sometimes seems to conflict, only to find out that isn't what's actually going on anyways...  and finding out a lot of what I thought I was helping others with was pure lollipop...

[TheRealZap]

yeah but going by a non-L6LINK cable gets you into ONE power amp....

the L6LINK cable allows you to reconfigure the power amp on the fly... class A/AB, Negative feedback, etc etc

[radatats]

  BFD... I rarely use any more than one configuration anyways... maybe we'll find out later that's all done pre power section anyways...  psyche... modeled relay switching...

[Brazzy]

I am just really tired of trying to figure out how this thing is really working, having to jump back and forth between multiple manuals for snippets of info that sometimes seems to conflict, only to find out that isn't what's actually going on anyways...  and finding out a lot of what I thought I was helping others with was pure lollipop...

 

I don't try to figure out these devices completely so what I do is just use my ears and keep trying different things and taking mental notes. Whenever I mess around with these things I allott a small amount of time to configuring and alot more time playing guitar this way I don't become obsessed with details and focus more on playing. I spend alot of time just playing guitar into a small amp with a bit of reverb just to keep my fingers tuned.

[TheRealZap]

makes a world of difference between sounding like a modeled amp and sounding like the real thing to me...

 

and it's not "faked" haha.

 

  BFD... I rarely use any more than one configuration anyways... maybe we'll find out later that's all done pre power section anyways...  psyche... modeled relay switching...

[radatats]

do they sound like modeled amps going FRFR when that option isn't even available?  hmmm...  I mostly prefer topology III...  I made a suggestion on idea scale to enable topology modeling in the full amp models...

[phil_m]

do they sound like modeled amps going FRFR when that option isn't even available?  hmmm...  I mostly prefer topology III...  I made a suggestion on idea scale to enable topology modeling in the full amp models...

 

Are you saying that you want to be able to choose the power amp topology in the models as well? That actually would be pretty cool. That would make it so you could build hybrid amp models within the POD itself. I don't know if something that's feasible or not. I like the idea, though.

[TheRealZap]

no... but you probably shouldn't be using the full models in an L6LINK situation... like you would in an FRFR situation...

you of course could... but anyway...

 

do they sound like modeled amps going FRFR when that option isn't even available?  hmmm...  I mostly prefer topology III...  I made a suggestion on idea scale to enable topology modeling in the full amp models...

[radatats]

Are you saying that you want to be able to choose the power amp topology in the models as well? That actually would be pretty cool. That would make it so you could build hybrid amp models within the POD itself. I don't know if something that's feasible or not. I like the idea, though.

 

yes, in the models, be able to choose the topology...  not for L6 link use, for FRFR use with just modeling.

[MartinDorr]

While we're all going at it I throw in a hunch (unverified observation) that if true will make you use Line 6 Link and not go directly to the effects loop return.

I tried in the past (not very successful considering the effort and outcome) to balance volume of different tones by measuring RMS levels via USB assuming this signal will be sent to the DT for amplification.

My assumption was that if I send balanced power levels to the DT _AND_ use the same power amp configuration I should end up with same level volume out of the speakers.

Not so. I got so frustrated from this not working that I gave up before remeasuring and tripple checking everything, but my conclusion was that the HD is sending at least the Drive setting to the DT via Line 6 Link and Drive is used by the power amp stage and thus changes the volume and tone the power amp stage produces.

In other words even though Drive changes the preamp level (besides the tone), balancing preamp output levels sent to the DT will not produce balanced volume even if the same power amp type is used if the Drive settings of the tones are different. The effect seems to be most pronounced with the higher feedback types.

As I said earlier this would need to be rechecked before it can be trusted because I really dropped the ball in frustration and went back just playing rather than measuring and looking for the ellusive truth we all seem to be hunting off and on.

[radatats]

As I said earlier this would need to be rechecked before it can be trusted because I really dropped the ball in frustration and went back just playing rather than measuring and looking for the ellusive truth we all seem to be hunting off and on.

 

thanks bro... probably right.  Just play the damn thing and quit trying to figure it out.  I mean it, I am going to lay off the help and advice and let our resident experts chime in instead.  I will keep my separate patches too.  I still have one more piece to get to complete my FRFR rig and I will decide then if I am going to keep both.

[tankaviator]

Ok, so to try to bring this back a bit....

 

• Low Volume Mode On, Amp in Standby = Direct Out signal consists of the “Full†(preamp + power amp) Amp Model with no analog amp.

• Low Volume Mode Off, Amp On (not in Standby) = Direct Out signal consists of the “Preamp†Amp Model with the analog amp.

• Low Volume Mode On, Amp On (not in Standby)= Direct Out signal consists of the “Full†Amp Model and the analog amp.

 

This *seems* to indicate that LVM on, STDBY using the XLR out should provide a signal with the effects loop applied to it. According to iknowathingortwo's post above (which mirrors my own experience) the only time the effects loop is included in the XLR out is when the amp is fully on...

 

Low Volume mode OFF:

Amp On (not in standby):   FX Loop heard on direct out

Amp Off (in standby):  Nothing

 

Low Volume Mode ON:

Amp On (not in standby): FX Loop NOT present on direct out

Amp Off (in standby); FX Loop NOT present on direct out

 

 

So the only time it works is when the amp is fully on.

 

So, is this the expected behavior or not? I don't necessarily care how the master volume is wired up as long as it controls the overall volume in an intuitive manner. But the effects loop being bypassed is really bad. Of course the effects loop on a POD is applied before the XLR out and doesn't suffer the same fate as the 1/4" connectors (assuming an L6Link cable is used). Is this just a way to push people towards getting a POD? Honestly I'm starting to think I should sell my DT 25 and go looking for a decent head with nice clean and eye watering distortion channels (oh I would love to get a Nitrox).

[innovine]

'expected' is a bit of a loaded term. Sure, teh fx loop doesn't work with LVM, but personally I think LVM sounds bad anyway, and I don't use it, so the fx loop thing doesn't bother me. Turning the channel volume down works better than LVM for low volume, for me.

[tankaviator]

No, 'expected' isn't an overloaded term in this case. We use it all the time in the software industry. It just means that these modes were intentionally created like this (for whatever reason) as opposed to being a side effect or byproduct of some other decisions or a bug in the firmware.

 

I can try full volume mode with the master turned down. Is the direct out signal line level or does it vary with the master volume? When I play at home I use headphones from my mixer (which is connected via the XLR cable) which is why I am curious. 

[innovine]

I'd say its working as designed, but customer expectation would be that the fx loop always works.

 

The signal from the direct out is mic level and varies with the master. I do like this: set master pretty low. Set channel volume to taste. You can also set pod hd500 master lower if thats in the chain*. Then run the direct out to a good mic preamp. This gives me low room volume, fx loop and a usable direct signal. I wouldn't commit to a serious recording \ike this but its fine for scratch tracks or composing, jamming, etc

 

*this is preffered over channel volume if you have pod fx after the preamp. Channel volume attenuates aft'r the preamp, then come possible effects, then the pod master attenuates as the signal leaves the pod and enters the dt25. I don't know if the dt master is before or after the fx send but its definitely before the return :( I don't use the fx loop much, perhaps someone else can chime in for that

[talwilkins]

Low Volume mode OFF:

Amp On (not in standby):   FX Loop heard on direct out

Amp Off (in standby):  Nothing

 

Low Volume Mode ON:

Amp On (not in standby): FX Loop NOT present on direct out

Amp Off (in standby); FX Loop NOT present on direct out

 

 

So the only time it works is when the amp is fully on.

 

 

Just recorded something via XLR in Low Volume Mode and in Standby.

I have a ZOOM G5 in the effects loop.

The effects from the ZOOM were part of the signal, no doubt about it.

[innovine]

Just recorded something via XLR in Low Volume Mode and in Standby.

I have a ZOOM G5 in the effects loop.

The effects from the ZOOM were part of the signal, no doubt about it.

 

Are you sure you are not mistaken? I am most certainly not hearing any fx loop action on my direct out in LVM mode and in standby.

I am using a DT25 with no pod connected.

guitar -> dt25 in -> dt25 fx send -> dist pedal -> echo pedal -> dt25 fx return -> xlr out 

There is NO dist or echo in the signal (and i can even disconnect the input to the dist pedal), makes no difference when the amp is in LVM and standby

[talwilkins]

Sorry, my bad.

I am using the POD and of course have the ZOOM in its effects loop not the DT's

:unsure:

[ColonelForbin]

It does work that way... The master volume has no effect on the power section output. It's easy to prove. Simply plug something into the effects return. The master volume knob doesn't do anything when you do that. So going into the effects return plugs you into the power amp with the power amp full open. The master volume attenuates the input going into the power amp. This is the same way the Spider Valve amps work. The channel volume is simply that. It controls the volume of each channel in the preamp. The master volume is the overall preamp volume.

 

Sort of. Try this: using the MIDI editor, set up a channel on a DT to have 'no amp model'. Guess what? The gain and channel volume no do nothing, but ya know what? The master volume still functions just fine, and that master controls the power amp volume. However, what you are saying is likely accurate in the more common scenario with an amp model defined in the DT.

 

I use this trick when Linked to my HD500x when I want the JTV acoustic and reso models to sound good. If you want to test it with the HD, be sure to also define 'no amp model' in your HD patch.

 

It's a worthy topic to revisit with the impending release of the Helix, because the more folks understand how the signal flow of the DT works, the more options they will have to make them play well together. Like, the fact that the DT reverb is applied before the DT fx loop send. OR that there is a 'boost' setting that does impact the volume on the DT25, not just the DT50, and you can switch it on or off for any of the 8 channel / A-1-4, B-1-4 amp configurations.

 

I tend to agree, that the power amp is always going 'full open', because when I set up my DT like this - with no amp model - it's way louder than with the channels that have preamps assigned.

[MartinDorr]

Sort of. Try this: using the MIDI editor, set up a channel on a DT to have 'no amp model'. Guess what? The gain and channel volume no do nothing, but ya know what? The master volume still functions just fine, and that master controls the power amp volume. However, what you are saying is likely accurate in the more common scenario with an amp model defined in the DT.

 

If you plug an anlog signal into the DT effects return you have no DT Master control. If you link to the DT via L6 Link or via the normal Guitar Input and AD conversion you end up in the DT DSP and even if you select no amp model you exit via DT Master controlled DA conversion (optionally sent to effect send).

 

I use this trick when Linked to my HD500x when I want the JTV acoustic and reso models to sound good. If you want to test it with the HD, be sure to also define 'no amp model' in your HD patch.

 

The most flexible way of doing this is to setup a dual path tone with the power amp selection in HD path A and muting path A in the mixer. HD path B is used to setup an effects only, or a possibly a different (pre)-amp model.

 

It's a worthy topic to revisit with the impending release of the Helix, because the more folks understand how the signal flow of the DT works, the more options they will have to make them play well together. Like, the fact that the DT reverb is applied before the DT fx loop send. OR that there is a 'boost' setting that does impact the volume on the DT25, not just the DT50, and you can switch it on or off for any of the 8 channel / A-1-4, B-1-4 amp configurations.

That is interesting! Are you saying there is a MIDI command for the DT25 (same as for DT50) or do you rely on a known side effect of selecting selective preamps that boost the DT25 signal level to engage the DT power amp setting?

[ColonelForbin]

 If you plug an analog signal into the DT effects return you have no DT Master control. If you link to the DT via L6 Link or via the normal Guitar Input and AD conversion you end up in the DT DSP and even if you select no amp model you exit via DT Master controlled DA conversion (optionally sent to effect send).

 

Interesting, I hadn't thought about it like that. I wasn't sure how much processing happened when not using the onboard DT preamp. It does seem that since the master volume is defeated when using the FX return input only vs. the guitar input, that something different is occurring.

 

I didn't set out intending to do this, I stumbled upon it! I posted which preamp models have that boost 'on' by default in a previous post. What I am most zoned on is, skipping the DT preamps, while still being able to adjust the power amp / topology settings, for use with the Helix. I still haven't head any official 'yay' or 'nay', about using this no preamp setup, and then routing the XLR out of the DT (with no cab modeling or mic modeling) back to the Helix to run through IR's / Helix cabs / Helix mic models.... It seems feasible, in theory..

 

In general though, one would guess that since you can adjust the topology and power settings with the DTEDIT midi editor standalone, independent of the preamps, IE, with no preamp defined onboard the DT, that you can probably also figure out what those MIDI commands need to be, from Helix or some other device that can do MIDI commands.  I have very little MIDI experience, so I haven't gone down that rabbit hole yet..

 

I had tried the dual path / mute trick that you mentioned, way back when Radatats first suggested it - same basic idea. Skip the preamp, and just use the power amp.

 

What I wasn't thinking of, was that the input jack, even when skipping the DT preamps, was still going through some sort of DSP or digital / A/D/D/A conversion. In my head, since it skipped the preamp, it skipped the A/D - but since the master does function in that scenario, your observation seem the most likely to be accurate.

[MartinDorr]

Where did you post your list of amps with and wo boost? I am real curious to compare with my own 'list'.

I found I can do the power amp boost via preamp selection in the HD and then mute the path A. I am attaching my list.

Will be interesting to see how they line up.

 

There 2 more interesting things I found out about the DT power amp section:

1. There is no builtin preamp that can select boost for Type II, but your direct control may work and be either on or off.
2. Presence on the DT has impact on power amp tone when higher than 50% to different degree for different Types (for Type III it does not do anything)

I did not get the model packs, i.e., have not checked how they fall into the different groups or show new behaviors ...

 

Enjoy,

Martin

 

DT25 Power Amp Parameters.pdf