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#1 leewhit6

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Posted 21 August 2013 - 08:19 AM

Just wondering if anyone knows why the capacitor values of some guitars are not standard? Is this the way Line 6 intended or is it a mistake? Some examples: Tele models are .22, not .047, Strat models are .047, not .22. The Gretsch models are off correct specs too. I think there are some others not quite on as well. Does anyone think this is the way they meant for it to be because it sounded better to them? Maybe those particular modeled guitars were altered that way? Could it just be a glitch?

    


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#2 snhirsch

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Posted 21 August 2013 - 08:33 AM

While we're on the subject of cap values, I remain puzzled as to why the Variax does not model volume pot bypass caps.  Many electric guitar models use these to brighten the tone at low settings and I find it critical to getting a good, cleaned-up rhythm sound.  This should certainly have been a simple effect to model.  It doesn't even need to be linear,  a lookup table based on volume pot position probably would have done the trick.


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40 years of Rock-n-Roll and proud of it!

 

PRS Custom 24 (1990) w/ GK-3 Hex PU

James Tyler Variax JTV-69(k) w/ Strat Neck

Roland GR-55 Guitar Synth

QSC K10 FRFR

 


#3 ozbadman

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Posted 21 August 2013 - 10:54 AM

While we're on the subject of cap values, I remain puzzled as to why the Variax does not model volume pot bypass caps.  Many electric guitar models use these to brighten the tone at low settings and I find it critical to getting a good, cleaned-up rhythm sound.  This should certainly have been a simple effect to model.  It doesn't even need to be linear,  a lookup table based on volume pot position probably would have done the trick.

 

The reason it's important on standard guitars is that turning down the volume knob reduces the peak of the resonant frequency due to it's passive circuit with the cable capacitance. That is, turning down the volume knob actually changes the tone, which is an unintended consequence. It's possible that Line 6 didn't model this (some would say, unfortunate) characteristic and therefore, volume pot bypass modelling is unnecessary. I don't have my JTV to test this but personally, I would prefer they didn't model the volume pot tone variations as it's not very useful. I want my volume to control volume only. I can use tone when I want to change the tone. Does anyone know if the tone changes on the JTVs when you reduce the volume using the volume control? (I'm talking about with clean signals, not an overdriven amp).


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#4 snhirsch

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Posted 21 August 2013 - 11:13 AM

From an electrical standpoint, that's not quite correct.  What it does is form a first-order high-pass filter when the control is at lower settings.  The volume pot acts as a voltage divider and you can think of the cap as allowing higher frequencies to "bleed around" it and thus not be reduced as much as lower ones.  There is some unavoidable interaction with cable capacitance as well.  Some day when I have some time on my hands, it would be fun to do a SPICE simulation (electrical model) of the entire pickup, volume, tone and cable circuit. Maybe when I retire :-)

 

But anyway, technicalities aside, I agree with you that not everyone will want this effect.  That's why it should be an option in the HD workbench, just like tone control capacitance. 

 

I've always relied on the effect to clean up my guitar when backed down for rhythm parts.  Since it's a standard feature on a lot of production guitars, I'm probably not the only person who likes it.


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40 years of Rock-n-Roll and proud of it!

 

PRS Custom 24 (1990) w/ GK-3 Hex PU

James Tyler Variax JTV-69(k) w/ Strat Neck

Roland GR-55 Guitar Synth

QSC K10 FRFR

 


#5 stevekc

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Posted 21 August 2013 - 11:45 AM

I've always relied on the effect to clean up my guitar when backed down for rhythm parts.  Since it's a standard feature on a lot of production guitars, I'm probably not the only person who likes it.

 

Count me in  - I also enjoy the effect of the 150pf cap across the two hot leads on my 500K volume pot. On some of my guitars I can switch this cap in or out as needed.

 

In the past i have used a guitar with P90's with a volume pot bypass cap mod, and set the Vol on "7" (= brighter tone) + a EHX  LPB-2 Booster to achieve a Roy BuchananTele lead tone from my LP Junior.

 

The volume pot bypass cap  is also good for nailing funk rhythm parts too.


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#6 stevekc

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Posted 21 August 2013 - 11:55 AM

For me, one of the advantages of active guitars is they don't have this issue.


But then you are stuck using an "EMG" like tone without any warmth all the time.

Myself - I really like both my Tyler Variax's (JTV-59 and JTV-69 ) - but truth be told I only use the Variax modeling for Alt tunings - or those times when the first set at my live gig must be low volume "acoustic" set.

90% of the time I use GFS Rectotrons (poor mans TV Jones Filtertron sound) + a pair of Duncan Tripleshot rings to dial in my tone.(Sereis / parallel/ or select which single coil is active) IMHO - Variax still has difficulty nailing many palm bridge Muting tones that a guitar with normal passive mag pickups can easily achieve

1372711222_1186581443_20130523_022424_zp


All details on this guitar here:
http://www.vguitarfo...g62105#msg62105
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#7 snhirsch

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Posted 21 August 2013 - 12:00 PM

Actually, the volume control acts as a voltage divider and the upper part of the pot acts a damper of the resonant frequency of the inductor with the cable capacitance.

 

 

So I'm a little confused. Are you saying you rely on the tonal variations when you decrease the volume for rhythm parts? I thought you originally were saying you wanted to be able to disable this so that you could maintain your high frequencies while turning down the volume (although I would call it characteristic frequency response). Do you find when playing rhtyhm you prefer the sound of a volume pot at, say, 50%?

 

I agree that it's a standard thing on passive guitars (although the exact variation will depend on the cable and amp), so it's possible some would miss it. For me, one of the advantages of active guitars is they don't have this issue. Turning down the volume on a Strat makes it lose it's strat-like sound, albeit that's the way it's always been. I'd be interested to know if this is currently modelled or not.

 

The issue of which electrical effect dominates is certainly up for discussion - only a set of analog simulations at various frequencies, pickup impedances, cap values and control settings will reveal all.  Getting a reasonable coverage of the variable space would be a bit time-consuming. Are you aware of any papers on the subject?  It sounds like something that one or more of the botique pickup vendors might have done.  And, now that I think more on it, this is an obvious subject for an undergrad EE paper.  Someone has certainly done this - more likely many someones.

 

And - sorry for any confusion - I'm indeed saying that I want the effect.  I've come to rely on it to dial in on a good rhythm sound.  I generally start with volume full-up and dial in a solo tone, then back down (sometimes way down, depending on how far into overdrive I was) until I get a more zingy rhythm sound.  Sometimes it takes a couple of rounds to converge on something that works.  It's just the way I've always done it.  Again, maybe not for everyone.


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40 years of Rock-n-Roll and proud of it!

 

PRS Custom 24 (1990) w/ GK-3 Hex PU

James Tyler Variax JTV-69(k) w/ Strat Neck

Roland GR-55 Guitar Synth

QSC K10 FRFR

 


#8 ozbadman

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Posted 21 August 2013 - 12:00 PM

Hey Steve,

 

Slightly off-topic, (well, miles off-topic) and I don't want to hijack the thread, but I bought the triple-shot rings myself and when I went to install them, the screw-holes didn't quite line-up. Did you have to drill into your 59 to make this fit?

 

Thanks,

 

David.


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#9 ozbadman

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Posted 21 August 2013 - 12:09 PM

The issue of which electrical effect dominates is certainly up for discussion - only a set of analog simulations at various frequencies, pickup impedances, cap values and control settings will reveal all.  Getting a reasonable coverage of the variable space would be a bit time-consuming. Are you aware of any papers on the subject?  It sounds like something that one or more of the botique pickup vendors might have done.  And, now that I think more on it, this is an obvious subject for an undergrad EE paper.  Someone has certainly done this - more likely many someones.

 

And - sorry for any confusion - I'm indeed saying that I want the effect.  I've come to rely on it to dial in on a good rhythm sound.  I generally start with volume full-up and dial in a solo tone, then back down (sometimes way down, depending on how far into overdrive I was) until I get a more zingy rhythm sound.  Sometimes it takes a couple of rounds to converge on something that works.  It's just the way I've always done it.  Again, maybe not for everyone.

 

Yeah. Sorry, I re-read your original post and it became clearer, so I deleted my post.

 

Helmuth Lemme has just released his excellent book in English, which I think is a must-read for anyone who's interested in guitar electronics and why different guitars and pickups sound the way they do. "Electric Guitar Sound Secrets and Technology". It was originally in German, so the translations are a bit dicey, but one can work out what he means.

 

Some of his work is here:

 

http://buildyourguit...esources/lemme/

 

So I gather that as of right now, the JTVs keep their characteristic sounds as the volume control is changed (unfortunately, mine is in another country at the moment, and I haven't tested this).
 


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#10 leewhit6

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Posted 21 August 2013 - 12:12 PM

There is a "load tone and volume defaults" tab on HD Workbench. For some reason the models are not preset to the correct values for all of the models. You must click that tab and pick the appropriate settings. Once that is done, it does make quite a big difference. The models sound much better in most instances. Sometimes it may show the correct match up on the tab, but click something else then go back and click the one that matches up with the model you have selected. Even though it may read as though it matches, sometimes it actually does not.
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#11 stevekc

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Posted 21 August 2013 - 12:13 PM

Slightly off-topic, (well, miles off-topic) and I don't want to hijack the thread, but I bought the triple-shot rings myself and when I went to install them, the screw-holes didn't quite line-up. Did you have to drill into your 59 to make this fit?

 

Indeed yes -  I did have to drill new mounting holes for the Tripleshot rings. (Factory Line6 Tyler JTV-59 pickup rings are slightly larger than Gibson, and identical to Godin xTSA PU rings - FWIW)

 

I found the factory holes on my JTV-59 to a bit random, On the bridge PU ring, I only have to drill three new holes - yet the end result both Tripleshot rings now line up and look "correct" to my eyes.

 

Some of his work is here:

 

http://buildyourguit...esources/lemme/

More Guitar Electronics resources (click link on left then British flag for English)

https://hps.hs-regen...itarre_eng.html

 

http://www.gmarts.org/index.php?go=200

http://www.gmarts.org/index.php?go=241

 

Response Effects of Guitar Pickup Position and Width (see attached)
http://www.till.com/...onse/index.html
By J. Donald Tillman


See Also:

Response Effects of Guitar Pickup Mixing
http://www.till.com/...xing/index.html

Pickup Response Demonstration Applet (Java)
http://www.till.com/...Demo/index.html


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#12 snhirsch

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Posted 21 August 2013 - 12:25 PM

Helmuth Lemme has just released his excellent book in English, which I think is a must-read for anyone who's interested in guitar electronics and why different guitars and pickups sound the way they do. "Electric Guitar Sound Secrets and Technology". It was originally in German, so the translations are a bit dicey, but one can work out what he means.

 

Some of his work is here:

 

http://buildyourguit...esources/lemme/

 

Yes, that's a great article.  I think the reason I always regarded it as a simple RC high-pass filter was because this same scheme is widely used for guitar amp channel volume controls.  There, you are not generally dealing with an inductance on either the source or load sides, and the load impedance is >> than the pot value (for a tube amp at any rate).   I think the original designers in the pre-R+R era were thinking about Fletcher-Munson loudness curves and trying to approximate that behavior on the high end.  Loudness compensation was a real staple on classic stereo gear, but I don't recall seeing a loudness switch in recent decades.  Now that I've thoroughly dated myself, I'll stop wandering off-subject :-). 


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40 years of Rock-n-Roll and proud of it!

 

PRS Custom 24 (1990) w/ GK-3 Hex PU

James Tyler Variax JTV-69(k) w/ Strat Neck

Roland GR-55 Guitar Synth

QSC K10 FRFR

 


#13 ozbadman

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Posted 21 August 2013 - 12:32 PM

My dad's stereo has a loudness pot!

 

Actually, I'd love to see a loudness (Fletcher-Munson EQ compensator) stompbox so my HD500 sounds I dialled in in my bedroom could be much closer when I get to a venue, rather than having to adjust the board so much. Anybody want to build one?


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#14 stevekc

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Posted 21 August 2013 - 01:18 PM

Actually, I'd love to see a loudness (Fletcher-Munson EQ compensator) stompbox so my HD500 sounds I dialled in in my bedroom could be much closer when I get to a venue, rather than having to adjust the board so much. Anybody want to build one?

 

 

Actually a Loudness Control (Fletcher-Munson EQ compensator) was part of the last Line-6 Vetta Firmware.

 

http://line6.com/sup...ve/thread/36600


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#15 ozbadman

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Posted 21 August 2013 - 01:26 PM

Actually a Loudness Control (Fletcher-Munson EQ compensator) was part of the last Line-6 Vetta Firmware.

 

http://line6.com/sup...ve/thread/36600

 

 Oh wow. Very sweet. Now, do I need a Vetta? Hmmm.


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#16 Sonny1096

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Posted 21 August 2013 - 07:33 PM

Just wondering if anyone knows why the capacitor values of some guitars are not standard? Is this the way Line 6 intended or is it a mistake? Some examples: Tele models are .22, not .047, Strat models are .047, not .22. The Gretsch models are off correct specs too. I think there are some others not quite on as well. Does anyone think this is the way they meant for it to be because it sounded better to them? Maybe those particular modeled guitars were altered that way? Could it just be a glitch?


I can't speak for L6 and answer the "why" part of your question, but I can confirm that this is real and not just your imagination. I noticed yesterday while exploring an issue from another thread, and was as surprised as you to find many of the values are not ideal for the pickups/models they are emulating. Not a huge deal as they can be changed to whatever you want in workbench... just seems sloppy as a starting point.
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#17 snhirsch

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Posted 22 August 2013 - 04:10 AM

My dad's stereo has a loudness pot!

 

Yeah, yeah, rub it in :-)   I suspect I'm closer to your Dad's age.


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40 years of Rock-n-Roll and proud of it!

 

PRS Custom 24 (1990) w/ GK-3 Hex PU

James Tyler Variax JTV-69(k) w/ Strat Neck

Roland GR-55 Guitar Synth

QSC K10 FRFR

 


#18 Charlie_Watt

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Posted 22 August 2013 - 05:36 AM

Me Too!  I still have one of those Stereo's (Stereo is pretty dated too!)


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#19 stevekc

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Posted 22 August 2013 - 11:09 AM

Im in the USA and the typical convention is to use microfarads - while nanofarads is used more in the UK / EU

http://www.translato...icrofarad-[µF]/

 

http://www.diystompb...p?title=DIY_FAQ

 

 

For those who want to know here is a conversion chart to make sense of the Workbench HD cap values

============================

1.1nF = .0011 uF (microfarads)

 

2.2nF = .0022 uF (microfarads)

 

4.7nF = .0047 uF (microfarads)

 

11nF = .011 uF (microfarads)

 

22nF = .022 uF (microfarads)  =  Typical Gibson Tone Cap with 500K Tone pot)

 

47nF = .047 uF (microfarads)=  Typical Fender Tone Cap with 250K Tone pot)

 

(.1uF) 100nF = .1 uF (microfarads)


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#20 stevekc

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Posted 22 August 2013 - 11:21 AM

http://www.tdpri.com...r-interact.html

tone_control_response_500K.jpg

TDOWNS Wrote

Ok. You just had to ask. So, I spent a little time with PSPICE today so you can see the electrical response of the tone pot. The pickup is a Tele bridge. The conditions are as follows:

    Pickup inductance = 3.2H
    Pickup resistance = 7.4K
    Pickup interwinding capacitance = 160pF
    Volume pot = 500K (set at max CW)
    Tone Pot = 500K but 442K actual
    Tone cap = 0.05µF
    Cable = 20ft
    Amp input impedance = 1MEG
    Amp input capacitance = 100pF


The labels on the graph are TONE KNOB SETTING (0 thru 10)/RESISTANCE. Remember it is a audio (non-linear) pot. The resistance values for the 0 through 10 positions are based on experimental data I collected on audio pots a few years ago.



Notice the resonance peak with no tone pot connected aka the no-load pot. You can now see how the TBX would give you everything between the max CCW and almost open.

I doubt some of you would experience the same no-load response as plotted because every amp input impedance is not as high as 1 meg. If the amp input impedance is more like 500K, that no-load response will be less pronounced. But, a Fender Twin is 1MEG input impedance.

Look at the curve for the 500K pot set on "8". Having a 250K pot (277K on the plot) is like a 500K pot turned down to "8".

Regarding the tone cap value, it matters most at a setting of "0". With the 0.05µF cap, the resonance is moved down to 300Hz. At other points on the dial, it is simply destroying the resonance at ~3.5kHz. If you used a smaller cap value, that resonance would be higher than 300Hz.
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