What part of a amp's design gives the best chance for high gain pinch harmonics?

[leftu2]

Newbie here trying to learn amps. Have read a lot on here and on rob robinette's site.

This is a question I've had for yrs (way before I knew anything about how amps work).


Anyways, trying to finish up the mods on my peavey vtm 120 (has many jcm 800 traits).

***  as far as maintenance/upgrades go, I've done a full cap pwr job with F&T caps and replaced all the caps in the amp except the one on the output board as you gotta drill some pop rivets to pull the board up, previous owner installed an adjustable bias pot and resonance control. Amp is running fairly new JJ 6L6s and I put in a new set of EH12ax7s ***

I have this amp doing exactly what I want except for 1 thing which is, I have to use way too much gain to get good pinch harmonics.
Let me stop here and say IT'S NOT A PLAYING TECHNIQUE PROBLEM......LOL.
I've spent many many yrs playing satch, vai, gilbert type music.
I swear, I posted this on another forum and reply after reply was about technique...???????

I know it's not the pickups (I'm using a rg550 with a original dimarzio evo). I want the pinch harmonics to be very easy to get. Listen to the opening lick on the DLR version of tobacco road and you can here what I'm talking about. If I use a ts-9 I get them easy but there is waaay to much distortion. I have a slo 100 homebrew that has el34s. On the crunch channel with a ts9, the pinch harmonics are easy as pie to get.......with much less gain than I have to use with the peavey vtm. I know they are totally different amps.....lol.

I have a feeling my answer is (and I'm guessing here) it's the way the preamp tubes are configured as far as not being pushed enough into asymmetrical distortion with out a pedal or is it the cold clipper value? The peavey has dip switches,position 1 &  2  are gain boosts. The 1st dip switch add a 4.7k (R14) in series (I think) with the standard 6.8k (R5) for the cold clipper. I think they wanted to try to get close to the 10k marshall rating when combined. With the 1st gain switch on, still can't get hardly any pinch harmonics, but gets closer...the amp is trying for lack of a better description (the notes are chocked). Again, with the ts-9 and the gain 1 dip switch engaged, piece of cake but it's over kill on the gain. Vai isn't using nearly that much on the tobacco road track.


Again, what part of the amp design makes getting pinch harmonics easier than others?


1. Do I need to change the preamp tube components (plate/cathade resistors etc)? I'm still at the stk  vtm cathode values and plate values.

2. Do I only need to increase the cold clipper value?

3. Is there some filtering in the peavey that's preventing it?

4. (out of curiosity), on the 2nd dip switch I know it's adding a .68 cap to the cold clipper circuit but what is the function of the 1k resistor (R15) that's in series right after that .68 cap? More gain?

Again, I'm really trying to learn this stuff so I welcome your answers

(Here's the vtm schem and layout if anyone is interested.)

[SILVERGUN]

Again, what part of the amp design makes getting pinch harmonics easier than others?

1. Do I need to change the preamp tube components (plate/cathade resistors etc)? I'm still at the stk  vtm cathode values and plate values.

2. Do I only need to increase the cold clipper value?

3. Is there some filtering in the peavey that's preventing it?

4. (out of curiosity), on the 2nd dip switch I know it's adding a .68 cap to the cold clipper circuit but what is the function of the 1k resistor (R15) that's in series right after that .68 cap? More gain?

Again, I'm really trying to learn this stuff so I welcome your answers

(Here's the vtm schem and layout if anyone is interested.)

I'd love to help more but that schematic gave me a headache. If you really want to tweak your amp then it would be a huge help to see an actual, cleaned up version of a schematic that includes the mods you have made.

1) That is part of it but there are different ways of approaching the issue....need clear schematic
2) No
3) There are 2 main types of filtering that happen. DC power supply filtering which doesn't really effect TONE and interstage R/C filtering that is done to "voice" the amp. So, yes, you'll need to adjust some interstage filtering to achieve your goal.
4) I can't see it in the schematic (blurry) but I'll just believe you. If there is a 1K resistor in series with the .68 bypass cap then I would consider that a "boost limiting" resistor, and it does just that by limiting the effect of the .68 cap.

I have to use way too much gain to get good pinch harmonics.

#metoo 

[EL34]

The answer is "Your thumb"

[PRR]

I accept that your technique is FAR-FAR better than mine. But: It's a finger/string thing. I don't see how the amplifier would know how the sound was generated.

[leftu2]

I accept that your technique is FAR-FAR better than mine. But: It's a finger/string thing.

I swear I'm not trying to be a jerk and get on my soap box as far as the technique goes. I just want to stress it's not the issue. I'm as humble as they come.....lol

I don't see how the amplifier would know how the sound was generated.

My understanding is that you can make amp distortion more asymmetrical to enhance even order harmonics.
I knew about the symmetrical vs asymmetrical clipping but didn't understand it very well untill I found this site today:

https://www.effectrode.com/knowledge-base/guitar-preamp-tone-explained/

An excerpt from it on symmetrical clipping:
 
 "The fundamental is a 440Hz sine wave (‘A’) and strong 3rd, 5th, 7th, etc harmonics are clearly present in the output signal. Even harmonics are also present, however at reduced amplitude in comparison to the odd harmonics. Although center biased symmetric clipping distortion is beginning to approach a square wave, the rounded edges ensure that brittle-sounding high order harmonics are absent."

Imho, this...."the rounded edges ensure that brittle-sounding high order harmonics are absent..... might be one of the reasons why amp design has something to do with it. I'm assuming the rounded edges are preventing me from making it do what I want. Am I reading this wrong?

From the same article on asymmetrical clipping:

"Asymmetric clipping generates a signal rich in even and odd order harmonic overtones. The second harmonic is particulary strong , which is almost certainly one of the reasons tube amps sound so musical – the second harmonic is exactly one octave above the fundamental. Both symmetric and asymmetric clipping occur in a multi-stage tube preamp and it will consequently produce a tone that is a complex mix of even and odd order harmonics."

Also the artical clearly states that :
"Cold biasing is used in many modern triode high gain tube amp designs as it adds rich, harmonic content...."

The slo has a 39k cathode resistor. Most marshalls have a 10k.




 

[leftu2]

I do appreciate everyone's help. Please be patient with me

[shooter]

symmetric

put a couple clipping diodes at the grid to the 2nd ax7, you'll have to find an "example" schematic, my plates full

[66Strat]

Have you ruled out the speaker? There are a lot of guitar speakers where the frequency response drops of significantly at around 5k hz.

[leftu2]

symmetric

put a couple clipping diodes at the grid to the 2nd ax7, you'll have to find an "example" schematic, my plates full

Thanks for the suggestion. I'll try to find a schematic.

[leftu2]

Have you ruled out the speaker? There are a lot of guitar speakers where the frequency response drops of significantly at around 5k hz.

I don't think it's a speaker as when using the soldano, I've not found a speaker that won't do what I want it to do. I've probably played through 4 or 5 different types. Actually my main cab is a old hughes & kettner 2x12 cab from the 90s that has some fairly dark speakers in it compared to most I've heard. They are rockdriver vintage series v12s that were made for h&k by eminance (I confirmed this via email with them).

[BrassElephant]

The abundance or absence of even harmonics vs odd harmonics probably won't make even the slightest difference in the ease of pinch harmonics sounding out. (The terms 'harmonics' should not be conflated here, they are referring to two different phenomana.) You'll have far more variances trying different drive/compressor pedals before an amp.

Think of it this way, the amp adds even/odd harmonics to the sound that is INPUT into the amp. It doesn't dramatically increase the CHANCES of that input being a pinched harmonic sound. It's totally in your fingers.

Try this; list your top 10 favorite pinched harmonic moments in music. Research relentlessly each artist and their respective rigs.

Do all 10 use the same amp?

Yes? Build that amp.

No? What else does each rig have in common? Pedals? Guitars? Strings? Picks? Etc, etc

(Hint: the common thing to each rig is gonna be the fleshy bits attached to their hands)

[pdf64]

My guess is that it may work better to turn the gain low and volume high.
A lower power amp may help with that.

[tubeswell]

High impedance pups will help.
Sticking a fuzz pedal in front of any tube amp will help with sustain and pinch harmonics. If its battery powered, there's a point at which the battery starts to go flat in most fuzz pedals, where you get really great sag and bloom effects.
The harder you drive the amp, the better.
A bit of feedback from the PA to push the margins of stability is great too.


JM2CW

[VMS]

Here is little more readable schematic:


https://el34world.com/charts/Schematics/files/Peavey/Peavy_vtm_120.pdf


I would probably first try removing c16 (.001) and c15 (470pf) caps and see if that has any effect.

[SILVERGUN]

Because, of course the amp has a huge part in this.
Put Zach Wild in front of a Twin Reverb and he gets boooo'd offstage.
Replace that with an SLO and it squeals like a pig in a bear trap and thousands of black t-shirts find the meaning of life.

That schematic is much better VMS. Thanks!...it didn't strike me to look in Doug's closet

The first thing I saw was the same C15 - 470p dumping some highs to ground.


leftu2, if you don't have any alligator clip jumpers, now's the time.
Sign below to let me know you won't electrocute yourself.
______________________

In case you haven't seen it, here is some great circuit theory reading for the SLO:
https://www.ampbooks.com/mobile/classic-circuits/soldano-slo/

[shooter]

Sign below to let me know you won't electrocute yourself.
______________________

when I typed clipping diodes in audio path I found this

https://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

personnaly I'd hunt up a friend that has a scope that can display in frequency or a spectrum analyzer so you can experiment AND see, ears are kinda wonky, test equipment comes in handy to eliminate "mojo" 

[Rustynuts]

As a guitar player I know what your after.  You said your H&K was a dark sounding amp.  Personally I love this type of amp but they are harder to get those pinched harmonics happening.  An eq adjustment in the top end will definitely help.  Different speakers can help too.  Pedals often amplify certain frequencies, try and work out which ones and adjust the tone on your amp to suit.  Make sure your using the bridge pickup and the vol and tone are flat out.  New strings are a must. A heavier pick definitely helps too. You may know all of that already but I thought I'd mention it.  There's nothing like a nicely placed pinched harmonic.  🤘😎

[nandrewjackson]

+1 for removing c15 and c16.


Everything else,  aside from "response modifications "  is fairly straightforward jcm800/2204.  An extra DC coupled cathode follower after the FX send/return. But mostly a jcm800/2204. 


C15 and c16 can go.

[leftu2]

Try this; list your top 10 favorite pinched harmonic moments in music. Research relentlessly each artist and their respective rigs.

Do all 10 use the same amp?

Yes? Build that amp.

No? What else does each rig have in common? Pedals? Guitars? Strings? Picks? Etc, etc

For sure Marshalls are going to win the "type of amp the artist used argument" Satch once said marshalls are the most revealing amps you'll ever plug into. I love amps that show every little nuance. My slo does that. As far as owning a marshall goes, this  vtm is the closest to a marshall I've ever owned. I'll look into the drive pedals they used for sure.

[leftu2]

Because, of course the amp has a huge part in this.
Put Zach Wild in front of a Twin Reverb and he gets boooo'd offstage.
Replace that with an SLO and it squeals like a pig in a bear trap and thousands of black t-shirts find the meaning of life.

I agree

leftu2, if you don't have any alligator clip jumpers, now's the time.
Sign below to let me know you won't electrocute yourself.
______________________

Lol....consider it signed. I have jumpers. I built a cap bleed tool using a large resistor and have already performed a cap job. I'll stay safe...

In case you haven't seen it, here is some great circuit theory reading for the SLO:
https://www.ampbooks.com/mobile/classic-circuits/soldano-slo/

I've seen that and read it a few times, it's a bit advanced for me right now but I've picked up some stuff for sure.

[leftu2]

when I typed clipping diodes in audio path I found this

https://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

personnaly I'd hunt up a friend that has a scope that can display in frequency or a spectrum analyzer so you can experiment AND see, ears are kinda wonky, test equipment comes in handy to eliminate "mojo" 

Thanks for the link, unfortunately I don't know anyone who has that stuff.

[leftu2]

As a guitar player I know what your after.  You said your H&K was a dark sounding amp.  Personally I love this type of amp but they are harder to get those pinched harmonics happening.  An eq adjustment in the top end will definitely help.  Different speakers can help too.  Pedals often amplify certain frequencies, try and work out which ones and adjust the tone on your amp to suit.  Make sure your using the bridge pickup and the vol and tone are flat out.  New strings are a must. A heavier pick definitely helps too. You may know all of that already but I thought I'd mention it.  There's nothing like a nicely placed pinched harmonic.  🤘😎

My amp isn't a H & K, the cab is. I sold the matching attax 100 tube/ss hybird to a buddy yrs ago. Funny, with a ts-9 into the lead channel, that thing roared and reproduced everything I threw at it. I do like a heavy pick, I use 1mm claytons.

[leftu2]

+1 for removing c15 and c16.


Everything else,  aside from "response modifications "  is fairly straightforward jcm800/2204.  An extra DC coupled cathode follower after the FX send/return. But mostly a jcm800/2204. 


C15 and c16 can go.

Thanks to you and silvergun for those suggestions, I'll give 'em a shot.

[KeithR]

With that amp I don't know if you'll will be able to get to there from here. A friend of mine bought that amp because he had read a review stating it bad been used by Vivian Campbell on the whitesnake song here I go again. Of course he thought they were referring to the high gain sustaining riff that carries the song. when in fact the vtm was used for that brief solo where you can hear every single note played in rapid succession with a lot of compression. He ended up selling it for less than half off at what he paid. So I guess what I'm saying is without a lot of work on that PC board, and the resulting headaches therein,y will not find what you're looking for.