Hiwatt dr-103 tone stack after preamp section

[traktop]

I sent my amp to a tech to be serviced. We were talking for a long time about different kind of amp circuits, and he suggested me trying to move the tone stack after the preamp section; that way It would be more "usable", (specially when cranking it). I like what the tonestack does on a "clean setting", but it´s a fact that when cranking the amp, the tone stack feels almost invisible, (not a bad thing, since that tone is killer).
I was wondering if someone tried this before, and if that would change the character of the amp too much, (for good or bad, or just different...).
Cheers, Gilberto.

[Stevem]

If you like it leave it!
About the only thing I have do to a couple of customers 50 and 100 watt models and due to that fact that they play them cranked is to go into the tone stack it self and roll off some of the highs and this lets the treble control get opened up more, and in regards to the Bass that is always turned down to around 2 or 3 at those volume levels I roll off some Bass response with a lower value cap and then the player can open up the Bass control more and that end of the tone stack then sounds more natural as it acts like less of a restriction!
Basically my line of thinking is that if you have a axe that you like the sound of then backing down on the amps tone controls to get the sound you want only serves to choke the signal flow to use a non tech term and removes some touch and feel from the amps response!

[JoeCon]

Steve
"go into the tone stack it self and roll off some of the highs and this lets the treble control get opened up more."
Could explain more how you did this and what values you choose?

Thanks...

[Stevem]

Sorry, I need to correct myself somewhat!
In regards to the high end roll off I did that with a small value cap across the plate load resistor of V2A.
The low end I rolled back by dropping the value of the coupling cap on the Bass pot wiper.
The Partridge output transformers in these original made amps are of such high quality and over built that even when the amp is running flat out the highs get rolled back very little and with enough odd order harmonics coming thru by means of distortion from the preamp section this excess high end kills!
My buddy has 5 of these amps and I have made mods to all of them with different value components and he is still un desided as to which amp he or I like best!
So as of right now I can not pass along what to try out, but one thing is sure, that being these mods need to be done almost with one guitar in mind in terms of pickups used!

[traktop]

...if you have a axe that you like the sound of then backing down on the amps tone controls to get the sound you want only serves to choke the signal flow to use a non tech term and removes some touch and feel from the amps response!

My tech agreed with that.
Actually I tried to "tune" my amp with selected speakers/preamp nos tubes. I reached a point where sometimes I eq my amp just with preamp volume knobs and the presence knob while leaving the rest of the tone stack at noon, (I know that´s not really flat since the treble knob is -4/+10 and the mid knob is just 0/+7...), but almost any configuration would sound "decent".
Sometimes I like to tweak a little, but I realized that because of the interactiveness of the tone controls, when you attenuate, you are pumping the other frequencies as well and viceversa. That means that if you find the amp being dark, if you open the treble knob, by the time you reach your brightness point, you loose the original bass and mids.
My understanding on what you do when swapping cap values, is that you just get more "pot running" but no real changes on sound , right? Or you mean that changing caps values and using less the pot the amp would feels more "natural"...
I sometimes roll off some bass, but not becuse it sounds bassy... is just to let some warm mids breathe... It is fun and versatile but quite often seems like black magic or someting. Sometimes I feel like a rabbit pursuing a fast moving carrot, but never quite getting it.
The amp feels so good, but sometimes I feel that the eq is so far away from the output section that get lost on the way. So I was wondering if moving the PRE-PI-MV after the PI, and putting the tone stack just behind the MV, the eq would have more AUTHORITY so to speak...
Thank you anyway, just guessing here, and just wanted to know if something did something similar.

[Stevem]

Being able to too keep the pots in the tone circuit more wide open so to speak helps to keep the tone stack from draining away the tone and response you like from your guitar!
Also think about this, every time your guitars signal gets passed thru a cap its phase get shifted, so this is a manipulation in and of tis self and is why small class A amps with only two gain stages and than a output stage sound so good and natural, granted they are limited in volume unless you build a custom 30 watt parallel class A set up, and for some people they will not have enough gain and or distortion, but once you pass the signal thru 3 caps than on average what was the in coming signal is now 180 degrees out of phase with itself and not only does this change what was the natural sound you had, but this is the root cause of oscilation issues in amps that do not have a good build layout!
In light of this phase change issue, just look at the average tone stack that takes the signal as passes it thru 3 different caps just right there and there is no promiss that each cap will apply the same amount of phase shift!!!
In effect you are cutting the signal up and hoping it goes back together right pretty much!
Also note that the tonal nature of that first tube your signal passes through will be passed on down through the whole signal chain, so just in light of this I use my little blackface Fender Champ as a gauge for picking good sounding V1 preamp tubes for my customers and in all my personal amps!

Spending 24 bucks on a new highly tested preamp tube is no guarranty of good tone!

[traktop]

...every time your guitars signal gets passed thru a cap its phase get shifted, so this is a manipulation in and of tis self...

Interesting information, thank you. I was wondering if that same thing applies to the "presence" knob. I mean, leaving apart the fact that cranking the presence knob would turn my amp into an "ear butcher weapon" but knowing that I could play with different cap values to reduce that effect, would cranking the presence pot be the best scenario here in order to achieve a less "phase affected by the cap" sound¿
Cheers.

[martin manning]

Also think about this, every time your guitars signal gets passed thru a cap its phase get shifted, so this is a manipulation in and of tis self and is why small class A amps with only two gain stages and than a output stage sound so good and natural, granted they are limited in volume unless you build a custom 30 watt parallel class A set up, and for some people they will not have enough gain and or distortion, but once you pass the signal thru 3 caps than on average what was the in coming signal is now 180 degrees out of phase with itself and not only does this change what was the natural sound you had, but this is the root cause of oscilation issues in amps that do not have a good build layout!
In light of this phase change issue, just look at the average tone stack that takes the signal as passes it thru 3 different caps just right there and there is no promiss that each cap will apply the same amount of phase shift!!!
In effect you are cutting the signal up and hoping it goes back together right pretty much!

Phase shift through RC networks is frequency dependent. For RC HP and LP filters it's plus (HP) or minus (LP) 45 degrees at the corner frequency. At mid-band, a decade or more away from the corner frequency, the phase shift is negligible at less than 6 degrees. In the case of a typical TMB tone stack the phase shift depends upon the control settings, but the largest swing is at the mid scoop frequency where it is anywhere from zero to about +/- 70 degrees.

[Stevem]

Yup, thanks for the detail Martin!