Peavey Bandit 112 Dampening Adjustment

[QReuCk]

Fear you didn't understand me fully, or my limited english striked again and I didn't explained properlly. I am not trying to say I cannot obtain the tone and dynamic response I want from my gear, which happens to be a US made Peavey Envoy (or from any tranny I had a chance to test for that matter), whatever guitar might be plugged in (and this includes a nylon accoustic powered with a simple piezzo, a high output level Yamaha RGX and a more common Les Paul type electric).
What I am saying is that when testing some tube amps, I often have to drastically refrain my playing dynamics in order for the amp not to exaggerate it. I am also often very happy with how pure accoustic instruments respond to the variation of string attack I make.

Sure I didn't try the Fender Blues Junior long enough to fully adapt my playing, but I really chocked me how any attack just a bit stronger than usual resulted in a sound both considerably louder than what I expected and with a lot of unpleasant harmonics. I know how to EQ out these harmonics, but then softer parts would just be hidden behind the mix. I surely don't have these problems to that extent with a lot of other gears I tried and that includes trannies, but also oversized tube combos.
I am just curious what could explain such a difference and thought this dampening thing might have something to do with it.

Edit:
I just had the opportunity to test the BJ longer. Interestingly enough, some tweaking of the Volume and Master knobs enable to lessen the booming effect and dynamics were far more controlable. I guess a lot of components/features are interacting to influence the end-result. Still on my quest to understand what happens.

[Kaz Kylheku]

I looking at adding a dampening factor adjustment to one of my SS amps. I'm looking at loosening up the feel a bit and before I put it under the soldering iron I thought I would ask around here.. My first impression would be to add more series resistance in the neg feedback loop at R108 any other thoughts?

Looking at the PDF, I see your Bandit is loaded with piece of crap RC4558 op-amps (if we are to believe that the schematic gives the part number that is actually installed).  Nobody in their right mind would use this for a serious piece of audio gear.

The explanation for this is schematic date: 1989!

The first thing I'd do is replace all these with something for audio quality, like LM4562 or NE5532. 

In 1989, an NE5532 was maybe still a bit of an expensive part for an amp like this, and the LM4562 was nearly 20 years away from development.

After putting in better chips, I'd play the amp and re-evaluate if it's worth it to muck around in its current feedback structure.

[Kaz Kylheku]

So I stick to my guns about having independently invented and applied mixed feedback technology in 1972.

No argument from me JM, quite a few things have been invented independently in more than one place, Calculus for example.   :cheesy:

Just to note that the RCA scheme I posted above is a bridge that actually allows the current feedback to be varied through zero to either phase.

Variable Damping Factor Control by Charles A. Wilkins, Audio, September 1954
http://www.aikenamps.com/vardamp.pdf

Quote: "A voltage is developed across the 0.47-ohm and the 0.27-ohm resitors that is proportional to the current flowign through the speaker load. This current-proportional voltage is sampled by the slider on the 25-ohm potentiometer and fed back through low-pass filter RC as current feedback  to the cathode of the first stage where it is added with the over-all negative voltage feedback."

"Added with the overall negative voltage feedback" means "mixed feedback"!

[phatt]

Fear you didn't understand me fully, or my limited english striked again and I didn't explained properlly. I am not trying to say I cannot obtain the tone and dynamic response I want from my gear, which happens to be a US made Peavey Envoy (or from any tranny I had a chance to test for that matter), whatever guitar might be plugged in (and this includes a nylon accoustic powered with a simple piezzo, a high output level Yamaha RGX and a more common Les Paul type electric).
What I am saying is that when testing some tube amps, I often have to drastically refrain my playing dynamics in order for the amp not to exaggerate it. I am also often very happy with how pure accoustic instruments respond to the variation of string attack I make.

Sure I didn't try the Fender Blues Junior long enough to fully adapt my playing, but I really chocked me how any attack just a bit stronger than usual resulted in a sound both considerably louder than what I expected and with a lot of unpleasant harmonics. I know how to EQ out these harmonics, but then softer parts would just be hidden behind the mix. I surely don't have these problems to that extent with a lot of other gears I tried and that includes trannies, but also oversized tube combos.
I am just curious what could explain such a difference and thought this dampening thing might have something to do with it.

Edit:
I just had the opportunity to test the BJ longer. Interestingly enough, some tweaking of the Volume and Master knobs enable to lessen the booming effect and dynamics were far more controlable. I guess a lot of components/features are interacting to influence the end-result. Still on my quest to understand what happens.

Hi QReuCk,

Quite frankly I hate to death some of the peavey bandit or similar Amps and some are EXTREMELY harsh.

In Fairness there are many many models and I don't have a warehouse full of every amp ever made so some maybe better than others. Often it's what you get used to hearing, what style you play and how you play.

For the guitar player who wants to play chords and have lots of crunch will want a different response than a shredding player who rates his ability by notes per second. :duh

FWIW, here is my observation

The conundrum you refer to can be easily explained by the simple fact that 90% of the greatest Amps ever made have quite extreme *Band width limited* output. (Not HiFi Flat)
Some of this is due to circuitry quirks and some guitar pu's that where used and of course the speaker has a great impact.
A lot of those Small valve amps tend to be mid/high heavy and distort like crazy even at low volume/gain,, prolly not much use for Acoustic.

In my experience I've had far more luck by limiting the bandwidth and watching how each stage effects the EQ.

In a studio mixer situation a flat response input may well be a better starting point but for guitar Amps a dead flat hifi response is almost always going to sound crap.

If you are using an Acoustic with on-board preamp and piezo PU then these often have extreme hi freq response which often come out sounding harsh with far too much harmonic content (Too much B/width)
As an experiment insert a distortion pedal after the Acoustic and crank it high into peavey or similar and then without touching any dials,,, swap it for an Electric.

I doubt it will need any explanation as generally the electric (Passive magnetic pu) will,,, by design roll off the very high frequency and sound a little more pleasing to the ear. winky.
Piezo pu's have extreme hi end response while magnetic pu's are almost opposite.

Bandwidth and Tone shaping are super critical for the style of music you wish to play.

Sadly there is no easy one line answer to this situation as there are many ways that will end in the same result.

As a rule of thumb;
If you want great electric guitar sound don't use equipment that claims extreme 20/20 bandwidth response.

So it's rather obvious that if you want a good R&Roll Amp use a crap design.
On the other hand if you want to reproduce every string scratch from an Acoustic you may prefer the more hifi approach.
Either way wide bandwidth is always going to be harder to refine and dial in whereas a limited B/width will be easier to handle for most situations.

Phil.