Somewhere between 102 and 183

[erwin_ve]

Measure your pots, picking a treble pot on the high side and a bass pot on the low side and the amp will be much more bright.

Erwin

[talbany]

24. 250Pf Snubbers ala 102.

Going back to the original post. Hope that's ok. I built a 183 and I recently changed the snubbers from the 183 schematic values of 25pF to the 102 values of 250pF like Tony did here. I think 250pF takes off some of the top end fizz of an overdriven single coil pickup. So I have three questions:

1) Tony, why did you choose to go with 250pF snubbers?
2) Is it possible that the 183 schematic is incorrect w.r.t the snubbers and that 183 really had 250pF caps there? To me, 25pF doesn't make sense.
3) Are there any other known Dumble amps that use 25pF snubbers?

Thanks,
Don

My settling on the 250pF values was from both extensive testing and trying several different values and finally going with either a 250 or 270 depending on the plate load differences. I then cross checked this with many of the other well respected builders I know and trust with the sound I was after, to make sure I was not hearing things!
I will also add? I consider the snubbers as "Band-aids" and tone suckers so I want to try and keep those values as low as possible if I can..
As far as your question about 183. At the time of the layout Shad who actually blueprinted 183 insisted they were 25pF after interrogating he still stands by those values in the layout!.

IMO There are several reasons why I think Dumble did this 1.. 183 is a high plate amp with the higher value Drive/Level pot's(more low mids) both makes it less prone to the "fizz" effect.
2..It was voiced more aggressive (Rock) sound. This along with the fact that 183 also does not have any NFB on V1B the low value snubbers his choice of resistors in key spots also contributes to it's"Killer"Aggressive throat that makes this amp a wonderful Rock Machine.
To sum it up? subbers are a great tweak spot to as you say get rid of the fizz! So it all depends the sound your chasing and where the amps sound lands ie.. (Coax/tube types/part types.etc). another reason why I believe Dumble used the same type parts in key spots Depending on the model or Generation ODS of the day.. The problem with them is? Once they are in they are a Bitch to swap out.

Off hand I don't remember any other model ODS's with 25pF there.But wouldn't surprise me if he used them in more of his amps

I hope this makes sense?

Tony

[10thTx]

I'll toss out an idea that is heresy for Dumble cloning but has been useful to me. That is the use of an "enhance cap" across the LTPI entrance plate resistor.

I had a build some years ago where I was looking for something different then the Fender 10p "snubbing cap" which has always sounded like a thin blanket over my speaker when I tried it. The Fender snubbing caps have never worked for me.

There is a thread on the Hoffman forum about this: https://el34world.com/Forum/index.php?t ... #msg153636

After I 1st tried this, I foolishly thought I had "invented" a tweak for a couple of hrs until I learned Mesa Boogie has done this on an amp.

The best way I can describe it is that is doesn't seem to my ears to reduce, mute or remove the high frequencies but simply smooths them out.

I do find at times the smoothing caps on the Dumble preamp topology from plate to cathode can somewhat mute the high frequencies (especially with larger values like 330p or 390p) . To my ears, this enhance cap across the LTPI plate resistor is more subtle and doesn't eliminate the high frequencies like that.

Sort of like a kids top that wobbles when spinning (high end hash) vs. the top is spinning smoothly. It's still spinning (highs still there) but is spinning smoothly.

It's an easy experiment to try with a couple of insulated alligator clipped wires and a variety of cap values. I usually end up with 120p to 220p there. Just a thought to consider and not saying you "should" experiment with this.

I also have found using the enhance cap has allowed me to either eliminate some of the smoothing caps OR reduce their value which helps the amp sound more transparent.

With respect, 10thtx

[jcsifu]

I'll toss out an idea that is heresy for Dumble cloning but has been useful to me. That is the use of an "enhance cap" across the LTPI entrance plate resistor.

I had a build some years ago where I was looking for something different then the Fender 10p "snubbing cap" which has always sounded like a thin blanket over my speaker when I tried it. The Fender snubbing caps have never worked for me.

There is a thread on the Hoffman forum about this: https://el34world.com/Forum/index.php?t ... #msg153636

After I 1st tried this, I foolishly thought I had "invented" a tweak for a couple of hrs until I learned Mesa Boogie has done this on an amp.

The best way I can describe it is that is doesn't seem to my ears to reduce, mute or remove the high frequencies but simply smooths them out.

I do find at times the smoothing caps on the Dumble preamp topology from plate to cathode can somewhat mute the high frequencies (especially with larger values like 330p or 390p) . To my ears, this enhance cap across the LTPI plate resistor is more subtle and doesn't eliminate the high frequencies like that.

Sort of like a kids top that wobbles when spinning (high end hash) vs. the top is spinning smoothly. It's still spinning (highs still there) but is spinning smoothly.

It's an easy experiment to try with a couple of insulated alligator clipped wires and a variety of cap values. I usually end up with 120p to 220p there. Just a thought to consider and not saying you "should" experiment with this.

I also have found using the enhance cap has allowed me to either eliminate some of the smoothing caps OR reduce their value which helps the amp sound more transparent.

With respect, 10thtx

Similar to you, I have left off the snubbers of V2 and used a higher value cap as in the BM PI cap like this...

[10thTx]

When I have tried that "Fenderish" approach of the snubbing cap all away across from one plate resistor to another plate resistor on the LTPI, I did NOT care for it at all. Everytime I tried it, I quickly removed it as it sounded like a thin blanket over my speaker killing the highs.

What I am doing is putting a capacitor across one plate resistor. It sounds completely different to my ears. I don't know why it works for me but it does & I'm super happy with the results. I don't hear the highs being muted like I do with that Fenderish style of snubbing caps from one plate to the other.

All a subjective thing. On your amp, what you're doing may be fantastic! It just hasn't ever worked for me.

With respect, 10thtx

[jcsifu]

When I have tried that "Fenderish" approach of the snubbing cap all away across from one plate resistor to another plate resistor on the LTPI, I did NOT care for it at all. Everytime I tried it, I quickly removed it as it sounded like a thin blanket over my speaker killing the highs.

What I am doing is putting a capacitor across one plate resistor. It sounds completely different to my ears. I don't know why it works for me but it does & I'm super happy with the results. I don't hear the highs being muted like I do with that Fenderish style of snubbing caps from one plate to the other.

All a subjective thing. On your amp, what you're doing may be fantastic! It just hasn't ever worked for me.

With respect, 10thtx

I understand...

[talbany]

I'll toss out an idea that is heresy for Dumble cloning but has been useful to me. That is the use of an "enhance cap" across the LTPI entrance plate resistor.

I had a build some years ago where I was looking for something different then the Fender 10p "snubbing cap" which has always sounded like a thin blanket over my speaker when I tried it. The Fender snubbing caps have never worked for me.

There is a thread on the Hoffman forum about this: https://el34world.com/Forum/index.php?t ... #msg153636

After I 1st tried this, I foolishly thought I had "invented" a tweak for a couple of hrs until I learned Mesa Boogie has done this on an amp.

The best way I can describe it is that is doesn't seem to my ears to reduce, mute or remove the high frequencies but simply smooths them out.

I do find at times the smoothing caps on the Dumble preamp topology from plate to cathode can somewhat mute the high frequencies (especially with larger values like 330p or 390p) . To my ears, this enhance cap across the LTPI plate resistor is more subtle and doesn't eliminate the high frequencies like that.

Sort of like a kids top that wobbles when spinning (high end hash) vs. the top is spinning smoothly. It's still spinning (highs still there) but is spinning smoothly.

It's an easy experiment to try with a couple of insulated alligator clipped wires and a variety of cap values. I usually end up with 120p to 220p there. Just a thought to consider and not saying you "should" experiment with this.

I also have found using the enhance cap has allowed me to either eliminate some of the smoothing caps OR reduce their value which helps the amp sound more transparent.

With respect, 10thtx

I have used this method of snubbing highs across plate resistors before (Usually on a gain stage) However this is the 1st time I've seen it done at the PI. Given the power supply side of the plate resistor has a lower (AC) gnd potential your basically doing the same thing, snubbing highs on that side of the PI.
The Cap across the P.I is acting as a kind of NFB cap (canceling highs) since both plates are out of phase and both sit at (basically)the same gnd potential. Both methods are a legit way of doing the same thing,controlling oscillations a high volumes and snubbing high's
The "Bassman" method (Cap across the PI) is a great and easy way to smooth out the amp and you can go as high as 100pF there works best for my ears..I want to try Jeff's method.Thanks for the tip!

Tony

[JD0x0]

I've done the snubber across the plate resistor of one leg of the PI in many amps. I've also done the plate to plate cap across the PI in some of those same amps. My 'trick' is running a carbon comp resistor on one leg of the PI as an attempt to get some harmonic distortion from it. (Pretty big voltage swing on that stage, and fairly large voltage drop over the resistor.)
Then, I run the snubber on that plate so it kills off some of the more offensive high order content. I only do this on one leg of the PI with the intention that common mode cancelation doesn't get rid of what is trying to be generated.

I've never scoped it, but it sounds good to my ears.

This method of snubbing I dont really use for smoothing out preamp OD, but rather a precaution against oscillations, and perhaps to smooth offensive power amp distortion. Truth is, in a guitar amp, where you really dont need bandwidth above 5-6khz, most stages could benefit from a bit of snubbing, so they dont have to deal with high (or low) frequencies that the speakers/cab could never even come close to reproducing.

[donvan]

I hope this makes sense?
Tony

Thanks Tony that makes sense!

Increasing the snubber values to 250pF like you did was a better solution for me than doing it at the phase inverter like others did because I was totally pleased with the clean sound. I just wanted to slightly smooth out the OD channel without affecting anything else.

Don