power amp distortion

[rutledj]

Can anyone comment on how much of the Dumble sound is related to the power tubes distortion vs preamp. If I were to build a low wattage (6V6) version, maybe even single ended, would I still be able to achieve this greate buttery tone?

Thanks,
Rut

[d95err]

As far as I've heard, a dumble poweramp is supposed to run completely clean; any distortion is supposed to be generated by the preamp.

EDIT: That doesn't mean the poweramp does not matter for the sound though. Even a clean poweramp will color the sound in various ways.

[Harris]

Others have built 6v6 versions and gotten THE tone, but I don't think you can get there with a single-ended design. The power amp needs to be cleaner than a single ended amp can go.

[d95err]

Others have built 6v6 versions and gotten THE tone, but I don't think you can get there with a single-ended design. The power amp needs to be cleaner than a single ended amp can go.

Just curious - why would a single-ended poweramp be less clean than a push-pull poweramp? (E.g. comparing a 15W SE amp with a 15W PP)

[Darkbluemurder]

Personally I can hear three to four stages (I am not referring to gain stages) a power amp is running:

1st stage: no power amp coloring. All frequencies created by the preamp come through. This can be a bit harsh in a Marshall type preamp.

2nd stage: high frequency coloring. The highs are rounded off just a bit, at the same time the lows start tightening up. This doesn't affect clean tones as much. Crunch and OD tones greatly benefit from this. In a Marshall this stage takes away the harsh top end. This is where I like to run my amps with more than 2 gain stages in the preamp (which would include Dumble style amps).

3rd stage: low frequency coloring. By the time you enter this stage the power amp starts to cut off lows. In addition the tone controls become less effective. The clean tone will no longer be clean.

4th stage: you get additional coloring from the output transformer saturation.

The normal output transformer coloring (apart from saturation) is present at all stages.

Of course this is subjective and others may hear entirely different artefacts in power amp coloring.

Have fun
Stephan

[jaysg]

I recall a documented ODS shootout on Bill Morgan's site or one of the Japanese guys. They had some 100Ws, at least one 50W and one 6V6 version. They weren't all equal, but the nod went to some of the 100W amps. That said, a few of the amps here are running a straight Fender BF channel, which suggests cranking it. Also, Graydon Stuckey likes the ODS preamp out into a Marshall 18W. Never tried it myself.

Darkblue -- I have a question about your Series II amps. Did you implement ODS clean to overdrive switching on the amps' distortion channel so you have three channels? I have a clean BF side switching with the full ODS signal path on the other side, for two channels. It's cramped in there.

[Darkbluemurder]

Darkblue -- I have a question about your Series II amps. Did you implement ODS clean to overdrive switching on the amps' distortion channel so you have three channels? I have a clean BF side switching with the full ODS signal path on the other side, for two channels. It's cramped in there.

Jay,

I have the straight BF clean and the hardwired ODS channel. I do not have a capability to use the ODS channel in a clean mode. I am not good at installing channel switching.

Cheers Stephan

[paddy]

Hi Rut
i built the Hybrid A and then changed many values to bring it closer to Gils version( the one with all those beautiful pictures) Everone who's played the amp,loves it.Only one guy criticised the fact that he would like to see the clean channel stay clean at loud volumes.It does breakup nicely with clean master at 12 o'clock and volume on about 3 o'clock.
I checked this out on a scope with a 500mV p-p input(my guitar with humbuckers delivers this level easily) and noticed that the input to the power amp was clean yet the power stage was distorted.The 6L6's are biased using the cathode current method at around 70% idle plate dissipation.The amp is running a single pair of o/p tubes so it is a 50 Watt version,perhaps i could clean it up by making it 100 Watt but i love the sound of the clean channel wound up a bit.Plugging in a Strat tames things considerably but you can still get it to bust up.My 12AX7's are strong so this may be a factor. Cheers Paddy

[Funkalicousgroove]

just put the rock/jazz switch in the "jazz" position, should stay claen all the way up.