Going From 15 Watts to 7 to Improve Tone: Worth it?

[The New Steve H]

1. What happened to the malware warning? I miss my malware.

2. I decided what to do with the amp parts I have sitting around. I built a 15-watt amp with four 6BM8s and a Bassman preamp, and I love it. I am thinking I would like to build a 7-watt version (two fewer tubes) so the output will be a little lower. It seems like the lower you turn a PPIMV, the worse the amp sounds, so I am hoping I can get a little bit of an improvement at low volume. I know halving the output isn't a giant step, but the design is push-pull, so I need at least two tubes.

A 7-watt version would be a little lighter and smaller, so that's a plus, and when the output tubes go, you only have two tubes to change.

Think it's worth the effort, or should I just make another 15-watt amp? It seems like it makes more sense to try to build something new instead of repeating myself.

3. A friend says I should consider adding an effects loop. Worth it? I have never used one, so I don't know a lot about it. I have read up on it, and apparently they're most useful on high-gain amps.

I see the malware thing comes back when you try to post.

[Stevem]

If you want faster output stage clipping as volume wise your not gonna hear much of a difference .

[10thTx]

An idea for you. Since the tone stack is off the cathode follower, you can simply add an FX recovery gain stage and have an active effects loop.

Then the FX would act effectively as a master volume for you. Or you could go the PPIMV route in addition also.

I've used this approach on my D'Mars ODS and the recent HoSo56-OD.

IF you don't like the idea of a 5879 in V1, you can use a single 12A_7 triode or parallel a 12A_7.

With respect, 10thtx

[JMFahey]

If 15W is unusably loud, 7W is still too loud.

Think 0.5W or 1W for bedroom levels or leave as is but insert a good attenuator.

[The New Steve H]

I don't expect a big reduction. Just thinking I would be able to turn the PPIMV up a little more and avoid the change in sound the PPIMV causes when you crank it down.

The more I think about it, the more I like this idea. I like the idea of a lighter head. If that's the only significant change, it's worth it.

I guess I'll see what happens.

[The New Steve H]

Thanks for the schematics.

[10thTx]

If 15W is unusably loud, 7W is still too loud.

I think there are times that your statement is certainly true.

I also think sometimes that one can find a "sweet spot" for overdrive at a lower level with 2 tubes in the output then with 4 tubes in the output.

With respect, 10thtx

[sliberty]

Why not replace the PPIMV with a VVR? Much more transparent I'd expect. I've used them on Rockets with great results.

[strelok]

+1 for the VVR. Cost of the parts is about $10 + shipping. So it can't really hurt to try.

Also have you tried removing half the output tubes and doubling the load impedance? Would give you a good idea if building a 2 tube version would give you what you want. Of course this assumes you're not using 2 of the triodes in the 6BM8's for anything

[pdf64]

An idea for you. Since the tone stack is off the cathode follower, you can simply add an FX recovery gain stage and have an active effects loop

There looks to be the potential for a significant degree of impedance to be placed between the buffer for the tone stack and FX send.
ie worst case of treble control and send level control around mid settings, it may reach ~200k, which, even with a low capacitance send cable of around 500pF, would create a low pass filter that's -3dB at 1k6Hz.
I guess that the parallel nature of the loop allows full bandwidth on the dry path and so avoid the end result seeming too muffled; and the use of very short patch cable to the first fx unit would move the -3dB frequency higher.
However, in regard of the 'transparency' of the loop, I suggest that adding a second buffer after the tone stack, and use of a much lower value send control (eg 25k), would be an improvement, as it would allow the loop to be used with a longer send cable without the top end of the audio range being rolled off.
It would only take a second MOSFET to implement.