JMI Vox AC10 add-on top boost?

[seveneves]

Hi there,

I am planning out a Vox JMI AC10 build/clone. The normal channel is known for being somewhat whimpy. Had a chance to play an original one recently that was just serviced and I would agree with that sentiment.

So I got to thinking about adding top boost to it, if that would be possible?

Based on some high level research, seems I can add it in a similar location as in the AC30:

JMI schematic:



Thomas schematic:



Top boost schematic, for reference:



What do y'all think?

[sluckey]

That'll work.

[seveneves]

Thanks sluckey.

What would be great would be the ability to have this switchable, say, with a DPDT... but something tells me I wouldn't be able to do that (safely) during operation. If so, would it help if the switch were shorting instead of non-shorting?

[B Ingram]

What would be great would be the ability to have this switchable, say, with a DPDT... but something tells me ...

I suppose you haven't played an original 1960s AC10 yet?

If you had, you would probably leave the Top Boost always engaged on the Normal channel, and select between it and the EF86-equipped Trem channel.

I won't be adding Top Boost to my '65 AC10, but I only play through the Trem channel of that amp. When you get your amp built, turn off the trem, play through the Trem channel, and try turning the trem Amplitude control up/down. See what you think...

[seveneves]

I suppose you haven't played an original 1960s AC10 yet?

The normal channel is known for being somewhat whimpy. Had a chance to play an original one recently that was just serviced and I would agree with that sentiment.

[seveneves]

I suppose you haven't played an original 1960s AC10 yet?

The normal channel is known for being somewhat whimpy. Had a chance to play an original one recently that was just serviced and I would agree with that sentiment.

Of course the magic in that amp is with the EF86. But I do like the ECF82 straight for certain things. Having a top boost injected there would probably be a nice add for me. Switchable (if possible) would allow for either.

[sluckey]

Do you want to REPLACE the normal channel with the Top Boost channel? Or do you want to ADD the TB channel so you have three channels?

[seveneves]

Do you want to REPLACE the normal channel with the Top Boost channel? Or do you want to ADD the TB channel so you have three channels?

Is it possible to switch the TB in/out of the normal channel? The ECF82 on it's own has it's place in my sonic palette but I think I may also find the top boosted ECF82 useful too. Don't want to add another channel.

[sluckey]

I would do something like this...

[seveneves]

I would do something like this...

Thank you but I'd prefer not to do that... I want to keep the ECF82 for the trem...

FWIW, I'm working with a replica AC10 chassis and don't want to change the form factor/drill more holes for more tubes.

I presume I can't use a DPDT to switch in/out the TB circuit for the stock normal channel?

[B Ingram]

The normal channel is known for being somewhat whimpy. Had a chance to play an original one recently that was just serviced and I would agree with that sentiment.

Sorry I missed that! The text is tiny, and the schematic is gigantic on my screen.

I presume I can't use a DPDT to switch in/out the TB circuit for the stock normal channel?

You probably could. I'm just skeptical that it would be useful, and it raises issues about how to route the wiring without creating oscillation, etc.

When I first started in amp-building, I wanted "all the features" and "everything switchable" for "maximum flexibility." As time has gone on, I'd look to pedals and loop-switchers for "flexibility" and I mostly just want a couple of great sounds from an amp. These days, I generally changes amps to change sounds (and typically vintage amps instead of my own builds).


I would recommend getting the AC10 built first & working. If you want to put a switch on afterward to jumper-past the Top Boost circuit, you can. If you went whole-hog and built the Top Boost like the add-on units (that mounted on the panel covering the chassis), I suspect the switch to bypass it would be quite easy.

[sluckey]

You will have to add one dual triode if you want top boost. I guess you could put all the circuitry on one of those small add on chassis like Vox did. Should be fun.

[sluckey]

This may be closer to what you have in mind...

[seveneves]

Sorry I missed that! The text is tiny, and the schematic is gigantic on my screen.

Ah, gotcha. I can see that now... my bad.

I would recommend getting the AC10 built first & working. If you want to put a switch on afterward to jumper-past the Top Boost circuit, you can. If you went whole-hog and built the Top Boost like the add-on units (that mounted on the panel covering the chassis), I suspect the switch to bypass it would be quite easy.

Ya, that's a great reminder. Food for thought!

[seveneves]

You will have to add one dual triode if you want top boost. I guess you could put all the circuitry on one of those small add on chassis like Vox did. Should be fun.

Oh ya, fully aware. Yes, was thinking it could be accommodated via the top boost bracket put on the back panel.