Where would be the best place to insert a reverb circuit into a tweed tremolux 5G9?

[Dandrix]

I am looking for some help adding reverb to my 5g9 build. I have all the components layout on my board, as well as the two tube sockets and RCA jacks with reverb transformer. Was hoping for some advice and experiences with this idea. I am using a idea that is titled compact reverb from a AA1164 fender Princeton amp. It looks like this:






I have hopefully added this pictures successfully? Sorry about the drawing for my layout.
I left the tone Stack of the 5g9 off to the left of the drawing of the layout. Insertion of signal in and out is my hang up at the
moment. I really appreciate some guidance.

Thanks again

[Dandrix]

No takers on this tweak? Has anyone done this mod with a fender 5e3 build? Same tone stack setup? Correct?
One person has said on the forums that “The reverb is brought back to the bottom of the PI rather then to input of PI”
Has anyone have opinion on either way of the PI? Best results I am asking?
Your help is appreciated

[Chuck H]

I think the reason you're not getting responses is two fold. There is more to consider here than what you propose and the design itself isn't the best for adding a reverb effect.

First, you'll need to alter the power supply. The amp is underfiltered as it is for adding a reverb so an additional dropping resistor and filter cap would need to be added. Second, and more importantly, that design has only one triode gain stage feeding the PI. Which means that ALL of your clipping is coming from the PI and power tubes. That means your reverb would be in the circuit before any clipping stages and that can sound anywhere from "just ok" to nasty depending on how it works out.

That said, the problem of all the clipping being in the PI and power tubes is shared by every Fender blackface and silverface design that uses a reverb too. Though most players don't use the reverb when clipping the amp. YMMV.

I think your best option would be to build a separate small amplifier that is dedicated to reverb that drives the reverb pan with the 6g9 speaker output. That way you are reverberating the clipped signal rather than clipping the reverberated signal. I have built one of these and the results are very good. It also has the added benefit of allowing you to place the "reverb" amp anywhere in the room (or on the stage) to create different ambient effects AND you can use the dedicated reverb amp to add reverb to ANY amp that doesn't have reverb, not just your 6g9.

I went ahead and modeled the 6g9 circuit to see what adding an inverting gain stage would do to the symmetry characteristics compared to the stock amp because this can sometimes be a problem. I also experimented with a couple of different summing options. Including coupling the reverb to the "other" side of the PI. There are pros and cons to both options. I'll go into it more if you're still interested in adding the reverb on board in the 6g9 rather than building an outboard reverb.

[Chuck H]

As promised

I know this doesn't look like the AB763 reverb circuit. This will be more transparent in your amp. The mixing stage has much lower series resistance and the gain structure of the original design will be unaffected. I've used this circuit before with excellent results and in simulations of your design it was the best option. Better than the 3.3M/10p pad and reamplify circuit or the PI insertion circuit. It should be invisible to your main signal and the amps stock operation.

[Dandrix]

This is the space I got, I could move cathode components to pins of preamp sockets? Would rather not because of space constraints.

[g1]

Are you able to translate Chuck's schematic to a layout?

[Dandrix]

I gave It a shot, chuck said he would help me out but, had some time on my hands and parts have not arrived yet.
Once again I apologize for the bad drawing, hopefully chuck has something more professional? I have never used a dual gang pot so, I will need a single point lesson how wire that up. Can’t wait to fire this circuit up.
Thanks again chuck!

[Chuck H]

I'll need to see everything in situ. That is, as it will actually be with the board and pots in place in the chassis. Layout, lead dress and where things are grounded can be critical for stability and low noise. I can't develop and/or put my stamp on anything without a very clear picture of these things. Maybe just set the board in the chassis so I can see where existing components are in relation to existing pots, etc. I need to know what end of the space we're working with has the .02 cap feeding the PI and other things. Thank you.

[Dandrix]

I'll need to see everything in situ. That is, as it will actually be with the board and pots in place in the chassis. Layout, lead dress and where things are grounded can be critical for stability and low noise. I can't develop and/or put my stamp on anything without a very clear picture of these things. Maybe just set the board in the chassis so I can see where existing components are in relation to existing pots, etc. I need to know what end of the space we're working with has the .02 cap feeding the PI and other things. Thank you.

[Dandrix]

Here’s a couple more:

[Chuck H]

Ok. Great. Is this your tube function layout?

[Dandrix]

Ok. Great. Is this your tube function layout?

No, just like the fender 5g9, left to right: 5u4gb> 6v6> 6v6> speakers jack on top, tremo. Pedal jack below> (reverb section) first rca jack out>
Recovery 12ax7> rca input jack> driver 12at7 > Trem. Tube 12ax7> PI 12ax7 tube > v1 preamp tube 12ay7

[Chuck H]

No, just like the fender 5g9, left to right: 5u4gb> 6v6> 6v6> speakers jack on top, tremo. Pedal jack below> (reverb section) first rca jack out>
Recovery 12ax7> rca input jack> driver 12at7 > Trem. Tube 12ax7> PI 12ax7 tube > v1 preamp tube 12ay7

I might suggest that you lay it out like the amended picture I posted. Putting the reverb tubes at the end of everything poses several problems. It shouldn't be too difficult unless you're averse to rewiring the sockets.

[Dandrix]

I could rewire the sockets. Take me about an hour?

[Dandrix]

Is this more helpful?