Two Rock JM Preamp

[dragonbat13]

That is quite a nice build! I see this project in my future.

Very nice craftsmanship.

[dragonbat13]

Ordered five of the power supply boards this morning.

What enclosure are you using?

[dorrisant]

I have used these SMPS. They are rock solid and very quiet. Sounds like you may have shorted and thus cooked something like the 7806 regulator. Can you verify voltage in on pin 1 and voltage out to pin 3 of the regulator. Also, check for continuity between pin 2 of the regulator and either pins 4&5 or 9 of the preamp tubes.

I have a PCB for these SMPS that has a slightly larger footprint for ease of mounting.

[Was!]

Yes that extra gain stage and simulating the signal changes with the reverb circuit is what really makes the JM Sig sound.
If your after that sound than you will need to add those changes. I have tried and without those changes its always different.

How would you add the extra gain stage? And where would you connect the output of send pot?

[Guy77]

Yes that extra gain stage and simulating the signal changes with the reverb circuit is what really makes the JM Sig sound.
If your after that sound than you will need to add those changes. I have tried and without those changes its always different.

How would you add the extra gain stage? And where would you connect the output of send pot?

You can see all the gain stages here in this layout I posted that shows the 5 preamp tubes. Its also the effect of the way the Reverb is implemented in the JM/Wonderland amp and the Overdrive Reverb #13 and the way it effects the clean signal.
I attached a layout of the Wonderland/JM amp and you can see the signal going from just before V1b to V2A via a 68K resistor.

file.jpg

[Was!]

That was clear but you were talking about adding an entire gain stage to simulate what really happens in the amp.
Rephrasing the question, how do you implement v2a gain stage in this scenario?
Do you mean to just wire grid, anode and cathode as some sort of load without connecting coupling cap and send pot?

[Guy77]

Yes I imagine you could do it that way. I have not tried building it as just a stand alone preamp.
I have always built the complete amp and did several with reverb coming off of V1B to V2a and several without that scenario and I noticed a difference in the clean tone.
I liked it better with reverb coming off of V1B to V2a with the 68K resistor

Cheers
Guy.