Increase reverb signal

[Joe6v6]

What needs to be done to increase the reverb signal on the attached schematic. The amp I built works fine & the Reverb is very nice but it seems like there should be more of it. I have tried several different tanks & swapped a few AT7's with no help. I see mods for AB763 reverbs but this looks different.     .      .      Joe

[tubenit]

Have you tried increasing either the send or return pots from 100k to 250k or more?   OR increase the 220k grid resistor in the "return" to 470k.

With respect, Tubenit

[sluckey]

I would abandon that circuit and use the simpler AB763 circuit. Fewer tubes and more reverb than anyone needs.

[terminalgs]

short reply: +1 on sluckey's advice.


longer:  lots of ways to fiddle with it, but the entire circuit seems overly complex.  V1B produces enough gain to go straight to the PI and even side-chain a reverb circuit as well.  Instead a 1M/68K divider knocks it down  -23dB only to have V4B provide +30dB gain, then hit mix resistors 68k/205k.   


instead of looking for more wet reverb in the mix just give yourself more dry signal by changing your 1M/68K voltage divider.  Better yet,  rip out the 1M/68K and V4B and connect directly to your 1M level pot..    bring wet reverb in with a mix resistor somewhere.. (do you want reverb going to an effects loop?) . keep going, ditch V4A..  now we are getting close to sluckey's advice...

[Joe6v6]

Dam I wish I had known all this before I built the thing! but at this point I want to keep the circuit as is & change some values to get the reverb to a more useable level & button it up. 

 I added a 250k resistor off the send pot to ground and it was a big step in the right direction. Im thinking of changing that pot to 500k or 1m. What would I change on the 68k/1m voltage divider to up the signal? Raise the value of the 68k ?
Thanks for the replys  .   Joe

[sluckey]

Let's work on the reverb driver side first... Change the send pot (I prefer to call it dwell) to 1M audio taper. Use a 12AT7 for V3. Change V3 cathode resistor to 2k2/3W. Remove the reverb transformer top lead from node 2A and connect directly to node 2 in the power supply. This makes the driver look like an AB763 circuit and should give plenty of drive to the reverb tank. Try this first.

The recovery circuit should have plenty of gain already, but if you still need a bit more reverb then remove the local feedback circuit (10M/.05µF) from V4A to increase it's gain.

Let's see where these simple changes get you.

[PRR]

Nothing very wrong with that over-complicated plan.

Check your cathode caps. (Tack a good cap in and see if signal gets better.)

Check plate grid cathode voltages against similar stages and plans.

Check that the tank IN and OUT have not been switched.

[MFowler]

I built an amp from that schematic and it is the best sounding clean amp I have and it was sold immediately to gigging musician that loves it.


I did not change any values, but the reverb is very subtle non Fendery which I like.


Many have changed that voltage divider and in fact a newer schematic and layout was posted on TAG with changes.


Mark

[sluckey]

What would I change on the 68k/1m voltage divider to up the signal? Raise the value of the 68k ?

That voltage divider affects the dry signal level, not the reverb (wet) signal. You can increase the 1M or decrease the 68K to reduce the dry signal even more. Then when the reduced dry signal is mixed back with the reverb signal, the reverb signal will be larger in respect to the dry signal and the reverb effect will be greater. It's worth a try. Maybe even temporarily replace the 68K with a 100K pot to see if the results you want can be dialled in satisfactorily. If so, just measure the setting of the pot and replace with a fixed resistor.

I know you have tried several reverb tanks. I'm unfamiliar with the tank in your pic (over at TAG). Have you tried a 4AB3C1B or 9AB3C1B tank? I know those should give a lot of reverb effect in that circuit.

[Joe6v6]

The 1meg send pot took it up another notch and it is very useable in the middle of the dial now.

I did not change any values, but the reverb is very subtle non Fendery which I like.

I think like Mark says here its a very nice sounding Reverb but its not Fender over the top, which I also like.

         

I know you have tried several reverb tanks. I'm unfamiliar with the tank in your pic (over at TAG). Have you tried a 4AB3C1B or 9AB3C1B tank?

Yes- I have a brand new MOD9AB3C1B but that one makes even more reverb so ive been using it for testing.  Its a Folded Line unit out of a Hammond AO44 it says on the lable "made by beautiful girls in controlled atmosphere conditions" Sounds good to me.

Check that the tank IN and OUT have not been switched.

Been there, not the first time ive crossed my wires but their good now.

Im going to call this one done & put it in its cabinet tomorrow, it really is a great sounding amp with a lot of tonal control, but theres a lot of parts in there compared to some other great sounding amps ive built. I will post a pic of it once I have it buttoned up. Thanks everyone for the advice & help getting this one in the can.   ..     Joe

[terminalgs]

I wrote:

give yourself more dry signal by changing your 1M/68K voltage divider.

Sorry! that was the wrong advice! opposite really, that would increase dry.


Picture looks great.  Like you said, lots of components.. but well organized and clean!

[tubeswell]

You could try eliminating some/all of the local feedback in V4a


Otherwise, the single gain stage for the reverb recovery in V2B is trying to compete with the cascaded gain stages in V1a and V1b, and it will never win like that. Your typical reverb recovery stage is trying to amplify a very weak signal from the pan's output transducer, whereas your dry side has 2 x gain stages working off a guitar level input signal, and even though it has a tone stack in between, the combined output signal is still way higher then your single reverb recovery stage. (The pair of local NFB stages in V4 don't change this equation, so something has to change to boost the wet signal level in the mix)


I'm only staying this seeing as how you have already built the amp. Otherwise, what sluckey said.