Thinking ahead. Reverb question.

[pinkphiloyd]

I'm about to do a JM build. I'm finalizing all the details now, getting everything ordered. But I'm such an obsessive asshole I can't help thinking ahead.

Most of the demos of Two Rocks I've seen, I really love the reverb. But I prefer the voicing of a classic blackface Fender. I don't really understand much about reverb. I get the big picture, so to speak, (amplify the signal enough to drive it though the springs, "recover" it on the other side, mix with dry signal) but I'm sketchy on the details.

What, if any, would the issues be if I wanted to build, say, a Princeton reverb, only utilizing the JM reverb circuit as opposed to the classic Fender reverb circuit? I thought something relatively simple like this might be a good hands on way to learn.

[Stevem]

Can you post a schematic of the JM reverb circuit?

[pinkphiloyd]

Can you post a schematic of the JM reverb circuit?

Sure. Borrowed from this board, for the record. I just want to be clear that I'm not trying to steal anyone's work, or anything.

I'm thinking...I might just try replacing the tone stack half of V1 with a classic blackface tone stack and see if that gets me there. I mean, there are other differences in the circuits, obviously, but I would think that would be the big one.

[robrob]

The JM is getting a lower level signal after only one preamp stage and after the tone stack. It makes up for that by adding two more gain stages to the reverb circuit--it's a meaty reverb.

The Princeton Reverb gets a higher level signal after: preamp - tone stack - preamp.

Mixing and matching will probably require some post build tweaking.

I've never heard anyone complain about the PR's reverb though. Are you sure you want to mess with it?

[Stevem]

It's a tad different than the standard Fender reverb circiut with having that send control, but in the end it will sound like the Fender reverb due to being transformer driven with its low end and high end roll off taking place!

[pinkphiloyd]

The JM is getting a lower level signal after only one preamp stage and after the tone stack. It makes up for that by adding two more gain stages to the reverb circuit--it's a meaty reverb.

The Princeton Reverb gets a higher level signal after: preamp - tone stack - preamp.

Mixing and matching will probably require some post build tweaking.

I've never heard anyone complain about the PR's reverb though. Are you sure you want to mess with it?

I had wondered about that, the way the gain stages were set up and how that would affect the outcome. I wouldn't necessarily say I'm complaining about the reverb of the PR, more that I'm intrigued by the versatility(?) of the Two-Rock circuit. But when it comes down to it, the main reason I really want to try it is my incessant desire to tinker. And hopefully learn something along the way...
But mostly the never ending desire to tinker.

[pinkphiloyd]

So...

The "dwell mod" that I've read about in the past. The one that involves replacing the 1M resistor on the first reverb tube with a pot, that's essentially implementing a send control, then?

I apologize if I'm incoherent. I'm sitting here having to interact with my coworkers, try and think, and type at the same time.

[robrob]

The "dwell mod" that I've read about in the past. The one that involves replacing the 1M resistor on the first reverb tube with a pot, that's essentially implementing a send control, then?

If you mean replacing the PR's reverb driver tube's 1m gridleak with a 1m pot then yes, that would be equivalent to a 'Send' control.

The JM is a pretty cool looking design. I'm saving that schematic.

[rfgordon]

In a typical Fender reverb circuit, because the signal goes to the reverb driver after two gain stages (and the Vol and tone stack), the amount of signal sent increases as the volume/gain is increased. In practical terms, this means that as the amp is turned up, you have no way of controlling the splash as the signal hits the reverb tank.

In the standalone reverb, the Dwell control works on that problem. What I do to be able to tweak the splash is put a 100 Ohm pot on the output of the reverb transformer.