Multiple pans in an Outboard Reverb

[BJosephs]

I'm building a Fender-ish Tube outboard Spring reverb. I intend to fiddle a little with the design (of course) - something like a pre-spring tone stack and a post -spring bright/dark/fat/thin switch arrangement...

I was pouring over the different spring models and some corresponding "performance" accounts, trying to decide on a long or short decay spring.

I was wondering if it would be silly to drive two pans (of different decay lengths) with one drive circuit and have two recovery amps with a variable blend control? I can work out the blend and a recovery stuff, I am just wondering about how this will affect the transformer impedances on the drive section and pans.

Two power tube drivers? Just use two 10 ohm pans in parallel on a 4 ohm secondary? One high impedance in parallel with one low impedance?

Any thoughts?

[Satamax]

May be to keep it simple, you could just use a DPDT switch to change between long and short! May be with a footswitch and relay, and you could have two settings for different tunes or rythm and lead.

[Steve Conner]

Sounds like a great idea. I think Craig Anderton did something similar with the Hot Springs project.

Just connecting two low-impedance pans in parallel to a single driver should be fine. The match isn't really that critical. One change that might be worthwhile is a bigger driver tube than the wussy little 12AT7, after all, Fender used a 6V6 in their standalone unit. The harder you can twang those springs, the less you have to amplify the return signal, so the less you have to worry about hum and feedback.

I recently tried a self-split 12AU7 with a push-pull reverb driver transformer in a combo amp that I built and it seemed to work pretty well. It was kind of an accident, since I accidentally wrecked the single-ended driver transformer and had this small P-P one kicking around.

[BJosephs]

Just using a switch to choose between the two is very reasonable, perhaps it is the best choice.

I was going to use a 6V6 instead of a 12AT7 with an 12AX7 pre-amp (with reduced gain) into a small Hammond 5w SE OT I have (sounds like a champ). Perhaps this is all overkill for reverb but it might sound better. Any thoughts on how distortion performance affects reverb? Will I notice much difference if my driver circuit is clipping?

If I don't have a 6V6 could I drop a 6L6 or 5881 in place? Will the larger power tube thrive in an "easier circuit" or try to blast 10 watts out or something?

I think the Hot Springs used two identical pans with separate "out of phase" drivers to create a sort of hum-bucking effect - cancels out the boings and impact noise. Great name for a reverb too.

[mpeg2]

I built one of these a few years back - started with the classic Fender circuit (6G15) - drove two pans in parallel off of a 6K6 (I can't recall the impedance of the pans - but in parallel, they were within a factor of 2 of the impedance of the driver transformer). I used a short delay pan and a long delay - added another recovery circuit for the additional pan - with a "blend" control between them.

It was a pretty easy build & sounds very nice.

If someone pans the long/short blend control while you're playing, it sounds like the room is changing size...

Rich