ANOTHER DIY Tube Spring Reverb! Help Debugging, Please!

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slor

Member
Joined
Mar 4, 2012
Messages
11
I've built a standalone reverb unit based around a Hammond "necklace" spring unit. I more or less used the Fender / Wave design, tweaking a few component values here and there as the unit is designed to be used in a studio environment, not as a guitar effect. The unit needs to interface with a line input on a console, which is expecting to see a low impedance signal.

Right now, output is uncomfortably distorted. Some of this may be due to the send side being overdriven, although through a speaker, the reverb transformer output actually sounds pretty good.

My thinking is that the recovery side is the main issue. I started by trying to address the overdrivenness of the thing, experimenting with a cathode follower output (too little gain) and playing with the values of the components on the recovery tube (I decreased the second grid resistor to 470k). Eventually I substituted a 12AU7 instead of a 12AX7 as the recovery tube. Best results so far, but still distorted. All other values for this stage are currently as shown on the attached schematic (note there is currently no V4 in my build).

What's the best approach to getting reasonably clean, low-impedance signal out of this thing? Could I use the 12AU7 in parallel as the recovery tube, with cathode follower output? (Thinking still not enough gain.)

Or half of the 12AX7 as recovery, then driving the 12AU7 in parallel with cathode follower output?

the_wave_schematic.png
 

PRR

Well-known member
Joined
Jan 30, 2010
Messages
11,144
Location
Maine USA
Can you find the original plan for the "necklace" reverb?

I fear it may be quite different from the tank reverbs.

It is also possible your necklace is damaged.
 

slor

Member
Joined
Mar 4, 2012
Messages
11
Sure, here's at least one circuit that uses the "necklace" (there may be others). It IS a bit oddball, as Hammond uses a transistor as recovery. But the resistances on the tank worked out to the fairly standard 8 Ohms input, roughly 500 - 600 Ohms output. So apparently, it should work in a Fender-type circuit, no?
 
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