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Author Topic: Adding spring reverb to a 6V6 guitar amp  (Read 149 times)

jpcar

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Adding spring reverb to a 6V6 guitar amp
« on: March 18, 2020, 08:56:18 PM »
Hi,

I recently built an amp from this design by Dvnator. It's called GA-40 Lite. He says it's inspired by Gibson GA-40. He designs lots of amps on his website. Check him out.
http://chasingtone.com/dvnator

The amp works great! I'm very happy with it.

Now, I'm trying to add a spring reverb into the circuit. I got information from Rob Robinette's website. It uses a TL072 opamp for reverb driver and recovery. The same circuitry as a Fender Hot Rod Deluxe.
https://robrobinette.com/Compact_Reverb.htm#Solid_State_Spring_Reverb

The problem is when I turn the volume up I get really loud squealing feedback. With the volume down I can hear the springs in the spring tank, so I guess the recovery part is working. But I still hear it with the reverb pot up or down. The pot doesn't change it.

My feeling was that adjustments need to be made for R40 (220K) which brings to dry signal to the grid of the phase inverter, and R38 (470K) which brings the reverb signal to the grid of the phase inverter.
Since the amp originally had a 100K in this place, I changed R40 to 100K. And I changed R38 to 220K to reflect the same ratio. No change. Problem remains the same.
Both schematics for amp and reverb circuit are attached.

Any ideas anyone?


phatt

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Re: Adding spring reverb to a 6V6 guitar amp
« Reply #1 on: March 19, 2020, 07:50:27 AM »
Assuming you have this new rev circuit on a separate board.
Then my first thought is,,,Check you have a ground path back to the main amp circuit?
Phil.

jpcar

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Re: Adding spring reverb to a 6V6 guitar amp
« Reply #2 on: March 19, 2020, 06:51:10 PM »
Yes, this is on a separate board. I have made sure it's getting a ground path from the main board.