'22 Standard Reverb

[lukasott]

Hey there, I built the '22 standard reverb pedal, which you can find at this link: https://bentfishbowl.wixsite.com/electronics/post/22-standard-reverb.

Unfortunately, the pedal isn't working as expected, and I'm getting some distorted sounds from the reverb tank. I'm not sure how to pinpoint the issue.

Here are the details:

I'm using a 4AB3C1B reverb tank, so I didn't make any changes to the vero layout.

Instead of BD139/140, I use BC639/640. According to the article, they should be interchangeable.

You can listen to the sound the pedal is producing at this link: sound.

images

072:
1:-0.19
2:-0.19
3:-0.13
4:-6,7
5:0
6:0
7:0.04
8:9

5532
1:-0.2
2:-1.84
3:-0.16
4:-6.7
5:-0.03
6:-0.04
7:-0.04
8:9

1044
1:9
2:5.17
3:0
4:-2.74
5:-6.7
6:4.2
7:5.6
8:9

BC639
E:-0.184
C:9
B:0.49

BC640
E:-0.181
C:-6.75
B:-0.87

I would greatly appreciate any help or advice you can offer. Thanks!

[Rob Strand]

FYI, the link goes to a set of images and you need you scroll through to find the 22 ckt with the output buffer.

The voltages don't look too bad.

It could be a bad connection.  Try wiggling some wires to see if you can hear any crackles.

Disconnect the input to the reverb tank and see if you still get the bad sound, or if it changes the character.

Next reconnect the input to the reverb tank then disconnect the output to the reverb tank and see if you still get the bad sound.  Unfortunately you might get a lot of noise which can be reduced by temporarily shorting the input terminals of the recover amplifier instead of leaving them open.

Those two experiments might narrow down the area causing the problem.

These transistor booster circuits can oscillate.   It's not uncommon that you need to add a small capacitor between pin 1 and pin 2 if the NE5532 (IC1A).   However because the feedback resistors are low values the cap might turn out to be not so small, maybe 10nF.    At first don't worry about the value just try a few values between 1nF 10nF 100nF to see if the problem goes away.  Next find the smallest value the works and use a value little larger than that.   The cap might not do anything if the problem isn't oscillation.

Other possbilities relate to the DC/DC converter.

I'm using a 4AB3C1B reverb tank, so I didn't make any changes to the vero layout.

5th character: Connector arrangement
A = input grounded, output grounded
B = input grounded, output insulated
C = input insulated, output grounded              *****
D = input insulated, output insulate

According to this table that's actually the correct coil to use.
You need the tank input side to be isolated.

[PRR]

> 5532
> 2:-1.84

All the other signal pins are real close to zero.This stands out. And does not agree with transistor base voltages?

[duck_arse]

your transistors appear to be fitted backwards. check your datsheets even if the guy sez.

[lukasott]

Thank you all for your replies. I messed up and had the transistors mounted incorrectly, sorry...