Effect volume/gain much lower than bypass. Magnatron Delay.

[tony311]

I have build the Magnatron Delay. It works perfectly. The only issue is that the effect volume is about half the volume bypass. I have read elsewhere here on this forum, but that turned out to be that the wrong resistor values were used. I have checked all my resistor values and have the gain trimpot on full.

Does anyone know which resistor or trimpot I could alter to increase the gain of the effect? I looked at Res 103, and tried a different value but it made little difference.
I have the circuit attached.

Thanks.

[GibsonGM]

To start, you might try checking the values of R18/R19.....R14/R10.....R2/R3, and be sure each pot is the R value it's supposed to be.

I know you said you checked them ALL, but maybe have another look?  I don't think the designers would allow this to be 'half bypassed volume'. 

Do you have an audio probe?  After you've checked R's again, there are a few places you can check the volume in-circuit to see what's going on...

[ElectricDruid]

+1 agree, Mike's right. With the gain turned up to max, the dry path alone should be *louder* than the bypassed signal. There's gain of x1.5 on the first stage, and x1.2 on the mixer stage - that's about 4.9dB louder. Plus it should have delayed signal too, which adds another few dB.

Get an audio probe and test the signal going through to find where it goes quiet, and then start hunting for a bad solder joint, or a bit of muck shorting two tracks or something else untoward.

[tony311]

Ok, I agree that sounds like good advice. I do have an audio probe. I will do that and see how it goes. Thanks for the advice.

[tony311]

To start, you might try checking the values of R18/R19.....R14/R10.....R2/R3, and be sure each pot is the R value it's supposed to be.

I know you said you checked them ALL, but maybe have another look?  I don't think the designers would allow this to be 'half bypassed volume'. 

Do you have an audio probe?  After you've checked R's again, there are a few places you can check the volume in-circuit to see what's going on...

Thank you for that... Just goes to show you, you can't check enough. Turns out I had a bag of resistors I purchased. The place had marked them as 12k. In reality, they were only 1.2k. So I used one of those without checking its value in R14. As soon as I replaced it with a 12k. Its spot on.....

Thank you again.

[GibsonGM]

You're welcome Tony, happy building!   

[ElectricDruid]

Good catch! And thanks for filling us in on the end of the story.

Enjoy the pedal now it's going.