Problems with effects loop on HRM OD clone

[Fummelfinger]

Hi everybody.
I recently added a built-in Dumbleator based effects loop to my HRM OD clone. The loop seems to work reasonably well but when it is switched on or off (with a manual dpdt bypass switch) I get a rather loud “thump”. And what is worse, engaging the OD when the loop is in the cirquit now causes a similar “thump” that wasn’t there before. This makes the OD function practically useless in a live situation. Has anyone here tackled a similar problem?

[ic-racer]

Bad coupling cap or something causing DC at the output of the effects loop?

[Fummelfinger]

Maybe there is a leaky cap, even if the amp is built quite recently. I must admit that my version of the Dumbleator loop is somewhat simplified. I omitted the bright switches along with the 10M/0.22uf/10M neg feedback chain. And since the input is already taken off V1B thru a 0.05 cap, I saw no reason also to include the 0.05 input cap that the Dumbleator schematic shows..

[groovtubin]

Maybe there is a leaky cap, even if the amp is built quite recently. I must admit that my version of the Dumbleator loop is somewhat simplified. I omitted the bright switches along with the 10M/0.22uf/10M neg feedback chain. And since the input is already taken off V1B thru a 0.05 cap, I saw no reason also to include the 0.05 input cap that the Dumbleator schematic shows..

PUT the cap BACK IN!

jim@Omegaamps.com

[Fummelfinger]

Yes, of course that cap had to be there. Silly me. The loop works fine now, thanks for putting me on the right track!

Thordur