DR- no reverb/ help!

[Sea Chief]

Hi chaps, got a mind-numbing issue I need fixing asap. My DR build uses a 1/4" stereo ftsw & I had both rev/ vib were working but with a thump on the trem on/ off. My kind amp tech saw I'd wired the TRS socket slightly wrong (the 220k was out of the circuit).. so I rewired with his directions. Double/ triple checked. Thump gone.. but now no reverb.

Can you help me debug? Im desperate as the amp is sold, the buyer coming any day.

Can the reverb function w'out the ftsw so I can at least determine if its working with my TRS rewired?

Thanks Sea Chief.

[drewl]

Yes, reverb works without footswitch.

Check that reverb footswitch jack connection isn't touching ground.

[Sea Chief]

Ok the reverb does not work when the ftsw is removed.

[Sea Chief]

Solved.. had the sleeve/ ring wired viceversa.. but opened another can of worms! nevermind I'll stick there its a minor thump/ pop on ftsw Vib but I was here before & cant shift it/ it'll have to be or I'll go insane trying. thanks Drewl.

[Sea Chief]

[JazzP thanks so much for the reply].

Isnt there any really simple fix for this thump? surely a cap between x & y ought to do it.. but Ive no idea as of where.

[Chuck H]

The thump could be how or where something is grounded or a slight wiring error that doesn't affect trem function. That's a lot of things specific to your build that we can't really know about. What I'm wondering is why your tech thought the mistake on that 220k in the reverb circuit was causing the trem switching to thump.?. But then NOTHING should cause the trem switch to thump because the oscillator is isolated from the audio path. That is, the oscillator starts and the signal volume is modulated. So nothing switched from the oscillator end should be audible. Is your circuit exactly like a DR? Other than any 220k resistor mistakes I mean.

[Jazz P Bass]

R36 (10K) & C18 (4.7uf/50V) should 'debounce' the switch.

Test point 26 indicates that the FtSW socket Tip should have -6.8Vdc on it with Tremelo Off/ 0.20Vdc with it on.

Easy enough to check with a voltmeter.

65_deluxe_reverb.pdf

[Sea Chief]

Hi ChuckH- I think my tech saw my wiring wasn't quite correct with the 220k 'not in the circuit' as I had it.. he just told me to redo the TRS wiring, not neccessarily thinking the thump would be solved I think, more just for good practice.

My circuit is exactly like a DR yes, just using the 1/4" TRS socket rather than a pair of rca's like the orig fender/ or weber layouts. The only thing different.. my ftsw is a 2 button affair from a PV bandit 65.

I've got tmrw to solve this only. Just to reiterate: the trem button thump/ pop only happens with the reverb also switched on. Reverb button is fine, as is the trem button with the reverb switched OFF.

[Sea Chief]

R36 (10K) & C18 (4.7uf/50V) should 'debounce' the switch.

Test point 26 indicates that the FtSW socket Tip should have -6.8Vdc on it with Tremelo Off/ 0.20Vdc with it on.

Easy enough to check with a voltmeter.

[ATTACH]45374[/ATTACH]

Hi JP- I'll look into this tmrw & test this point (to gnd? or across s'thing?). thanks SC

[g1]

Standard Fender wiring has the shield on the reverb line and not the vibrato. Having the shield on the wrong wire can cause various issues.

[Sea Chief]

Standard Fender wiring has the shield on the reverb line and not the vibrato. Having the shield on the wrong wire can cause various issues.

g1- but the shield (I assume you mean on the ftsw cable etc) splits onto both switches' 'cold' terminals.

[Sea Chief]

R36 (10K) & C18 (4.7uf/50V) should 'debounce' the switch.

Test point 26 indicates that the FtSW socket Tip should have -6.8Vdc on it with Tremelo Off/ 0.20Vdc with it on.

Easy enough to check with a voltmeter.

[ATTACH]45374[/ATTACH]

But JP this is Reissue DR schematic. Pretty sure a p-to-point ab763 doesn't have a 'r36' 10k or a 'c18' 4.7u/50..

[Chuck H]

But JP this is Reissue DR schematic. Pretty sure a p-to-point ab763 doesn't have a 'r36' 10k or a 'c18' 4.7u/50..

Jazz is using those schematic designations to identify the parts. It's up to you to recognize their location in the circuit. That is, in context of the circuit. Now it's up to you to decide if you want to alter your circuit, which pops or thumps, to this circuit, which doesn't because of the parts identified by Jazz.

Short of that, which WOULD involve great circuit modification, you can try this:

In the schematic below, locate the trem switch. You'll need to associate it's location in your circuit for yourself. I'll guess that since you built the AB763 circuit that you have a 10M resistor on hand, so... Put a 10M resistor across the trem switch. Well, not across the switch itself because you're using the Peavey switch. But in the amp from the trem switch hot lead to the ground terminal on the jack (I hope that's a clear enough description). I don't expect this to activate the oscillator, but it may allow the circuit to modify your bias. So you will need to check for this. If this happens you'll need to find another way. But if the 10M installed DOESN'T start the oscillator and DOESN'T affect your bias it will likely stop the thump. Good luck.

https://schematicheaven.net/fenderam...b763_schem.pdf

[Sea Chief]

Thanks Chuck- ok I understand the point of JP's post.. but still cant recall any such 4.7u/50 I put in this amp.

Not quite understanding.. a 10m from the TRS socket Tip to socket Sleeve? is there anything similar I could try in the ftsw itself 1st?

[Sea Chief]

Damn not understanding 'I don't expect this to activate the oscillator, but it may allow the circuit to modify your bias. So you will need to check for this' either. shoot.

Ok let me go back a step. Is this small thump/ pop an issue per se, or can it be catagorised as 'normal service'.. ie just s'thing often found etc.