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Let's Get Technical => Troubleshooting Problems => Topic started by: ang3lus on April 13, 2020, 04:25:23 PM

Title: no sound on outputs A and B, effects loop works
Post by: ang3lus on April 13, 2020, 04:25:23 PM

Hey all,

I know this is somewhat of a double post, but the last thread got too crowded with my ground loop problem.

I've recapped the PSU and tube board and now have got no hum but also no sound thru outputs A and B, when i connect SEND to a power amp or another amp i get sound

what is left now is this

Front volume doesn't do anything (all other controls work)
no outputs from A or B

I measured the front pot (back side as it is dual ganged) and it reads 50k from pins 1 to 3 and whene connected to pins 2 and 3 (ohmmeter) i can see the resistance changing.

any ideas on what can i check ?

Title: Re: no sound on outputs A and B, effects loop works
Post by: rnolan on April 14, 2020, 02:54:51 AM

Hey ang3lus, I put my ideas on your other thread based on the send works, I'm thinking maybe Fx return jack problem ? as it comes just before the chorus > A/B outs.  Front volume controls A/B output, seems the signal is not getting that far.
This is out there but I have to ask, have you turned up the patch master vol ?  It comes after loop > chorus stages and wont affect the send volume (which, as you say, works).  It also defaults to 0 on new patches until you program it.
Guit > input > gain (OD1/OD2) > eq > send > rtn > chorus > master vol > front vol > A/B out

Title: Re: no sound on outputs A and B, effects loop works
Post by: ang3lus on April 14, 2020, 04:43:44 AM

well i connected the headphone out and am getting good output and also the chorus works well, so the chorus is good i think.

i also plugged the RECIEVE jack into an amp, very low output but am still getting sound and the patches are working well.

so what's left ? volume pot and NE5532 opamp ? any way to test in circuit ?

Title: Re: no sound on outputs A and B, effects loop works
Post by: MarshallJMP on April 14, 2020, 11:40:28 AM

Do you have a MP-1 with a  top switch?

Title: Re: no sound on outputs A and B, effects loop works
Post by: rnolan on April 15, 2020, 01:27:32 AM

Quote from: MarshallJMP on April 14, 2020, 11:40:28 AM

Do you have a MP-1 with a  top switch?

Good point MJMP, the outputs may be switched to Inst level not line (which is what the top switch does (slider switch located on the top panel in the middle, used in the earlier model MP1s)) or it may have a dirty switch...
So headphone out works well, it feeds off the output area I think just before top switch attenuation for A/B out

Guit > input > gain (OD1/OD2) > eq > send > rtn > chorus > master vol > front vol > top switch > A/B out...> caps > Headphone out
The signal is split off through some caps to reduce top end (sudo cab sim) to feed the headphone out just before the A/B outs.  The top switch units reduce the A/B output to guit/inst level (to plug into a guitar amp input) or leave it at line level to feed amp returns or power amp inputs.