No volume with FX loop on with 2 ch dual

[rjf]

I have an "F" 2 channel Dual recto and it sounds great with the effects loop switch completely off in the back. As soon as I turn the knob to any of the effects loop settings, I have no volume, just a slight hint of sound as quiet as a whisper. I tried adjusting the level on the front and the mix knob on the back and nothing changes. I also notice the green FX light on the front is real dim and changes brightness as I switch the FX knob.

Am I missing something here or is there a problem with my effects loop?

 

[94Tremoverb]

You may have a bad V4, which is the FX loop tube. Try moving it around in its socket and see if it's making a poor contact, and replace it if that doesn't fix it.

The light on my Tremoverb varies in brightness too and sometimes goes right off - it's just a poor contact in the LED holder, if you tap it if comes back on. I don't know if yours is the same though.

 

[Jerrick]

Yeah, replace the tube first, try it out, check if there are any loss connections. If anything, one or two pots for your fxloop are just dead and need replaced. Very quick and cheap fix if you know how to do some soldering. A tech can do it pretty cheap for you too.

Hopefully its nothing more than that.

 

[rjf]

Just tried swapping out V4 with a different 12ax7-a and no difference. Looks like I'm going to have to run it over to Mesa.

 

[mikey383]

Probably an LDR that has gone bad. Cheap part, but labor could cost you a bit.

 

[kcocking]

i hate to ask something dumb, but do you have anything plugged into the effects loop? if nothing is plugged in the effects send and return loop, you won't hear any sounds.

 

[mikey383]

i hate to ask something dumb, but do you have anything plugged into the effects loop? if nothing is plugged in the effects send and return loop, you won't hear any sounds.

Not true. It should work regardless if there is anything plugged into it or not.

 

[SteveO]

Try putting a patch cable between the send and return jacks of the loop. No effects, just a straight cable. If things start working, you may have a faulty jack. One of the jacks in the loop should be a shorting jack, meaning that it completes the signal path between the two jacks if nothing is plugged into them. If the little metal tong that makes the contact is tweaked, it won't make a solid connection and there will be intermittent sound or none at all.

Edit: This applies to series loops. Not sure about parallel loops.

 

[rjf]

Mine is a revision F with a serial loop.

Tried the patch cable, no effects, just the 6" cable from send to return.

Nothing...

 

[94Tremoverb]

If it has a mix knob on the back, it's a parallel loop. mikey383 is right, with a parallel loop you will still get signal through via the dry path even if the contact in the jack is faulty.

What happens if you turn off the loop using the footswitch? You can use your channel switch to try it. If it now works, it's probably the LDR after the FX mix (assuming the loop is the same as the one in the Tremoverb).

If it still doesn't work, the possibilities are the main loop switching relay, part of the control circuit for it, or the send pot. There's pretty much nothing else that will kill it completely - not that's likely to fail anyway. If the front panel light is flickering (and it doesn't just seem to be a loose LED), I'd guess the relay control circuit, maybe the rotary switch itself.

 

[rjf]

Mine has a serial loop. I shouldn't have said "mix", as it's labeled as "send level."

Tried the footswitch through the effects with still, no volume at all. Plus, it was making weird sounds (similar to a microphonic tube) and the light for the orange channel starting strobing erratically, only on the switchable setting of the loop. :shock:

 

[94Tremoverb]

It sounds like a fault with the rotary switch, or more likely the LDR/relay switching circuit it controls. Try some contact cleaner spray in the switch (you'll need to get into the chassis) - but if that doesn't fix it, it's a job for a tech very familiar with these amps, unfortunately.

 

[rjf]

Looks like I'm going to just run it over to Mesa then. I've never pulled a chassis out before and don't think I want to anytime soon. Buddy of mine is having trouble with the FX loop in his 3 ch Triple, so we'll just head up there to Petaluma and get them worked on, take the tour, blah blah. :lol: