PCB 6X 4CM Assistance

J

JBO

Member
Hello - any assistance would be much appreciated.

Routing: I have the pcb6x routed to two jcm 800's - as per page 18 of the manual. Using correct insert cables. The outputs (1and2) are also going via a source audio EQ2 pedal which I have set to stereo in/stereo out configuration. E.g. pcb6x outputs -> SE EQ2 -> Returns on JCM 800.

Issue: With both amps connected - when setting insert loop 2 (=) and output 2 to ON and insert loop 1 (+) and output 1 to OFF - I have no issue and get the correct signal and output from 1x JCM 800. However when I engage (turn on) the insert loop 1 and output 1 - I get a very LOUD high frequency signal from the amp. (Not ground hum in this case, but a loud high frequency signal). The same occurs when I have only one JCM800 connected but toggle (or go to a preset with) the INS1 and OUTPUT1 to be ON in the pcb6x.

I have done similar many times - what am I missing/doing wrong here? Assistance much appreciated.
 
Are they stock JCM800s or modified? Have you tried moving the amp in insert 1 / output 1 to insert 2 / output 2 to see if anything changes?
 
Hi - yes stock amps with series fx loop. I did do a switch test - the result was i can run either amp successfully in isolation (so either combo of ins1/output1 or ins2/output2 works - but not at the same time.

*I will double check - I haven't somehow :"criss-crossed": the ins1/2 and output 1/2 somehow on the board...but if I had - it shouldn't work at all right? Any issue with using the EQ2 after the outputs?

Q: is there an issue with having both ins1/2 and output1/2 set to "ON" whilst only using either of them? E.g. so I can do swap tests. or should the inactive ins and out be switched off if not in use?
 
I misunderstood your original post, I thought that the amp in Send 1/ Output 1 would make noise on its own.

You probably have a ground loop - have you tried using isolation transformers on one amp?
 
I have a humno on the power to the amp which has rectified previous ground loop issues. Can you recommend an iso transformer for the return? A link would be great and I'll try that next:)
 
rjmmusic said:
I misunderstood your original post, I thought that the amp in Send 1/ Output 1 would make noise on its own.

You probably have a ground loop - have you tried using isolation transformers on one amp?
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Hi:) I have narrowed down the (repeatable) issue after performing multiple tests. The INS loop has both SEND and RETURN set to STEREO. Both OUPUT A and B are enabled. This is to allow 4CM for a two amp rig. Each of the OUTPUTS going to amp FX loop RETURN function with a normal signal. Each of the SENDS going to amp INPUTS function with a normal signal. However only 1 RETURN going to from device to the amp FX loop SEND functions with a normal signal - the other only emits a very "weak" signal. Any ideas would be much appreciated. (This have replaced that particular insert cable twice, with the same result). Thanks
 
JBO said:
Hi:) I have narrowed down the (repeatable) issue after performing multiple tests. The INS loop has both SEND and RETURN set to STEREO. Both OUPUT A and B are enabled. This is to allow 4CM for a two amp rig. Each of the OUTPUTS going to amp FX loop RETURN function with a normal signal. Each of the SENDS going to amp INPUTS function with a normal signal. However only 1 RETURN going to from device to the amp FX loop SEND functions with a normal signal - the other only emits a very "weak" signal. Any ideas would be much appreciated. (This have replaced that particular insert cable twice, with the same result). Thanks
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When you say it emits a weak signal, are you saying that the amp is emitting a weak signal? Because the return jack on the PBC is an input.

And, you say only 1 return has a problem. Which one?
 
Yes understood regarding the return being an input. Specifically the weak signal I'm referring to is the overall rig signal when that "side" of the return is used. To clarify i can successfully use either output a/b going to amp fx return and either INS send L/R going to the amp input, but can only use INS L return going to amp fx send. When using INS R return to amp fx send To my hears it sounds like one that side of the return is not receiving the amplifier preamp send back - hence the signal is barely audible.

My device config:

1704189227180.png
 
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Have you tried swapping the left and right amps in the insert loop to see what happens?
 
It's possible that there's something going on with the PBC's switching matrix. If you want to send it in, I could test it.
 
rjmmusic said:
It's possible that there's something going on with the PBC's switching matrix. If you want to send it in, I could test it.
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OK- how best to do that? I'm in Melbourne, Australia! (Alternatively is there something you could step me through remotely? I'm reasonably adept technically, to a point:)
 
You could run its self tests and see what it says. You'll need two TRS cables and one mono to stereo cable (TRS on one end and TS on the other. Both ring and tip on the TRS end connected to the tip on the TS end).

If you have that available, I can tell you what's next.
 
rjmmusic said:
You could run its self tests and see what it says. You'll need two TRS cables and one mono to stereo cable (TRS on one end and TS on the other. Both ring and tip on the TRS end connected to the tip on the TS end).

If you have that available, I can tell you what's next.
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Yup - have 2xTRS and 1xInsert on hand
 
An insert isn't going to do it, unfortunately. What you need has one TS on one end and one TRS on the other. Without that, all the self tests on the stereo loops are going to fail.
 
rjmmusic said:
An insert isn't going to do it, unfortunately. What you need has one TS on one end and one TRS on the other. Without that, all the self tests on the stereo loops are going to fail.
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Understood. I'll get one and revert back.
 
Just awaiting my TRS to TS cable to arrive. Don't know if it's related - but when I created an additional loops page (Loops2) - when scrolling via the function button - when arriving at Loop2 - another press of the Function button wouldn't take me to Switches (Page 5) - and all the device buttons would become unresponsive (essentially frozen) - the fix was to power the device off and on, returning the device to the presets page. This happened more than once.
 
It sounds like you're going to a blank page. How is the function button programmed on page 2? It seems like whatever page it's programmed to access has no buttons defined.
 
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