Problem with loop 6505MH

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modus2000
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Problem with loop 6505MH

Post by modus2000 » Mon May 08, 2023 7:17 am

Hi

I have strange behavior of my 6505MH
When I add BOSS RV6 rever (or any other pedal) to loop sometimes it start make huge noise like "microphone feedback"

Does somebody have any idea how to fix? Do you have electric circuit scheme of 6505MH ? (I have no dealer service near)

WrldEatr9
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Re: Problem with loop 6505MH

Post by WrldEatr9 » Wed May 10, 2023 2:49 pm

Perhaps it's the pedal power supply.

modus2000
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Re: Problem with loop 6505MH

Post by modus2000 » Wed May 10, 2023 11:19 pm

I tried battery - same result (

WrldEatr9
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Re: Problem with loop 6505MH

Post by WrldEatr9 » Thu May 11, 2023 9:44 am

While not a fix, a noise gate should take care of the noise.

modus2000
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Re: Problem with loop 6505MH

Post by modus2000 » Thu May 11, 2023 9:57 am


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dak
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Re: Problem with loop 6505MH

Post by dak » Thu May 11, 2023 10:18 am

Well, effects are normally inserts but you managed to make a loop here. What did you connect where exactly?

modus2000
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Re: Problem with loop 6505MH

Post by modus2000 » Fri May 12, 2023 3:10 am

scheme is following:

Send -> input of BOSS RV6
output of Boss RV6 -> Return
If I turn "level" on Boss rv6 more than 25%, it start whistle.

This pedal works well on another Marshall amp without any noise.

Deffect audible only if both Send/Return jack inserted into 6505MH.
This deffect was absent before and arose recently. I tried different cables/pedals with battery/electric sockets/other amp - the problem is inside loop of 6505MH.

Before I bring it to service, I want to understand is "effect loop" is analog or it is digital. If the loop is analog I can bring it to any service, but if it digital - I need Electric Circuit Scheme, because I don't have official Peavey service in my country. Please help to obtain scheme.

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dak
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Re: Problem with loop 6505MH

Post by dak » Fri May 12, 2023 4:25 am

Here is my guess: the effects loop return socket has a switch that separates send/return. This switch is not operative, resulting in input and output of the Boss pedal being connected and consequently prone to feedback. Maybe try a different cable with a thicker plug for the return socket.

Should be a comparatively straightforward repair since this does not sound like something that would easily happen with digitally switched signal paths (unless the connection is made with a bidirectional FET instead of a mechanical switch, but I doubt it).

modus2000
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Re: Problem with loop 6505MH

Post by modus2000 » Fri May 12, 2023 5:29 am

When I put empty jack to "Return" without any signal - amp should switch off the sound from guitar? Right?

So, if I put jack to Return and continue hearing guitar this means "Return" switch is broken?

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dak
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Re: Problem with loop 6505MH

Post by dak » Fri May 12, 2023 3:41 pm

modus2000 wrote:
Fri May 12, 2023 5:29 am
When I put empty jack to "Return" without any signal - amp should switch off the sound from guitar? Right?

So, if I put jack to Return and continue hearing guitar this means "Return" switch is broken?
Right. Use the same cable as you use for your pedal. It's either that, or the cable is not like the switch expects it to be. Like the cable being TRS (with a ring between tip and shield) and the switch being operated by the plug area between ring and shield that happens to be thicker when there is no separate ring.

modus2000
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Re: Problem with loop 6505MH

Post by modus2000 » Sun May 21, 2023 7:10 am

Finaly I fixed it :)

The problem was that "Return" didn't cut signal when I put jack there. The reason was injured smd transistor near "Return" Q26 (J174 P-Jfet 30V SOT23).
Thanks Peavey support who sent me electric circuit scheme.
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dak
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Re: Problem with loop 6505MH

Post by dak » Sun May 21, 2023 7:46 am

At some time I will need to look at some newer circuit diagrams... Using a JFET for switching instead of some direct plug-operated switch will allow for much more direct routing of the analog signal, reducing the susceptibility to hum and the influence of iffy contacts.

Less hands-on for diagnosis and repair, of course. There is no spray for fixing JFETs...

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Re: Problem with loop 6505MH

Post by j0nsnell » Sun May 21, 2023 10:37 am

modus2000 wrote:
Sun May 21, 2023 7:10 am
Finaly I fixed it :)

The problem was that "Return" didn't cut signal when I put jack there. The reason was injured smd transistor near "Return" Q26 (J174 P-Jfet 30V SOT23).
Thanks Peavey support who sent me electric circuit scheme.
Looks like someone plugged something in that shouldn't have been plugged in there, killing the FET and a couple of SMD components.
Easily done.

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