Amp tech people! Need help diagnosing a problem with a Boogie Mark V

rossyamaha

Hello clever people. 

So I have an interesting issue with a Boogie Mark V head. everything is great until you plug in jacks to the external channel switching (not the normal footswitch) at which point there is a pretty bad mains hum. A noise gate set high gets rid of a small amount of it but it's still there and very audible so it's not gain related. It's only present when using channel 3 switching socket. 

Any ideas? Something I might be able to sort myself (remember I'm an idiot from Mansfield). 

DJH83004

What are you plugging into the jack sockets? they need a straightforward latching footswitch, tip to ground arrangement or a master switching unit  via a midi controller. If you have a simple latching footswitch (mono jack), try plugging it into each of the four inputs and see if a) it switches and b) if it is generating any mains hum.     

ICBM

Is whatever is controlling the external switching on the same power circuit or ground connection as pedals that are plugged into the front of the amp, or the FX loop? It sounds like you may have a ground loop, although why it only occurs when using the Ch3 jack I'm not sure. I don't have a schematic for the MkV and I've never worked on one.

rossyamaha

I’m using a Gigrig G2 to do the switching but tried it with a Helix and get the the same effect. I’ve mailed Westside but not heard anything back yet. I was wondering if one of the relays had gone a bit ducky and was causing the earth hum. Might give the US a shout tonight to see what they say. 

ICBM

rossyamaha said:

I’m using a Gigrig G2 to do the switching but tried it with a Helix and get the the same effect.

Does it still do it if you use the two units separately, one for the signal and one for the switching? (On different power supplies and not touching each other.) Obviously that's not how you would want to run it in practice, but it would help identify the problem.

rossyamaha

ICBM said:

rossyamaha said:

I’m using a Gigrig G2 to do the switching but tried it with a Helix and get the the same effect.

Does it still do it if you use the two units separately, one for the signal and one for the switching? (On different power supplies and not touching each other.) Obviously that's not how you would want to run it in practice, but it would help identify the problem.

It does. Tried just about everything and think I’ve narrowed it down to the channel 3 switching jack. Everything is perfect and silent until that gets involved. 

DJH83004

I would just get right back to basics and forget any power supply driven switching kit and just plug in a simple latching footswitch if you have one (not TSR), because for all their complexity the upstream equipment is just switching a pair of contacts.