# channel switching lag



## Guest (Sep 3, 2015)

I have an 80's Marshall Reverb 75 112 combo 2 channel SS (5275). It's my 
main amp for jamming. Weighs about as much a twofour of beer. For the past
couple of years, the gain channel would cut in and out (push/pull pot). Recently, 
I've acquired a simple SPDT footswitch to change the channels. Works fine except 
when I change from gain to clean. There's a volume drop and then a lag when it 
comes back up to the setting I have it on. I'm wondering if it's the pot (which
needs to be changed) or something in the circuit? It is 30 years old after all.


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## gtrguy (Jul 6, 2006)

Channel switching in that one is handled by a CA3046 IC.... could be a problem with that chip or perhaps the surrounding circuitry, I'd be inclined to look at the caps in the switching circuit. C9 and C51 on this schematic:

http://www.drtube.com/schematics/marshall/5275.gif


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## jb welder (Sep 14, 2010)

Also, C10 & C18 could be related. Or a leaky transistor TR2.
Does the lag happen with the Pull EQ switch in either position?


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## Guest (Sep 4, 2015)

I'll have to check it out with the pot in/out. Didn't think of that.
As to the schematic, I may as well be looking at hieroglyphics. lol.
I'll try to get a sound clip a well.
Thank you gentlemen.


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## High/Deaf (Aug 19, 2009)

A real outside chance, but I've seen channel switchers with reverb where they temporarily mute or ramp up the channel you are switching to so the verb doesn't wash over (or maybe its just the reverb level they mute, but it's noticeable).


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## Guest (Sep 4, 2015)

Reverb is turned right down.
The mic on my old camera sucks, but you can hear what I'm
talking about as the led light goes on/off (30 sec mark).


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## jb welder (Sep 14, 2010)

Not sure if I'm deaf (or daft), but I don't hear any difference as far as dirt/clean, just the volume dropout. Do you have the dirt levels fairly equal, or is the gain channel not doing much?
Just wondering if the dropout is the only issue or if there is more wrong with the gain channel?


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## Guest (Sep 4, 2015)

It's my camera's mic. It doesn't quite pick out the difference 
between the clean/dirt (it's loud and distinct in my living room). 
And yes, the two channel levels are set close to each other.
But, yeah. It's the dropout that's the issue.


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## jb welder (Sep 14, 2010)

From the looks of the video, without the footswitch, the amp is in clean mode.
If that's the case, C9 should not be the problem, but it's easy enough to replace anyway.
C51 is for the reverb, so it can be ignored.
C9, C10, and C18 are all possible suspects, so it's easy enough and cheap enough to replace all three.
Even if you don't understand the schematic, I believe the parts are labelled on the circuit board. In some of these era amps, some components were tacked onto the solder side of the board. If you can't find those 3 caps labelled on the board, post some pics of both sides of the board and we may be able to point them out to you.


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