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Presence Knob Not Working help!
http://forum.grailtone.com/viewtopic.php?f=4&t=26793
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Author:  Key [ Sat Jul 12, 2008 3:31 pm ]
Post subject:  Presence Knob Not Working help!

So I have a 3 channel triple rec. I was playing around with it today and on channel 2 the presence knob is doing nothing. Everything else works just fine but I am getting nothing out of the presence. Any help would be great. Thanks for your time.

Author:  Elpelotero [ Sun Jul 13, 2008 6:26 pm ]
Post subject: 

It may be loose on the inside. Take a look inside the amp, without touching anything, and look at the pot. There's a few very small tabs that if loose, make the pot have no contact and thus unusable. If so, tighten the little tabs and that's it.

Author:  Ibanez [ Mon Jul 14, 2008 8:46 am ]
Post subject: 

On my ROV, lead channel, the presence is only perceptible at very very high settings. If you didn't notice any changes with the presence maxed, you probably have a problem. What are your gain and other knob settings ?

Author:  Key [ Mon Jul 14, 2008 3:51 pm ]
Post subject: 

Well I did some testing today and the presence will only work on the vintage mode. It will do nothing on raw or modern. Any idea on what this could be. I called Mesa and could not get in contact with anyone. :(

Author:  Key [ Fri Jul 18, 2008 4:19 pm ]
Post subject: 

Anyone else?

Author:  7 Strings of Hate [ Tue Jun 19, 2018 2:19 pm ]
Post subject:  Re: Presence Knob Not Working help!

I'm having the same problem. Presences knob on channel 1 only works for vintage, not modern. Anyone have any advice? I'v tested each preamp tube with some spares and they are working fine.
Mine is a 2 channel mid 90's dual.

Author:  deeman [ Wed Jun 20, 2018 8:42 am ]
Post subject:  Re: Presence Knob Not Working help!

Check the manual to be sure, but I think for the 3 channel recto, the 2nd channel's presence is optimized for the Vintage setting and the 3rd channel for modern. That may be the problem too.

Author:  woodbutcher65 [ Fri Jun 22, 2018 9:00 pm ]
Post subject:  Re: Presence Knob Not Working help!

The way I read the schematic....



Check the mode switch on channel 2. If it's not that then it's most likely to be the 2n6426 transistor that feed relay 8. When it's engaged, the presence control will be in the vintage circuit configuration.

Those transistors sometimes short. Less likely but not impossible: A sticky relay. Tapping on relay 8 with the eraser end of a pencil might free it up but once a relay goes sticky it needs to be replaced because it'll stick again sooner or later.


The way that circuit is set up is very interesting. I had to study it for a bit to get comfortable with my diagnosis.

My guess is, in order of likelyhood according to my lights: Bad R8 relay driver transistor, bad mode switch, sticky R8 relay.

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