Demeter pre-amp problem

Mailliw · Jun 14, 2007

Hello,

I took apart my Demeter VTMP-2 preamp and while I was inspecting the board, I noticed one channel was missing a capacitor.

I couldn't find a schematic on the internet, so sketched one and re-drew it on the computer for your eyes' sake.

I am not sure what sort of tube stage that is, is it a sort of cathode follower?. I find it strange that the preamp functions perfectly without that capacitor. :?

The power supply board had a burned solder joint that looked really bad, but still functioned. I resoldered it anyway. What causes those? I was thinking maybe it started to break away and arc.

Thanks!
William

okgb · Jun 14, 2007

Are you sure you drew the ouput stage correct ?
usually the plate drives the cathode of the second stage [ white followers]

Of course other may correct me here , but ..here hope this helps you fix it

Mailliw · Jun 15, 2007

Thanks Greg.

I doubled checked this morning, my schematic appears to be correct. The schematic you posted doesn't show this, but the final output does connect to the last 12BH7's plate.

Bigger version of okgb's schematic

It is noted on that schematic that there is "no connection" for that .12uF capacitor. Still strange how 1 channel has it and 1 doesn't.

Thanks

okgb · Jun 17, 2007

nc , that the cap connects to the top plate and not the resister to ground

yeah strange that it would be one channel and not the other ,
must not affect usual operation [ outer freq range ? ]
does it look like it just got missed and was unintentional ?

tonedude · Apr 30, 2015

Okgb, would you mind sharing a igger version of the Demeter pre schematic? I'm thinking about reverse enginer my Demeter MH1 pre and it vould be nice to have the vtmp2 to compare with.

- Mattias

johnny_lot · Dec 15, 2019

Hey,

Can you please post the schematic again?
The old link is broken and I need the schematic to service mine.

Thanks! :

salomonander · Dec 20, 2019

Can anyone help out with the schematic? Sorry for resurrecting a dinosaur

Ps: i found it in the tech section. But can someone tell me what transformers are used? I know its a jensen - but which one? Same for power xformer. Thanks

Demeter pre-amp problem

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