Mellotronists

Hi all-
My M400 tone control is non-operational, thought I
would dig into the problem. Tested it, wiper appears
to be open. Reads 32K for the full value between the
other terminals. Is this a correct value, and is this
pot linear or log(audio) taper? I don't have
schematics yet. This machine has 2 cards in the
preamp box, pots have plastic shafts. May as well get
the volume pot value, too, if it is not too much
trouble.

Thanks

-Bruce Daily
M400 #1221

PS- The control knobs on Mark Wallis' WEM Audiomaster
mixer look quite familiar...






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Bruce Daily wrote:

Hi all-
My M400 tone control is non-operational, thought I
would dig into the problem. Tested it, wiper appears
to be open. Reads 32K for the full value between the
other terminals. Is this a correct value, and is this
pot linear or log(audio) taper?

Hi Bruce, Tone Control is 25K log-taper ,volume is 10K log-taper.
Dave Kean had a note in his svc. manual to use a 10K log-taper
for better range in tone control. Tried this in a few cases, slight improvement.

BTW, it's becoming increasingly difficult here in the USA to find audio-taper pots
with 2-inch long shafts (brass,alum,plastic,etc).

I don't have
schematics yet. This machine has 2 cards in the
preamp box, pots have plastic shafts. May as well get
the volume pot value, too, if it is not too much
trouble.

Thanks , -Bruce Daily , M400 #1221

PS- The control knobs on Mark Wallis' WEM Audiomaster
mixer look quite familiar...

Those cards are the venerable WME289 and WME290 line amp and preamp
boards,resp. Control knobs on WEM and M400's are the same, mfgd.
by Bulgin, England.

Cheers, -- Jerry Korb at the Mellotron Ranch