Pro Audio Design Forum

The preamp schematic would give us a clue about the head impedance. The active preamp would be the best one to look at. I would think either the MM or MC preamp could be adapted.

I have a sheet with the impedance of the heads in Henries. The heads on each machine are a different impedance IIRC. I'll scan both preamp versions. I'm thinking of this more as 'proof of concept' than trying to get a finished build.

i think i heard somewhere sometime that the VU bridge is the culprit. wasn't it that the non-VU A80s hat low-Z heads and that for the the VU-machines, studer had to develop new high(er)-Z heads? and could it be that you can't put a VU bridge on a machine that didn't have one ex-factory – and on the other hand the heads of the VU-machines can't be used with the electronics of a non-VU machine?

if you can give me the serial number(s) of the machines, i'll ask simon kummer who once explained the differences to me.

(and he should know it as he services the tape machines in some of switzerland's very good mastering and recording studios. he just finished a complete restauration of a non-VU A80 for a friend of mine. he put in new heads from a US specialist. the electronics were recapped where neccessary and appropriate but otherwise left unmodified. we listened to the master tapes of a recording we made last summer, live to two track with a gorgeous 1972 neve console feeding a 1962 C37. we mastered with the original session tapes [selected takes cut and assembled them to a new original for mastering]. i'm quite familiar with the sound of the tape since i was present during the recording sessions. i heard the tape in the mastering studio played back on a Telefunken A10 and on my friends restored A80. it sounded more "natural" on the restored A80 whereas on the M10, the sound was a tad punchier, crisper which somewhat "compensated" the slightly rolled-off top end of the C37's tube preamps. the crisper sound of the M10 was good for cutting the lacquers. but i preferred the A80 just for listening and enjoying to the music on the tapes.)

My machines all have the correct heads for the given electronics. The machines have been completely restored and gone over by Dan Zellman and Bob Shuster. Both are factory trained Studer technicians with decades of experience servicing them.Nothing is broken. The machines work like new. I’m looking to improve the sound without doing anything that would precent it from easily putting it back to stock. They aren’t worth anything unless they are stock.

I didn’t think the Telefunken M10 had a standard set of electronics. I had one in a Neumann SP66 console. The playback electronics were manufactured by an RFT company that wasn’t Neumann. I forget which one. That setup didn't sound as good as the M15 which sounds fabulous.

I’ll have a chance to scan the schematics on Friday.

Now that I think about it the M10 had some of the edginess I don’t like. Coincidentally there was a long cable run from transport to electronics.

Here is a scan of the transformer less preamp that is used with 1/2" heads. I'll scan the 1/4" preamp soon.

Paul -

I'm not sure I can read the values.
What is the value of the resistor that terminates the head?
Is it 56K?

Wayne,

I didn't want to make the scans so big you couldn't see the whole circuit. I can see the component values aren't readable that way. I could post the full size version for download if that would be better.

Anyway R20 is 56K. That's the first resistor at the input between each end of the coil into T110.

Based on the termination resistance (56K) I'm wondering if the MM board would be a better option.

Cool. What would it take to convert the RIAA EQ to an NAB or AES EQ?