Revox A77 Problem

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demto

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Can anybody help.

I have a Revox A77 Mk3. Unfortunately the VU meter trimpots
have been put out of adjustment and I want to reset them.

Does anybody know how many millivolts should be applied to the
AUX input in order that the VU meters will show 'Odb'.

The manual mentions '35Mv input' but doesnt say whether this is
for Odb, +6db, or whatever.

A friend of mine has a A77 mk4. His machine shows Odb on the
meters for a 20Mv input.

So I am confused.

Is it 35mv for Odb on meters
Is it 20Mv for Odb on meters

or does this have to be set according to type of tape used?.

I thought that adjusting the machine for tape being used was
made by altering the outputs of the record and playback boards
and not by altering the sensitivity of the VU meters which only
show the input signal strength on the A77.

As you can tell I am totally confused by this, and if anyone can
help I would be very gratefull.
 
Yes and no. Your machine needs calibrating, and preferrably you should do a complete calibration, and for that you need reference tapes, and which one to get depends on what tape you use and other shtuff. Read more here:
http://home.flash.net/~mrltapes/

However, to answer your question, the VU meters should be at 0 when you send a reference level signal to it. In your case this most likely means a -10db reference. You can create such a reference signal eitehr with a tone generator (everyone has that under their bed, right? No?) or with a synthesizer. Make the synthesizer do continous droning sine-wave. Put it through your mixer. Make sure the VU meters on the mixer says 0 on the output. You now have a -10db signal on the tape out of the mixer.

You have no mixer? OK, then you need an oscilloscope and a calculator, and that process is to complicated for me to describe in the blind. I'd probably get some detail wrong. :)
 
REGEBRO

Thanks for your interest in my problem.

Unfortunately I do not have a mixer so I have no meters to
register Odb output or any other value.

I do have a scope. signal generator. multimeter, and AF voltmeter

I am trying to obtain an alignment tape but do not have one yet.
 
You might want to get the service manual for the deck too as it would document the correct test signal levels to use.

Or, wait a little bit and see if some here has the documentation and can give you the correct value.

Were you lead to believe that only the VU meter calibration pot has been messed with and nothing else or, does the entire neck need a complete calibration procedure?

Cheers! :)
 
Well, -10dbV, which I assume that is what you want it on, is 0.3162 volts. So your references to 20 or 35 millivolts are totally way off. It should be 316 mV. Problem is, I don't remember if that is peak to peak, or mid to peak, or average....
 
REGEBRO

Thanks for you help.

I do have the manual, and I know the meters are out because I
altered the trimpots myself by mistake. What an idiot.
One of the Revox agents here in the Uk has a pay as you go
technical advice line and was very helpfull. The meters are now
OK.

Once again Regebro, thanks for taking an inerest in my problem.

Demto
 
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