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From: Tim Perry on 17 Jun 2008 11:11

"Eeyore" <rabbitsfriendsandrelations(a)hotmail.com> wrote in message
news:4855EBBA.A4E4E902(a)hotmail.com...
>
>
> Tim Perry wrote:
>
> > See alt.binaries.schematics.electronic
> >
> > Made with adobe audition and Mia Midi soundcard.
> >
> > As one would expect, the waveform is substantially different that what
is
> > seen on an oscilloscope.
> >
> > It was interesting to find that the waveform of the glitch is inverted
on
> > all left - right pairs and the low and mids the inversion was opposite
of
> > the HF outputs.
> >
> > It was also interesting to note that the HF content of the glitch seemed
to
> > be greater when preceded by a 96.9 Hz tone as opposes to a 991 Hz tone
or no
> > tone.
>
> Thanks for all your effort on this Tim.
>
> From your earlier post am I correct in saying that the switch-off glitch
was
> symmetrical on both audio phases and would therefore be effectively
rejected by
> properly balanced inputs ?

The oscilloscope check seemed to indicate this. I believe you could roughly
emulate the effect by wiring the amplifier inputs 2 & 3 together and tapping
them with a 3 volt battery referenced to pin 1.

note: there is no guarantee all of these units have precisely the same
output glitch. I only speak for the one on my bench.

It would seem to me that 12 poles of relay contact operated by one of the
transformers secondary (or a third transformer) would be needed to
effectively mute the power off glitch. the XLR conductors are accessible
internally without pulling the PC board.
An alternitive would be 6 buffer amps on a seperate supply.

> We run everything balanced (bar the guitar and keys
> leads before they reach the DIs !).
>
> I'm only really mostly concerned about the HF drivers, yet on reflection
these
> are the only ones (EV DH7s) that have NEVER blown. Taken out the
protection
> lamps a couple of times but never had to fit new diaphragms.
>
> Note the clarification there, the HFs DO have protection lamps, I should
have
> remembered but wanted to check the schematic I'd temporarily mislaid.
>
> many thanks, Graham
>
>


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