Shure m68 mixer mod

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"splitlips" <splitlips@gmail.com> wrote in message
news:1119676364.349427.167940@g47g2000cwa.googlegroups.com...
> Hi,
> I'm new to this group, was wondering if any of you guru's could help
> me with modifying this mixer :
>
> http://www.shure.com/pdf/discontinued/m68.pdf
>
> to act as a 4 channel mic preamp with unbalanced outputs?
>
> I imagine it should be simple but I'm not great at deciphering
> circuitry, just soldering...
> -James.
>

you will be much happier with a couple of dual behringer or blue tube or
similar. however just clip the wire from the center pin of each level pot
and cable out from that point.

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"splitlips" <splitlips@gmail.com> wrote in message
news:1119751120.607192.60720@g14g2000cwa.googlegroups.com...
> Thanks,
> Simple enough!

But once you've done it, I bet you run out and buy a Behringer pretty
quickly. The M68 was not one of Shure's cleaner mixers.

> looks like I can also reverse the output transformer for another input
> and do 5 channels too without too much hassle.

Into what? There are only four sets of preamp electronics. And the output
transformer is probably....well, never mind, there's no place to connect it
anyway.

Peace,
Paul

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Paul Stamler <pstamlerhell@pobox.com> wrote:
>> "splitlips" <splitlips@gmail.com> wrote in message
>>
>> But once you've done it, I bet you run out and buy a
Behringer pretty
>> quickly. The M68 was not one of Shure's cleaner mixers.
>>
>>> looks like I can also reverse the output transformer for
another
>>> input and do 5 channels too without too much hassle.
>>
>> Into what? There are only four sets of preamp
electronics. And the
>> output transformer is probably....well, never mind,
there's no place
>> to connect it anyway.
>
> The output transformer is different than the input
transformers.
> They are not the same ratio.
>
> And I will agree that the M68 was... well... kind of
nasty-sounding.

How can that be? None of that *nasty* stuff that some
audiophiles hate like ICs or loop feedback! ;-)

Archived from groups: rec.audio.pro (More info?)

"splitlips" <splitlips@gmail.com> wrote in message
news:1119828722.394213.21470@g49g2000cwa.googlegroups.com...
> > And I will agree that the M68 was... well... kind of
> nasty-sounding
>
> I'm not expecting it to sound fantastic, It looks pretty easy to
> overload as is. I think wiring in pad switches before the transformers
> and wiring the pots before the preamp electronics might help. I mean
> there's no provision in the stock unit to prevent clipping, only to
> lower the volume once it does...
>
> If nothing else I'll have learned a lot so I can't really go wrong.

Unless you try to use it on a recording that matters.

Easy to overload is the understatement of the year. The one we used to use
for dances required a 20dB inline pad on each microphone to avoid clipping,
with dynamic mics; for condensers I'd want at least 30dB pads, maybe more.
Wiring the pots before the electronics will, unless I misremember the
schematic, load the transformers wrong and ruin the noise performance.

Besides, even when these circuits weren't overtly clipping, they still
sounded pretty bad.

On the other hand, as you say, you'll have learned a lot. And if you
actually make them sound decent, my hat will be off to you. Just make sure
you have a better preamp on hand to compare.

Peace,
Paul