Re: Broken SoundMeister

[dempson@actrix.gen.nz (David Empson)]

<retromod-Apple-II-newsgroups> wrote:

> My SoundMeister sound board seems to be partly broken.  That is, I can
> do audio input with it, and all audio records fine.  However, the
> audio output is silent.  I have to turn the volume on my stereo very
> high to get any sound from either of the audio output jacks (and that's
> very whooshy sound).

Do you know what might have caused this?

I managed to blow up one of the output stages of my SoundMeister shortly
after I got it, by plugging in a stereo while it and the computer were
powered on.

The details are now extremely hazy, and I doubt I can find any notes I
might have made at the time.  I have just pulled the card out to have a
look.  The repair made was obvious: we put a socket on the board in case
the chip blew again.  It is the 8-pin chip in the top centre of the
board labelled U3, a TL072 op-amp.
  
I assume you know that the two outputs are at different levels: one is
line level and the other is amplified for connection to speakers.

If there is a problem in the audio generation for the line level output,
then neither output will work, because the amplified output is derived
from the line level one.

This isn't necessarily the faulty chip, but it would be a good thing to
check.

> Cost/availability?

Not sure, but it is pretty common.

The fundamental part of the line level output circuitry on this card is
shown in the IIgs Hardware Reference as an example of how to decode
stereo from the Ensoniq output.  There is a second amplifier circuit
which makes use of the LM2877 (the chip with the heatsink that hangs off
the front of the card) for generating the amplified output.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand