I am seeking advice on how to approach a potential project. I have an
Alesis Microlimiter, which I bought new in 1987. I was 'inexperienced'
with audio to say the least, and was using what little gain it produced
to amplify a mic-level signal for vocals, which I recorded onto my old
Porta-One. Just turn up the input and output to maximum, plug in mic -
and crank up those tiny rubber trim pots while you're at it.

The Microlimiter, unsurprisingly, didn't like this treatment at all,
and quickly died an ozone-scented death. Sigh.

So here we are, eighteen(?!) years later, and I dig this thing out of a
box in my folks' basement. On a whim I take it home, thinking that
maybe it'll be salvageable somehow, and this morning I popped it open
for a look at the insides. I'd call my electronic skills 'pre-novice',
so very little of what I see means much to me, but I'm encouraged by
the clean, accessible design to think that maybe this is something I
could handle working on.

I have two questions:

1. Given the way in which it was killed - driven with maximum gain for
long periods - should I be looking from the outset at any particular
part? I'm not expecting anyone to have an encyclopedic knowledge of
this design of course, but any general speculation would be welcome,
I'm not sure what tends to be vulnerable as a rule. Dead capacitors
maybe? Dead ICs?

2. Would it be worthwhile to try upgrading the parts while I'm in
there? I understand that this device is a one-trick pony at best, but
I'm willing to try my hand at replacing caps and ICs if there might be
a sonic benefit. If it helps at all, the ICs a

1 x LM340T12
2 x LM339N
4 x TL084CN
1 x CEM3381
1 x "7912" (voltage regulator I think?)

I appreciate any and all advice on this. It's an oddball processor, and
not good for a whole lot, but it seems like it could be fun to work on,
and I do need to start getting my feet wet with the soldering iron...
metaphorically, anyway.

Thanks!

- Eric

"e.a.rowe" wrote ...
I am seeking advice on how to approach a potential project. I have an
Alesis Microlimiter, which I bought new in 1987. I was 'inexperienced'
with audio to say the least, and was using what little gain it
produced
to amplify a mic-level signal for vocals, which I recorded onto my old
Porta-One. Just turn up the input and output to maximum, plug in mic -
and crank up those tiny rubber trim pots while you're at it.

The Microlimiter, unsurprisingly, didn't like this treatment at all,
and quickly died an ozone-scented death. Sigh.

So here we are, eighteen(?!) years later, and I dig this thing out of
a
box in my folks' basement. On a whim I take it home, thinking that
maybe it'll be salvageable somehow, and this morning I popped it open
for a look at the insides. I'd call my electronic skills 'pre-novice',
so very little of what I see means much to me, but I'm encouraged by
the clean, accessible design to think that maybe this is something I
could handle working on.

I have two questions:

1. Given the way in which it was killed - driven with maximum gain for
long periods -

It seems very unlikely that any audio mic-level or line-level
device could be "killed" by any amount of signal abuse. I'd
bet the cause is something much more ordinary like simple
component failure.

should I be looking from the outset at any particular
part? I'm not expecting anyone to have an encyclopedic knowledge of
this design of course, but any general speculation would be welcome,
I'm not sure what tends to be vulnerable as a rule. Dead capacitors
maybe? Dead ICs?

Even if you could identify fried components by looking (which
is quite possible), it wouldn't necessarily mean that you had
found THE offending component (or all the damaged components)
just by looking. Without service information (at least schematic
diagram), it is pretty nearly a lost cause.

IIRC these things have a pretty negative reputation and are not
well regarded even when operating "nominally" (a fancy $2
NASA word :-) Or is that the Microverb that is a dog?

2. Would it be worthwhile to try upgrading the parts while I'm in
there? I understand that this device is a one-trick pony at best, but
I'm willing to try my hand at replacing caps and ICs if there might be
a sonic benefit. If it helps at all, the ICs a

1 x LM340T12
2 x LM339N
4 x TL084CN
1 x CEM3381
1 x "7912" (voltage regulator I think?)

I appreciate any and all advice on this. It's an oddball processor,
and
not good for a whole lot, but it seems like it could be fun to work
on,
and I do need to start getting my feet wet with the soldering iron...
metaphorically, anyway.

If you can't locate a schematic diagram, your chances of
doing anything with it seem slim to none. OTOH, you may
find it fun to dissect just to see how they made it.

On Tue, 11 Oct 2005 22:07:26 -0700, "Richard Crowley"
wrote:

It seems very unlikely that any audio mic-level or line-level
device could be "killed" by any amount of signal abuse. I'd
bet the cause is something much more ordinary like simple
component failure.

If designed with a barely-adequate power supply, I suppose it could
have overheated.

It seems very unlikely that any audio mic-level or
line-level device could be "killed" by any amount of
signal abuse. I'd bet the cause is something much more
ordinary like simple component failure.

My first guess was that being driven too hard for too long caused
something to fail from overheating, but I don't know enough about the
properties of various components to know which would be most
vulnerable.


snip
Without service information (at least schematic
diagram), it is pretty nearly a lost cause.

I'll try to find a schematic online. Who knows, I might get lucky.


IIRC these things have a pretty negative reputation and
are not well regarded even when operating "nominally"
(a fancy $2 NASA word :-) Or is that the Microverb
that is a dog?

The whole 'micro' series is considered dubious by most pros, but I've
heard that this box can be used for squashing the heck out of drums and
bass, if you like that sort of thing. I think it might be fun to play
with.


If you can't locate a schematic diagram, your chances
of doing anything with it seem slim to none. OTOH, you
may find it fun to dissect just to see how they made it.

That's really what this is all about. I need to start tweaking stuff to
see how it works, so a pocket-size fixit project like this is perfect.
The board is pretty spartan, so I'm reasonably confident that I can
figure it out given enough time. Even if I don't like the sound, the
knowledge gained should be worth the effort.

- Eric

"e.a.rowe" wrote ...
It seems very unlikely that any audio mic-level or
line-level device could be "killed" by any amount of
signal abuse. I'd bet the cause is something much more
ordinary like simple component failure.

My first guess was that being driven too hard for too long caused
something to fail from overheating, but I don't know enough about the
properties of various components to know which would be most
vulnerable.

Mic-level and line-level devices, particularly low-end ones
like this don't heat up from high signal levels. It is more
likely marginal power supply components (as Mr. Payne
suggested). It would likely have failed exactly the same
way even if you had put no signal at all into it.

Richard Crowley:
It seems very unlikely that any audio mic-level or
line-level device could be "killed" by any amount of
signal abuse. I'd bet the cause is something much more
ordinary like simple component failure.

Laurence Payne:
If designed with a barely-adequate power supply, I
suppose it could have overheated.

The power supply itself, you mean? Hmmm...

I don't think I ever tried swapping out the PS when it failed, but
there was a very sharp ozone smell coming from inside the unit at the
time, so I wouldn't have thought to check the external wall-wart. Also,
the manual (Alesis has pdfs online) does state that a single AC adapter
could power several units at once, so I'm not leaning toward that just
yet.

However, that does give me an idea. Could the op amps have overheated
and failed maybe? Asking a limiter to work its butt off as an amplifier
does sound like a recipe for too much heat... I'll have to look more at
those. I wonder if there's some way to test an IC without removing it
from the board...?

Thanks!

- Eric

"e.a.rowe" wrote in message
oups.com...
It seems very unlikely that any audio mic-level or
line-level device could be "killed" by any amount of
signal abuse. I'd bet the cause is something much more
ordinary like simple component failure.

My first guess was that being driven too hard for too long caused
something to fail from overheating, but I don't know enough about the
properties of various components to know which would be most
vulnerable.


snip
Without service information (at least schematic
diagram), it is pretty nearly a lost cause.

I'll try to find a schematic online. Who knows, I might get lucky.


IIRC these things have a pretty negative reputation and
are not well regarded even when operating "nominally"
(a fancy $2 NASA word :-) Or is that the Microverb
that is a dog?

The whole 'micro' series is considered dubious by most pros, but I've
heard that this box can be used for squashing the heck out of drums and
bass, if you like that sort of thing. I think it might be fun to play
with.


If you can't locate a schematic diagram, your chances
of doing anything with it seem slim to none. OTOH, you
may find it fun to dissect just to see how they made it.

That's really what this is all about. I need to start tweaking stuff to
see how it works, so a pocket-size fixit project like this is perfect.
The board is pretty spartan, so I'm reasonably confident that I can
figure it out given enough time. Even if I don't like the sound, the
knowledge gained should be worth the effort.

- Eric



IME, the majority of faults are not down to the signal circuitry, which is
generally pretty reliable, but due to power supplies, connections, pots,
switches, dry joints etc. If there is a chip failiure, it is often the one
closest to the outside world - i.e. the input and output buffers.

The very first thing you should do for any repair is check the power
supplies are working. You should have + and - 15 volts or thereabouts for
the audio, and +5 volts if there are any computing chips on board. My guess
is you don't have these voltages. Finding them will give you a better idea
of these types of circuit topologies, and a better idea of what happens when
things break.


Gareth.