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Daniel Fox
 
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Default "flashing" the gain on a power amplifier question

We have an Alesis Matica power amp used for non-critical listening in a
computer lab environment. It exhibits the following problem: every
once in a while the left side goes out and will come back only if you
quickly crank the left side gain knob. It's like it needs to be
"blown" out, kind of like the "italian tuneup" for cars.
What causes this and how can it be fixed?
By the way - everything else in the signal chain has been swapped and
ruled out as problematic.
Thanks,

Dan Fox
Zumix, Inc

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Scott Dorsey
 
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Default "flashing" the gain on a power amplifier question

In article . com,
Daniel Fox wrote:
We have an Alesis Matica power amp used for non-critical listening in a
computer lab environment. It exhibits the following problem: every
once in a while the left side goes out and will come back only if you
quickly crank the left side gain knob. It's like it needs to be
"blown" out, kind of like the "italian tuneup" for cars.
What causes this and how can it be fixed?


Look for leaky coupling caps and cold solder joints around bias resistors.
What is happening is that the DC level on some stage's input is floating
around, and eventually it rises or drops to the point where the stage turns
off completely. Applying a high signal level temporarily fixes it.

Also clean the pot. I'm assuming it's not a dead spot in the pot, although
that does sometimes happen.

By the way - everything else in the signal chain has been swapped and
ruled out as problematic.


My personal feeling is that this amplifier is not worth your time to fix
it, but I am not impartial.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Richard Crowley
 
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Default "flashing" the gain on a power amplifier question

"Daniel Fox" wrote ...
We have an Alesis Matica power amp used for non-critical listening in a
computer lab environment. It exhibits the following problem: every
once in a while the left side goes out and will come back only if you
quickly crank the left side gain knob. It's like it needs to be
"blown" out, kind of like the "italian tuneup" for cars.
What causes this and how can it be fixed?
By the way - everything else in the signal chain has been swapped and
ruled out as problematic.


The gain pot itself?


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Posted to rec.audio.pro
hank alrich
 
Posts: n/a
Default "flashing" the gain on a power amplifier question

Scott Dorsey wrote:

Daniel Fox wrote:
We have an Alesis Matica power amp used for non-critical listening in a
computer lab environment. It exhibits the following problem: every
once in a while the left side goes out and will come back only if you
quickly crank the left side gain knob. It's like it needs to be
"blown" out, kind of like the "italian tuneup" for cars.
What causes this and how can it be fixed?


Look for leaky coupling caps and cold solder joints around bias resistors.
What is happening is that the DC level on some stage's input is floating
around, and eventually it rises or drops to the point where the stage turns
off completely. Applying a high signal level temporarily fixes it.


Also clean the pot. I'm assuming it's not a dead spot in the pot, although
that does sometimes happen.


By the way - everything else in the signal chain has been swapped and
ruled out as problematic.


My personal feeling is that this amplifier is not worth your time to fix
it, but I am not impartial.


I've met a similar problem with Cret PL series amps, and traced the
problem to oxidation of the chip-pins-to-IC-socket scene. Removing and
replacing thge chips with a blast of Caig in between fixes it, until
next time.

--
ha
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