Text 357, 51 rader
Skriven 2006-11-01 06:38:00 av Greg Mayman
     Kommentar till en text av Thomas K
Ärende: VOICE MODEMS
====================
 -=> Thomas K said to Greg Mayman
 -=> about "VOICE MODEMS" on 09-26-06  22:06.....

 TK> Well as they say, you know you're a geek if you have a spare
 TK> oxy-acetylene torch for when your main one gets confiscated! <G>

<LOL> Yes, indeedy!

 TK> Take care,
 TK> Thomas

Indeed I will.

Meanwhile I have a problem with a transistor PA amplifier that
motorboats when unloaded or feeding the 100 volt line output, but
stops when a speaker is connected to the 8 ohm terminals.

Increasing the decoupling capacitor from 1000 to 2000 uF doesn't
make any difference. But if it was a decoupling problem it should
get worse when the output is loaded up, due to the extra current.

One possibility is oscillation at supersonic frequencies but the
oscilloscope should show that up and it doesn't show anything
untoward, except for this high level oscillation at very low
frequency about 10Hz.

It's really weird. I think I'll have to start disconnecting
stages to see whether I can isolate the problem that way.

I have been tempted to rip out the output stages of the amp and
fit an LM3876 56 watt integrated amp. The existing power supply
has enough voltage to drive it to about 40 watts, but it would
mean a lot of changes to the chassis of the amp to accomodate the
IC on the rear heatsink.

If I had to go that way, it would be more straight forward to
salvage the power and line output transformers and rebuild the
power amp on a new chassis, and replace the mixer front end with
a completely new unit in a separate box.

Ah, well, it is a possibility.

.
.   ,-./\
.  /     \ From Greg Mayman, in beautiful Adelaide, South Australia
.  \_,-*_/    "Queen City of The South"    34:55 S  138:36 E
.       v
___ Blue Wave/386 v2.30

--- FLAME v2.0/b
 * Origin: Braintap BBS Adelaide Australia (3:800/449)