My Rare bird has arrived.. say hello to my little friend!! (56k warning!)

[MatthewS]

There I was.. staring at the makeshift page for cops towing, a towing company that sells what they yank out of the cars. Located in Oregon, and it only happend to make it's way in front of me because I was googling to find a particular amplifier model to disect and study (more on that later)

Scrolling down the amplifier page I seen a small, blurry picture and could barely make out 'Audio Control system90' and whole bunch of adjustment knobs on the top. I remember thinking at first 'Equalizers don't belong here..'

It was going for about 90 bucks and it looked fancy so I hobbled by google again and dug up what little I could find on it (it's rare.. google it I dare ya!)

Apparently the System90 was an amplifier line produced with several models that included various goodies like EQ lineout's, PFM (programable match filters), etc.

Deciding that I just had to have a peek inside it knowing AC's quality reputation, I contacted cops and asked if they would ship. The answer was yes.

Low and behold.. the Audio Control System90, Model 50.. Disected for cleaning and viewing pleasure.






































Specs:

Four channel Bridgeable power amplifier
Four channel Equalization
18db/per octave crossovers
Programmable Frequency Match (PFM)
Selectable low pass / full range output
Speaker level inputs
50 watts x 4 or 150 watts x 2

PS stage -

6x IRFZ34N
TL494 PWM
Isolated transformer

AUDIO stage (per ch) -

TIP35/36C matched output pair
MPSW56/06 Pre-drive
External damping diodes

Overall Dimensions - 13"l x 5.6"w x 2.5"h

NOTES: Has 4 IRFZ34N's mounted to sinks center of amplifier board, and in vicinity are two LM393's.. Any ideas what they did here?

Let me know what you thin of it.. for 90 bucks I know I didn't go wrong.

- Matt

[Eva]

Those four IRFZ34 could be used for output current sensing. There don't seem to be any emitter resistors on output transistors.

[MatthewS]

Originally posted by Eva
Those four IRFZ34 could be used for output current sensing. There don't seem to be any emitter resistors on output transistors.

Thats a good shot! But if you look REALLY closely at the one pic that is a closeup on the mosfets I mentioned, and look at were each channel card you can see mounts right angel to the PCB you will see tucked away and partially hidden emitter resistors.

Any other guesses?

- Matt

[ppia600]

Nice amp, from back when they were made by people who didn't really care how they looked. Quality was what mattered. I see some rectifiers but not the emitter resistors, maybe I'm not looking close enough?

[MatthewS]

Originally posted by ppia600
Nice amp, from back when they were made by people who didn't really care how they looked. Quality was what mattered. I see some rectifiers but not the emitter resistors, maybe I'm not looking close enough?

See the red arrows..

- Matt

[ppia600]

Oops, I thought those were for the audio output transistors..?

[MatthewS]

Originally posted by ppia600
Oops, I thought those were for the audio output transistors..?

The previous poster termed them emitter resistors on the outputs.. Not the same thing?

Am I stuck on semantics here? someone help me understand, maybe it's me.

- Matt

[ppia600]

I'm sure the outputs use emitter resistors, I have no clue what those mosfets in the center are though. If Eva said they are for current sensing, I'm sure that's the case. Maybe he didn't notice the emitter resistors on the output transistors, though. Is there a pair for every channel?

[1moreamp]

Evening,
Nice Old School amp from Audio Control, I was looking over your pics, perhaps you should visit Amp-guts and post them there along with the others from this era in Car audio. I am sure everyone would appreciate you efforts...
Thanks for the peek

[MatthewS]

Originally posted by ppia600
I'm sure the outputs use emitter resistors, I have no clue what those mosfets in the center are though. If Eva said they are for current sensing, I'm sure that's the case. Maybe he didn't notice the emitter resistors on the output transistors, though. Is there a pair for every channel?

Yeah, one pair per channel. The 'cards' appear to be part of the modular design and seem to host the entire channel on each of them. Thats what I gathered at a glance anyway, I wanted to take the time to really dig into tracing the routes on those mosfets but just didn't have the time.

Originally posted by 1moreamp
Evening,
Nice Old School amp from Audio Control, I was looking over your pics, perhaps you should visit Amp-guts and post them there along with the others from this era in Car audio. I am sure everyone would appreciate you efforts...
Thanks for the peek

Thank you, I didn't need another amp but I couldn't pass it up. I have actually been trying to get a good pic set for amps that are not on the ampguts site and I'm slowly submitting them. The last amp I submitted a few weeks ago has not made it's way up yet. Not sure what the update scedule looks like over there.

- Matt