Pioneer GM 120

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#101
Well, I did find another Pioneer service manual stuffed in a binder, but it's for the AD-304 power amplifier:

"15 watts minimum RMS per channel into 4 ohms over a frequency range of 40 ~ 20,000Hz with no more than 1% distortion."

It uses speaker level inputs, a single supply (cap. coupled outputs), and is enabled by turning on head unit (like the GM120).
 
#102
I installed these new in the late 80s, maybe 1987? The low input level was a hassle with all the Pioneer stuff then and caused a lot of noise issues. The GM120 then had a metal screen kind of cover IIRC and was black. Everyone said they were good amps but were a pain to run non-pioneer due to being such an odd setup in the low input mv and the din. Since we also sold linear power and RF, the gm120 was not considered that powerful. Even the kenwoods were larger. Much like the early alpine not having RCA was really looked down upon by installers, lol, but at least you could put an adapter on the alpine and run it easily. The pioneer HU seemed to work quite well though, but the place I was at did not push them that hard like they did kenwood. Of course back then getting adaptors/din plugs was difficult and altering the electronics was out of the question for us mere mortals.
 
#108
Hi Danny,

I just read your post and was wondering if you could help me out... I own two gm-120 amps, one of them is ok the other started to burn up when I connected it to my head unit :-(
I was thinking on repairing it my self, due to the fact that is an old amp and there isn't anyone around that can fix it... LOL
Please let me know if you can give me a hand 🙂
Thanks in advance.

Rod.
 
#110
Hi Marc

First off I would like to thank you for your reply to my post 🙂

The head unit is a KPX-9000 which is installed in my car, and by the way is working fine with two other amps... (GM-4 and GM-120)

So I have no idea what went wrong... aside from the fact that it can only be due to the fact that the amp (GM-120) is faulty...

Yes I plugged in the the amp using original (NEW by the way lol) CD-115 cable.

Once again thanks in advance ;-)

Rod.
 
#113
Any luck on finding out how to wire the GM 120 to a newer head unit?

thatsupraguy said:
I have the same question. I know it's a vintage amp, which is exactly why I want to use it in my vintage Supra. But I want to cheat a little and use a newer head unit. (In addition to the power wire, ground wire, and speaker outs), The amp originally used an 8-pin plug to attach only to vintage Pioneer head units for its input signal. I went ahead and cut and disected the cord trying to figure out how to connect it to a newer head unit. Inside the outer wire braiding (similar to co-ax), I found 3 wires: a red 18awg single conductor, an orange 18awg single conductor, and a grey multi conductor. The grey multi-conductor contains two smaller wires (red and white) surrounded by wire braiding (again like what you find in cable TV coax).
Anybody know, or even care to take a guess, (or can tell me how to test to find out), which wire does what.
Click to expand...
 
#115
Here's pin-out.............

________________________________________________Rick..............
 

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#116
I'm knew to electronics, so i still dont understand how to connect my GM 120 to a new head unit. It seems like I'd have to connect it w RCA connections. I have a Pioneer DEH-X55HD head unit, just curious if it would be compatible w the GM 120 amps. If so, could someone tell me how to make this happen. Thanks!!!
 
#117
One problem with the GM120 is that it is turned on by sensing the load of the head unit switching on.

I would advise leaving the GM120 in the museum and just picking up a newer amp that performs better and has better protection. $44 got me a 4 channel American-made RF 4-channel amp at a local pawn shop, but I've passed up $5 amps at yard sales. Check out collector auto parts swap meets as well; sometimes there's guys from wrecking yards with all kinds of gear salvaged from scrapped cars.
 
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