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JLH 14th September 2011 11:08 PM

Pioneer GM-H100 switch SW901 function?
Pioneer Gm-H100 Amp Guts - YouTube

Don't worry, this isn't my amp. Mine is near mint and very clean. The one in the video looks like it went through a flood.

In the above video you can see the switch at the 0:46 mark. It is lined up to the left of the MOSFET driver transistors (black & green). It has two positions, L and H. In the video and on my amp, it is in the H position. It is labelled SW901. Is it possible that this is a switch to change the rail voltages?

Perry Babin 14th September 2011 11:24 PM

It's the BFC (beat frequency compensation) switch. It changes the operating frequency of the supply slightly. This is sometimes required/helpful if the amplifier is causing problems with AM reception.

JLH 15th September 2011 01:13 AM

I have no idea how you know all this stuff, but I'm thankful that you do and are willing to share it. So, just leave it in the H position?

This is one of my favorite amplifiers from when I was much younger and deep into car audio. This is one of the most overlooked SQ amps. I remember when I purchased an Alpine 3525 to replace it because it was supposed to be a better amp. The GM-H100 absolutely trounced it in SQ. I even compared it to my Soundstream Class A 6.0 and it gave it a run for its money. The 3525 ended up on subs and the 6.0 was on HLCD and the GM-H100 ran 5.25" A/D/S mids. After looking at the quality of the signal components, its no wonder why the GM-H100 sounds so good. It has ELNA caps throughout its signal path and the power supply is over built. I'd love to get ahold of its smaller brother, the GM-H50. It was a nice amp too.

Perry Babin 15th September 2011 06:18 AM

The position doesn't matter if there is no interference.

1998993C2S 16th September 2011 12:17 AM

Hey JLH -
Might you have an opinion on the current (no pun) Pioneer car audio amp lineup?
Here's a link:
I've begun the equipment assembly stage of a SQ install for my MY98 911 coupe. Its an active Dynaudio arrangement with a Pioneer DEX-P99RS DSP head unit (understated state of the art) and then a few Pioneer PRS A900 a 4ch. amps. Their a class A/B structure, dual ch. power supplies, uber quiet @ 108 S/N, etc, etc, etc.... The build quality is said to be Tier One with an excellent sound quality. After this short introduction my question is,,, do you any familiarity with these amps? The 3 remaining Stage 4 series amps are class D structures; 2 mono versions and a 4ch. Could you have a look at the PRS-A900 chassis photos and give me your 2 cents? Please disregard the stupid MSRP cost A900 amps for much less.
Thanks again.

Cheers, Mike

JLH 16th September 2011 03:11 AM

I do not have any familiarity with these newer amplifiers. My knowledge base is on the amplifiers from the mid 80's up to the late 90's. Sorry I can't be of better help to you.

1998993C2S 16th September 2011 03:14 PM

Ahh, it was worth a try. All the best.

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