Modifying auto power on sensitivity?

Sillyboy · 2nd July 2006, 08:10 AM

I have the 150w plate amp from MCM for my sub. works peachy, except I have to get volume up a decent amount before it kicks on.

Is there any easy way to adjust that? I would like it to kick on at lower volumes.

AndrewT · 2nd July 2006, 09:06 AM

Hi,
had a quick look at the schematic.
Something does not add up.
Gain is supposed to be 68k/1k+1 =69times.
But it specifies 3.4V for maximum output. I note the 68k has been re-typed. Can you check component values against the PCB? It might be 6k8!

The crossover on p9 seems to be losing 12db to 15db!

I think q202 and u205 are the sensitivity setting for the auto on facility, but I would need a lot more time to try and understand exactly how it works/can be altered.

The bass response of the amp is pretty poor (-3db @16Hz) and again this appears to be the crossover at fault.

For sub-bass use this should be at least 2octaves lower and preferably 3 to 4octaves lower. Then allow the user to adjust the response to suit the surroundings.

Btw. although this amp is specified for 4ohm duty, it performs poorly at this reactance. I think it would be better to use it as an 8ohm amplifier.

Sillyboy · 2nd July 2006, 05:27 PM

What did you expect out of a $50 amp?

btw, you can see this thread for info on the sub (just an 8" driver) Silly's 1st Sub -- 8" MCM 55-2421

Thanks for taking a look. If you come up with a theory on the auto-on circuit, let me know

AndrewT · 2nd July 2006, 05:31 PM

Hi,
I agree, value for money seems incredible.

2nd July 2006, 08:10 AM	#1
Sillyboy diyAudio Member Join Date: Mar 2006 Location: Seattle	Modifying auto power on sensitivity? I have the 150w plate amp from MCM for my sub. works peachy, except I have to get volume up a decent amount before it kicks on. Is there any easy way to adjust that? I would like it to kick on at lower volumes.

2nd July 2006, 09:06 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, had a quick look at the schematic. Something does not add up. Gain is supposed to be 68k/1k+1 =69times. But it specifies 3.4V for maximum output. I note the 68k has been re-typed. Can you check component values against the PCB? It might be 6k8! The crossover on p9 seems to be losing 12db to 15db! I think q202 and u205 are the sensitivity setting for the auto on facility, but I would need a lot more time to try and understand exactly how it works/can be altered. The bass response of the amp is pretty poor (-3db @16Hz) and again this appears to be the crossover at fault. For sub-bass use this should be at least 2octaves lower and preferably 3 to 4octaves lower. Then allow the user to adjust the response to suit the surroundings. Btw. although this amp is specified for 4ohm duty, it performs poorly at this reactance. I think it would be better to use it as an 8ohm amplifier. __________________ regards Andrew T.

2nd July 2006, 05:31 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, I agree, value for money seems incredible. __________________ regards Andrew T.

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2nd July 2006, 05:27 PM	#3
Sillyboy diyAudio Member Join Date: Mar 2006 Location: Seattle	What did you expect out of a $50 amp? btw, you can see this thread for info on the sub (just an 8" driver) Silly's 1st Sub -- 8" MCM 55-2421 Thanks for taking a look. If you come up with a theory on the auto-on circuit, let me know

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