Schematics for Heathkit AA-2500 Power Amp?

PB2 · 25th January 2005, 02:44 PM

Anyone have schematics for this amp?
It's a Harmon Kardon from Heathkit.
There's mention of it being an Otala design.

Netlist · 25th January 2005, 05:15 PM

Did you Google?
I know there's a lot out there.
I ones bookmarked a site with almost everything from Heathkit but can't find it at the moment.

Edit: This fellow seems to have it.
Homepage: http://www.d8apro.com/

/Hugo

djk · 26th January 2005, 07:50 AM

I think it is the same as an HK870.

PB2 · 26th January 2005, 10:25 PM

I did Google but didn't find much, thanks for the link.

Yes I think it is the HK870.

djk · 27th January 2005, 09:54 AM

http://manuals.harman.com/HK/service...HK870%20sm.pdf

PB2 · 29th January 2005, 03:06 PM

Thanks to all who commented, that's the one djk thanks for the link.

PB2 · 15th May 2009, 01:01 AM

Anyone ever notice if the LF time constants are screwed up with this amp? I'm seeing large subsonic woofer excursions with it.

It's possible that the electrolytic cap values have shifted with age but I'm seeing it in both channels.

Pete B.

DigitalJunkie · 15th May 2009, 01:46 AM

Maybe PSU instability?
I'm sure the old filter caps have dried up and are in need of replacement..

PB2 · 15th May 2009, 02:36 AM

Took a quick look at the schematic, and the feedback is DC coupled. Only a cap, huge 220uF back to back at the input. The power supply is a bit odd, 4700 uF on the driver stages but with RC filters also.

Noticed that the spec -3dB point is .1 Hz on the low end, so it will pass everything from upstream.

Pete B.

25th January 2005, 02:44 PM	#1
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	Schematics for Heathkit AA-2500 Power Amp? Anyone have schematics for this amp? It's a Harmon Kardon from Heathkit. There's mention of it being an Otala design.

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25th January 2005, 05:15 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	Did you Google? I know there's a lot out there. I ones bookmarked a site with almost everything from Heathkit but can't find it at the moment. Edit: This fellow seems to have it. Homepage: http://www.d8apro.com/ /Hugo

26th January 2005, 07:50 AM	#3
djk diyAudio Member Join Date: Feb 2001 Location: USA	I think it is the same as an HK870.

26th January 2005, 10:25 PM	#4
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	I did Google but didn't find much, thanks for the link. Yes I think it is the HK870.

27th January 2005, 09:54 AM	#5
djk diyAudio Member Join Date: Feb 2001 Location: USA	http://manuals.harman.com/HK/service...HK870%20sm.pdf

29th January 2005, 03:06 PM	#6
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	Thanks to all who commented, that's the one djk thanks for the link.

15th May 2009, 01:01 AM	#7
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	Anyone ever notice if the LF time constants are screwed up with this amp? I'm seeing large subsonic woofer excursions with it. It's possible that the electrolytic cap values have shifted with age but I'm seeing it in both channels. Pete B.

15th May 2009, 01:46 AM	#8
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	Maybe PSU instability? I'm sure the old filter caps have dried up and are in need of replacement..

15th May 2009, 02:36 AM	#9
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	Took a quick look at the schematic, and the feedback is DC coupled. Only a cap, huge 220uF back to back at the input. The power supply is a bit odd, 4700 uF on the driver stages but with RC filters also. Noticed that the spec -3dB point is .1 Hz on the low end, so it will pass everything from upstream. Pete B.

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