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Old 20th October 2009, 08:40 PM   #1
von Ah is offline von Ah  United States
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Question Back to the Future - repurposing old amps for Class D

My first thread here. I mostly just lurk and wish I could actually have the time to DIY some things I've read about.

Recently I've been thinking that it would be interesting to take an old non-working (or unwanted) amplifier with good iron, gut the existing circuits and adapt it for class-d use with modules from one of the usual suspects we see here.

I wonder if that sort of thing has been done much here. I think there must be others like me who love the look and feel of the old big-metered power amps from yester year, but would rather have a taste of the new technology along with the efficiency of class-D. Plus, there is the earth-friendly bonus of reuse, recycle.

The one amp I would really like to do this with is a broken Hitachi HMA-8500II I've had for years and have not been able to get repaired.

Of course, there is no way that I could personally do the work (no skill, no time ), but it might be possible to *encourage* others to give such a thing a try...

Regardless, has anyone repurposed old gear for new class D use? At the very least I'd like to see pictures.

Marc

Last edited by von Ah; 20th October 2009 at 08:44 PM.
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Old 21st October 2009, 05:44 PM   #2
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The easiest way to re-utilize an older amp like that is to cut the traces on the circuit board to all the external switches and jacks, then solder up wires from them to the i/o connectors on any class D module. Most boxy amps/preamps have lots of interior space and you can pretty much mount any low or medium powered class D board in them, even using hot glue if you want to be real ghetto. For high powered boards, you'd have to figure out some way of mounting any external mosfets/devices to a heat sink. Some high powered class D boards already have a heat sink mounted, but depending on the size of the amp you're repurposing, you may not have enough room for those modules.
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Old 21st October 2009, 08:00 PM   #3
Pano is offline Pano  United States
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It's a great idea I've always want to try on some big old 70s-80s stuff.
You'd have a nice case, connectors, selector switches, even a volume control. Maybe some power supply parts, if you're lucky.

But I never have. Always liked the old amps too much to cannibalize them!
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Old 21st October 2009, 08:08 PM   #4
paulb is offline paulb  Canada
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I've retrofitted two amps, but neither with Class D modules. I used a chipamp board for one, and ESP P101 boards for the other (the chipamp board was from ESP as well). Whether it is practical or not depends entirely on the amp (/receiver). Older stuff seems to be easier.
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Old 22nd October 2009, 07:35 PM   #5
von Ah is offline von Ah  United States
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Good ideas, thanks!

Wouldn't this just be awesome with a TA3020 hiding inside?

Click the image to open in full size.

Click the image to open in full size.

I haven't checked the numbers on the iron, but I'll bet something would fit...

Mine took an unfortunate fall with some physical damage, and two techs gave up on fixing the mystery BZZZZT problem before the fall, so a resurrection with class d would not be sacrilege.

For something a little smaller, this 35 wpc amp would be great:

Click the image to open in full size.

Last edited by von Ah; 22nd October 2009 at 07:48 PM.
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Old 24th October 2009, 11:56 AM   #6
nitrate is offline nitrate  United Kingdom
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LOL, This seems like an excellent idea as they dont make retro cases like those shown above much nowadays. It's now all black boxes with silly blue LED's. I just don't have the heart to gut my old MusicalFidelity A100 even tho its been resurected more times than Dracula, But i have a really rubbish AcousticSoloutions A100 hanging about. Nice case, handy LCD but very very very bad ( and previously dangerous ) circuitry that is just begging me to drop in a couple of my diy ClassD modules :-)

just my thoughts..
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Old 24th October 2009, 12:48 PM   #7
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I really like the look of the one with the power meters on it.
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Old 24th October 2009, 01:20 PM   #8
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I retrofitted my nephew's guitar amp with a Class-D module from Texas Instruments. What a thing of beauty -- takes up a fraction of the space and delivers 2x the power with the same battery (previously it had used an NEC Chipamp).
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Old 24th October 2009, 03:51 PM   #9
Pano is offline Pano  United States
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Yeah, this actually got me cruising eBay again looking for donor cases.
Most of the consumer gear from the 90s on is just so boring. Ugly black boxes.

A lot of the older Japanese gear is quite handsome.
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Old 24th October 2009, 07:54 PM   #10
von Ah is offline von Ah  United States
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Cases are one thing, but I would want to go the extra distance and use the power transformers (yummy dual mono, unless the EI's use more energy than within reason) and meters, too. Feel like collaborating on a project, pano?

By collaborating I mean you do it.

Quote:
I really like the look of the one with the power meters on it.
They both have meters.

Last edited by von Ah; 24th October 2009 at 07:56 PM.
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