Two Amp Projects: 8x100W DIY & H/K 770 Restoration

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Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Wed Dec 16, 2015 3:52 pm

http://www.silentpcreview.com/Two_Amp_P ... estoration

This is a show-and-tell about two amplifiers I worked on in the past year. One is a DIY custom assembly of class-D amp modules and an SMPS PSU into an 8-channel power amp in a single chassis. The other is the restoration of a classic 1980 Harman/Kardon HK770 dual-mono power amp with complete replacement of all 44 capacitors.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by nagi » Thu Dec 17, 2015 11:04 am

Looks clean and gorgeous so far. :)




I did play around with the notion of building an amp a couple years back, but as I'd need optical in and 5.1 DTS/Dolby decoding.... that can't be done in a clean DIY fashion.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Thu Dec 17, 2015 11:56 am

nagi wrote:Looks clean and gorgeous so far. :)

I did play around with the notion of building an amp a couple years back, but as I'd need optical in and 5.1 DTS/Dolby decoding.... that can't be done in a clean DIY fashion.
Actually, integrating an appropriate sound card into the enclosure which holds the amps shouldn't be too hard... no?

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Thu Dec 17, 2015 3:11 pm

added HK770 part.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by matt_garman » Thu Dec 17, 2015 3:35 pm

Hey Mike,

If you want more power in a class-D amp, check out those based on IRS2092. There are lots of vendors selling IRS2092-based PCBs, including Sure Electronics. The "LD15R" modules by "LJM" have a good reputation over on diyaudio.com (and the designer himself hangs out there too). ConnexElectronic generally has good stuff too, and he also sells IRS2092-based boards. I highly recommend his power supplies, by the way. I use them almost exclusively in my own amp builds.

I used to have an IRS2092-based amp by the company Class D Audio. I liked it a lot, but it was overkill for my needs, and I downsized to something based on the TI tpa3116.

Speaking of TI, if you're not in a hurry, keep your eye for boards based on their new TPA3251 chip, see this thread on DIYAudio. More power and multichannel support, should do exactly what you're looking for if I'm not mistaken.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by LostHighway » Fri Dec 18, 2015 2:57 am

One minor correction with regard to Harmon Kardon, the companion preamp to the Citation Twelve was the Citation Eleven not the Seventeen. For someone looking for a 1970s receiver to restore they could do far worse than the HK 330c, 430 or 730. Higher power SS gear from the 1970s and 1980s typically sounded worse (if you can accept such a notion) than their lower output siblings. The original HK Citation 16 (150 wpc into 8 ohms, a "big" amp for the mid 1970s) was quite grainy and harsh sounding, the later revision to 16a was better but still probably not a good candidate for a restoration project. The rare Citation XX (I've never heard one) supposedly did sound good for the era (early '80s). It was sort of the last gasp of Harmon Kardon as a serious high end audio marque (it went out of production in 1984) and if you find a cosmetically good example cheap I suggest you grab it

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Fri Dec 18, 2015 8:09 am

LostHighway wrote:One minor correction with regard to Harmon Kardon, the companion preamp to the Citation Twelve was the Citation Eleven not the Seventeen...
Silly typo -- fixed.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Fri Dec 18, 2015 8:41 am

matt_garman wrote:Hey Mike,

If you want more power in a class-D amp, check out those based on IRS2092. There are lots of vendors selling IRS2092-based PCBs, including Sure Electronics. The "LD15R" modules by "LJM" have a good reputation over on diyaudio.com (and the designer himself hangs out there too). ConnexElectronic generally has good stuff too, and he also sells IRS2092-based boards. I highly recommend his power supplies, by the way. I use them almost exclusively in my own amp builds.

I used to have an IRS2092-based amp by the company Class D Audio. I liked it a lot, but it was overkill for my needs, and I downsized to something based on the TI tpa3116.

Speaking of TI, if you're not in a hurry, keep your eye for boards based on their new TPA3251 chip, see this thread on DIYAudio. More power and multichannel support, should do exactly what you're looking for if I'm not mistaken.
Thanks for the links, esp the TPA3251 info. Looks promising.

In the meanwhile, I recently came into possession of 4 of the slightly older UcD180ST Hypex amp modules. Couldn't resist, $ was too good. Power rating on these is "180W" if you believe their marketing. I much prefer relying on the distortion/power curves, and like so many of these class D amps, the power output rating is taken at a ridiculous point in the curve -- at 1%, it well up the steep rise portion of the curve when the amp is obvious screaming up to clipping. If you examine where the distortion starts to rise, you'd give them a much more realistic 60~70W (at 8 ohms) rating. Got two appropriate 500VA Connex SMPS for them. These amp modules should be good for the mids & highs of my Orions.

Then decided I might as well go whole hog with another 8-ch amp. Got 2 Connex "400W" modules, which are just $40 each + 800VA SMPS for them. Those 400W modules will probably do at least 200W at 8 ohms, which is enough for each of my Orion Peerless 10" XLS drivers. And if there is any compromise in the signal, at least it's only up to 100Hz of so -- that's one of the big advantages of active xovers, the amps are required to work it such narrow bands, very easy loads.

At this point I wanted to explore what the current Hypex technology was about, so I ordered a couple of VcD400HG from Hypex. Not with the HxR-regulators... which I can always add later. This might end up being used as the midrange am, assuming its sonic qualities are superior to the VcD180ST. Another 800VA STMPS from Connex will power these.

I'm planning to stuff all of these into the gutted chassis of an old HUSH ATX fanless PC. Some SPCR old timers might recall these. German fanless PCs that look like sleek power amps with big banks of heatsinks on the sides. I like the irony of actually using these cases for the purpose they were meant to only emulate.

Just toying with layout ideas for now.
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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by matt_garman » Fri Dec 18, 2015 3:16 pm

Mike, I've never actually heard the Hypex UcD series of amps, but have read plenty of good things. You're probably already aware of this, but their "nCore" line gets all the publicity now. I've heard those are awesome (again, only hearsay), but they are significantly more expensive, especially if you want eight channels.

Please post pics when your project is completed!

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Fri Dec 18, 2015 3:20 pm

matt_garman wrote:Mike, I've never actually heard the Hypex UcD series of amps, but have read plenty of good things. You're probably already aware of this, but their "nCore" line gets all the publicity now. I've heard those are awesome (again, only hearsay), but they are significantly more expensive, especially if you want eight channels.

Please post pics when your project is completed!
yeah ncore is too rich for me and doubt i'd hear much of the benefit in a multi ch active setup like mine. For a passive spkr system I'd consider them but for Orions, no.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by Rusty075 » Sat Dec 19, 2015 3:10 pm

That's some beautiful work Mike. You should do a piece giving readers a little tour of your whole audio setup. I think people would find that interesting.

Where'd you source that enclosure for the 8x100W? I'm gathering parts for an amp build of my own, and I like the looks of that.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Sat Dec 19, 2015 4:09 pm

Rusty075 wrote:That's some beautiful work Mike. You should do a piece giving readers a little tour of your whole audio setup. I think people would find that interesting.

Where'd you source that enclosure for the 8x100W? I'm gathering parts for an amp build of my own, and I like the looks of that.
Hey Russ, thanks & good to see you back again. 8)

A tour of my audio setup... I was under the impression most readers know about this...? Maybe later.

ebay was where I found that case -- http://www.ebay.com/itm/251532504119 Low base price, but pricey shipping from China. Be careful when you thread the machine screws in -- the tapped holes in the case strip very easily. Do it just once, if possible, and don't over-tighten.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by Rusty075 » Sat Dec 19, 2015 4:46 pm

Oh, I'm never too far away Mike. Always floatin' around in the background.

Dang, I think my PCB is 330mm wide...just a little too big for that enclosure. Will have to hunt and see if they're available in other sizes. How sturdy is that top panel? I've got some heavy iron to mount to it.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by Gadgety » Sun Jan 03, 2016 4:40 pm

Great reading about these two projects of yours. Doing stuff, making, taking things apart, putting them together. So much more fun than just buying ready made stuff.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by HammerSandwich » Thu Jan 07, 2016 11:00 am

Mike, just out of curiosity, have you measured power consumption for any of your amps? Seems that the switchers should be MUCH better, but this is SPCR - we like numbers.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by MikeC » Thu Jan 07, 2016 11:20 am

HammerSandwich wrote:Mike, just out of curiosity, have you measured power consumption for any of your amps? Seems that the switchers should be MUCH better, but this is SPCR - we like numbers.
I have, but didn't record them. I do recall being very surprised at how little power was needed for all the amps I measured, even at very high volume. This might reflect the fast changing nature of music, with short extreme peaks and the inability of my AC power meters to track them. Leaving it plugged in and looking at the energy draw (kwh) over a longer set time period at specific volumes would probably give more relevant info.

I know my Anthem 500 AV receiver pulls 50W AC just idling, but it doesn't really go much higher when playing movies -- maybe peaks of 75W when cranked high in the small room (11x12'), but generally much less, close to the idle level.

My main system w/ Orion spkrs and 8-ch Rotel amp -- this is a real surprise. 27W idle, maybe 60~70W peaks when playing rockish jazz quite loudly. I don't recall whether I've seen it hit 100w at any time.

I also measured the 8-ch class D amp I made; this was about 25% less than the Rotel during play, and about 13W at idle, iirc.

Linn AV5105 amp -- 2 ch, 100W/8 ohms, 2x that into 4 ohms. AB design, with switching psu: 32W idle, no data during play.

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Re: Two Amp Projects: 8x100W DIY & H/K 770 Restoration

Post by HammerSandwich » Thu Jan 07, 2016 11:34 am

Thanks for the details. Very impressed by the Rotel - it's lower than I'd have guessed.

Also, this sounds completely legit:
Leaving it plugged in and looking at the energy draw (kwh) over a longer set time period at specific volumes would probably give more relevant info.

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