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ullus  
#1 Posted : Thursday, June 28, 2007 6:09:33 AM(UTC)
ullus

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Location: france

hi,

I wanted to share the pictures of my first DIY amp with MyRef RevC, JoshuaTree, and Darwin, all in a compact UPS case.

The case, the mains-plug-filter, the fan, the filter&relay board (which could easily be eliminated), the uncommon but practical outlets (for speakers), the front-panel LEDs, as well as the heat sink employed, are parts re-used from a blown 700W online-UPS (such used devices trade under 10 euro at ebay, in working condition or broken).

I needed 3 days to solder all PCBs, and 2 days for mounting and testing, the time to locate and correct one bad soldering point on a PCB included.

Please note, I'm a dilettant. The realization of the amp shown here does not constitute any recommendation for imitation; especially I suspect that toroids should not be mounted vertically.

I like it very much when JT mixes the bits at power-up; you hear the relays clicking fast for two seconds, which seems to be his way to say "moin, moin!" ;)

best,
ullus

Edited by user Sunday, September 15, 2013 6:59:10 PM(UTC)  | Reason: removed note about power switch; added links to kits and Mauro Penasa's original design; attache

ullus attached the following image(s):
ups-my_ref-revc01_.JPG (115kb) downloaded 10 time(s).
ups-my_ref-revc02_.JPG (98kb) downloaded 10 time(s).
ups-my_ref-revc03_.JPG (138kb) downloaded 15 time(s).
ups-my_ref-revc04_.JPG (139kb) downloaded 11 time(s).
ups-my_ref-revc05_.JPG (137kb) downloaded 18 time(s).

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Russ White  
#2 Posted : Thursday, June 28, 2007 6:22:04 AM(UTC)
Russ White

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Wow!!! Very good work, especially considering the tight spaces! Very twisted! I love it. :)
ullus  
#3 Posted : Thursday, June 28, 2007 6:32:47 AM(UTC)
ullus

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Location: france

thank you!

the speaker cable is a twisted pair of conventional, isolated main power household installation copper wires.

internal signal cabling uses Suhner RG174/U (surplus from another project; 100m remain ;)

There's still reserve space; if I'd remove the 2nd big mains filter PCB which has 3 big white caps, 2 coils and a big black relay, I could add a pre-amp, if desired.

Edited by user Thursday, June 28, 2007 8:04:44 AM(UTC)  | Reason: Not specified

ullus  
#4 Posted : Friday, June 29, 2007 2:19:14 AM(UTC)
ullus

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Location: france

Attached is the complete wiring diagram for the above amp; it also illustrates the extremely short signal flow path.

The signal, from RCA-plug input to amp-output, neither goes to the front panel, nor to the transformer side of the case, except for the cable going to speaker plugs.

There are six LEDs with common GND (pin) on the front panel which I use as input-channel-indicators; +5V is switched on second hand of input-channel-selector.

Disclaimer: I'm a dilettant; this sketch is intended to be used for illustrative purposes only; it is not intended to provide any compliance in electrical design; use the diagram at your own risk!

good luck!

p.s.: Concerning the (re-used UPS) mains-filter circuit-board:
The filter eliminates any feedback to mains from the internal circuit.
The separator relay (CE) cuts off the internal circuit from main input for the case the power plug is pulled out, to avoid that a defect of the UPS would put 230V on the mains input connector or plug-pins. An UPS specialist recommended me to leave this filter/separator board in the amp because it provides additional security protection; it is inbetween fuse and transformers and is not contained in the above drawing. (The [small] EMI filter shown in the diagram is integrated in the main-power connector.) I assume the filter/separator-board has no influence on sound quality.

p.p.s.: in case you are wondering about - the amp has no power-switch since the UPS enclosure had none. I later added a switch on the bottom of the enclosure which cuts off the main-transformer to save power when only the input-channel-selector is needed, e.g., for (wire-less) headphone. I later also replaced the hugely-oversized smaller toroid by a low-power, plug-transformer; see photo attached.

Edited by user Sunday, September 15, 2013 7:03:04 PM(UTC)  | Reason: added note about power switch. attached schematic and new photo.

ullus attached the following image(s):
IMG_0128.jpg (90kb) downloaded 12 time(s).
myref-revc-jt-darwin-radierung-signalflow.jpg (115kb) downloaded 10 time(s).

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Russ White  
#5 Posted : Friday, June 29, 2007 4:52:46 AM(UTC)
Russ White

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Ullus, for a first DIY amp project this is very well thought out and executed. You seem to have taken all the right precautions. I commend you! :) I wish my first few amps were not anything like that elegant. Once again, great work! Thanks for sharing. Other will find this info valuable I am sure.

Cheers!
Russ
ullus  
#6 Posted : Monday, July 2, 2007 6:56:12 AM(UTC)
ullus

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Location: france

Hi,

just read this in a DIY audio thread:

> the polarity of the ac leads going to the rectifiers can be reversed on one channel. He feels this works better than connecting up the usual way.

does that mean, it is better to reverse the wires going to AC1/AC2 in one of the channels?

ciao,
ullus
Russ White  
#7 Posted : Monday, July 2, 2007 7:00:23 AM(UTC)
Russ White

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It does not produce much change, but the theory is that any residual waveform from the rectification that gets by the PSRR of the amp will be present in opposite phase from each stereo speaker, thus "cancelling" in theory. In pactice out of phase waveforms on speakers in a room rarely actually fully cancel. But I still do this out of habbit. :) I just like symmetry. And wiring them up opposite just feels right. :)

Cheers!
Russ
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