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Old 19th June 2006, 04:56 AM   #1281
DIAR is offline DIAR  Finland
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I usually have 230 V +/- 1V. That's more or less the same as 120 V concidering the how the transformer primary windigns are connected. Could it be the frequency that makes the difference. We have 50 Hz instead of 60 Hz.

I'll probably use 0-rings for power supply mounting. I wonder what kind of mounting Naim uses in their devices.
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Old 19th June 2006, 06:05 PM   #1282
DIAR is offline DIAR  Finland
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I just bought myself over 400 O-rings

I uploaded a few more pictures here:
http://www.dvdplaza.fi/galleria/show.../1/ppuser/3104

Click the image to open in full size.
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Old 19th June 2006, 06:13 PM   #1283
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Quote:
Originally posted by DIAR
I just bought myself over 400 O-rings

I uploaded a few more pictures here:
http://www.dvdplaza.fi/galleria/show.../1/ppuser/3104

Click the image to open in full size.

What are those red caps?

p.s I have no buzzzzzz at all.
And I love this DAC.
I do this: FLAC->foobar(kernelstreaming)->DAC->DIY OpAmp Headphone Amp-> Koss 271 Headphones. And I love it.
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Old 20th June 2006, 07:04 AM   #1284
sangram is offline sangram  India
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Hi, need help with hum problems in my 4780 built from PD's kit.

The values are the stock supplied with the kit. Input series resistors are not used. Each chip is wired in parallel mode, and two such chips are driven off a balanced input for bridge operation, at +-30 volt supply.

Each channel has its own 440VA EI, and like I said, is the fully stock kit. The PG+ and - on each half of the amp for one channel are connected using 18 AWG stranded wire.

One channel, built with chips from PD, is deathly silent but has 50mV of output offset (well within reason). The other channel was built from NS samples, has only 1mV of output offset, but a very faint hum which is probably at 120-180 Hz.

The hum is inaudible from more than 6 inches away from the woofer cone, but it's definitely there.

Exchanging transformers for the channels has not helped, neither has switching inputs. The hum is only due to the amp.

Like I said it's very faint, but I would like to eliminate it. Do I need bigger caps or is there another way to fix this?
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Old 20th June 2006, 03:29 PM   #1285
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Does the hum disappear when you disconnect one of the inputs?

That type of humming is most probably due to grounds wiring and without having access to actual curcuit it is very hard to recommend any changes.
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Old 21st June 2006, 10:02 AM   #1286
sangram is offline sangram  India
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Hi Peter

First I must say the amps sound absolutely fantastic, better imaging than some really expensive gear, and spot-on accurate.

When I disconnect the input the hum gets masked by the slight white noise of an open input, but it's detectable under that noise.

It is undetectable after the input level has risen to above -86 dB, and is undetectable from more than three inches from the woofer cone or above the noise of the computer which is used as source, so it's not creating an audible problem as far as I can tell. SO it's just a wish to remove that last trace of (almost inaudible) hum before I start demoing the amp to my friends.

The way the amp is configured is exactly your instructions for parallel mode, and one amp is perfectly well-behaved so it's not a circuit design or layout problem as far as I can tell.

The only differences between the two channels circuit-wise are the actual chips used (the chips you sent are perfect, the NS samples have a slight hum) and the channel with the hum has wires from the primary to the board that are about 10 cm longer than the good channel.

Will fitting larger caps help with the hum? Right now I'm using only the 1500 + 10 uF that came with the kit. I had added some 10000 uF caps but I hated the sound so I removed them. I can try them once more for kicks...
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Old 21st June 2006, 04:34 PM   #1287
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Adding bigger caps won't help, this is certainly related to wiring. I asked if the hum disappears if you disconnect only one channel RCA input (not both).
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Old 21st June 2006, 04:35 PM   #1288
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Here's some pics of new DAC board, as I mentioned, the circuit is not inverting now.
Attached Images
File Type: jpg newdac2.jpg (67.0 KB, 1325 views)
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Old 21st June 2006, 04:42 PM   #1289
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I was sort of "forced" to redesign the board, as I run out of DIP version of CS8412 receiver chip.

The new layout has been improved, with easier cap mounting and shorter PS and signal traces.

No major difference in overall design was made, as circuit has proven itself over the last 2 years and I don't see a way to improve it. One may experiment with I/V resistors and coupling cap choices, as will provide a slightly different sonic signature, but overall sound characteristic will remain unchanged.
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File Type: jpg newdac1.jpg (98.2 KB, 1111 views)
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Old 22nd June 2006, 04:46 AM   #1290
sangram is offline sangram  India
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Quote:
Originally posted by Peter Daniel
Adding bigger caps won't help, this is certainly related to wiring. I asked if the hum disappears if you disconnect only one channel RCA input (not both).
Sorry Peter, it doesn't, and it's not RCA but balanced XLR input. I will recheck the wiring and report back.
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