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Old 1st September 2009, 10:58 AM   #21
Luke is offline Luke  New Zealand
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why fishy?
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Old 1st September 2009, 12:02 PM   #22
beeger is offline beeger  United States
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Default Dac-Magic

I helped a friend with one of these Cambridge units and the results were worth a little effort. This was not a full-on assault, just a cost effective tune up. Mouser Electronics sells an 8 Amp/12Volt transformer, part number 553-F8-12 that works very well and is quite audible if you also change the four small surface mount diodes in the audio section of the power supply. We used six Amp fast recovery diodes. The audio section is a bit unusual in that it uses cap coupled Voltage doublers to create the plus and minus supplies at sufficient Voltage to regulate down to fifteen Volts for the audio op-amps. There is only a two wire twelve Volt AC line coming into the chassis, so it was necessary to use the doublers. Replace the op-amps with something better and then move on to the output caps. Black Gates will work much better than the stock ones and are still available and reasonably priced. You could also replace some of the supply caps if you are motivated after the above changes. After a brief break in period, the sound was fuller and more dynamic with much better clarity and focus. I hope this information will be useful to anyone with one of these dacs. They are quite a value. That said, I must add that the internal USB converter proved to be of limited use. An outboard one sounded better.

Beeger
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Old 1st September 2009, 12:16 PM   #23
wwenze is offline wwenze  Singapore
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Originally Posted by Luke View Post
why fishy?
Because seller lives next to a fish market.

Nah, eBay, big square box of unknown, undisclosed parts, maker's skills uncertain, riding on a name (of DacMagic)

Doesn't this remind you of those "wonderful" upgrades to your $2000 CDP?
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Old 1st September 2009, 10:49 PM   #24
Glenn2 is offline Glenn2  United Kingdom
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I have one of these. A few things:

1) The unit cooks with 12V AC. There is over +/-30V going into the 7815/7915 regs for the output stage. Using a 9V AC unit this comes down to 20V. Sound did not suffer but the unit ran much cooler. (This is in London where my mains is around 250V most of the time - if yours is on the low side you may not have the same headroom, YMMV, etc.) My original PSU melted anyway!

2) The output coupling caps (100uf electros with WIMA mkp bypasses) are blocking virtually nothing. I measured all 6 outputs (L, L+, L-,R, R+, R-) and the highest was just under 3mV. I bypassed each pair of caps with wire. The improvement in sound was substantial.

3) Each phase of the balanced signal is generated from a pair of DAC outputs. There are two DACs in mono mode, so each DAC is producing a pair of identical balanced outputs, each pair fed into a differential amp (N5532).
L+, L- => L+
L-, L+ => L-
R+, R- => R+
R-, R+ => R-
These are fed to the XLR sockets, and also summed and buffered in the OP275 to produce the unbalanced signals.
Now do we really need to combine them for our unbalanced output? No, just take the L+ and R+ from the XLR sockets and you bypass the OP275 stage. Sounds MUCH better this way. Hook it up both ways and A/B it if you like. Sure you might lose a few dB of S/N or something but you're still getting the benefit of L/R isolation. Looking around the net I see that others have stumbled across this fact too. I made my own adaptors as I didn't want the negative phases shorted to ground like they are in some shop-bought XLR->RCA adaptors (intended for balanced amp inputs).

Do 2) and 3) and it's a much better sounding unit, and it was already great.

Not being able to resist the temptation to tweak further, mine's currently in pieces with a Zapfilter2 hooked up to it. I had one lying around anyway, though I'd have to re-box the unit to make it permanent, and I'm not sure so far that the improvement is worth the effort.

By the way, I think those TI NE5532 are a lot better than the old ones were.
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Old 1st September 2009, 11:50 PM   #25
FauDrei is offline FauDrei  Bosnia and Herzegovina
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Glenn2,

Excuses for my limited knowledge and perhaps silly questions...

When bypassing caps in step 2) and OP275 in step 3), beside soldering some additional wires, do you have to take them out (caps and opamps) or there is some more elegant way of doing it?

In your opinion, is it worth replacing four NE5532? If so, any replacement recommendations? LME49860MA, 2xAD797BRZ on 2to1 adapter...
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Old 2nd September 2009, 07:16 AM   #26
Glenn2 is offline Glenn2  United Kingdom
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Quote:
Originally Posted by FauDrei View Post
Glenn2,

Excuses for my limited knowledge and perhaps silly questions...

When bypassing caps in step 2) and OP275 in step 3), beside soldering some additional wires, do you have to take them out (caps and opamps) or there is some more elegant way of doing it?

In your opinion, is it worth replacing four NE5532? If so, any replacement recommendations? LME49860MA, 2xAD797BRZ on 2to1 adapter...
Not silly at all....

The caps can stay in, you need only bypass them with wire. Easy to reverse!
The OP275 can be bypassed simply by taking your signal from the XLR sockets instead of the RCA sockets.
Pin 1=Gnd, Pin 2= + phase, Pin 3 = - phase.
So take signal from pins 1 and 2 and leave pin 3 alone.

Click the image to open in full size.

It may be worth replacing N5532 but I've not done it yet. The rails are +/-15V so some are ruled out without changing the regulators (AD8620, AD8066). My personal favourites are AD8066 and AD825(x2). I also have some AD8599 which I have never tried.

Last edited by Glenn2; 2nd September 2009 at 07:19 AM.
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Old 2nd September 2009, 09:42 AM   #27
wwenze is offline wwenze  Singapore
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A question to ask the experts, is there any harm connecting just one side of the XLR connector to get a single-ended signal out of a balanced one? What is the use of OP275 above?
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Old 2nd September 2009, 11:49 AM   #28
Glenn2 is offline Glenn2  United Kingdom
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Quote:
Originally Posted by wwenze View Post
A question to ask the experts, is there any harm connecting just one side of the XLR connector to get a single-ended signal out of a balanced one? What is the use of OP275 above?
No harm - that is what I am actually suggesting!

The OP275 is to combine the two halves of the balanced signal to get an unbalanced one.
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Old 2nd September 2009, 07:14 PM   #29
FauDrei is offline FauDrei  Bosnia and Herzegovina
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Me again... With a couple more questions...
Quote:
Originally Posted by Glenn2 View Post
The caps can stay in, you need only bypass them with wire. Easy to reverse!
Huh?!? So, basically, I just short the leads of all 6 output electrolytic capacitors? No bangs and/or fumes expected?
Quote:
Originally Posted by Glenn2 View Post
The OP275 can be bypassed simply by taking your signal from the XLR sockets instead of the RCA sockets.
No need to cut some tracks to/from OP275 or to RCA output connectors? The XLR to RCA wiring is pretty much straightforward, but would it not OP275 still "send something" to RCA outputs since it would still be connected?

Again, sorry for, to some but not to me, obvious questions - I just want to be double sure before taking soldering iron in my hands...

Last edited by FauDrei; 2nd September 2009 at 07:29 PM.
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Old 2nd September 2009, 10:49 PM   #30
Glenn2 is offline Glenn2  United Kingdom
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Quote:
Huh?!? So, basically, I just short the leads of all 6 output electrolytic capacitors? No bangs and/or fumes expected?
Correct.

Quote:
No need to cut some tracks to/from OP275 or to RCA output connectors? The XLR to RCA wiring is pretty much straightforward, but would it not OP275 still "send something" to RCA outputs since it would still be connected?
You are just taking the signal from a different socket - why would you need to cut anything? You don't even need to open the unit for this.

If you are inexperienced in these things, just build or buy some XLR to RCA leads and leave it at that. It's the biggest improvement of all the things I suggested.
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