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
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
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?
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.
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.
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...
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.
An externally hosted image should be here but it was not working when we last tested it.
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.
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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.
Me again... With a couple more questions...
No bangs and/or fumes expected?
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...
Huh?!? So, basically, I just short the leads of all 6 output electrolytic capacitors?
No bangs and/or fumes expected?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...
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Correct.
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.
If it could be done your way with better sound quality, why would the designers still put the OP275? Surely there's something missing. Impedance matching maybe?
An extra few dB of s/n ratio for the spec sheet perhaps.
When you put the +ve an -ve phases into a differential amp, you get twice the signal coming out (the signal is lowered again, but also is the noise).
Other than that I don't know.
Also see:
http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=141041
When you put the +ve an -ve phases into a differential amp, you get twice the signal coming out (the signal is lowered again, but also is the noise).
Other than that I don't know.
Also see:
http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=141041
Ah, I understand now.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.
But since I connect XLRs to one headamp and RCAs to other headamp, I should, most probably, need to desolder original RCA contacts and connect them internally with pin 1 & 2 of appropriate XLR socket.
Thanks Glenn2
Hello,
things are on progress....did anyone change the l7805 for the Dac Chips
to something better? Maybe changing to reg like paul hynes is selling.
Anybody who changed the X3 clock to something better like from tent
labs?
And last question goes to glen2
you really changed the transformer so 9V? I did not measure all the
voltages but why didn´t they build in the 12V instead?
Greetings Ulf
things are on progress....did anyone change the l7805 for the Dac Chips
to something better? Maybe changing to reg like paul hynes is selling.
Anybody who changed the X3 clock to something better like from tent
labs?
And last question goes to glen2
you really changed the transformer so 9V? I did not measure all the
voltages but why didn´t they build in the 12V instead?
Greetings Ulf
9V would not give enough headroom for the output stage regulators if your mains line voltage is on the low side. Mine is usually around 250V.
I get +19V/-20V going into the 7815/7915 which is perfect.
The + rail sags a bit more then the - because the load is heavier (it powers the 7805 for the DACs).
If my mains was 230V I would get more like +17.5V which is very near to the minimum dropout voltage. If you go below 230V...
I get +19V/-20V going into the 7815/7915 which is perfect.
The + rail sags a bit more then the - because the load is heavier (it powers the 7805 for the DACs).
If my mains was 230V I would get more like +17.5V which is very near to the minimum dropout voltage. If you go below 230V...
Hello Glenn2!
I just bought DacMagic and read your post about improving the sound with XLR/RCA adaptor.
You saying take signal from Pin1 & Pin2 and leave Pin3 alone. In my local store I can buy good quality adaptor for very resonable price but unfortunately it has Pin 3 grounded (like most other adaptors on the market) and it can't be taken apart for modification.
So I wanted to ask if the adaptor with Pin3 grounded is really such a bad solution? Will it degrade the sound compared to adaptor with Pin3 alone?
Sorry for my loussy english and thank you very much for your answer!
Hi, sorry I did not see this or your pm (I rarely get notified for some reason).
If you use this adaptor, it will make the RCA sound distorted, see this thread:
Cambridge DACMagic, anyone? (THREAD II) - Page 22 - Head-Fi: Covering Headphones, Earphones and Portable Audio
If you don't need to use the RCA as well you should be OK. By shorting pin3 you are making the unused op-amp drive a very low impedance.
If you use this adaptor, it will make the RCA sound distorted, see this thread:
Cambridge DACMagic, anyone? (THREAD II) - Page 22 - Head-Fi: Covering Headphones, Earphones and Portable Audio
If you don't need to use the RCA as well you should be OK. By shorting pin3 you are making the unused op-amp drive a very low impedance.