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Black Gate caps

I recently replaced the 10uf Gemcons in my Creek plaer with OsCon SGs. These are paralelled by 10nf ceramic caps, is there any benefit to replacing these too? If so, what should I use?
 
I prefer to leave the ceramic caps in my Arcam, if you want to try some others make sure they have low inductance, I tried polypropylene and siemans stacked film ones but it made my cdp sound to smooth, I suppose it all comes down to personnel taste, but changing the bypass caps does make a difference to the sound
 
You can try any single op-amps for the I/V and filter, I prefer OP27 for both,

The reason I'd favour a CFB or discrete stage here is that one wants the DAC output to see a virtual ground with a low and constant impedance.

The DAC o/p is of a non-constant impedance and any deviation in source Z vs. I-V input Z gives rise to non-linearities.

You can only achieve low Z over the range the op-amps open loop gain is high - the dominant pole of most precision op-amps means that the input Z is rising as the open loop gain falls off, in this application. This roll-off starts at a very low frequency, often 100Hz or so.

A CFB amp, with low i/p Z and a much wider open-loop could be better, a discrete circuit can be low and have very wide bandwidth, which can be advantageous to dealing with any HF noise at the DAC o/p in a more linear fashion.

Failing that an op-amp with lower open-loop gain, but wider OL b/w may be worthwhile trying (AD817 / AD825 amongst others). i wonder if you tried these, the AD817 is a DIP drop-in option.

Andy.
 
Ron,

Thanks for the advice, I think I will leave this until I have got the power sorted. I think replacing the DAC's three power regulators with super regs should have a pretty beneficial effect :)

Ed

PS. does anyone have any experience with the three terminal regulators sold at audiocominternational.com, they are a very neat looking package.
 
Andy,
I have been playing around with the I/V conversion, I have tried AD825, It was a pain soldering them onto the board because they are smd's, it didn't sound bad but the sound became too warm, I also tried AD811,I don't think they are gainstable, I probably need to change some of the circuit to use these, maybe the AD825 would sound better aswell, the other op-amps I have that I can think of are LT1028,Lm6171,LM6181,OPA627,OPA637,OPA604,AD8065,AD8610,AD797

I was thinking about trying just a small resistor from the output of the dac to ground and using 2sc369's, I'm not sure, I did try the discrete circuit that TNT audio use for their diy dac but it didn't sound very good, any idea's would be much appreciated, I also realise the regulators could be improved,( once the output stage is sorted) would your super regs be ok?the Audiocom ones seem good and small but cost a fortune, there is so much to tweak in these cdp's it's knowing when to stop:confused:

Ron
 
hi Ron,
that's great info, plenty to go at there.
The beauty of the Arcam layout is that it is quite easy to see the different stages of the circuit even for non techies like me.


The power to the audio board comes in via the pins underneath therefore quite a simple job to use a seperate 25v supply.
The only fly is the pin marked "kill".
Would you know what this is and is it ok to leave it connected whist running a supply to 25+ 0v 25-.



dogrun.gif
 
Hi,
The kill is for the muting circuit, if you have taken the muting transistors out then you don't need it:)
 
Sorry for being dumb.... can someone please define what is meant by coupling and de-coupling caps? I'm not certain that everyone has the same understanding. And what is the correct term for a DC-blocker that sits between different stages of a circuit to keep DC current from crossing from stage to the next?

Just so we are all on the same song-sheet....
 
Jo,

Coupling caps are the DC blocks in the signal path - they block DC and couple AC.

Decoupling are the caps that couple AC signals to (usually) ground, most commonly PSU rails.

You could refer to the 47u in the gain stage, which decouples the AC to ground, providing LF rolloff as decoupling, but it's also closer the the direct signal path than most, which means selection of a suitable cap may be different from one for a PSU.

Andy.
 
hi,
thanks Ron.
I took a look at the circuit and you've confirmed what I hoped for.
I can now look at a seperate supply for the audioboard.

dogrun.gif
 
Sounds an excellent idea, let us know how you get on, does anybody have any advice what transformers would be good to use with the Arcams audioboard?
 


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