Help me get to know my DAC-AH. (280kb pics)
Mar 1, 2006 at 10:33 PM Thread Starter Post #1 of 149

Samgotit

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I have not had time to read "The Art of Electronics" yet so I need your help.

What do the 2 large sets of caps do in the DAC?

I was comtemplating changing the ps to a STEPS before it arrived (b/c I assumed it to use DC in the range of 12-24v), but this thing puts AC into the pcb at 3 different points if I'm interpreting it right, so STEPS is out...correct?. Is a power supply upgrade an option? Can someone explain this "3 way" ps relative to a DC ps. The specs for the ps are:
Transformer: High quality R-Core
Power supply: 3 regulated isolated power supplies

It's been modified to use socketed op-amps (Burr-Brown OPA627 now) and Black Gate coupling caps. What are coupling caps and why is it nice to have BG-NX caps there?

Here is the schematic link (obviously I can't read it very well
confused.gif
):
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

Thanks for your help,
Sam


DAC%20AH.jpg

DAC%20AH%20pcb.jpg
 
Mar 2, 2006 at 6:44 AM Post #2 of 149

Garbz

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The large caps are the filter caps for the powersupply. They smooth out the 50hz ripple so that the regulators can do their voodoo. There are 3 powersupplies, one is 5v 8v and +/-15V. They are similar to the STEPS in design already except they use fixed regulators instead of the adjustable ones.

Were you the same person complaining about noise in the source forum? The Powersupply's parts all have regulators which should drop the noise floor well below 70dB. The OPAMPs will lower this further as they reject some power noise too. Design wise it should not be under normal circumstances causing audible noise that you can't hear notes decay to black.

Anyway back to the DAC. The 3 powersupplies are needed in a DAC (bottom left of the schematic). 5V for the S/PDIF receiver (top left of the schematic), 8V for the DAC chips (middle of the schematic and the DAC of which there are plenty of them), and +/-15V for the Output stage. (bottom right of schematic).

Coupling caps are C35 and C36. They are needed because the DAC chips run of a single ended supply and will swing their signal output around the 4V. So 0-8V. The end result will be 4V DC offset as an educated guess without looking at the datasheet. Coupling caps eliminate this as they only allow AC to pass through. The problem is that most of the coupling caps in these positions typically need to be a large value >5uf to prevent bass rolling off. So the only option is to put electrolytic caps which are the least linear of caps directly in the signal path. BG-NX caps are argueably the most linear of electrolytic caps and should be placed with an equal to or greater value then what's already there.
 
Mar 2, 2006 at 7:19 AM Post #3 of 149

Samgotit

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Quote:

Originally Posted by Garbz
Were you the same person complaining about noise in the source forum? The Powersupply's parts all have regulators which should drop the noise floor well below 70dB. The OPAMPs will lower this further as they reject some power noise too. Design wise it should not be under normal circumstances causing audible noise that you can't hear notes decay to black.


Wasn't me, but I posted to that thread about upgrading the power supply. Now I see that that is really not an option for my meager skill level. It's sounds as if the ps is quite adequate anyway. I have virtually no noise floor will this DAC + Millet.


Thanks for the information,
Sam
 
Mar 3, 2006 at 2:12 AM Post #4 of 149

randyruiz

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Quote:

Originally Posted by Garbz
The large caps are the filter caps for the powersupply. They smooth out the 50hz ripple so that the regulators can do their voodoo. There are 3 powersupplies, one is 5v 8v and +/-15V. They are similar to the STEPS in design already except they use fixed regulators instead of the adjustable ones.

Were you the same person complaining about noise in the source forum? The Powersupply's parts all have regulators which should drop the noise floor well below 70dB. The OPAMPs will lower this further as they reject some power noise too. Design wise it should not be under normal circumstances causing audible noise that you can't hear notes decay to black.

Anyway back to the DAC. The 3 powersupplies are needed in a DAC (bottom left of the schematic). 5V for the S/PDIF receiver (top left of the schematic), 8V for the DAC chips (middle of the schematic and the DAC of which there are plenty of them), and +/-15V for the Output stage. (bottom right of schematic).

Coupling caps are C35 and C36. They are needed because the DAC chips run of a single ended supply and will swing their signal output around the 4V. So 0-8V. The end result will be 4V DC offset as an educated guess without looking at the datasheet. Coupling caps eliminate this as they only allow AC to pass through. The problem is that most of the coupling caps in these positions typically need to be a large value >5uf to prevent bass rolling off. So the only option is to put electrolytic caps which are the least linear of caps directly in the signal path. BG-NX caps are argueably the most linear of electrolytic caps and should be placed with an equal to or greater value then what's already there.




Thanks for the reply Garbz! Other than the coupling caps are there any other "low hanging fruit" upgrades you would recommend? I have already upgraded the opamps to opa627's.
 
Mar 4, 2006 at 9:40 AM Post #5 of 149

tilt

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"low hanging fruit"?
as in easy to obtain?

bypassing the output stage is pretty easy, all you need is an exacto knife, 2 wires, 2 Caps, and 2 resistors. But it looks like you already have some nice opamps in there.

You can do what this guy did:
dacah1.jpg


I think those are 100k resistors
 
Mar 4, 2006 at 9:45 AM Post #6 of 149

tilt

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IMG_1411.JPG

Bypass. (picture taken by Bg4533)
 
Mar 6, 2006 at 7:40 AM Post #9 of 149

tilt

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Quote:

Originally Posted by MisterX
Additional performance can be obtained from the N/NX/NH
non-polar types by configuring them as an “L Canceling Pair”.
This involves paralleling two identical capacitors so that the
starting foil lead of one is connected to the ending foil lead of the other and vice versa. This arrangment lowers the ESR, cancels
the internal inductance, and eliminates resonance, allowing
the Black Gates to function as pure C into the GHZ range.
This combination is the “Super E-Cap”.

Translation:
Parallel two N series caps with the polarity's reversed and get Super E.
(each cap should be half the value of the cap you are replacing"



In that picture BG4533 use 47uf's, Im not sure what type. Like Mr.X recommended, Blackgate NX's are meant to be pretty linear.

I haven't had a chance to do it to mine yet, im still waiting on parts connexion to send. I have heard it opens up the highs and removes that opamp feel...whatever that means
smily_headphones1.gif

Im gonna try it with 2 47uf's in super E. Don't quite know why i didn't order 22uf's but we'll see what happens.
 
Mar 6, 2006 at 10:01 PM Post #11 of 149

tilt

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Quote:

Originally Posted by bg4533
You definately don't need the 220uF you mentioned in the first post. The DAC isn't meant to drive headphones directly and will need an amp. The high input impedence of the amp allows you to use smaller output caps. 220uF will work, but lower valued higher quality caps should might sound better and be cheaper.


...
 
Mar 6, 2006 at 10:13 PM Post #12 of 149

shlomomofo

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man, where'd you pull that quote from? i thought i looked at all the threads concerning this issue... oh well. thanks for digging that up for me.
icon10.gif


i also sent a pm to lan, and this is what i got from him regarding the caps...

Quote:

I used blackgate NX Hi-Q I believe. That is the best cap from them. I had some left over so I tried 47uf but you don't need to have it that big. 470uf is too much. I think super-e is weird in this configuration because that means two paths for the signal which might not be good. But i've never tried that. Since this is DIY, why don't you try various things? It's a learning experience and you have your own tastes. I would alternatively try some film caps like auricaps which are good. I'm trying some ICW clarity caps now.


 
Mar 7, 2006 at 1:56 PM Post #13 of 149

shlomomofo

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here's some more info from lan via pm...

Quote:

The size will determine how much the bass rolls off. Too little is like <.1uF which will have less deeper bass. You see values like .1uF, .22uF, .47uF being used in portable amps like CMOY. Too much is not good also because bigger isn't better not that you'd get too much bass. But different sizes and brands will sound different so there's no "correct" one as it just depends what you like. I think 47uF is already overkill but that's what spare parts I had on hand at the time. I think something like 1uF to 10uF makes more sense to fool around with.


 
Mar 7, 2006 at 9:09 PM Post #14 of 149

tilt

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hmm, i wonder how some nice film caps would sound over the blackgate NX
 

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