# Help me get to know my DAC-AH. (280kb pics)



## Samgotit

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
	

	
	
		
		

		
			





):
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

 Thanks for your help,
 Sam


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## 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.


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## Samgotit

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


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## randyruiz

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.


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## tilt

"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: 





 I think those are 100k resistors


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## tilt

Bypass. (picture taken by Bg4533)


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## Garbz

a passive output. Nice!


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## shlomomofo

tilt- i wanna do that to my dac-ah! what kind of caps are those? is there any real benefit to doing the "super e" configuration? thanks.


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## tilt

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 
	

	
	
		
		

		
		
	


	



 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.


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## shlomomofo

thanks for the info on super e. now i'm wondering about the correct value for the caps... 47uf or 470uf? (super e - 2x22uf or 2x220uf)

 in this thread on diyaudio, both 22uf and 220uf figures are used... i'm a bit confused.


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## tilt

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._

 

...


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## shlomomofo

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. 
	

	
	
		
		

		
		
	


	




 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.


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## shlomomofo

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.


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## tilt

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


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## Samgotit

Could you guys explain the bypass in a little more detail please. I can't trace the path in Tilt's picture too well.

 Thanks,
 Sam


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## tilt

the image is too big for this thread.

layout


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## dsavitsk

Quote:


  Originally Posted by *tilt* 
_hmm, i wonder how some nice film caps would sound over the blackgate NX_

 

For some background on frequency rolloff as well as a comparison of coupling caps (especially useful here as the test rig was a TDA1543 based DAC), see http://www.ecp.cc/cap-notes.html


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## shlomomofo

just finished doing the bypass mod. 
	

	
	
		
		

		
			





 thanks to all for your help. tilt- thanks for posting the picture of the completed mod... i couldn't have done it without it!

 i just used some cheapo 1uf film caps from the local parts store. i think i'll try some better ones now as it will be a cinch to swap them out.


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## Samgotit

I am so annoyed that I can't read a schematic well! I have it in front of me so here goes. I have a lot of question (which should show may lack of understanding) so please be patient with the newbie. 
	

	
	
		
		

		
		
	


	




 C36 and C35 are 22/40 PHL (propagation delay)? How do I interpret this as far as capacitance?

 In the schematic, exactly where before the op-amp do you bypass and where on the PCB does that correspond. 

 I have 4 of those Aerovox AFPS caps at 3uf 400V. They are highly rated in the article linked by Dsavitsk. If I use them do R40 and R39 need to be changed from 47k in a bypass. Since those resistors are in the output path should they be of high quality?

 Thanks,
 Sam


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## shlomomofo

sam- if you are just looking to bypass the opamps, then that picture posted by tilt is worth 1000 words. i just copied what's there, more or less, and it works fine. i used about $3 worth of parts. i'm thinking there's room for improvement by just using better caps which will be easy since you don't even need access to the bottom of the pcb. 

 first impressions: sounds better. 
	

	
	
		
		

		
		
	


	




 more detail throughout. better soundstage. more air. not a bad upgrade for 3 bucks!

 fwiw, i've got the dac hooked up to a tad-60 tube amp and axiom monitors.


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## Samgotit

Let pretend I am a 3 year old, and you're trying to teach me to make a hanging mobile out of complex origami. Alternatively, lets pretend you're trying to teach you grandfather how to use a cell phone (had to do this recently). I am nothing but newbie with a cheap soldering iron who has way too much confidence after building a cmoy. 
	

	
	
		
		

		
		
	


	




 Sorry for the bother, but I need someone to hold my hand. Those Aerovox caps look like candy. I need to get them in my DAC before I eat them.

 Thanks,
 Sam


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## dsavitsk

By the way, another cheap upgrade, though slightly harder to do, would be to replace C5, 6, 7, 8, 12, 13, 14 and 15 with a higher quality film cap. It appears that they used a metalized polyester, and a polypropylene will be a marked improvement. BC2054-ND from Digikey should fit the board, or anything with a 5mm pin spacing.


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## shlomomofo

sam- i'll work on doing a step-by-step, maybe later tonight. it's really simple. the hardest part was taking out the 18 billion screws that hold the chassis together! 
	

	
	
		
		

		
		
	


	




 btw, you actually have more experience than i do! this was the first time i ever picked up soldering iron. but i had a friend to give me some tips, too.


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## Samgotit

You are a brave man.

 Thanks!

 If they cut the case screw number in half they could sell it for $100. It looks like they designed it to hold bees or anthrax.

 Sam


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## shlomomofo

ok, 814 easy steps to bypass the opamps in your dac-ah, as written by someone with only the very slightest idea of what he is doing...

remove top panel.
remove front and sides (these come off together).
remove two screws from front of pcb.
remove all screws from bottom panel. four of these hold the power supply. be careful not to lose the nuts that hold the ps in place from inside the chassis.
there should now be only one screw holding the pcb to the bottom panel of the chassis, at the back end. swing the bottom panel out of the way so you have access to the bottom of the pcb.
get two lengths of wire. look at tilt's picture for ideas about length.
strip both ends of the two wires.
put the end of one wire through the hole near "c12" and solder the wire to the board from the underside.
do a similar thing with the other wire in the hole near "c13". again, see tilt's pictures for details.
now, you can desolder the wires from the rca signal out. these are the striped wires running from the points marked "r out" and "l out". leave the "gnd" wire connected. put some electrical tape or heatshrink over the desoldered ends.
ok, take one cap and solder one lead to the end of the wire coming from "c12".
solder the other lead to the signal out on the white rca out jack (i.e. where you desoldered the wires).
take a 100k resistor and solder it from rca signal to ground. look again at tilt's picture to be sure you get all of the connections right.
do the same thing with the other wire, resistor, and cap, attaching them all to the red rca jack.
position all of the leads/wires so that they don't touch each other.
in the end you should have something looking very much like the get-up in tilt's picture.
"rebuild" the chassis. the ps is a pain to get back on... be sure to reattach the ground lead too.

 that's it! enjoy! 

 fair warning: i make no claims to knowing anything about this stuff. you may want to wait for more knowing eyes to look at these instructions and comment before you attempt to do the mod. on the other hand, if i can do it, then so can you! 
	

	
	
		
		

		
		
	


	




 i really don't know much more than is written here, but i can try to clarify certain steps if you post questions here.


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## tilt

Hmm, bass isn't as present as it was before. Im thinking its because of the added air and less top end roll off. Overall, it makes for a nice balanced DAC.


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## Samgotit

What caps did you use?

 Sam


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## tilt

BlackGate NX-HI Q 47uf *2 each channel
 and Kiwame 100k Ohm

 Does anyone think super E in this application is detrimental to the sound?


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## dsavitsk

Quote:


  Originally Posted by *tilt* 
_Does anyone think super E in this application is detrimental to the sound?_

 

No, but my experience is that the Kiwame as an I/V can be a bit mushy on the bottom end, especially before it breaks in. Give everything some time and things will improve a bit. Also, C37 may be a bit small for having a passive I/V. If things don't improve you might look there. Last, as mentioned above, higher quality 0.1uF caps by the chips will tighten up the bass a bit.

 Edit: As I look at your picture, the Kiwames are not I/V's, and are probably a waste as that position is not so important. Oh well, give the caps sometime.


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## tilt

i wonder what c37's value is... i have some wima 100nf's just laying around maybe i could stack them  no seriously tho, can I?


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## shlomomofo

Quote:


 Hmm, bass isn't as present as it was before. 
 

i agree that the bass is not as present after the bypass, but it just makes it seem cleaner and more well-balanced in my system...


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## dsavitsk

Quote:


  Originally Posted by *tilt* 
_i wonder what c37's value is... i have some wima 100nf's just laying around maybe i could stack them  no seriously tho, can I?_

 

C37 (and actually C28 which feeds the other half of the chips), from the schematic above, is 220000nF, so the 100nF wimas won't do much as a replacement, though they might work as a decnet replacement for the bypass caps. My own tda1543 based dac has tons of bass, so lack of bass is not inherent in a NOS design. I use a high quality 680uF cap for one chip, this dac uses a low quality 220uF cap for 4 chips.


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## Samgotit

We have to stick to ~8mm diameter here. 

 Would this be a decent upgrade for C37, 28:


 470uf 25v Panisonic FM
http://www.digikey.com/scripts/DkSea...479054&Site=US
 P12389-ND

 Thanks,
 Sam


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## dsavitsk

No reason to use 25V here as the cap will only see 8V. But, the Panasonic FM range is a good choice. It looks like the 680uF or 1000uF 10V or the 680uF 16V will fit, though you need to be sure you get the L version


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## Samgotit

Finished the bypass! (thanks for the hand holding everyone). I too have lost bass, but It seems significantly less grainy. I'll reseve judgement until I replace the other caps per dsavitsk. If the bass is restored I'll be one happy camper, if not I guess I'll just have to build the one on his web site.

 I used 3uF Aerovox caps. Pics to come.

 Thanks all,
 Sam


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## Samgotit

Quote:


  Originally Posted by *dsavitsk* 
_No reason to use 25V here as the cap will only see 8V. But, the Panasonic FM range is a good choice. It looks like the 680uF or 1000uF 10V or the 680uF 16V will fit, though you need to be sure you get the L version_

 

Thanks!

 Updated Digikey part numbers C37, 28 :
 P12354-ND 1000uF 10V 
http://www.digikey.com/scripts/DkSea...479009&Site=US

 or 

 P12378-ND 680uF 16V
http://www.digikey.com/scripts/DkSea...479042&Site=US

 Replacements for C5, 6, 7, 8, 12, 13, 14, 15:
 BC2054-ND
http://sales.digikey.com/scripts/sal...emseq=34443076


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## shlomomofo

thanks for the info and links on the other caps. i just ordered a couple 1000uf's from digikey. i've also got some of those aerovox film caps coming. i'll be sure to post impressions and pics when i'm done.


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## dsavitsk

Quote:


  Originally Posted by *Samgotit* 
_If the bass is restored I'll be one happy camper_

 

Altering R35 and R36 can change the tonal balance a bit. You can do this either by using different types of resistors or by altering the value. Higher values will be warmer and fuller, but will also add distortion. Too high will be all distortion.

 How to calculate these can be seen here: http://www.diyaudio.com/forums/showt...ht=#post173483

 and some other background info is here: http://pinkfishmedia.net/forum/print...?threadid=9739


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## Samgotit

Taken from the post linked by dasavitsk:

  Quote:


 "Anyway, our absolute, maximum output swing is 1.8V to +V -1.2V. So for 5V this is 5V -1.2V -1.8V = 2V" 
 

 Is the 5V supply voltage in the above statment a measured value between pins 4 and 5 on the TDA1543 or is he using typical supply voltage as shown in the data sheet?

 I get 6V at VDD on all of the DACs. This gives me 3V/2.3mA (R=V/I) = 1304 ohms. So I could "safely" the replace the 270ohm resistors with ~1.2kohm?

 edit: forgot to add a picture of the bypass.







 Thanks,
 Sam


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## dsavitsk

You've got 8 chips there, not one. The currents aggregate.


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## Samgotit

Ok..

 May I try again:
 So I've got 2 banks of 4 chips per resistor? With current being additive from each bank?

 3V/((2.3e-3A(4)) = 326 ohms for each resisitor? Is this any better. 
	

	
	
		
		

		
		
	


	






 Thanks,
 Sam


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## dsavitsk

Quote:


  Originally Posted by *Samgotit* 
_ Is the 5V supply voltage in the above statment a measured value between pins 4 and 5 on the TDA1543 or is he using typical supply voltage as shown in the data sheet?_

 

According to the schematic, you should have 8V. Try measuring again, or see why the LM7808 isn't giving you 8V, or if your dac has different regulators.


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## tilt

ohh, take a picture after you've replaced the other caps too!


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## Samgotit

Hmm, Regulators are 7808 so I should get 8V (as you stated) between pins 4 (gnd) and 5 (vdd) on each dac...correct? I still get 6V. Thers is nothing in the path to cause a drop in voltage I can see. Is this the whole story: 8V output from 7808 = 8V at Vdd on the DAC? I can't get to the pins on either 7808 from the top for a measurement 
	

	
	
		
		

		
		
	


	




 . The regulators are NEC. Are Fairchilds a better option? 

 Could someone else measure the voltage at the DACs for a comparison. Here is the data sheet for pin reference:

http://www.diyparadise.com/TDA1543.pdf

 One more barrage of quetions,
 Sam


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## Samgotit

I just pulled the board off and I am only getting 6V out of the regulators. Oddly, I'm getting 16.5V in! Schematic reads In voltage at 10.5AC? The heat sinks on the the regulators are very hot. If I got new (or real) LM7808s that would be MAX supply voltage to the TDA1543's 
	

	
	
		
		

		
		
	


	




. Good for sound?

 Sam


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## wolfy

Can you check the voltages out of the tranny?


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## Samgotit

Quote:


  Originally Posted by *wolfy* 
_Can you check the voltages out of the tranny?_

 

Transformer 13.5V AC
 Bridge rectifier 16.5V DC
 Regulators 6.0V DC out


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## shlomomofo

here's a picture of the bypass i did, using 3uf 200vac aerovox caps. there is a bit less bass now than with the 1uf mylar caps i was using before. bass is also muddier. there is a bit more detail in the mids and highs, however. hopefully the bass gets better as the caps break in, as has been suggested. 

 i've got replacement caps for c37 and c28 (1000uf) on the way from digikey. i'll post a pic and thoughts after i get those puppies in...

 sam- you used the higher voltage aerovox caps? i noticed that yours have both leads on one side. is there any reason to think they would sound different? just curious...


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## Samgotit

Quote:


  Originally Posted by *shlomomofo* 
_sam- you used the higher voltage aerovox caps? i noticed that yours have both leads on one side. is there any reason to think they would sound different? just curious..._

 

I suspect that our caps are basically the same thing. Please, someone let me know if I'm wrong. Here is part of a PM sent by dsavitsk:

  Quote:


 Any non-polar cap will have both a DC and an AC rating, though they usually only state one, and which they state is usually determined by where the cap will generally be used. To figure out the other rating, multiple an AC rating by 1.414, or divide a DC rating by 1.414. my guess is that the DAC-AH doesn't have any voltages higher than 30V or so, so I am sure your Aerovox caps are fine. 
 

My 400VDC/1.414 = 282.8VAC
 Your 200VAC * 1.414 = 282.8VDC

 The leads on my caps are actually axial. One lead is just bent upward and runs up the side of the cap. It is then covered by the label.

 I hate to make statments like this without reference, but either time or placebo has restored some of the bass. I like it over active.

 Sam


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## shlomomofo

Quote:


 ...either time or placebo has restored some of the bass. 
 

you are not imagining the increased bass... i've noticed a definite increase in punchiness and tightness over just a few hours. even now, it sounds better than the mylar caps i replaced. i was a bit worried when i first turned it on earlier, but now i'm happy.


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## shlomomofo

i also have 6 vdc between pins 4 and 5 on the dac chips...


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## Samgotit

I posted this question in another thread :

 Could we repace the whole 10.5V supply section with a TREAD by hooking it up to the transformer leads and remove the two LM7808s and the Monolithic bridge (TREAD uses the LM317T and it's own bridge) that supply the DACs. We could control voltage (up to 8V max) to the DACs that way? Would this be worth the trouble.

 Power supply section to 8 TDA1543s:






 If so what would need to be done to the capacitance in that section.

 I'm learning, so if this is ridiculous or I'm missing something please don't hold back.

 Full Schematic
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

 Thanks for any help,
 Sam


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## shlomomofo

just got the panasonic 1000uf caps in the mail, to replace c37 and c28. can someone give me a hint as to whether it matters which direction i put the caps in? my best guess is that the positive (long) lead should go toward the 1543's.

 also, i've been curious but have yet to ask... do i need to physically cut the link to the opamps somehow to complete the bypass?

 thanks.

 edit: i think i figured it out... it seems like the stripe on the side of the cap lines up with the negative lead. is this universally true? if so, i'll just put the new caps in the same way as the old ones.


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## dsavitsk

The longer lead is positive. On the stripe, you will see a bunch of minus signs. This indicates that the stripe is in line with the negative lead. If you put the cap in backwards it will explode and make a big mess.


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## shlomomofo

note to self: do not, for absolutely any reason whatsoever, put the caps in backwards! 
	

	
	
		
		

		
		
	


	




 thanks for the info, dsavitsk.


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## Samgotit

That was fast. I didn't have a chance to order yet. 
 Borrow an old welding helment, power up the DAC, and let us know what you think!


 BTW, I believe it is the dropout voltage from the regulator that's giving us 6v at the DACs. Maybe its time for a LM7809 or LM7810? 
	

	
	
		
		

		
		
	


	





 Take Care,
 Sam


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## dsavitsk

Quote:


  Originally Posted by *Samgotit* 
_That was fast. I didn't have a chance to order yet. 
 Borrow an old welding helment, power up the DAC, and let us know what you think!


 BTW, I believe it is the dropout voltage from the regulator that's giving us 6v at the DACs. Maybe its time for a LM7809 or LM7810? 
	

	
	
		
		

		
		
	


	





 Take Care,
 Sam_

 

The 7808 shoud put out 8V. The dropout V is 2V meaning that so long as the input V is 10V or higher, everything should be fine. I have no idea why you only have 6V ... have you tried using a different meter or changing the meter's batteries? 

http://www.national.com/ds/LM/LM340.pdf


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## Samgotit

Or...Maybe we should just make our own power supply for this section using the transformer leads.

 See bellow:
http://ourworld.compuserve.com/homep...den/page12.htm

 Cheers,
 Dr. Frankenstien


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## Samgotit

Quote:


  Originally Posted by *dsavitsk* 
_The 7808 shoud put out 8V. The dropout V is 2V meaning that so long as the input V is 10V or higher, everything should be fine. I have no idea why you only have 6V ... have you tried using a different meter or changing the meter's batteries? _

 

I see. Thanks.

 Shlomomofo and I are getting 6V. My meter is less than stellar, but when I check it against a 9V battery I get 9V.

 I'm getting 16v out the transformer. I don't get it.

 Thanks,
 Sam


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## shlomomofo

ami doing this correctly to get the right voltage after the regulators? (see picture attached)

 meter is set to "200 DCV"...


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## Samgotit

Quote:


  Originally Posted by *shlomomofo* 
_ami doing this correctly to get the right voltage after the regulators? (see picture attached)

 meter is set to "200 DCV"..._

 

That's right.

 Sam


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## shlomomofo

Quote:


 First thing to go were the three rectifier modules, these I replaced with BYV26E ultra fast diodes. The next items were the two small digital input caps, these I replaced with RTX MIT film caps and this was followed by removing the two 390R feedback resistors and replacing them with HOLCO\'s. last but not least, resistors R35 and R36 were replaced with 274R CADDOCKS. 
 

some more ideas, from a user review at the diyclub website. 
	

	
	
		
		

		
			





 what are those diodes he's talking about? is that a good idea? might it fix the mysterious problem of the missing 2V? what kind of impact would those 2V have on the sound, anyway...


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## Samgotit

I remember reading about fast diode replacemet at one time. That quote might even have been it. From limited reading I think the jury is out on fast diodes as far as an audible difference is concerned.

 The diodes (monolithic bridges) are at BR1 2 and 3. They convert AC to DC which is then passed on to the requlators. I think.

 R36, 37 "need" to change after we get the power issuse resolved. I think. 

 I'd also like to know what 2V would do?


 Sam


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## Samgotit

I forgot to mention. 

 This is how I understand we calculate the values of those I/V resistors. Here is link originally provided by Dsavitsk:
http://www.diyaudio.com/forums/showt...ht=#post173483

 I'll use 8V as an example: 

 8V-1.2V-1.8V=5V (The other values are from Voc on the data sheet)

 We have 8 DACs connected with each resistor for L and R channels, so for each resistor:
 5V/(2.3e-3*8) = 272 ohms

 I think. 





 Sam

 Revised!

 Revised again!


----------



## tilt

Quote:


  Originally Posted by *shlomomofo* 
_just got the panasonic 1000uf caps in the mail, to replace c37 and c28._

 

And the verdict is.......?


----------



## Samgotit

Quote:


  Originally Posted by *Samgotit* 
_I forgot to mention. 

 This is how I understand we calculate the values of those I/V resistors. Here is link originally provided by Dsavitsk:
http://www.diyaudio.com/forums/showt...ht=#post173483

 I'll use 8V as an example: 

 8V-1.2V-1.8V=5V (The other values are from Voc on the data sheet)

 We have 8 DACs connected in series with each resistor for L and R channels, so for each resistor:
 5V/(2.3e-3*8) = 272 ohms

 I think. _

 

Looking at the schematic I can't tell if these resistors are in the path anymore. Can someone verify if R36 and R35 are still in the signal path in the bypass configuration? 

 Thanks,
 Sam


----------



## shlomomofo

sam- those resistors are still in the signal path, immediately before the bypass coupling caps. and thanks for the info on the rectifiers. when i read it the first time, i thought he said he replaced the "regulators"... but of course i was wrong. 

  Quote:


 And the verdict is.......? 
 

i won't be putting in those caps until tomorrow. i'll give my impressions after my amplifier comes back from the shop early next week (warranty issue - dealer is trying to isolate the source of some parasitic oscilation. actually he's just sending a new one, but that's a topic for another thread 
	

	
	
		
		

		
		
	


	




 ).


----------



## Samgotit

Ok, Great! 

 It looks like the stock I/V resisotors at 270 ohms are the optimal value for 8V. I guess we need to work on our skimpy 6V supply voltage.

 Thanks,
 Sam


----------



## shlomomofo

can someone point me to the place in the schematic where it says specifically that the supply voltage should be 8v?


----------



## Samgotit

It does not say specifically. The power supply in the schematic to the DACs is 10.5V from the transformer, but the LM7808 regulators are rated at 8V supply out (7.7V min). Why we are not getting that is the $64,000 question. There is nothing in the path between the regulators and the DACs?

 Cheers,
 Sam


----------



## dsavitsk

What does the regulator chip on the board actually say? Maybe they changed things from the schematic?


----------



## Samgotit

Quote:


  Originally Posted by *dsavitsk* 
_What does the regulator chip on the board actually say? Maybe they changed things from the schematic?_

 

They are completly blocked and I can't read them from any angle. The regulator for the CS8414 is the NEC LM7805A. I think I'll just order regualtors and replace them?

 Thanks,
 Sam


----------



## shlomomofo

Quote:


  Originally Posted by *Samgotit* 
_They are completly blocked and I can't read them from any angle._

 

i should be able to read the writing on the regulators when i take out c28 and c37 later tonight. i'll let you know what i find...


----------



## shlomomofo

mystery solved! i wonder why diyclub used 7806's instead of the 7808's in the schematic... cost cutting or "better" sound? in any case, 6 volts is certainly within the specs for supply voltage to the 1543's (5v typical and 8v max). does anyone think it would be worthwhile to swap out the regulators for 7808's?


----------



## shlomomofo

... and here's a picture of the new caps in the c28 and c37 positions. like i said, it's tough for me to judge this one. i'm using my old yamaha amp (decent solid state) while my tad-60 (awesome tube amp 
	

	
	
		
		

		
		
	


	




 ) is out of commission. 

 listening to some thievery corporation -- bass seems tighter, and it seems like there's more of it... but take that with a grain of salt, for sure. you will just have to swap those caps out to find out for yourselves! it's a cheap and easy mod, anyway.


----------



## Samgotit

Excellent!!!!!!!!!! Caps look great.

 Thanks for getting to bottom of this little mystery. 

 LM7808? What will voltage do for sound quality? That is the question.

 Take Care,
 Sam


----------



## shlomomofo

Quote:


  Originally Posted by *Samgotit* 
_LM7808? What will voltage do for sound quality? That is the question._

 

+2V or not +2V... that is the question.


----------



## tilt

now who's going to take the plunge and do the mods to replace C5, 6, 7, 8, 12, 13, 14, 15


----------



## shlomomofo

my query to diyshop...

  Quote:


 i bought a dac-ah from you a while ago. i've been doing some slight mods, and i noticed that the voltage supplied to the dacs from the regulators is only 6v (measured between pins 4 and 5 on any 1543 chip). isn't it supposed to be 8v? why is it lower and how do i fix it? dac-ah sounds awesome anyway... 
 

... and their respone.

  Quote:


 Hello,
 The new DAC-AH is 6V
 Regards

 Johnny 
 

after deciphering the nuances of their response, it seems to me that the switch to 6v was fully intentional.


----------



## tilt

C5, 6, 7, 8, 12, 13, 14, 15, 28, 37 are all on the way, i'll post impressions.


----------



## Samgotit

Quote:


  Originally Posted by *tilt* 
_C5, 6, 7, 8, 12, 13, 14, 15, 28, 37 are all on the way, i'll post impressions._

 

Me too. Ordered last night. I'm going to try Frankensteining the DACs with an 8V regulator (LM7808) as well. 

 Sam


----------



## tilt

change the reg before you change anything else!! i wanna hear what the 2v does


----------



## tilt

if 274 is optimum for 8v, what IV vaule should we use for 6v?


----------



## Samgotit

Quote:


  Originally Posted by *tilt* 
_if 274 is optimum for 8v, what IV vaule should we use for 6v?_

 

6V-1.2V-1.8V=3V (The other values are from Voc on the data sheet)

 We have 8 DACs connected in series with each resistor for L and R channels, so for each resistor:
 3V/(2.3e-3*8) = 163 ohms

 Here some backgroud provided earlier:
 The link in the quote is where the equation is provided.

  Quote:


 I/V Resistors

 These exert a large influence on the final sound. The correct resistance depends on the TDA1543 supply voltage. Thorsten Loesch explains how to calculate it in this diyAudio.com post. I use +6v, I/V 1k2, 1k3 Iref.
http://www.diyaudio.com/forums/showt...ht=#post173483

 With a +8V supply, the dac functions well with 3k0 I/V and 1k5 Iref.

 Welwyn RC55 sound rather dark, grainy and harsh. Not recommended. For a less brutal version of this more aggressive sound try SMD resistors from Multicomp, 0.125W 1% 1206.

 Audio Note tantalum resistors have a lush, chunky sound without much air.

 Vishay bulk foils sound luminous and very detailed, to the point of sounding a little fuzzy and soft.

 Cheap carbon resistors from Farnell.com seem to impose the least sound, leaving you to tweak the dac elsewhere, and the tiny 0.125W version fits into awkward places. Try them if you like but can't afford Vishay bulk 
 

Sam


----------



## shlomomofo

Quote:


  Originally Posted by *Samgotit* 
_3V/(2.3e-3*8) = 163 ohms_

 

here's a question to show my utter lack of understanding of electrical systems... 
	

	
	
		
		

		
		
	


	




 why is it (2.3e-3*8) instead of just (2.3*8)?

 and another question about the following....
  Quote:


 To get the output to the new midpoint of 1.8V+(5.6V/2) = 4.6V. We will have to have 4.6V/2k4 = 1.92mA flowing in our 2k4 resistor, plus our 1.15mA DAC digital silence current, so 3.07mA. In our reference resistor 3.07mA/2 = 1.535mA need to flow, so 2.2V/1.535mA=1.43k, NPV 1k5. 
 

 is this to get the values for the resistors that come before the dacs?

 thanks


----------



## Samgotit

Quote:


  Originally Posted by *shlomomofo* 
_here's a question to show my utter lack of understanding of electrical systems... 
	

	
	
		
		

		
		
	


	




 why is it (2.3e-3*8) instead of just (2.3*8)?

 and another question about the following....
 is this to get the values for the resistors that come before the dacs?

 thanks_

 

The e-3 (1x10^-3) is the conversion factor for mA to A (1mA = .001A).

 Our Vref is controled by that lonesome 1k trimpot at VR1. You can measure Vref b/w pins 4 and 7 on the DAC. Trim pot may need to change to get optimum Vref. I need to read more on this. 
	

	
	
		
		

		
		
	


	




 Sam


----------



## Samgotit

I forgot to add:

 Minimum Vref is 2.10V at only 5v supply voltage. I'm getting a scant 2.05V with a 6v supply. The trim pot is maxed. A fixed resistor may be a better option here. I just have to figure out how to calculate it based on that post. 
	

	
	
		
		

		
		
	


	




 Anyone care to comment? Please? 

 Sam


----------



## shlomomofo

i'll take a stab at the ref resistor for an 8V supply...

  Quote:


 Now Vref is fixed at nominal 2.2V...

 Our output Voltage swing can now be 1.8V to 8.6V - 1.2V = 7.4V or 5.6V peak-peak (2V RMS). Our full scale current is still only 2.3mA, so our I/V resistors become 5.6V/2.3mA=2.43k NPV = 2k4.

 To get the output to the new midpoint of 1.8V+(5.6V/2) = 4.6V. We will have to have 4.6V/2k4 = 1.92mA flowing in our 2k4 resistor, plus our 1.15mA DAC digital silence current, so 3.07mA. In our reference resistor 3.07mA/2 = 1.535mA need to flow, so 2.2V/1.535mA=1.43k, NPV 1k5. 
 

8V-1.2V-1.8V = 5V peak-peak
 5V/(2.3e-3*8) = 272 ohms I/V
 1.8V + (5V/2) = 4.3V midpoint
 4.3V/272 ohms = 0.0158A = 15.8mA
 15.8mA "plus our 1.15mA DAC digital silence current" = 16.95mA
 16.95mA/2 = 8.48mA = 0.00848A
 2.2V/0.00848A = 259 ohms






 well, i tried!


----------



## shlomomofo

and with a 6V supply, for the sake of completeness....

 6V-1.2V-1.8V = 3V peak-peak
 3V/(2.3e-3*8) = 163 ohms I/V
 1.8V + (3V/2) = 3.3V midpoint
 3.3V/163 ohms = 0.0202A = 20.2mA
 20.2mA "plus our 1.15mA DAC digital silence current" = 21.35mA
 21.35mA/2 = 10.68mA = 0.01068A
 2.2V/0.01068A = 206 ohms

 not sure if any of this is correct, as sam seems to be getting only ~2V at Vref with ~1000 ohms of resistance... (right sam?)


----------



## tilt

wouldn't it be better to leave the dac at v6, and just change the IV's to 160ohm.

 The TDA1543s get pretty hot at 6v, i'd hate too see them at 8. Also, does heat shorten the life of the chips. Would ram sinks help?

 either way, LM7808's are on the way


----------



## Samgotit

Quote:


  Originally Posted by *tilt* 
_wouldn't it be better to leave the dac at v6, and just change the IV's to 160ohm.

 The TDA1543s get pretty hot at 6v, i'd hate too see them at 8. Also, does heat shorten the life of the chips. Would ram sinks help?

 either way, LM7808's are on the way_

 

That's a good question. 

 Being generally ignorant on the subject I am operating on the assumption that bigger is better 
	

	
	
		
		

		
			





. More voltage sounds good to me. Absolute max is 9V. I've seen many other TDA1543 based DACs using 8V. 
 See this:
http://www.dddac.de./
http://www.geocities.com/TDAC1543/

 Now that you bring it up heat concerns me too. We can always get taller sinks, cut a hole in the top, and give it the smoke stack look. We can order these the same time we order new facny resistors for IV and Vref (or trim pot).

 The other consideration is Vref. By increasing supply voltage Vref can increases as well up to 2.30V. Again, whether bigger = better I have no clue.

 In the end the supply voltage will probablly not matter as much as getting quality I/V resistors and matching/adjusting Vref. I'm considering simply replacing the trim pot for Vref with a Bourns form Mouser for now. Still don't know what value to use though. 

 Sam


----------



## tilt

Argh! i came home to see a sticky note from purolator on the door. If they don't come by again i'll pick them up tomorrow. I'll replace the regs first and do a quick a/b. Then the caps near the regs, then all the 0.1uf's.

 Im not sure what you mean by Vref. What IV resistors are you thinking of getting?


----------



## tilt

For the IV maybe some new old stock Shinkoh Tantlums?

 Dsavitsk, i read on one of your other posts about a "maxed out DAC" using Riken's as I/V's. Is that personal preference or just something you have easy access too?


----------



## Samgotit

Quote:


  Originally Posted by *tilt* 
_Argh! i came home to see a sticky note from purolator on the door. If they don't come by again i'll pick them up tomorrow. I'll replace the regs first and do a quick a/b. Then the caps near the regs, then all the 0.1uf's.

 Im not sure what you mean by Vref. What IV resistors are you thinking of getting?_

 


 For I/V I ordered Holco from mouser:

 Mouser# 279-274
http://www.mouser.com/index.cfm?hand..._pcodeid=02040

 Sam


----------



## dsavitsk

Quote:


  Originally Posted by *Samgotit* 
_For I/V I ordered Holco from mouser:_

 

I think these are the new versions with steel end caps. They are generally not considered any good. You need to find NOS Holcos. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *tilt* 
_Dsavitsk, i read on one of your other posts about a "maxed out DAC" using Riken's as I/V's. Is that personal preference or just something you have easy access too?_

 

Yes. Peter Daniels at DIYAudio.com suggested them, and I agree that they are a good choice. I also like Kiwames, though I am not sure I'd recommend them. The sound is a bit soft and pillowey, but kind of nice. I've also had decent luck with PRPs. Truth is, I haven't tried anything that was terrible, just a few things that were a lttle better. If you look elsewhere, you'll see that Rick likes Vishay Bulk Foils. I've not tried them, thought.


----------



## Samgotit

Quote:


  Originally Posted by *dsavitsk* 
_I think these are the new versions with steel end caps. They are generally not considered any good. You need to find NOS Holcos. 
	

	
	
		
		

		
		
	


	



_

 

Darn, I vaugley remember reading that here. It slipped my mind when I ordered them. 

 Given this, I think it would be a good idea to socket these resistors. Different values and different types all day long. Would really be nice to do some of the comparisions on my own ears. 

 Mouser# 575-113120 for the pins
http://www.mouser.com/index.cfm?hand..._pcodeid=57508


----------



## tilt

The BASS! she has returned!!! 
	

	
	
		
		

		
		
	


	










 pics comming soon
 -----





 2 LM7808
 2 Panasonic FM 1000uf
 8 BC Components Polypropylene Film 0.1uf

 I/V Resistors had to be moved to the underside of the board to make room.


----------



## shlomomofo

kewl!!! was it easy to put in the new regulators?


----------



## Samgotit

Quote:


  Originally Posted by *tilt* 
_The BASS! she has returned!!! 
	

	
	
		
		

		
		
	


	










 pics comming soon
 -----

 2 LM7808
 2 Panasonic FM 1000uf
 8 BC Components Polypropylene Film 0.1uf_

 

She's the most beautiful thing I've ever seen! How did the desoldering go?

  Quote:


 I/V Resistors had to be moved to the underside of the board to make room. 
 

There goes the socketed I/V restitors.

 Ok tilt, you need to get on to reclocking and stacking 8 more DACS 
	

	
	
		
		

		
		
	


	




.


----------



## shlomomofo

Quote:


  Originally Posted by *Samgotit* 
_reclocking and stacking 8 more DACS_

 

wha?? can you seriously just start stacking up more dac chips in this design? i know that in the dddac1543 mk2, you can have multiples of 12 dac chips. man that would be sweet. and what is this about reclocking?

 this is very awesome, but sadly (not really. 
	

	
	
		
		

		
		
	


	




 ) i'm going to be away from home (in the USA) for at least a few months. i'll be sure to look this thread up when i get back... i'm sure i will have a lot to do to catch up! good luck with the new mods.


----------



## Samgotit

Quote:


  Originally Posted by *shlomomofo* 
_wha?? can you seriously just start stacking up more dac chips in this design? i know that in the dddac1543 mk2, you can have multiples of 12 dac chips. man that would be sweet. and what is this about reclocking?

 this is very awesome, but sadly (not really. 
	

	
	
		
		

		
		
	


	




 ) i'm going to be away from home (in the USA) for at least a few months. i'll be sure to look this thread up when i get back... i'm sure i will have a lot to do to catch up! good luck with the new mods._

 

I would not even no where to start with reclocking 
	

	
	
		
		

		
		
	


	




 .
 Here is a"Pro" Reclocking mod:
http://www.effectiveaudiomod.com/Comp_LiteDAC.htm

 I think you can stack as many chips as you like with the right power supply. LM7808 is rated for 1A. 16 chips would use 60mA*16 = 0.960mA/2 regulators, so I think we would be OK. Change I/V and Vref to match. Of course, I'm sure the are other variables I'm not aware of, but it may be an option. Sure would be fun. Whether it's worth it is the queston.

 Sam


----------



## tilt

oooo! stacking, i like it!


----------



## tilt

Quote:


  Originally Posted by *shlomomofo* 
_kewl!!! was it easy to put in the new regulators?_

 

Regs were a bit tricky.

 It would have been easier with a little 20w iron and a needle tip.

 when i first put it in, the bass seemed a little boomy, but even now i can hear it start too tighten up. Its also probably because i was used to the recessed bass from before. I think it will compliment the K701's (supposed to have weakish bass) If they ever arrive, sigh


----------



## tilt

Quote:


  Originally Posted by *Samgotit* 
_That's a good question. 

 Being generally ignorant on the subject I am operating on the assumption that bigger is better 
	

	
	
		
		

		
		
	


	




. More voltage sounds good to me. Absolute max is 9V. I've seen many other TDA1543 based DACs using 8V. 
 See this:
http://www.dddac.de./
http://www.geocities.com/TDAC1543/

 Now that you bring it up heat concerns me too. We can always get taller sinks, cut a hole in the top, and give it the smoke stack look. We can order these the same time we order new facny resistors for IV and Vref (or trim pot).

 The other consideration is Vref. By increasing supply voltage Vref can increases as well up to 2.30V. Again, whether bigger = better I have no clue.

 In the end the supply voltage will probablly not matter as much as getting quality I/V resistors and matching/adjusting Vref. I'm considering simply replacing the trim pot for Vref with a Bourns form Mouser for now. Still don't know what value to use though. 

 Sam_

 

K, i wanna replace the vref too... what should i use? (if i were to use a resistor)


----------



## Samgotit

I replaced the trim pot with a 1k bourns. I adjusted the resistance to give me a Vref of 2.20V. I cannot tell a difference in sound. Sadly, this is all I've had time to do. I really need to get to the bigger stuff.

 Shlomomofo did the calculations earlier for replacing the Vref trim pot with a resistor. I came up with the same numbers. I Do NOT know if they are right.

 Cheers,
 Sam


----------



## tilt

Quote:


  Originally Posted by *shlomomofo* 
_and with a 6V supply, for the sake of completeness....

 6V-1.2V-1.8V = 3V peak-peak
 3V/(2.3e-3*8) = 163 ohms I/V
 1.8V + (3V/2) = 3.3V midpoint
 3.3V/163 ohms = 0.0202A = 20.2mA
 20.2mA "plus our 1.15mA DAC digital silence current" = 21.35mA
 21.35mA/2 = 10.68mA = 0.01068A
 2.2V/0.01068A = 206 ohms

 not sure if any of this is correct, as sam seems to be getting only ~2V at Vref with ~1000 ohms of resistance... (right sam?)_

 

hmm


----------



## tilt

Quote:


  Originally Posted by *Samgotit* 
_I replaced the trim pot with a 1k bourns. I adjusted the resistance to give me a Vref of 2.20V. I cannot tell a difference in sound. Sadly, this is all I've had time to do. I really need to get to the bigger stuff.

 Shlomomofo did the calculations earlier for replacing the Vref trim pot with a resistor. I came up with the same numbers. I Do NOT know if they are right.

 Cheers,
 Sam_

 

Next time you're in there, messure the resistance across your vr1


----------



## d-cee

hi all,

 I've received my DAC-AH (green PCB - everyone else on this forum seems to have red PCB)

 anyways, i'm waiting for some sprague paper and oil capacitors to arrives and i had a couple of quick questions

 i understand the polarity of electrolytic capacitors is important, however, i am under the impression somehow that paper and oil caps don't have this issue - please correct me if i am wrong to save this exploding in my face =S

 and lastly, if i perform the passive output mod will it require me to de-solder the opamps in there or can i leave them be?

 thanks


----------



## Samgotit

i Quote:


 understand the polarity of electrolytic capacitors is important, however, i am under the impression somehow that paper and oil caps don't have this issue - please correct me if i am wrong to save this exploding in my face =S 
 

They are non-polar AFAIK.

  Quote:


 and lastly, if i perform the passive output mod will it require me to de-solder the opamps in there or can i leave them be? 
 

Take them out and replace with sockets in case you latter want to try opamps, but I preferred it passive.


----------



## mrarroyo

Quote:


  Originally Posted by *Samgotit* 
_i

 They are non-polar AFAIK.



 Take them out and replace with sockets in case you latter want to try opamps, but I preferred it passive._

 

Which OP Amps can I use w/o having to modify the circuitry? Thanks.


----------



## Samgotit

Quote:


  Originally Posted by *mrarroyo* 
_Which OP Amps can I use w/o having to modify the circuitry? Thanks._

 

Never did try opamp rolling, but most single channel, unity gain stable opamps that can take up to 15V should be ok. This is mostly a guess. There could be other variables to consider and this shoud be backed up by someone with more experience. Here's the link to the schematic if someone wants to help verify this:
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

 One example is, of course, the OPA627, which works fine. A few others that look good: OPA227, AD8610, and so on.


 Here's the data sheet on the NE5534 which is the stock opamp. You can go from there:
http://www.ampslab.com/PDF/ne5534p.pdf


----------



## izquierdaste

I have a dac-ah with opa 627's on the way. I am thinking of replacing the stock coupling capicators with sprague vitamin q 12uF 200V. The schematic says 22/40 phl. Would the 12uF capacitors be enough? Any help would be great. I don't want to do the passive bypass yet, so the capacitors would still be connected to the opamps

 Thanks,
 Brian


----------



## d-cee

Quote:


  Originally Posted by *Samgotit* 
_Take them out and replace with sockets in case you latter want to try opamps, but I preferred it passive._

 

i am assuming from this statement that i must remove the opamps completely or put in a socket for the passive output to work?


----------



## ozshadow

tag for later reading


----------



## Samgotit

Quote:


  Originally Posted by *izquierdaste* 
_I have a dac-ah with opa 627's on the way. I am thinking of replacing the stock coupling capicators with sprague vitamin q 12uF 200V. The schematic says 22/40 phl. Would the 12uF capacitors be enough? Any help would be great. I don't want to do the passive bypass yet, so the capacitors would still be connected to the opamps_

 

See this:
http://www.ecp.cc/cap-notes.html
http://tangentsoft.net/audio/input-cap.html

 22/40 phl - I still have no clue what this means. 
	

	
	
		
		

		
			





  Quote:


  Originally Posted by *d-cee* 
_i am assuming from this statement that i must remove the opamps completely or put in a socket for the passive output to work?_

 

Yes.


----------



## shlomomofo

hmmm... my dac-ah worked ok after doing the bypass, and i did not take out the opamps.


----------



## Samgotit

Quote:


  Originally Posted by *shlomomofo* 
_hmmm... my dac-ah worked ok after doing the bypass, and i did not take out the opamps._

 

You're probably right shlomomofo, I answered based on tilt's pics on the first page where they are missing. I didn't recall that the pads for Lout and Rout are not used in the bypass (mine is now disassembled). My apologies.

 To the person with the green board: It may be interesting to see what voltage your regulators are supplying the DACs. Many of us with the red PCB had 6V regulators where the schematic called for 8V.


----------



## d-cee

Quote:


  Originally Posted by *Samgotit* 
_You're probably right shlomomofo, I answered based on tilt's pics on the first page where they are missing. I didn't recall that the pads for Lout and Rout are not used in the bypass (mine is now disassembled). My apologies.

 To the person with the green board: It may be interesting to see what voltage your regulators are supplying the DACs. Many of us with the red PCB had 6V regulators where the schematic called for 8V._

 

how would i find out? mine is a 220/240v australian spec one

 edit: also, does anyone else notice that the heatsink closest to the centre gets really hot? but the other two stay cool/warm?


----------



## Samgotit

Can you take a photo of you're board. 

 The heat sink closest to the middle, near the row of resistors, is for one of the LM7808 (or LM7806, whichever you have). It feeds four of the eight DACs. The one next to it is also a LM7808, feeding the other four, and theoretically should be about the same temp if the boards have the same layout.

 To measure the voltage of those regulators you will have to remove the board and measure at the solder joints. The middle pin is the ground. (See this for the pin out: http://www.fairchildsemi.com/pf/LM/LM7808.html click "data sheet". Measure from the middle joint to the output. The output will be the pin closest to the middle row of resistors. You should get either 6V or 8V DC. Again, this if for the red pcb, so please take a picture of yours to be sure they are the same.


----------



## TheMarsVolta

From reading through all the DAC-AH mod threads, here's an attempted summary of mods people have mentioned, sorted from my rough understanding of cost-benefit. 

 Comments from those who have done these mods would be great, I'm getting some parts together as I anxiously wait for my DAC to arrive in the mail.

 1. Bypass the active output stage into passive output, using blackgate or paper-oil caps and higher quality resistor for I/V section.

 Question - if the active stage is bypassed, is the +/- 15V section of the power supply still needed? (for the ground channel?)

 2. Upgrade power supply caps

 3. Replace the 8 DAC chip film caps with something better quality - such as PP

 4. Upgrade regulators

 5. Add heat sinks to TDA 1543 chips

 6. Upgrade RCA and power connectors 

 Getting more exotic:

 7. Stack the TDA1543 (and adjust power supply voltage etc. accordingly)

 8. Does having the power supply transformer so close to the PCB cause measurable noise? would moving the PS external to the DAC be worth the effort? I noticed DIYCLUB sells the bare case for $16, it could be used to house the transformer only.

 9. Reclocking unit


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## izquierdaste

Question moved to new thread.


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## Halide

Hi guys... I'm interested in doing the passive mod + 8v mod. 

 First of all, I need about all the output I can get because I like to listen to music relatively loud and I am using bookshelf type speakers with a 70 watt per channel power amp (which needs a good signal to get loud). So, I'm wondering, if I do the passive mod, will it even have enough signal to "get loud" anymore? Also, how much more output signal will the 8 volt mod give?

 Thanks in advance for your help.
	

	
	
		
		

		
			





 Also, what are some good capacitors for the passive mod that would cost less than ~$50 (for both), preferably less?


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## blah1134

can i use 1uf or lower for the bypass caps ?


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## Samgotit

Quote:


  Originally Posted by *blah1134* /img/forum/go_quote.gif 
_can i use 1uf or lower for the bypass caps ?_

 

Try these articles:

http://www.ecp.cc/cap-notes.html
http://tangentsoft.net/audio/input-cap.html


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## Halide

Ok, I ordered microsinks for the dac chips and 2x 3.3uF Auricaps for the bypass. If I don't get enough output voltage I'll change the voltage regulators to 8v. 

 Can someone tell me if the 100k resistor from the RCA out to ground needs to be high quality or can I just use the 5% radio shack resistors?

 Also, what exactly does that resistor do? (I'm an electronics newbie)


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## Halide

I did the passive mod 
	

	
	
		
		

		
		
	


	




 and the good news is... my dac still works!


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## Halide

I just ordered LM7808s, going to do that next


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## Halide

i should have thought twice about changing out the voltage regulators. that was SO hard to desolder... especially with the crappy solder sucker i had. 

 i just unscrewed the ones that were there and basically ripped them off with some needle nose pliers. then pulled each leg out one by one. i lost 2 solder rings (on the bottom of the pcb) and amazingly after putting in the new regulators it still plays music. maybe i am lucky?...


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## MCC

I'm considering acquiring a DAC-AH and am planning on doing all of these mods. Since this DAC is so cheap I can afford to go all-out (well, to a certain extent...) I'm planning on using 275ohm Vishays for I/V (VISHAY-50437 @ partsconnexion) and 3uf Auricaps for the bypass (AURICAP-63054). Are these suitable for this mod? I'd really hate to waste $45 USD on a couple resistors and capacitors if they won't be optimal.

 It is my understanding that high-end resistors aren't needed @ the RCAs (100ohm). Would old generic electronics kit resistors work here, or are those _too_ cheap? 

 Finally, are the Auricaps polar? If so, which color wire goes where?

 And the thread lives again...


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## shlomomofo

i think i used 4.7uf auricaps and 270ohm rikens. also swapped in 8v regulators.... essential reading here


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## regal

Quote:


  Originally Posted by *shlomomofo* /img/forum/go_quote.gif 
_i think i used 4.7uf auricaps and 270ohm rikens. also swapped in 8v regulators.... essential reading here_

 


 You don't want to do the resistor and the 8v regulator, this will just send the DAC-AH back into outputing a clipped signal. Do one or the other not both!


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## MCC

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_You don't want to do the resistor and the 8v regulator, this will just send the DAC-AH back into outputing a clipped signal. Do one or the other not both!_

 

Are you sure? From what I can tell from looking at the schematic, a 270ohm resistor in R35/36 is actually the correct value for an 8v source, not 6v. That makes the unmodded value incorrect, right? I might be missing something though, my knowledge of electronic engineering is rather slim.

 shlomomofo, thanks for the link. 
	

	
	
		
		

		
		
	


	




 Edit: That link seems to confirm my conclusions. Hmm. Yo soy confused.


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## regal

Quote:


  Originally Posted by *MCC* /img/forum/go_quote.gif 
_Are you sure? From what I can tell from looking at the schematic, a 270ohm resistor in R35/36 is actually the correct value for an 8v source, not 6v. That makes the unmodded value incorrect, right? I might be missing something though, my knowledge of electronic engineering is rather slim.

 shlomomofo, thanks for the link. 
	

	
	
		
		

		
		
	


	




 Edit: That link seems to confirm my conclusions. Hmm. Yo soy confused. 
	

	
	
		
		

		
		
	


	


_

 


 The original value 270 ohm is correct for 8V. You don't need to change it unless you want a boutique resistor. The original is fine for 8V regs.


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## shlomomofo

and the newer stock units come with 6v regs... so you need to change the regs or the resistors. or both if you want boutique resistors. 
	

	
	
		
		

		
		
	


	




 read through this thread and the thread i referenced and you'll be set as far as mods go.

 edit: typos... too much scotch


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## MCC

Sounds great! One final question though. I already have a very nice Zu Pivot mini 1/8"-stereo RCA cable. To use it I'd like to install a 1/8" jack in the DAC but I can't seem to find a suitable quality component anywhere. At all. Everything I can find is either not gold plated or incredibly cheap looking. Suggestions?

 Edit: Ignore this, it really seems that such a thing doesn't exist. My dad has some decent RCA cables I can "borrow", and I can sell the Zu Pivot to help pay for the DAC. Problem solved.


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## Puffin

Can somebody just confirm that you do not need to remove the op-amps to complete the passive mod ? I removed caps 35 & 36 and substituted with new caps and resistors as per the photo supplied by Tilt in post #5.


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## Puffin

This is the picture.


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## Puffin

Sorry, here it is.


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## d-cee

Quote:


  Originally Posted by *Puffin* /img/forum/go_quote.gif 
_Can somebody just confirm that you do not need to remove the op-amps to complete the passive mod ? I removed caps 35 & 36 and substituted with new caps and resistors as per the photo supplied by Tilt in post #5._

 

my opamps are still in there (cos i couldn't freaking remove them!) and it's working fine


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## Puffin

I carried out the mods as in my previous post above. Because I cannot leave things alone I decided to remove the op-amps. After removing them, switched on - - No Sound !

 Looked at the start of this thread and connected the caps up where "Tilt" connected his (the holes by C12 & C13) Music again.

 Well that says to me that if you leave the op-amps in, they must still be in the signal path ?


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## thegeek

Well yes, the last picture posted above is not a passive output, it's merely a replacement of the coupling caps. It would improve the sound, but imho the passive out is without doubt the best.


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## VncentValntine

Hey guys, is there a uF range which I should keep the caps? Would a high quality 1uF cap be a good start? And would it really matter what brand or type of resistor I use that connect to ground? Am I good as long as it's 100 ohm?


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## Negatron

Quote:


  Originally Posted by *VncentValntine* /img/forum/go_quote.gif 
_Hey guys, is there a uF range which I should keep the caps? Would a high quality 1uF cap be a good start? And would it really matter what brand or type of resistor I use that connect to ground? Am I good as long as it's 100 ohm?_

 

The value of the output cap determines the low frequency cuttoff. If your DAC is looking into a 10K input, the -3db point will be 15.9Hz. Scale that up to a 20K input and you get an 8Hz f3. Much better. It's personal opinion, but I find smaller caps sound better/more detailed, so if possible change the input Z of the amp it looks into. Always a good excuse for a high quality pot upgrade.


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## VncentValntine

Okay I've completed the passive output mod, but now I have a question... When playing music, if there is absolute silence or very little music is played i hear this slight crackling in my right ear that is neither constant or consistent. Bad solder? Unbroken-in cap? Anyone have an idea? Thanks in advance


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## d-cee

Quote:


  Originally Posted by *VncentValntine* /img/forum/go_quote.gif 
_Okay I've completed the passive output mod, but now I have a question... When playing music, if there is absolute silence or very little music is played i hear this slight crackling in my right ear that is neither constant or consistent. Bad solder? Unbroken-in cap? Anyone have an idea? Thanks in advance_

 

hmm, yeah check the soldering for cold joint or maybe a short somewhere


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## VncentValntine

Okay I re soldered everything I soldered originally, still no dice, I should also add that it noticeably lessens through time


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## d-cee

Quote:


  Originally Posted by *VncentValntine* /img/forum/go_quote.gif 
_Okay I re soldered everything I soldered originally, still no dice, I should also add that it noticeably lessens through time_

 

it could be bad caps

 try reversing the caps and see if it happens in the left channel


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## VncentValntine

well damn! I switched the caps and it's still on the right side! What could I do to narrow this down? What numbers should I be looking for? Is it possible the 100k resistor might have something to do with it?

 EDIT: Well I fixed it, the cold solder joint was from the 100k resistor to ground... thanks d-cee


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## VncentValntine

BZZZ! wrong, just happened to be coincidental. I realized bad grounding should cause a hum, not this. And this crackling came back after like 30 min of use...


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