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DAC-AH Passive Mod (newbie needs help)

post #1 of 18
1/14/09 at 2:22pm
Thread Starter 
Hey guys,

I'm a newbie to the DIY scene and would like to embark on performing the passive mod on my DAC-AH as my first ever mod.
I'm a tad confused regarding some aspects of the mod though, and was hoping someone with a little more experience could lend me some advice please?


Here are my concerns-

1. Is there an "optimum" value for the caps I use to bypass the output stage? I've read that 2.2uf and .47uf are both good, I'm not sure which is best.

2. Basically I solder one end of Cap A to the "hole near C12" (description from another thread here at Head-Fi) and the other end to the black RCA jack's signal tab.
Then I solder one end of CAP B to "hole near C13" and the other end to the red RCA jack's signal tab.
Does this sound correct?

3. Do I need to solder in any resistors for the mod to work?
If so, what value should they be and where should I solder them?


Thanks very much for any help you can offer me!
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post #2 of 18
1/15/09 at 4:01am
Thread Starter 
I know it's not the most difficult mod in the world, but I'm a newbie to electronics and soldering so I could really use a helping hand from one of the more experienced guys on the board... please?
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post #3 of 18
1/15/09 at 8:13pm
You pretty much have it right. I used 2.2uF Jupiter Caps which sound great. Kind of costly but I'm pleased with the sound. I haven't tried other caps or other values so I can't offer a comparison. There is no need to involve resistors for the passive out mod if you use 2.2uF. I'm not sure about the .47uF version.

There is another mod which corrects the I/V resistor value which is wrong on some versions of the DAC-AH. That involves swapping out R35 and R36 depending on which voltage regulators you have in your DAC-AH. There are three powering the digital portion of the circuit.

1 x 7805 and 2 x 7808 or 2 x 7806. Here are the values to use depending on the version you have.

7808 8V regulators = 270ohm resistors
7806 6V regulators = 150 - 160 ohm resistors

BTW - The passive out does sound really nice and is fairly easy to do.
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post #4 of 18
1/15/09 at 10:52pm
Another cool addition to the passive mod is adding a Hammond 193L choke. Found that one at DIYAudio...here's the link diyAudio Forums - 193L in a Modded DAC-AH.. - Page 1

Lots of great info in the thread about the passive mod as well.


Peete.
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post #5 of 18
1/16/09 at 1:12am
Thread Starter 
Cheers guys. I feel much more confident tackling the mod now.

I think I'll go with 2.2uF caps and see what it sounds like. I'd also like to increase voltage going to the DAC chips to 8V from 6V at some point but I'll need to heatsink them first.

Out of curiosity, has anyone tried replacing some of the resistors on the left-hand side of the board with higher-quality, tighter tolerance versions? In particular I was thinking about the 24 resistors that connect directly to the DAC chips.
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post #6 of 18
1/16/09 at 2:54pm
I haven't but I was thinking about that too. One thing I do recommend is changing the resistors at R35 and R36. I used Riken Ohm Carbon's instead of the cheapies that were there before. These are directly in the output so will affect your sound.
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post #7 of 18
3/26/10 at 8:29am
Quote:
Originally Posted by recca View Post
There is no need to involve resistors for the passive out mod if you use 2.2uF.
Is this true? I'm looking to mod mine to passive this evening, and don't want to damage any of my other equipment. This dac will be feeding (separately) a Cambridge 650A and a PPA V2 if the amp makes any difference.

--Matt
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post #8 of 18
3/26/10 at 9:11am
I'm using 2.2uF Mundorf Silver In Oil caps for the output without resistors and it works just fine. Mine is the 6V version. I haven't actually measured the output, but I've had it hooked up to a modified Jade amp and a Meier Corda HA-1 amp for long periods of time with no ill effects.

I did have another Lite that was the 8V version and always used caps ranging from 2.2uF to 3uF with no trouble at all.
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post #9 of 18
3/26/10 at 3:22pm
Quote:
Originally Posted by ecclesand View Post
I'm using 2.2uF Mundorf Silver In Oil caps for the output without resistors and it works just fine. Mine is the 6V version. I haven't actually measured the output, but I've had it hooked up to a modified Jade amp and a Meier Corda HA-1 amp for long periods of time with no ill effects.

I did have another Lite that was the 8V version and always used caps ranging from 2.2uF to 3uF with no trouble at all.
Great news! Thank you! I also have a 6v unit. I'm going to replace the 274ohm resistors at R35 and R36 with 150ohm parts at the same time that I do the passive mod, have you done that on yours as well? I'm going to be using 2.2uf Auricaps. They seem to have enough good reports on this DAC. I'm glad to hear that the resistors aren't needed on the output. I'd prefer to have as little as possible in the signal path.

--Matt
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post #10 of 18
3/26/10 at 3:56pm
Yep...I did the following to mine:

1. Replaced the resistors at R35 and R36 with 160 Ohm Vishays
2. Pulled all the components on the right side of the board (Mundorf SIO are huge).
3. Upgraded the film caps in C5, C6, C7, C8, C12, C13, C14, C15 to Vishay Polypropylene Films
4. Upgraded the electrolytic caps in C28, C37, C25, C26 with Nichicons.
5. Added heatsinks to the 8 TDA1543 chips...just to be safe.

For me, modding the Lite was fun and rewarding. I also tried the Auricaps but prefer the Mundorf SIOs. I even liked the Mundorf ZN series in this DAC over the Auricaps, but only your ears can tell you which is better. Good luck and have fun!
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post #11 of 18
3/26/10 at 11:33pm
Thanks for the help. I finished modding mine a couple of hours ago. I replaced the 274 ohm resistors at R35 and R36 with Takman 150 ohm .5w resistors. I also took a page out of your book and removed everything on the right side of the board. The 2.2uf Auricaps sound better than the stock output stage already, which is surprising since they reportedly take 100 hours to break in. I'm very happy with the results so far, and am sure I'll be happier with a bit of break-in.

I adjusted the trimmer to get the outputs back up to 3.3v after letting the box warm up for a while with the top on. They dropped down almost .3v when warm. Once I get used to the sound after everything breaks in, I'll probably work on upgrading the remaining caps and sinking the TDA1543s. The ones on the ends don't seem terribly hot at the moment, but the 4 in the center seem pretty warm.

Thanks again.

--Matt
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post #12 of 18
3/26/10 at 11:44pm
Good for you! Glad it went well.

If you're worried about heat, I fastened some run of the mill motherboard standoffs in the screw holes for the top of the case and then screwed the top of the case into the mobo standoffs. This gives you a 1/4 inch or better gap to allow the heat to escape. I've seen other folks drill holes into the side of the case. IMO, the standoffs do the same thing without drilling the case and is easily reversible.

Cheers!
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post #13 of 18
3/27/10 at 1:08am
Couldn't have done it properly without your help! I just finished listening to The Black Saint and the Sinner Lady and cannot believe how big of an improvement this made. Pianos, saxophones, and trumpets sound so much more lively and realistic. The lifelessness in the midrange frequencies that disappointed me so much is all gone! Clarity has definitely improved.

Bass seems a bit lean on my speaker amp, but sounds spot on with my headphone amp. It sounds very controlled on the speaker amp, but I'm hoping some bass will come back with run-in. If not, it sounds like I may need bigger caps. I have plenty of space with the original output out of there.

Would you recommend upgrading the electrolytics or films next? I can't thank you enough!

--Matt
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post #14 of 18
3/27/10 at 12:50pm
I would replace the 8 polyester film caps with polypropylene next. Digikey has them for a fairly reasonable price. They really helped with the bass...at least to my ears.

Digi-Key - BC2054-ND (Manufacturer - BFC2 416 41004)

Or you can search for some Wima caps in that size. I haven't heard them, but have read good things about them.
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post #15 of 18
3/27/10 at 1:39pm
Thanks. I think I'll do that. I can't find any Wimas with a 5mm pin spacing, but I found tighter tolerance vishays that I think I'll get at: Vishay R. Film Caps

--Matt
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