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Circuit error in Lite DAC-AH: Easy fix - Page 5

post #61 of 210
Quote:
Originally Posted by regal
I'm confused I thought we were to add a 470ohm resistor on R35/36 but you used a 330ohm?
I think Kim used a 330R resistor to have more room to play with the trimpot.
post #62 of 210
Here are the pics of Kims modifications.....




post #63 of 210
Thread Starter 
Well, I've made a few more changes. I removed the 1000uf Blackgate caps that were between the DAC heatsinks and the LM7808 heatsink because they were getting too hot and replaced them with 220uf/16V Panasonic FC caps (C28,C37) near their original locations. I haven't noticed any more noise or reduced bass. I also added another pair of RCA jacks connected to the opamp outputs through bipolar Elna caps (included in the socketed opamp option from diykits). I added 680 ohm resistors in parallel with the 390 ohm opamp feedback resistors to lower the buffer stage gain to 1.48 from the original 1.76. This results in 2V RMS max output voltage from the opamps. I'm also using opa627 opamps. Finally, I twisted the wires going from the transformer to the board and moved them out from under the board. This totally eliminated the slight 60Hz hum I had at max volume.

Now I can directly compare the sound of the passive output and the buffered output. I was wrong in my earlier assessment. The passive output sounds much more transparent and "real" to me. It's sounds like the singer and musicians are performing right in front of me. Amazing! I definitely prefer the passive bypass to the opamp outputs.

I've tried increasing the 2.2uf Auricaps to 6.9uf (2.2uf and 4.7uf in parallel) and didn't hear much difference. I must admit that I haven't yet given the buffered output a fair chance yet since it still uses an electrolytic cap in the output. I may try installing an Auricap in the opamp output just to try it, but I'm so happy with the sound with the passive bypass that I'm not very motivated to do that. By the way, I'm listening through a World Audio Design HD83 tube headphone amp and HD600s.

I do plan to add more ventilation to the top panel since there's is still a lot of heat generated.

Anyway, I highly recommend trying the passive bypass. You don't necessarily have to do the 6V-to-8V mod. Changing to 8V does result in more heat and the necessity of DAC heatsinks and case ventilation. If you stay with 6V and change RLoad to 150 ohms, then the max RMS output will be about 0.9V. That's about 3db less than the standard line out spec of 2V. If you switch to 8V and change RLoad to 220 ohms, then the max RMS output will be 1.35V. On my second DAC-AH I'm thinking of staying at 6V and living with the slightly reduced output voltage.

If you don't want to get into extensive mods like this, then I strongly recommend at least correcting the resistor error and adjusting the trimpot. That alone will give you significantly better sound.

I hope this info is useful to you DAC-AH owners or those of you considering purchasing a DAC-AH.
post #64 of 210
Quote:
Originally Posted by Kim Hardee

I've tried increasing the 2.2uf Auricaps to 6.9uf (2.2uf and 4.7uf in parallel) and didn't hear much difference. I must admit that I haven't yet given the buffered output a fair chance yet since it still uses an electrolytic cap in the output. I may try installing an Auricap in the opamp output just to try it, but I'm so happy with the sound with the passive bypass that I'm not very motivated to do that. By the way, I'm listening through a World Audio Design HD83 tube headphone amp and HD600s.

Thanks for the update Kim! I am thinking of trying out the auricaps. Can you tell us a good place to buy them?

Thanks
post #65 of 210
Thread Starter 
I bought my 2.2uF/200V Auricaps at www.partsconnexion.com for $12 each plus shipping. They're not cheap, but a lot less than the PIO caps, and I think they sound great. The 2.2uF caps also fit perfectly in the DAC-AH.

Good luck.
post #66 of 210
Thanks for the heads-up. I lucked out and found 2x 3.3uf auricaps on ebay for $22 shipped. If you ever want to check out the pio caps, I would recommend scoping out ebay. I bought mine from a similar auction as:

http://cgi.ebay.com/4-ACU-CAP-GLASS-...QQcmdZViewItem
post #67 of 210
You can get paper in oil 5u caps from Surplus Sales of Nebraska for $7 each:
Sprague 500P9042F6
post #68 of 210
Thread Starter 
Quote:
Originally Posted by izquierdaste
Thanks for the heads-up. I lucked out and found 2x 3.3uf auricaps on ebay for $22 shipped. If you ever want to check out the pio caps, I would recommend scoping out ebay. I bought mine from a similar auction as:

http://cgi.ebay.com/4-ACU-CAP-GLASS-...QQcmdZViewItem

Thanks for the tip. I'd be interested in hearing how the Auricaps compare to PIO caps in sound quality.
post #69 of 210
Thanks Kim! I finally got around to making the resistance/voltage change last night. The DAC sounds great now. I am very pleased.
post #70 of 210
So im working on my dac right now and was thinking of pretty much removing every resistor, capacitor and regulator on the right side of the board (looking from the front) in order to make room for my HUGE mundorf caps to lay there. I wont go back from running passively btw. Will there be any complications from running the transformer without a load on the 18v side ?

Also, i was looking at the specs for the R26-99 R-type transformer and noticed that the 10.5v rail states 2.5A ( R26-99 primary 115 X2 :18-0-18(0.2A)、0-9.5(0.7A)、0-10.5(2.5A) ). Im making a bridge rectifier out of some Vishay SF4007 1A 1000V diodes. Will this be a problem ?
post #71 of 210
Thread Starter 
Quote:
Originally Posted by pelayostyle
So im working on my dac right now and was thinking of pretty much removing every resistor, capacitor and regulator on the right side of the board (looking from the front) in order to make room for my HUGE mundorf caps to lay there. I wont go back from running passively btw. Will there be any complications from running the transformer without a load on the 18v side ?

Also, i was looking at the specs for the R26-99 R-type transformer and noticed that the 10.5v rail states 2.5A ( R26-99 primary 115 X2 :18-0-18(0.2A)、0-9.5(0.7A)、0-10.5(2.5A) ). Im making a bridge rectifier out of some Vishay SF4007 1A 1000V diodes. Will this be a problem ?
Should be no problem with no load on the 18V side of the transformer. The 1A diodes should also be OK. The DACs should be drawing about 0.5A total. I'd love to see pics when you're done.
post #72 of 210
Heres a teaser pic for you guys. So far i have replaced C25 and C26 with 8200uF 16v Panasonic FC. C28 and C37 with 680uF 16v Panasonic FM. Replaced the 7806's with 7808's . C5,6,7,8,12,13,14,15 replaced with .1uf 63v Polypropylene Film caps. Then added heatsinks on the dac chips. Oh yeah , i also took some stuff off the board
More to come........
post #73 of 210
Thread Starter 
Your mods so far look really good! I can see how you'll have lots of room for the caps for your passive bypass on the right side of the board. I do question the use of a 16V cap for C26, though. I measured just over 16V on that cap. It will probably be OK, but a 25V cap and lower capacitance may be better. C26 is a 25V cap in the schematic.

By the way, I just put 2.2uf Auricaps in the opamp output paths to see if the difference in sound between the passive and buffered outputs was due to the output capacitors. Nope. The passive output still sounds noticably more transparent. I think this mod is a perfect match for HD600s or HD650s. I don't know about Grados. It may be too detailed for them.
post #74 of 210
Quote:
Originally Posted by Kim Hardee
I do question the use of a 16V cap for C26, though. I measured just over 16V on that cap. It will probably be OK, but a 25V cap and lower capacitance may be better. C26 is a 25V cap in the schematic.
My dac-ah actually arrived with 2 4700uF 16v caps in the c25 and 26 position so i assumed that the panasonics in 16v would work too.

Im pretty much done already but did have a hard time with r35 and 36. I had to place them under the board and folded out of the way. It was way to hard to get them to fit with c8 in the way. Ill post the pics later so you can see what i mean. Oh and btw, 1 of my mundrof caps takes up almost all the space that was cleared up . I used a mound of hot glue to keep it in place. The other cap runs parallel, below the other one, again on a mound of hot glue from the case.
post #75 of 210
Thread Starter 
I just completed a comparison of several older oil-type capacitors to the Auricaps and the difference is striking. I tried these in both the passive bypass and the opamp output.

The oil caps were in the 2uf to 8uf range, and the brands were Sprague (Vitamin Q), Motorola, and General Instrument. All of the oil caps sounded very similar and quite good. Compared to the Auricaps, however, the oil caps sounding veiled, with noticably less detail. The bass sounded about the same to me, but the midrange vocals, in particular, sounded much more real with the Auricaps. Again, with different headphones or speakers maybe the oil caps would sound better. Also, maybe the newer oil-type caps sound better than the older ones.

I haven't given up yet, and there are plenty of good caps out there, but so far I haven't found anything better than the Auricaps, IMHO. I may have to buy a pair of Mundorfs just to satisfy my curiosity.
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