Circuit error in Lite DAC-AH: Easy fix

[nichifanlema]

so...this applies for the original Lite DAC-AH?

or also for the Pacific Valve Modded DAC-AH M?

How about DAC-AH HA! ?

 

[pomdomz]

Quote:

Originally Posted by nichifanlema so...this applies for the original Lite DAC-AH? or also for the Pacific Valve Modded DAC-AH M? How about DAC-AH HA! ?

not all dac-ah are affected, the ones purchased years ago originally had 8V regulators.

just check with whoever you're buying the dac from, and ask them if the dac-ah is running 8V or 6V to the chips.

i recently bought one from coem audio and they actually have 3 versions of the dac-ah. 6v version with the resistors changed, 8v regulator version with heatsinks on the little dac chips and a passive output version.

if anyone is curious, i bought the 8v version with the phase corrected.

 

[Kim Hardee]

Quote:

Originally Posted by eladioc ok so i'm staring at the PCB of my DAC-AH. I see the resistors over R35 and R36. So what I should do is solder 330 ohm resistors to the existing resistors on R35 and R36? What is a good way to go about this? Any help with technique? So my final product will have two resistors (270 and 330) pretty much stacked on top of each other... yes? I'm a total newbie at this... so uh... thanks guys.

eladioc,
Yes, that's right. You will end up with the 330 ohm resistors on top of R35 and R36. Basically just cut the leads of the 330 ohm resistors to about 1/2" to 3/4" and bend the leads to match the size of R35 and R36. Solder a little bit of solder to the ends of the leads. Then hold the new resistors above and a little to the side of R35 or R36 and solder one lead to one side of R35 or R36. Then do the other lead. Do the same for the other resistor. The key is to keep the leads of the 330 ohm resistors long enough to give you room to do the job. This is not really the correct way to solder, but it works and doesn't require removing the board. Then don't forget to adjust the trimpot.

By the way, I've just completed an extensive mod of my DAC-AH including the following:

1. Swapped the LM7806 regulators for LM7808 to provide 8V to the DACs
2. Changed C25 and C26 from 4700uf/16V to Panasonic TC 4700uf/25V for reliability
3. Changed C27 and C28 from 220uf/16V to Blackgate 1000uf/16V.
4. Changed the bridge rectifier BR2 to IXYS fast/soft recovery bridge rectifier
5. Changed R35 and R36 to 221 ohm Vishay resistors
6. Bypassed opamps with 2.2uf Auricaps
7. Added heatsinks to the new bridge rectifier and the DACs
8. Moved the transformer to the side and further away from the board
9. Drilled a few holes in the bottom and rear panel of the case for ventilation

I haven't burned it in much yet, but so far the results are interesting. Overall I'd say that the sound is more detailed with a slightly leaner balance. It's a more refined sound. I'm not sure that I prefer it over the stock sound (actually with corrected resistors and bipolar output caps). I remember the original sound as being more "musical" with maybe more impact and lowend punch but less detail.

Now I plan to add an additional pair of output jacks connected to the opamp outputs so I can have it both ways as suggested by others. It's tempting to instead add an output switch to switch between the opamp and bypassed output, but that's generally not a good idea due to sonic degradation and the risk of damaging noise while switching. After I complete this I'll post the results.

I must say that either way I am just blown away by the sound of this DAC. Nothing has given me as much of that "Wow" factor in my years of playing with this stuff other than my World Audio Design HD83 headphone amp. In fact I just ordered another one to experiment with.

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee eladioc, Yes, that's right. You will end up with the 330 ohm resistors on top of R35 and R36. Basically just cut the leads of the 330 ohm resistors to about 1/2" to 3/4" and bend the leads to match the size of R35 and R36. Solder a little bit of solder to the ends of the leads. Then hold the new resistors above and a little to the side of R35 or R36 and solder one lead to one side of R35 or R36. Then do the other lead. Do the same for the other resistor. The key is to keep the leads of the 330 ohm resistors long enough to give you room to do the job. This is not really the correct way to solder, but it works and doesn't require removing the board. Then don't forget to adjust the trimpot. By the way, I've just completed an extensive mod of my DAC-AH including the following: 1. Swapped the LM7806 regulators for LM7808 to provide 8V to the DACs 2. Changed C25 and C26 from 4700uf/16V to Panasonic TC 4700uf/25V for reliability 3. Changed C27 and C28 from 220uf/16V to Blackgate 1000uf/16V. 4. Changed the bridge rectifier BR2 to IXYS fast/soft recovery bridge rectifier 5. Changed R35 and R36 to 221 ohm Vishay resistors 6. Bypassed opamps with 2.2uf Auricaps 7. Added heatsinks to the new bridge rectifier and the DACs 8. Moved the transformer to the side and further away from the board 9. Drilled a few holes in the bottom and rear panel of the case for ventilation I haven't burned it in much yet, but so far the results are interesting. Overall I'd say that the sound is more detailed with a slightly leaner balance. It's a more refined sound. I'm not sure that I prefer it over the stock sound (actually with corrected resistors and bipolar output caps). I remember the original sound as being more "musical" with maybe more impact and lowend punch but less detail. Now I plan to add an additional pair of output jacks connected to the opamp outputs so I can have it both ways as suggested by others. It's tempting to instead add an output switch to switch between the opamp and bypassed output, but that's generally not a good idea due to sonic degradation and the risk of damaging noise while switching. After I complete this I'll post the results. I must say that either way I am just blown away by the sound of this DAC. Nothing has given me as much of that "Wow" factor in my years of playing with this stuff other than my World Audio Design HD83 headphone amp. In fact I just ordered another one to experiment with.

Damn Kim you beat me to it.
BTW, why did you not replace C37 ? And how in the hell did you fit a 16mm width cap in that spot without hitting the LM7808 and C25, C26?!?!

 

[Kim Hardee]

Good questions.
I was wrong in my post. I replaced C37, not C27.
It was very tricky placing this capacitors. I ended up placing them between the heatsink for one of the LM7808s and the DACs. They're placed vertically with the ground leads soldered together and then to the ground point that either C28 or C37 used to occupy. Then the positive leads were soldered to convenient unused solder points on the board, one next to the same heatsink and one near the DACs. I slid insulation over the leads before doing this. It's a pretty tight fit between the LM7808 heatsink and the DAC heatsinks, but the capacitors are not touching the heatsinks. It's best to do this before adding the heatsinks to the DACs.

By the way, I ended up using the Microcool PLL heatsinks after sawing off one row of fins. They fit perfectly. I'll try to post a photo soon once I figure out how to do it.

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee Good questions. I was wrong in my post. I replaced C37, not C27. It was very tricky placing this capacitors. I ended up placing them between the heatsink for one of the LM7808s and the DACs. They're placed vertically with the ground leads soldered together and then to the ground point that either C28 or C37 used to occupy. Then the positive leads were soldered to convenient unused solder points on the board, one next to the same heatsink and one near the DACs. I slid insulation over the leads before doing this. It's a pretty tight fit between the LM7808 heatsink and the DAC heatsinks, but the capacitors are not touching the heatsinks. It's best to do this before adding the heatsinks to the DACs. By the way, I ended up using the Microcool PLL heatsinks after sawing off one row of fins. They fit perfectly. I'll try to post a photo soon once I figure out how to do it.

I read that 4 times over and i still cannot picture it in my head. You HAVE to take a picture of this. You also made me change my mind about the heatsinks and ended up ordering the micro sinks instead of the PLL's, and you actually bought the PLL's HAHAHA.

Also, why did you decided to go with a 2.2uF auricap ?

 

[Kim Hardee]

Quote:

Originally Posted by pelayostyle I read that 4 times over and i still cannot picture it in my head. You HAVE to take a picture of this. You also made me change my mind about the heatsinks and ended up ordering the micro sinks instead of the PLL's, and you actually bought the PLL's HAHAHA. Also, why did you decided to go with a 2.2uF auricap ?

Sorry. I'll definitely try to post a photo soon. It may still be a little confusing because the capacitor leads will be difficult to see since they're under the caps.

I actually ordered the microsinks too and one of the PLL heatsinks for the new bridge rectifier. Then I realized that the PLL heatsink would work great for the DACs if I just sawed off one row of the fins with a hacksaw, so I ordered a set of the PLLs and modified them. I thought you originally were going with the MOSFET heatsinks. I think they would have required a lot of filing to make them fit. What I like about the modified PLLs is that they fit nicely over each DAC so if you later need to replace a single DAC it's still possible. The microsinks may be OK, but the modified PLLs will dissipate much more heat. Mine get quite hot, which is good. That means they're working. I don't know if you need to drill ventilation holes in the case or not. I just went ahead and did it.

I have noticed that even with the heatsinks the DC ouput voltages of the DACs drift significantly lower as things heat up. I ended up powering up the unit with the top panel just resting on top of the case, waiting about 20 minutes, and then taking off the top panel and quickly measuring the DAC output voltages and adjusting the trimpot accordingly.

Good luck.

 

[Kim Hardee]

Quote:

Originally Posted by pelayostyle I read that 4 times over and i still cannot picture it in my head. You HAVE to take a picture of this. You also made me change my mind about the heatsinks and ended up ordering the micro sinks instead of the PLL's, and you actually bought the PLL's HAHAHA. Also, why did you decided to go with a 2.2uF auricap ?

I decided to go with the Auricaps because I've had good luck with them before and there are a few positive posts about using them in the DAC-AH. The 2.2uf version is a nice size and should be enough capacitance to drive any reasonable load. Besides they are resonably priced. I originally decided to use 4.7uf, but they are a little large and not really necessary.

 

[izquierdaste]

It is interesting that you think that you prefer the sound with opamps. I just switched out my resistors for 150 ohm NOS Dale wirewound resistors (thanks for the tip by the way) and decided to try the passive output mod at the same time (using the same 12uf acushnet paper in oil caps that I was using with the opamps). I also think I prefer the sound with the opamps. I am debating whether to add a second set of rca plugs, because my space is already getting pretty crowded and a second set of the acushnets would barely fit.

Which opamps are you using? I have the opa627s in mine.

I find that the this DAC is fantastic with music that focus on vocals and acoustic instruments, but maybe not as great (still pretty good) with rock and other types of music. You'll have to know your burns in. I still have components burning in on mine too.

Quote:

Originally Posted by Kim Hardee eladioc, Yes, that's right. You will end up with the 330 ohm resistors on top of R35 and R36. Basically just cut the leads of the 330 ohm resistors to about 1/2" to 3/4" and bend the leads to match the size of R35 and R36. Solder a little bit of solder to the ends of the leads. Then hold the new resistors above and a little to the side of R35 or R36 and solder one lead to one side of R35 or R36. Then do the other lead. Do the same for the other resistor. The key is to keep the leads of the 330 ohm resistors long enough to give you room to do the job. This is not really the correct way to solder, but it works and doesn't require removing the board. Then don't forget to adjust the trimpot. By the way, I've just completed an extensive mod of my DAC-AH including the following: 1. Swapped the LM7806 regulators for LM7808 to provide 8V to the DACs 2. Changed C25 and C26 from 4700uf/16V to Panasonic TC 4700uf/25V for reliability 3. Changed C27 and C28 from 220uf/16V to Blackgate 1000uf/16V. 4. Changed the bridge rectifier BR2 to IXYS fast/soft recovery bridge rectifier 5. Changed R35 and R36 to 221 ohm Vishay resistors 6. Bypassed opamps with 2.2uf Auricaps 7. Added heatsinks to the new bridge rectifier and the DACs 8. Moved the transformer to the side and further away from the board 9. Drilled a few holes in the bottom and rear panel of the case for ventilation I haven't burned it in much yet, but so far the results are interesting. Overall I'd say that the sound is more detailed with a slightly leaner balance. It's a more refined sound. I'm not sure that I prefer it over the stock sound (actually with corrected resistors and bipolar output caps). I remember the original sound as being more "musical" with maybe more impact and lowend punch but less detail. Now I plan to add an additional pair of output jacks connected to the opamp outputs so I can have it both ways as suggested by others. It's tempting to instead add an output switch to switch between the opamp and bypassed output, but that's generally not a good idea due to sonic degradation and the risk of damaging noise while switching. After I complete this I'll post the results. I must say that either way I am just blown away by the sound of this DAC. Nothing has given me as much of that "Wow" factor in my years of playing with this stuff other than my World Audio Design HD83 headphone amp. In fact I just ordered another one to experiment with.

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee I thought you originally were going with the MOSFET heatsinks. I think they would have required a lot of filing to make them fit. Good luck.

Im sorry, youre right. I was going to use the MOSFET sinks but they are basically the same as the PLL sinks are only 12mm square instead of the PLLs 15mm length x 12mm width.

After you mentioned that there is a voltage drift with the PLL sinks im thinking of making a custom heatsink for the DAC chips from an old amd athlon cpu. This should help keep things stable.

Anyone want to buy some micro sinks ?

 

[Kim Hardee]

Quote:

Originally Posted by izquierdaste It is interesting that you think that you prefer the sound with opamps. I just switched out my resistors for 150 ohm NOS Dale wirewound resistors (thanks for the tip by the way) and decided to try the passive output mod at the same time (using the same 12uf acushnet paper in oil caps that I was using with the opamps). I also think I prefer the sound with the opamps. I am debating whether to add a second set of rca plugs, because my space is already getting pretty crowded and a second set of the acushnets would barely fit. Which opamps are you using? I have the opa627s in mine. I find that the this DAC is fantastic with music that focus on vocals and acoustic instruments, but maybe not as great (still pretty good) with rock and other types of music. You'll have to know your burns in. I still have components burning in on mine too.

I'm using opa627s also.

 

[regal]

I also agree the OPA627's sound better than the passive mod after upgrading the output caps to p-i-o.

 

[Kim Hardee]

Quote:

Originally Posted by pelayostyle I read that 4 times over and i still cannot picture it in my head. You HAVE to take a picture of this.

I now have photos of my mods, but I can't seem to be able to post them. I downsized them to JPEG files that are smaller than the 25K limit, but this site still won't recognize them when I try to post them. The 25K limit is really severe, resulting in poor image quality. Can anyone give me some advice on this?

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee I now have photos of my mods, but I can't seem to be able to post them. I downsized them to JPEG files that are smaller than the 25K limit, but this site still won't recognize them when I try to post them. The 25K limit is really severe, resulting in poor image quality. Can anyone give me some advice on this?

Kim , email me the original pics and ill post them for you. You have a PM

 

[regal]

I'm confused I thought we were to add a 470ohm resistor on R35/36 but you used a 330ohm?