Circuit error in Lite DAC-AH: Easy fix

[pelayostyle]

Thanks for all your help Kim.
Btw, did you ever do those mods to your dac ?

 

[Kim Hardee]

I'm still waiting for the parts to arrive. I'll probably get around to the mods this weekend. Should be pretty easy. I'll post the results. I'll already really happy with this DAC since I fixed the clipping problem. If the new mods improve it even more I'll be a happy camper.

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee I'm still waiting for the parts to arrive. I'll probably get around to the mods this weekend. Should be pretty easy. I'll post the results.

Please post pics of the finished work

 

[revo_909]

i changed mine to LM7808, surely they run hot. i tried both 3.85 and 4.3, and i prefer the former, a lot smoother sound overall. this is probably the cheapest and most efficient mod to this dac so far.

definately those harshness in complex music passages is gone, but now the DAC chips are too hot to touch, not to mention the LM 7808 regulators. i hope they're fine in the long run.

hopefully when my parts arrive for passive mods, things will get even better

 

[Kim Hardee]

I am reconsidering running the DACs at 8V. I'm concerned about heat in a closed box. One advantage of 8V, however, is increased output voltage. With an 8V supply the maximum output signal with a passive bypass is about 1.8V RMS with 270 ohm I/V resistors. With a 6V supply the maximum output voltage is about 1V with 150 ohm I/V resistors. That's about 2.5db less output voltage compared to an 8V supply and about 3db less than a standard 2V RMS line level output spec. That means that with a 6V supply and passive bypass I will have to turn up the volume control on my preamp or headphone a little, but that's no big deal.

I'm not sure it's worth the risk of the extra heat to go to 8V unless the DACs sound better at 8V and not just because 8V is the correct voltage for the 270 ohm resistors. Maybe 6V with 150 ohm resistors will sound just as good (but with less output voltage) as 8V with 270 ohm resistors. Has anyone tried both? I found that when I changed from 270 ohms to 171 ohms (with 6V supply) the sound improved dramatically.

Anyway, I'm thinking that if I end up going to 8V I will definitely put a heatsink on each DAC and probably provide ventilation somehow to the enclosure. These DACs can supposedly handle 8V, but they also have a maximum temperature spec that must not be exceeded. Maybe that's why the manufacturer of the DAC-AH chose to reduce the DAC supply to 6V. Unfortunately, they didn't change the I/V resistors accordingly.

 

[Kim Hardee]

That's interesting that 3.85V sounds better than 4.3V. If you do the math, setting the outputs to 3.85V DC should result in clipping during maximum output. The lowest output voltage for this case would be 1.36V while the spec is a minimum of 1.8V. I assume that the reason that the clipping can't be heard is that a maximum sound level (all 1"s to the DACs) is rarely seen in recordings or that there is some margin to the 1.8V spec. Interesting. I'd go with whatever sounds best, but of course try listening to the loudest (on the recording) sections of music before deciding.

 

[pelayostyle]

I just purchased some of these for the DAC chips
http://www.sidewindercomputers.com/mimoch.html

I also bought the LM7808 voltage regs. and some caddok MK132 270R resistors for the I/V.

Edit , i couldnt help it and just bought some Mundrof Mcap supreme silver and oil 4.7uF caps and vishay vta-55 100R to do the passive mod. This thread cost me about $150 ..... i hate you guys =/

 

[Kim Hardee]

Those heatsinks look really good, but they may be a little too big. I think you'll find that 12mm is too long for each DAC and you'll have to file off about 1mm to make them fit. Also, the end DACs are going to be a problem. One of them has the power transformer partially over it and the other one is under the digital input switch and the left channel output jack. More filing will be required. The Microcool Microsink heatsink on the same website (8.5mm) would fit much better, but it would not draw heat away from the DACs as well. Maybe it's good enough though. I will try to make custom heatsinks by cutting sections out of a computer processor heatsink with a scroll saw. If this doesn't work I'll probably get the Micosinks.

I suggest moving the power transformer away from the PC board as I have done. I didn't like how it was pushed up against a bridge rectifier (that got pretty hot) and the capacitor next to the end DAC. Mine is now positioned to the left side (looking from the front) and slightly forward, next to the power switch. To do this I had to invert the power switch so the connections are now on top and re-solder the 2 wires from the transformer to the switch. Then I drilled 4 new holes in the bottom plate and slid the transformer over. This only provides a little space between the transformer and the board, but I think it's worth it. I also have more room now for a heatsink on the end DAC. I would post a photo but my DAC-AH is disassembled at the moment for more mods.

These mods can be a blackhole. Think twice before you enter.

 

[revo_909]

i just had a quick look at the schematic on this DAC and apparently the reservoir caps for the power supply section are 2200Uf 25V, while DAC-AH uses 5600uf 16V capacitor. i'm thinking of replacing them with 4700uf 35V nichicon muse, will they be sufficient?

 

[pelayostyle]

Quote:

Originally Posted by Kim Hardee I suggest moving the power transformer away from the PC board as I have done. I didn't like how it was pushed up against a bridge rectifier (that got pretty hot) and the capacitor next to the end DAC. Mine is now positioned to the left side (looking from the front) and slightly forward, next to the power switch.

Its funny that you posted this because i was actually planning on doing the same thing. Ill be moving the transformer to the left front as far as it can go without hitting the sides. Ill have to make the wires from the transformer to the IEC socket a little longer to accomodate for this move.
Regarding the heatsinks i posted, I noticed that its the LEFT rca socket thats going to hit the heatsink and not the digital selector switch so much, so im drillling another hole on the other side of the RIGHT ouput. Then ill put the LEFT where the RIGHT is now and the RIGHT to the new hole. I also ordered some SF4007 diodes just a while ago to make some custom bridge rectifiers. This thing is going to be so awesome when im done. Ill post pics of all the modding goodness.

 

[Superpredator]

Quote:

Originally Posted by Kim Hardee I strongly recommend that other owners of the DAC-AH consider this change, which is very easy, or to replace the LM7806 voltage regulators with LM7808s and run the TDA1543s at 8V. Then the 270 ohm resistors will be fine. The full change is to solder a 470 ohm resistor across R35 and a 470 resistor across R36. Then adjust the VREF trimpot until the outputs of the TDA1543s are at about 3.3V. That's it. If you decide to change the LM7806s to LM7808s, then don't add the 470 ohm resistors and adjust the outputs to about 4.3V.

I have no idea how to accomplish either of these fixes, and am saddened at the thought that my AH is flawed.

 

[pelayostyle]

Quote:

Originally Posted by Superpredator I have no idea how to accomplish either of these fixes, and am saddened at the thought that my AH is flawed.

Ill be doing the mods hopefully next week as the parts come in and ill take pics of EVERY step as i go along. Ill post the step by steps in this thread with the pics. It should help you fix your dac hopefully.

 

[Superpredator]

Quote:

Originally Posted by pelayostyle Ill be doing the mods hopefully next week as the parts come in and ill take pics of EVERY step as i go along. Ill post the step by steps in this thread with the pics. It should help you fix your dac hopefully.

That would be spooktacular. I'm not sure how to go about testing voltage, and I don't have a soldering iron, but I'm willing to follow an idiot-proof guide. You are (or will be) my savior.

 

[regal]

This would be very helpful. This DAC has a lot of potential, especially cleaning up the mistakes the Chinese made.

 

[Superpredator]

Quote:

Originally Posted by regal This would be very helpful. This DAC has a lot of potential, especially cleaning up the mistakes the Chinese made.

What exactly does this statement mean? Are you talking about other Chinese-made DACs?