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Old 21st January 2011, 03:58 AM   #11
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Quote:
Originally Posted by Karstenpg View Post
....

Learned from one post, that AOR/L ac voltage compliance is only within +- 25 mV as per TDA1543 data sheet. Had overread this. Therefore, original circuit 274 ohms and even my 150 ohms resistor I/V is far out of specs.

...
I confirmed this yesterday as I replaced R35 and R36 with 150 ohm resistors. The DAC sound became dead, like a good cassette player. No life. This is after trying the bias voltage at anywhere from 2.0 to 5.0 volts. Even the recommended 3.3 volts setting did not work. So back went in the 274 ohm stock resistors. Of course, the distortion is back too on very loud and complicated passages.

So, has anyone figured the correct ohm resistor? 230 ohm maybe?

I am not willing to go with the LM7808 regulators.

I did have a chance to tap in for the passive output using 2.2 uF caps.

Any suggestions for snap in Op Amps? I don't want to change the case types as some do.

Would not recommend this DAC to non-DIY people.
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Old 23rd January 2011, 03:41 AM   #12
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I will answer my own question since I found out by "resistor rolling" that 240 ohm resistors to replace the stock 274 ohm R35 and R36 provide the best balance on this DAC before you start to cut its legs off and also eliminate peak saturation and distortion on loud and complex recordings.

At least to my ears, the DAC now lives up to its reputation written about in all the threads. Up next is the passive mod and hear I am in for a treat.

So, to summarize 240 ohm resistors for R35 and R36 and about 3.0 - 3.3 V bias voltage.

The pictures show the now removed 150 ohm resistors. Also notice the CAT6 wire tap-ins for the passive mod that will be done next.
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Last edited by whaleman; 23rd January 2011 at 03:48 AM.
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Old 23rd January 2011, 07:35 PM   #13
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Default use active I/V Converter

whaleman, you might want to try my circuit. I am using two such modified DACs for over a year now. They sound good.
If I ever do another one, I will use a 6:1 transformer from the same manufacturer, only for the lower winding capacitance. I doubt though, that there will be any audible difference.
See the updated schematic (attached) for reference.

-Karsten-
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Old 31st January 2011, 02:59 AM   #14
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Quote:
Originally Posted by Karstenpg View Post
whaleman, you might want to try my circuit. I am using two such modified DACs for over a year now. They sound good.
If I ever do another one, I will use a 6:1 transformer from the same manufacturer, only for the lower winding capacitance. I doubt though, that there will be any audible difference.
See the updated schematic (attached) for reference.

-Karsten-
Thanks Karstenpg, I may try this with a second DAC AH. For now I've added the passive mod using Jantzen 2.7 uF capacitors and an additional pair of RCA jacks.

The sound is very nice, the bass is very tight and the highs cleaned up nicely. This DAC has a lot of potential, so I will probably do another and consider your mod.

The caps can be inserted from the top and soldered from there. A little heat rash to nearby components is almost inevitable.
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Old 17th April 2011, 02:55 AM   #15
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I had a hum in the right channel at loud volume, so I removed the passive mod, I thought it was picking something up and I really was not using it. Hum still there. Replaced caps with good quality and higher capacitance. Hum still there.

Then looking at the DAC, I notice the transformer next to the right channel DAC and components, presto! I removed it and placed it as far away as I could from the components on the board. Now, hum 80% gone. The rest is impossible to remove unless the transformer is moved outside the box. I know some have found this out already, but it is cool when you figure it out for yourself. Notice the before and after photos.

As a side benefit, now there is some ventilation for the once sealed case.
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Old 17th April 2011, 05:48 AM   #16
Cola is offline Cola  Singapore
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How about doing a grounded copper enclosure to shield your transformer. It may do some good
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Old 17th April 2011, 06:21 PM   #17
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@ Cola: copper shielding will have close to no effect against magnetic stray fields.

@ whaleman: EACH DAC chip contributes equally to BOTH audio channels (see circuit diagram).
The stray field of this type of transformer is far too small to induce audible hum current through the I/V resistors. Therefore, it is unlikely that moving the transformer alone did really reduce the hum. On one channel only?? Is it possible that you changed the overall setup / wiring in your installation somehow when you reinstalled the DAC-AH after moving the transformer?
I would suspect some kind of ground loop as the real cause instead. Try using the optical SPDIF input (ignore any tales about the negative influence of optical SPDIF on audio fidelity. You won't hear the difference).
If you cannot use optical coupling, modify the coaxial SPDIF input, as this input is not isolated:
** Remove the RCA connector from the DAC pcb.
** Mount an isolated RCA jack in the now free hole on the rear panel instead.
** make a 1:1 pulse transformer by winding 2 x 6 turns of suitably thin enameled wire on an Amidon BN 73-2402 binocular core (available from Mouser) or salvage the pulse transformer from a scrapped Ethernet PC interface (the old kind with a BNC connector). I am using the homebrew transformer.
I have not tried the Ethernet transformer but I have read somewhere that it works as well.
** Glue the pulse transformer to the DAC pcb in place of the removed RCA connector. 2 component epoxy will make a secure joint. Solder the wires: primary start to RCA inner connector, primary end to RCA outer connctor, secondary start to former SPDIF input, secondary end to digital ground.

Also, make sure that the power cord protective ground is connected to the power transformer shield winding (shield between primary and secondaries) only and has no connection to the DAC PCB.

This will prevent any ground loop between DAC and connected equipment and should solve your problem.
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Old 18th April 2011, 01:09 PM   #18
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Thanks Karstenpg for your detailed reply.

Moving the transformer is exactly what took away the hum since I did it in steps and that was the only thing that changed for that trial. The wiring followed the transformer along with the ground chassis wires. You can see the wiring in the before and after photos.

It has been my experience that with line level stuff like this, you can expect hum when getting a signal wire even less distant than the resistors were to the transformer, so I am not surprised if they were the "antenna" responsible for contributing the hum noise.

Currently, the only way you can hear faint hum is with the volume all the way up beyond 4 PM, where I never go past 11 AM on this amp, so for all practical purpose, this problem is solved.

This will be of benefit to future Lite DAC AH owners. Thanks for your tips, certainly of benefit.
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Last edited by whaleman; 18th April 2011 at 01:13 PM.
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Old 6th May 2011, 04:53 PM   #19
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Default Adding USB to the Lite DAC AH

How can I add a USB connector (to accept cable pictured) into this DAC? Do I need a separate receiver? or will the CS8414 handle the new input?

This is so I can hook up directly to a laptop USB out direct digital (bypassing the laptop sound card).

Thanks.
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Old 6th May 2011, 05:46 PM   #20
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Default USB interface for DAC-AH

You will need a separate little converter box USB to SPDIF. Various kinds are offered on ebay.
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