6,8
@tedsmith
I had some analog boards come in here that had high DC offset feeding the transformer primaries.
One even had 12mv. most others had at least one channel at 3mv. Would you think the R5 and R6 would be the culprit?
Ignoring secondary effects, the outputs of the video opamps should symmetric around the Vocm output level. The datasheet says the output balance error should be approx -70dB which is about 3mV. Is that what you are seeing? Then statistically they should average over the four opamps in parallel, but they might add in unfortunate circumstances.
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Thanks. Iāll give an update when I get the DS back.
-Alan
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I should have also said that hereās a good place for 0.1% resistors (R5 and R6). But the stock resistors are 1% so that could easily cause a bigger than 3mV differences between the opamps.
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Thanks Ted. I was thinking the same thing as 12mv seems excessive. Iāll change the R5 and R6 to thin film, 0.1%, 25 ppm/degree C resistors. I found some 0805 1/4watt which may be better here than 1/8 watt.
I like the 1/4W 805ās. I stick to the 1/8W for my BOMs since their more widely sourced.
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Same brand/type?
What do you recommend?
Iāve been using TE Connectivity and Vishay Dale resistors when I canāt get what I want from Panasonic. Theyāve been fine, but I canāt say I have any completely objective reason for these choices. Definitely thin film 25 degree/C and 0.1% or better. For production Iāve been using 0.1% almost everywhere.
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Thanks for your input and help Ted.
Ok. Today a group of us listed to both my DACās. My DS#1 has all mods done including the big Jensenās. DS#2 has just the VOCM mod using 4v 220uf tants and our new transformers with a USB shorting plug.
Everyone was blown away by the difference between the two. I have them both hooked up so we can do instant A/B comparisons.
I would have never thought that just a proper transformer would make such a large improvement. Better than any mod I did before combined. Itās like you can reach out and touch each instrument and vocals just float perfectly right in front of you. Best I have ever heard from any DAC.
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Nicely done Team APS!
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Canāt wait to hear what the MKII will sound like with them.
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Check tracks on the edge which should still sound natural on top end like this one or take care of the pronouncing of vocalsā āsā sounds on quite extended sounding recordings.
Havenāt the initially recommended tants been 47uF ones?
What changes with the 220uf and do you have the others in DAC 1?
What I always wanted to ask:
Are yourFR measurements from the output of the DAC or just the transformer behavior under optimal input conditions? Probably a silly question but I donāt know better 
Unfortunately, the information shared is not enough for me. I have a good electronics technician but he has no hifi device experience. I need a more detailed explanation. Both pilots of the 737 are disabled and it looks like an accountant is about to land the plane.
What parts do we need? and where to mount the analog board are difficult questions.
Also, close-up photography can be very helpful.
Thank you. @yuriy
Please read the notes in the sweeps
Been using them for some time now
Ah I seeā¦as you mentioned source impedance and secondary load, it shows you measured the transformer response alone. Didnāt get this so far.
Means, the DACās real output can be slightly different I assume.