A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

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Nightpuma

Member
Joined 2006
kartick said:
Hello everyone, out of the blue I felt like measuring the DC voltages off of my DDDAC. I use a 4 deck version with a Cinemag trafo coupling. This is what my DDDAC reads:

OUT-R
Common - POS: 2.73V
Common - Neg: 2.668V

OUT-L
Common - POS: 2.665V
Common - Neg: 2.673V

The supply voltages on the 12V and 5V are dead accurate so no issues there.

Questions:
1. Why am I seeing a variance between the left and right channel DC voltages? And additionally, why are there differences within the left and right channel voltages between Common-POS and Common-Neg itself?

2. How should i look to even this out or rather remove this difference?

3. Would this be apparent in a volume difference between the left and right? I think i feel an imbalance?

4. Should I look at how the wiring has been done from the DDDAC Motherboard to the transformers and then to the RCA posts? I think I read in Doede's post #7212 that we are supposed to leave the common unconnected when using the transformers? In my case this is connected for both L and R channels, does it mean I have been using the cinemag transformer wrongly wired all along?

Appreciate your responses.
Click to expand...

With transformers you connect pos and neg. Com is left unconnected.
 
Extreme_Boky

Extreme_Boky

Member
Joined 2003
kartick said:
Hello everyone, out of the blue I felt like measuring the DC voltages off of my DDDAC. I use a 4 deck version with a Cinemag trafo coupling. This is what my DDDAC reads:

OUT-R
Common - POS: 2.73V
Common - Neg: 2.668V

OUT-L
Common - POS: 2.665V
Common - Neg: 2.673V

The supply voltages on the 12V and 5V are dead accurate so no issues there.

Questions:
1. Why am I seeing a variance between the left and right channel DC voltages? And additionally, why are there differences within the left and right channel voltages between Common-POS and Common-Neg itself?

2. How should i look to even this out or rather remove this difference?

3. Would this be apparent in a volume difference between the left and right? I think i feel an imbalance?

4. Should I look at how the wiring has been done from the DDDAC Motherboard to the transformers and then to the RCA posts? I think I read in Doede's post #7212 that we are supposed to leave the common unconnected when using the transformers? In my case this is connected for both L and R channels, does it mean I have been using the cinemag transformer wrongly wired all along?

Appreciate your responses.
Click to expand...

I use CMF55 6.00K Rref resistors, 0.1% tolerance, old boards. But I ordered these Rref resistors in advance from Digikey as soon as I bought the kit.

R channel:
2.650
2.651

L channel:
2.656
2.657

Your I/V resistors are ALSO important, they should also be of a very low tolerance type. Mine are 33 ohms TX2575 naked bulk metal foil types, initial tolerance of 0.001% (!!)

The Cinemags should not have any connection with DDDAC common; just with a positive and with a negative out's. All the static shield wires and the Cinemags' case wire, should be connected to the amplifier common/ground (or the pre-amp common/ground). This is going to provide a full isolation between dirty DDDAC common and clean analog common.

I liked the Cinemags... but they could never provide the depth of the sound stage perspective like good caps. In fact, there was no depth perception with Cinemags, but they sounded very very nice. It comes down to what is important to you and the rest of your system.

With close to 100mV of imbalance that you have (R channel), you should de-magnetize the Cinemags.... just take any E core transformer, "open" the core (to allow the magnetic force to "radiate out") and then power the demagnetizer with another transformer with AC. This is what I used during cassette-decks' days with great success. Slowly approach the Cinemags with your demagnetizer powered-up by AC current, and then VERY slowly move the demagnetizer away from the Cinemags
 
Last edited:
K

kartick

Member
Joined 2012
Extreme_Boky said:
I use CMF55 6.00K Rref resistors, 0.1% tolerance, old boards. But I ordered these Rref resistors in advance from Digikey as soon as I bought the kit.

R channel:
2.650
2.651

L channel:
2.656
2.657

Your I/V resistors are ALSO important, they should also be of a very low tolerance type. Mine are 33 ohms TX2575 naked bulk metal foil types, initial tolerance of 0.001% (!!)

Here I dont think there should be a concern as I am using Vishay Z Foil naked resistors which are highly regarded and they are low tolerance as well.

The Cinemags should not have any connection with DDDAC common; just with a positive and with a negative out's. All the static shield wires and the Cinemags' case wire, should be connected to the amplifier common/ground (or the pre-amp common/ground). This is going to provide a full isolation between dirty DDDAC common and clean analog common.

Can you or anyone please provide me with the wiring schematics of connecting Cinemags to the DDDAC so I can recheck where I have gone wrong in my build.

I liked the Cinemags... but they could never provide the depth of the sound stage perspective like good caps. In fact, there was no depth perception with Cinemags, but they sounded very very nice. It comes down to what is important to you and the rest of your system.

With close to 100mV of imbalance that you have (R channel), you should de-magnetize the Cinemags.... just take any E core transformer, "open" the core (to allow the magnetic force to "radiate out") and then power the demagnetizer with another transformer with AC. This is what I used during cassette-decks' days with great success. Slowly approach the Cinemags with your demagnetizer powered-up by AC current, and then VERY slowly move the demagnetizer away from the Cinemags

How should this imbalance be perceived, should it reflect in the output coming out of the speakers?
Click to expand...
 
Extreme_Boky

Extreme_Boky

Member
Joined 2003
See attached
 

Attachments

  • Cinemag.JPG
    Cinemag.JPG
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  • CMLI-15-15B.pdf
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Extreme_Boky

Extreme_Boky

Member
Joined 2003
kartick said:
Here I dont think there should be a concern as I am using Vishay Z Foil naked resistors which are highly regarded and they are low tolerance as well.
How should this imbalance be perceived, should it reflect in the output coming out of the speakers?
Click to expand...
...and the Rref's ??

the imbalance should not affect the sound to the point of becoming noticeable... however, you should demagnetize the Cinemags and/or you may have other issues.
 
Last edited:
K

kartick

Member
Joined 2012
Extreme_Boky said:
Play a 1kHz wav file and check the DDDAC outputs, referenced to ground. If all good, connect the Cinemags and repeat to ensure you connected them okay. This will be the quickest way to get to the root cause of a problem.
Click to expand...

Quite honestly, I have been playing the DAC since I installed the Cinemags and I dont see any distortions or artifacts being outputted. Yes, I am not very happy with the output levels of the the dac pre and post the cinemags. As in I never saw a jump in the gain levels. Isn't the Vout and gain supposed to increase when one uses 4 decks or more with a transformer couple output?
 
dddac

dddac

Member
Joined 2003
blog.dddac.com
Paid Member
kartick said:
Will supply the photos shortly. But how much in % terms should the output increase when going from capacitors to transformers? I may not have noticed more than a 10% increase if I remember correctly.
Click to expand...

Output will double Kartick - when playing (just do it) a 1kHz tone at 0dBFS you will need to measure 2.4 Volt RMS at the output of the transformer - depending of the quality of your multimeter at AC, this can vary a bit, but most important is that the values for L and R should be close to each other within ~ 2%
 
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