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A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)
A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)
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Old 11th June 2019, 10:22 AM   #6961
dddac is offline dddac  Germany
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Quote:
Originally Posted by mbrennwa View Post
…… The advantage of using a transformer at the DDDAC output is that it can (should!) be used with the balanced outputs of the DAC chips, thus cancelling some of the harmonic distortion. …..
Good Point, but there is more benefit behind using a tranny…

It is not cancelling some of the harmonics, but all odd ones. As the d2 is the highest any way this is a major step.

secondly - and I thing imho the most important - it is not just a balanced output: there are REALLY two DACs inside the chip - One dac feeding the POS output and the other dac the NEG output.

so you ARE doubling the number of DACs - this is exactly the same as adding boards… Meaning a 4 deck DDDAC with a transformer is like a 8 Deck DDDAC with single ended output….

Also the low output impedance at low frequencies does a lot of good- I get a lot of feedback on the bass improvements using the Sowters. With a couple capacitor your out impedance is significantly higher at lower frequencies

example 1uF couple C has aprox 1k5 output imepdance at 100Hz - that is 20 times higher than with a transformer. at 20Hz it is ~ 8kOhm...
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Old 11th June 2019, 11:10 AM   #6962
Bfpca is offline Bfpca  Canada
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A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)
Quote:
Originally Posted by dddac View Post
Good Point, but there is more benefit behind using a tranny…

It is not cancelling some of the harmonics, but all odd ones. As the d2 is the highest any way this is a major step.

secondly - and I thing imho the most important - it is not just a balanced output: there are REALLY two DACs inside the chip - One dac feeding the POS output and the other dac the NEG output.

so you ARE doubling the number of DACs - this is exactly the same as adding boards… Meaning a 4 deck DDDAC with a transformer is like a 8 Deck DDDAC with single ended output….

Also the low output impedance at low frequencies does a lot of good- I get a lot of feedback on the bass improvements using the Sowters. With a couple capacitor your out impedance is significantly higher at lower frequencies

example 1uF couple C has aprox 1k5 output imepdance at 100Hz - that is 20 times higher than with a transformer. at 20Hz it is ~ 8kOhm...
Another benefit is the galvanic isolation. Also, a transformer is a much more ideal balanced source than the average balanced tube or solid state buffer. It also acts as a LPF, generally with a well damped 2 pole roll off that is very benign in terms of phase shift within the audio band. Transformers are a sort of magic when used properly. The key is to get the correct transformer for the job.
Just a note about DC offset between the + and - dac outputs. This is a concern for some transformers IMO. Small input transformers can be saturated by even a tiny amount of DC current. If you look at the various Sowter data sheets you will see a warning in some of them about avoiding DC. There is no spec given for minimum DC current flow. Without actually checking with the manufacturer we do not know how much DC will be acceptable. My guess is that in some instances the answer is 0.
Having a correctly spec’d and implemented output transformer in your DAC will make it a much more universal component. It will be at it’s best with anything you put in front of it.
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Old 11th June 2019, 11:49 AM   #6963
dddac is offline dddac  Germany
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Originally Posted by Bfpca View Post
Another benefit is the galvanic isolation. Also, a transformer is a much more ideal balanced source than the average balanced tube or solid state buffer. It also acts as a LPF, generally with a well damped 2 pole roll off that is very benign in terms of phase shift within the audio band. Transformers are a sort of magic when used properly. The key is to get the correct transformer for the job.
Just a note about DC offset between the + and - dac outputs. This is a concern for some transformers IMO. Small input transformers can be saturated by even a tiny amount of DC current. If you look at the various Sowter data sheets you will see a warning in some of them about avoiding DC. There is no spec given for minimum DC current flow. Without actually checking with the manufacturer we do not know how much DC will be acceptable. My guess is that in some instances the answer is 0.
Having a correctly spec’d and implemented output transformer in your DAC will make it a much more universal component. It will be at it’s best with anything you put in front of it.
Thanks for adding this. All very true ! You are right on the right transformer for the job, hence I worked with Brian Sowter to get the special dddac version....
And dc offset was one important point here among other more audiophile aspects
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Old 12th June 2019, 04:15 PM   #6964
SimonJ is offline SimonJ  United Kingdom
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Originally Posted by dddac View Post
here are two pictures - It is the green PCB. The Arduino board is piggy backed on it, but it is at the other side of the pcb, so you cannot see it here
Hey Doede

Do you sell the green board or as a kit?

Thanks
Simon
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Old 13th June 2019, 06:13 AM   #6965
dddac is offline dddac  Germany
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Hey Doede

Do you sell the green board or as a kit?

Thanks
Simon
Hi Simon, no kits or official sales - I do have one extra PCB (I had made two...) I can sell this to you. It is all well documented so should be no big issue for you.

send me a mail to my normal email address please
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Old 13th June 2019, 06:23 AM   #6966
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by SimonJ View Post
Hey Doede

Do you sell the green board or as a kit?

Thanks
Simon
I might also have some extra boards for my version with 27 switch positions that works with the standard Sowter 9335. Alternatively, you could just use a good old 27 position switch as recommended by Sowter instead of a PCB with an arduino and a bunch of relays.
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