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Old 24th February 2009, 12:13 PM   #1
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Default Pulse transformers SPDIF/AES-EBU

Most CD drives and players with SPDIF out do employ pulse transformers.
The PT is used of two reasons.
First of all it is often used as a step down transformer from the standardised ~3V to ~1V out.
Next it provides insulation and protection.

The downside of using PTīs is mainly hysteresis and thus jitter.

Iīve been trying a few experiments that occasionly might work for some.

I exchanged the PT with a resistor network, actually it is a simple voltage devider. To lower the output voltage 390 Ohm in series with the output is adequate, after that you put 90 Ohms parallel to ground. Thus you have 75 Ohms output impedance and 1V out.

But remember, you now connected your groundplane in your DAC with the groundplane in your source.
Donīt do that with a computer or any other source employing SMPS, it might be fatal to your DAC.

In the supplied scematic of the SPDIF out of a Denon DCD3560, it is obvious that this digital output was not intended for external conversion at all, it was more likely designed for recording use or something like that, as the external DAC was simply not invented at the time this CD player was designed.
But nowadays the design of digital outputs unfortunally is mostly the same.
Some small comapnies tried to make a difference http://www.scientificonversion.com is a company like that.

The CD player has in fact 2 SPDIF outlets, which makes it possible to compare Transformerless output with non transformerless output with ease. I recomend you try this out.
My impression is that a pulsetransformer in the SPDIF simply ads a small amount of bathroom sound to the signal.
I have seen the signals on oscilloscope, and the transformerless signal does not contain any ringing as the transformercoupled does. The difference is visually remarkable.

Would be nice anyone else did experience the same thing

Click the image to open in full size.
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Old 25th February 2009, 06:19 AM   #2
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Interesting, can you post up pictures the differences you saw on the oscilloscope?

Below is what the Teac PS2 used on their output.

Cheers George
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Old 25th February 2009, 08:38 AM   #3
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Sorry, that's Teac's P2S, one of Teac's best VRDS transports.
Cheers George
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Old 25th February 2009, 10:59 AM   #4
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Hey George!
Unfortunaltely I never made any screen shots of the signals, but maybe I can make them later, as i do not myself own an oscilloscope I borrowed one, and as I did not ruin it completely, I may be able to borrow it again
But I can tell you that there was pronounced ringing on the transformercoupled output, and nothing at all on the transformerless output. I actually also removed the elektrolytic cap C146 and replaced it with a suitable Oscon bypassed with Wima Film cap. But this was made in two steps where the removal of the puls trans is clearly the most important part.
In addition it is easy to hear the difference between these two outputs.
It also seemes to me, that using the transformerless output, the preference of digital cables turns somewhat towards true 75 Ohm cable as i.e. Belden 1694A with Canare plugs amongst others.
"Real" high end hifi digital cables with somewhat more idiosyncratic genesis , does IMHO not really fit in.

Btw. the Teac output does in fact look very interesting. I heard Teac transports now and then, and my impression is actually that the results I achieved making this transformerless output stunt on my Denon, makes it sound a bit more Teac like.

To emphasize the difference in a pretty stereotype way, you could call the transformer sound a bit like "the sound of the eighties" where the TL aproch is somewhat more "nineties" like.
It is though subtle, but still easily detected by ear.
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Old 25th February 2009, 01:37 PM   #5
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@George!

I see the P2S employs the same laser as does the Denon 3560.
itīs called kss151A and can be seen here http://www.acs-connec.com/uploads/File/KSS151A.jpg
That often also means that the complete control unit is also the same. Thus the similarity of transformerless sound I think.
Btw. Teac WRDS is indeed very nice and mostly overlooked.
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Old 25th February 2009, 09:30 PM   #6
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Use a hammer on that scientificonversion-trafo, so you will not be tempted to use it again.
It is really no good compared to a Newava trafo...even cheap chinese pulse-trafos are better.

Arne K
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Old 25th February 2009, 10:02 PM   #7
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It doesn't look like Kurt even bothered to try USING a SC trafo in this setup. If I read the first post correctly the denon supplied trafo was the basis for his test.

It's probably worth checking this post over at diyhifi.org for the difference a quality trafo can make to spdif output:

http://www.diyhifi.org/forums/viewto...p=23534#p23534
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Old 26th February 2009, 09:47 AM   #8
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I did not try out the Scientificonversion PT, as I wanted to try it out without any PT in one the two SPDIF outputs.

But I am open to suggestions for transformers that do not ad any overshoot to the SPDIF signal. Wonder if they exist at all.
My test was done as the standard PT against no PT, actually I never found a usefull PT to exchange the old one, as mostly PTīs are 1:1, mine is around 3:1.
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Old 26th February 2009, 09:52 AM   #9
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Quote:
Originally posted by Cobra2
Use a hammer on that scientificonversion-trafo, so you will not be tempted to use it again.
It is really no good compared to a Newava trafo...even cheap chinese pulse-trafos are better.

Arne K
In which way is the SC PT no good?
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Old 26th February 2009, 05:35 PM   #10
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Yes, good question. scientificonversion certainly talk a good game - what is it about the transfo you don't like?
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