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In Reply to: RE: In other words, signal quality matters greatly posted by jackwong96 on June 16, 2010 at 10:01:27
Hi,
> I like the idea of a tube SPDIF buffer, however,
> the tube buffer circuit in question fall short of a good design.
How do you know? Did you see and analyse my schematic for the module diyhifisupply sells? They only came back from the factory.
> This is simple electronics but no magic.
Yup. We just need around 0.5V PP into 75 Ohm. That is 6.66mA Peak-Peak, so we need to have a bit more than halve that as quiescent current, not very hard to do.
> I believe the true potential of a tube SPDIF buffer is yet to
> be unveiled, with improvement of circuitry, such as White's
> Cathode Follower.
I tested my buffer as under 1pS Risetime including the the drive signal from the FPGA. How would you like to improve this?
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Follow Ups:
Those are impressive risetimes at 1ps! Here's the digital waveform of a 1kHz tone (at 96000 Fs) done a few years ago:
Risetimes well into 10s of ns together with over- & under-shoot.
Due to commercial obligations you're unable to share your circuit design, however it would be interesting to see equivalent from your DAC's SPDIF output.
Hi,
Apologies for the delay in posting that, I just had to get around to measuring this and to taking a picture...
Here is a picture of a 48KHz signal from a commercial USB-> SPDIF converter which incorporates my design, the tube stage is fed directly from the FPGA output pin.
This picture is at a pretty extreme degree of zoom in, compared to most we see posted here. The whole picture covers around 1/3rd of a single period of a 3MHz signal (the base rate is 48KHz).
This trace is for the full system, that is USB-SPDIF converter, with tube stage, Canare "75R" RCA connectors (both ends) and 2m Cable. It tests the signal at the 75R terminated "far" end of the cable. I find this gives a far better representation of the actual performance than just testing the output.
Note that the loaded output voltage is just a touch over 0.8V Peak-Peak BTW.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Hi,I need to take a new trace when I get to test another unit. But the traces shown above are not that good at all.
I previously posted on my modifications for the Musiland Monitor 01 USD, which includes the traces from my mods without the tube section.
http://www.audioasylum.com/forums/pcaudio/messages/6/66884.html
The tubed output stage does better. The figure comes from the NEC Digiscope. I did a doubletake too, but the numbers came up like this.
I think it calculates the rise time from 30% to 70% around the zero crossing. Still, the output is very square, a lot better than the above.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Edits: 06/17/10
I used a cheap Creative soundcard (which outputs TTL and yes its crap) for that measurement (using ELAB-080 DSO). Your Musiland trace looks good and even better after mods.
A tube output stage makes a lot of sense. Given that BMC encoding is used for both S/PDIF & AES/EBU and they can be readily converted to/from, can the tube design be extended to AES/EBU?
Hi,
> can the tube design be extended to AES/EBU?
Sure, it just needs a different wiring up. This will all go into the Manual.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
hey Bro, remember dr. fikusz had tried on using AES/EBU however the result is NEGATIVE..
What he said:
I am sure that a single ended connection is best for S/PDIF signal. I do not like toslink and I don't like AES/EBU either.
The "pro" looking AES/EBU connection is using XLR and it looks OH SO PROFESSIONAL WOWIE ZOWIE. We buy by the eyes. But the AES/EBU is not invented to be better. It is invented to be LONG DISTANCE.
The RS422 industrial data transmission from which AES/EBU derives can travel as long as 1,8 km (over one mile) on the twisted pair balanced cable. The S/PDIF in coax cable can travel up to few single meters. THAT IS THE DIFFERENCE. But the S/PDIF signal on both ends exists ONLY as simple single ended asymetrical signal. We must make it balanced artificially by means of adding a balancing transformer which badly distorts the signal. Then we use in our systems one metre cable (not one mile !) and we must use de-symmertization transformer on other end again. That's two unnecessary transformers, two too many for me.
In analog systems, the ballanced XLR has more meaning - as described HERE, but in digital - the signal itself is never trully ballanced, it is the sending media that is ballanced to make long distance possible.
so why is the AES/EBU sounding better on many transport/dac combos ?
Answer is easy. Because the S/PDIF on all transports that I have seen, and I have analyzed about 40 different ones - is made wrongly and it uses an ugly separation transformer as well. So in that scenario - S/PDIF can not beat AES/EBU because they both have the biggest limiting factor - the transformer."
Like my previous post, removing the pulse trans will help in sound revealing transparency.
Hi,
> hey Bro, remember dr. fikusz had tried on using AES/EBU
> however the result is NEGATIVE..
Yes. But that this mean it is universally applicable?
Generally when done to equal levels of implementation, AES/EBU usually sounds better.
> But the S/PDIF signal on both ends exists ONLY as simple
> single ended asymetrical signal.
Actually, wrong. Almost all receivers out there have balanced inputs.
> We must make it balanced artificially by means of adding a
> balancing transformer which badly distorts the signal.
Wrong again. AES/EBU can be made "transformerless", secondly, the traces shown from the Musiland (as well as the Tube Stages I designed) use transformers. Transformers only distort the signal if used wrongly.
The key to understanding is that all these interfaces are radio-frequency designs. We can make wireless routers that work reliable at 2.4GHz. The 25MHz needed for SPDIF and/or AES/EBU are actually quite easy, this merely Shortwave radio frequencies.
> Then we use in our systems one metre cable
Ouch. A 1 meter coax cable is precisely the worst length or an SPDIF cable.
> Like my previous post, removing the pulse trans will help
> in sound revealing transparency.
Actually, you may wish to read the blog posts over at www.diyhifisupply.com. You are right insofar - removing the original tranformers (which are basically inappropriate) improved sound quality.
HOWEVER, correctly implementing some higher quality transformers improved the sound quality even further.
Then getting rid of the two daisy chained inverters that drive the digital outputs on the Musiland and using instead a linear tube stage while retaining the transformer produced further improvements.
The bottom line - as I often say, it is not what you do (e.g. use transformers in SPDIF or AES/EBU interfaces) but how you do it that makes the difference.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Hi Thorsten
> HOWEVER, correctly implementing some higher quality transformers
improved the sound quality even further.
What output transformer would you recommend for the Juli@ to replace the Hanrun?
Regards
Hi,> What output transformer would you recommend for the Juli@
> to replace the Hanrun?First, I do not know the Juli@ first hand, I have no idea of circuit implementation etc. So it is impossible to make an informed suggestion.
Second, simple transformer swapping gets you nowhere fast.
You need to be able to find a transformer that is sufficiently consistent in production (harder than you think) and characterise it's parasitic (unwanted) behaviours and then design a circuit that gets the best out of this transformer.
For example people ask me "Which transformer do you use for your musiland mod's, I want to try them."
My answer is always:
"Knowing Brand and type will not help you, unless you know my exact application circuit, which is not for public dissemination. And to avoid negativity from people using the transformers wrong and then complaining they are not good and this reflecting back badly on my designs I'm not telling the first part either."
I hope you understand.
Ciao T
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Edits: 06/18/10
hi there... mind to show your tube circuit of buffer stage?
Hi,
> hi there... mind to show your tube circuit of buffer stage?
The circuitry is applied to a commercial product, so I am not at liberty to disclose it, sorry.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
Thorsten, Your tube buffer design is perfect! I believe it can drive a 75 ohm headphone too. In such case, not much I can contribute.
Edits: 06/16/10
Hi,
> I believe it can drive a 75 ohm headphone too.
It can. To 0.5V Peak-Peak. Or 4mW RMS. And I doubt the output transformers are capable to go down into the audio range...
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.
(Translated from the song "Aus der ferne" by City)
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