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Old 29th December 2014, 03:22 PM   #51
mcluxun is offline mcluxun  United States
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Join Date: Nov 2010
Quote:
Originally Posted by Schussor View Post
The SK circuits for the filters should not be difficult to duplicate with RC LP filters, you may end up having one more gain stage depending on the number of poles and the Q of the filters. But then you are possibly high up enough in voltage to forego a real output stage.

One of the gain stages can be a transformer that can serve as a filter pole. That was what Ted Smith did. He wanted to forgo another active stage and RC filter and spec'd a custom wound trannie to work as a filter at his specified fc, and serve to be an output stage and decouple DC.

I have to say that as a result there is a hint of "transformer sound" to the PS Audio PW DSD. I think you can pick a transformer that is naturally (i.e. not by deliberate spec) rolling off at one of your preferred filter pole's fc and not necessarily use it for output.

A successful implementation of this passive RC + makeup gain is in Nelson Pass' First Watt B4 crossover. It can do 4th order filters with 2 gain stages and IIRC there might be a buffer at the output. I think the schematics were offered online at his DIY forum, might still be there.
I see where you going with this, a step up transformers followed by opamp or buffer as i/v+lpf?
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Old 2nd January 2015, 10:01 AM   #52
blackhole is offline blackhole  Italy
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Join Date: Oct 2004
I am already using this type of configuration:
HQplayer >= DSD128 --> Amanero --> passive filter --> volume transformer (isolation, +6 db gain, additional filtering) --> power amplifier. The transformer really is this one:
SACThailand --> search for STA-522A and look for frequency response. This has been also checked in a laboratory here in Italy and
output at the frequencies of DSD signal is virtually non existant.

Some discussions has been made about a PWM "DSD gain stage" between Amanero and passive filter (note: because of the low output and impulse response a 1st order filter has been used) but the influence of this on jitter could be a problem. The signal maybe should be reclocked after the gain stage and before the filter.

In general I am satisfied with the result., so I agree with the old idea of Ted Smith, that can be applied also to other type of interfaces.
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Old 2nd January 2015, 07:53 PM   #53
mcluxun is offline mcluxun  United States
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Join Date: Nov 2010
Quote:
Originally Posted by blackhole View Post
I am already using this type of configuration:
HQplayer >= DSD128 --> Amanero --> passive filter --> volume transformer (isolation, +6 db gain, additional filtering) --> power amplifier. The transformer really is this one:
SACThailand --> search for STA-522A and look for frequency response. This has been also checked in a laboratory here in Italy and
output at the frequencies of DSD signal is virtually non existant.

Some discussions has been made about a PWM "DSD gain stage" between Amanero and passive filter (note: because of the low output and impulse response a 1st order filter has been used) but the influence of this on jitter could be a problem. The signal maybe should be reclocked after the gain stage and before the filter.

In general I am satisfied with the result., so I agree with the old idea of Ted Smith, that can be applied also to other type of interfaces.
Amanero Combo384+CR LPF DSD256 unnecessary DSD DAC
Are you using this design here?
What's the sound signature like?
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Old 2nd January 2015, 09:51 PM   #54
blackhole is offline blackhole  Italy
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Join Date: Oct 2004
At the output of Amanero I have only one 33 Ohm resistance in series, a capacitor in parallel and the transformer. I don't need a coupling capacitor because of transformer. I don't need a higher resistance (this also because of transformer).

The isolation from Usb ground is made by a Gefen USB extender. Power amplifier ground is isolated with the output transformer.

The S/N is not exceptional, should be around 85/90 dB, but this configuration has been made for a tube power amplifier whose real S/N could be around the same. So no record dynamic range. Moreover the output signal is lower than 2 V
The output transformers of tube power amplifier will work also as a final filter before the signal is sent to the speakers (Audiostatic eletctrosatic modified).

The sound signature is of a very transparent sound. The sound is the opposite of dark but is not bright, because high frequencies are smooth and "liquid". There is an impression (as in all DSD reproduction I have tried) of a bass a little less present.

Confronting to iFI DSD micro in DSD there is no story: this configuration is a lot better, immediately more transparent. iFi idsd micro (to my knowledge) should use the analogic internal filter of the DAC chip and an active buffer. In my case on the signal path there are not transistors, chips, no feedback, only one resistance, one capacitor in parallel, one transformer.
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Old 6th January 2015, 02:03 AM   #55
mcluxun is offline mcluxun  United States
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Join Date: Nov 2010
I recently finished my DSC1 build.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Removed unused 3.3v regulator (it's the faulty one that causing the noise)
Replaced LT1086 with tps7a4700 (much less ripple)
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Old 6th January 2015, 04:37 AM   #56
mcluxun is offline mcluxun  United States
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Join Date: Nov 2010
For those who asking for boards, here are the projects on OSHPark I've created and shared.
Disclaimer: I didnt get my boards from OSHPark, but they are considered reliable and good quality.
DAC section:
https://oshpark.com/shared_projects/Dcm5mq1P
($160 for 3 boards)
PSU section:
https://oshpark.com/shared_projects/Zx4dezQf
($159 for 3 boards)
After all it might be cheaper to get PSU section by using kits from other source e.g. diyinhk: 4.17uV Ultralow noise DAC power supply regulator +-12/15V 1A - DIYINHK

Last edited by mcluxun; 6th January 2015 at 04:45 AM.
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Old 8th January 2015, 05:18 AM   #57
Schussor is offline Schussor  United States
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Join Date: Apr 2005
Location: Ohio
Quote:
Originally Posted by mcluxun View Post
I see where you going with this, a step up transformers followed by opamp or buffer as i/v+lpf?
Sorry I missed your comment earlier.


Yes, that is one option.

But look at how a good quality transformer behaves in the freq and time (phase) domain and it may work as the entirety of the filter stage while being the I/V stage too.

SAC Thailand
There is a version of this transformer without the multiple taps a 1:2.2

Unfortunately, this also has consequences in deep bass THD:

SAC Thailand

This interstage transformer is actually better than the TVC transformer above, having a top end rolloff at >60khz instead of 35khz, but they didn't publish THD info for it.

We were looking at the PW DSD from PS Audio which has an output transformer as the key filter and integral filter, and its bass is weak and woolly - at least before the last firmware upgrade which seemed to have found a compensation in the software domain. We found a partial solution by lowering the input to the filter/circuit by lowering the digital volume by 10db - which still leaves you at bitperfect up to dsd128 and PCM192. But takes you away from core saturation and lowers THD in the bottom octave in a big way.

So implementing the idea here, there would still need to be a drop from the Amanero or XMOS board's DSD on I2S from its 0.5-1v to <0.1V or so, or we would need to go to a very large (power amp output sized - or an actual power amp output transformer used in reverse) transformer.

In the case that we take the voltage down, there would need to be an active output stage. Perhaps something like this: http://www.amazon.com/preamplifier-p...eywords=ge5670

where you can remove the volume control.
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Old 8th January 2015, 05:45 AM   #58
Schussor is offline Schussor  United States
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Join Date: Apr 2005
Location: Ohio
Quote:
Originally Posted by mcluxun View Post
For those who asking for boards, here are the projects on OSHPark I've created and shared.
Disclaimer: I didnt get my boards from OSHPark, but they are considered reliable and good quality.
DAC section:
https://oshpark.com/shared_projects/Dcm5mq1P
($160 for 3 boards)
PSU section:
https://oshpark.com/shared_projects/Zx4dezQf
($159 for 3 boards)
After all it might be cheaper to get PSU section by using kits from other source e.g. diyinhk: 4.17uV Ultralow noise DAC power supply regulator +-12/15V 1A - DIYINHK
I like DIYinHK XMOS USB board and high precision clocks and low ripple regulators. (1uV) the XMOS USB board is supposed to have isolation features and allows you to run the XMOS chip off of onboard power rather than source (PC) USB power so the grounds should be (but I am not certain) isolated.
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Old 8th January 2015, 05:46 AM   #59
TNT is online now TNT  Sweden
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Join Date: Apr 2003
Location: Sweden
Quote:
Originally Posted by Schussor View Post
Sorry I missed your comment earlier.


Yes, that is one option.

But look at how a good quality transformer behaves in the freq and time (phase) domain and it may work as the entirety of the filter stage while being the I/V stage too.

SAC Thailand
There is a version of this transformer without the multiple taps a 1:2.2

Unfortunately, this also has consequences in deep bass THD:

SAC Thailand

This interstage transformer is actually better than the TVC transformer above, having a top end rolloff at >60khz instead of 35khz, but they didn't publish THD info for it.

We were looking at the PW DSD from PS Audio which has an output transformer as the key filter and integral filter, and its bass is weak and woolly - at least before the last firmware upgrade which seemed to have found a compensation in the software domain. We found a partial solution by lowering the input to the filter/circuit by lowering the digital volume by 10db - which still leaves you at bitperfect up to dsd128 and PCM192. But takes you away from core saturation and lowers THD in the bottom octave in a big way.

So implementing the idea here, there would still need to be a drop from the Amanero or XMOS board's DSD on I2S from its 0.5-1v to <0.1V or so, or we would need to go to a very large (power amp output sized - or an actual power amp output transformer used in reverse) transformer.

In the case that we take the voltage down, there would need to be an active output stage. Perhaps something like this: Amazon.com: Class A GE 5670 tube valve preamplifier preamp amplifier include transformer 110V: Electronics

where you can remove the volume control.
Appalling distorsion figures for those trafos....

//
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Old 8th January 2015, 06:17 AM   #60
Schussor is offline Schussor  United States
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Join Date: Apr 2005
Location: Ohio
Quote:
Originally Posted by TNT View Post
Appalling distorsion figures for those trafos....

//
That is at rated power - they could have done like Audio Note and used their high nickel permaloy cores to lower THD but chose instead to lower the size and cost of the trannies. The Audionote 80's % nickel core transformers cost more than 10X.

If you go down in current the THD values drop off more rapidly than the current. Going down in signal by 10 db would lower THD by 15-16 db.
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