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#51 | |
diyAudio Member
Join Date: Nov 2010
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#52 |
diyAudio Member
Join Date: Oct 2004
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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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#53 | |
diyAudio Member
Join Date: Nov 2010
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Quote:
Are you using this design here? What's the sound signature like? |
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#54 |
diyAudio Member
Join Date: Oct 2004
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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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#55 |
diyAudio Member
Join Date: Nov 2010
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#56 |
diyAudio Member
Join Date: Nov 2010
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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 05:45 AM. |
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#57 | |
diyAudio Member
Join Date: Apr 2005
Location: Ohio
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Quote:
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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#58 | |
diyAudio Member
Join Date: Apr 2005
Location: Ohio
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#59 | |
diyAudio Member
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#60 |
diyAudio Member
Join Date: Apr 2005
Location: Ohio
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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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