John Curl's Blowtorch preamplifier part II

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#34,124
A good digital volume implementation is not simple and then it needs to have the post ADC gain optimized to ensure you are not running at too much attenuation on the digital side. Dithering the attenuated output is important.

In a system environment it can be a good solution but with individual components will run a high risk of getting the gain structure non optimal. The Berkeley Alpha dac is a good volume implementation but really needs a separate preamp on the output to get the gains aligned in many cases.
 
#34,128
Esperado said:
As i use mainly Digital sources, my next solution for volume control will be exclusively in the digital domain. And i will add a ADC to deal with my analog sources.
JC will kill-me 😀
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Good move ... you won't be sorry, Christophe. My first CD player was the top Yamaha of the time, used an analogue volume out. Gave me hints of what was possible, but then started playing up, tracking problems. Dealer exchanged for the new model top unit, which used digital volume. This is when I started making real progress, and the breakthrough occurred ...

Frank
 
#34,129
1audio said:
A good digital volume implementation is not simple and then it needs to have the post ADC gain optimized to ensure you are not running at too much attenuation on the digital side. Dithering the attenuated output is important.
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Why? If totally in digital it works like charm, my still working 27 year old Yamaha beats the pants off nearly all digital plus analogue I've heard over the years. You just have to chuck the preamp ... sorry, John! 😀

Frank
 
#34,130
john curl said:
This pot was in a JC-2 preamp a few months old, at best. It was a MANUFACTURING DEFECT and it was UNIVERSIAL .... loadsa good stuff ....
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JC, thank you for these pearls of wisdom from the Jurassic days when you diidn't shy from getting your hands dirty with stinkin' measurements.

IIRC, you mentioned a wire wound pot which was your reference standard before Blowtorch.

Could you reprise your thoughts on these and explain how Blowtorch achieves its exemplary performance c/f supa dup wirewound?

You also hint at having done trials with some evil digitally volume controls eg PGAxxxx. Could you summarize your findings including any measurements you made? As these do not appear in any of your product, it won't matter if us Unwashed Masses misinterpret your measurements. 🙂
 
#34,131
Esperado said:
I don't know. My actual preamp and power amplifier have 1000V/µs of slew rate, and low IM distortion. I can reasonably suppose they do not produce too much of TIM ?
Really, i cannot explain why i do not like any (good) tweeter. May-be more a question of acoustical coherency due to filters.
Anyway, most of us are too old, here, to can experiment in a useful way: we need young girls to talk about HF limits.
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I font really have an idea. It could be phase shifts in the vocal range (but if you add a tweeter above 15k it shouldn't have any), or its not the speakers but the dac. Did u try with analog?

Btw I'm 35 and I can hear up to 19k.
 
#34,138
Esperado, qusp
Citation from oldier Wolfson white paper , claryfying my word "suboptimal"
Drawback of digital volume control is that the signal-to-noise ratio (SNR) worsens at low volumes. This is due to the quantisation error, which is inherent in any digital system and may result in audible noise. Its magnitude depends on the resolution of the digital audio data and/or the DAC. High-end audio systems are designed such that any noise is negligible compared to the magnitude of the audio signal, and therefore inaudible. However, when volume control is performed in the digital domain, the digital audio signal’s amplitude may be decreased by several orders of magnitude while quantisation noise remains constant, resulting in a lower SNR
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Always will be regulation in digital domain acompanied with relative increasing of quantizations errors and partially loosing of informations. You can manipulate 16 bit data with 32 bit resolution, but if you need e.g. 20dB attenution, lower valid data from original information get lost. That is why I prefer regulation in analogue domain, with fixed resistors ,at lowest acceptable impedance, and relay network. This solution offers best linearity and lowest own noise.
Whole pdf is in attachment, I can not find it currently on webspace.
 

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#34,139
People have this bizarre notion that somehow analogue S/N is always "magic", but digital S/N is bad, really bad. Well, I have yet to be offended by "poor" digital S/N, but my ears have been savaged by vile, offensive analogue S/N far, far too many times ...

Frank
 
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