It isn't wide-band noise though, its specific image tones. For example in measuring THD at 15kHz you're normally assuming that once you notch out the fundamental what's left is only 30k/45k/60k etc. But in the case of a NOS DAC with only minimal (6dB/8ve) filtering there's a massive component at...

What commercial NOS DAC has a sufficiently steep analog filter? I don't know of one that could keep the THD+N reading below 0.1% at all frequencies to 20kHz.

<pedantry> That's a pretty standard usage of 'v' to indicate ü as the Chinese name's written in pinyin. See here : http://pinyin.info/news/2009/v-for-u/ </pedantry>

No, I'm using a multibit DAC of my own design.

I tried 30Hz with my DAC, couldn't hear the faint sawtooth so I guess most likely it is your DAC. I can hear distortion at higher frequencies though with my DAC - not sure if that's the DAC, the amp, my headphones or my ears....

How are you generating the single frequency tones and what kind of distortion is it you hear ? Could you describe its character?

I'd be a little surprised to see AK4499 show up much under $500, unless the chip price reduces significantly. At present over on Octopart its listed at $80 in small quantities, falling to around $65 in high volume. To make using it worthwhile it needs a fair spend on power supply regulators and...

Yes, those transformers were what I was talking about. I agree 70euro is fairly cheap for a commercial signal trafo.

I'd guess deleting the output transformers shaved a very significant percentage off the BOM cost.

Strictly speaking its not current output, its an array of equal-valued resistors fed from a reference voltage. The output stage though should present the lowest possible impedance to the DAC (in order to achieve the lowest THD), in this sense its interfaced as if it were a current output DAC...

Post #21 - 'its possible to infer the saturation limit, <130mA'. The amp takes quite a lot more than 130mA. Curiously though Elvee says it doesn't really matter - yet @tomchr's measurements show ultrasonic noise as an issue.

The designer's power input filter doesn't work very well - its into saturation, as pointed out on the DIYA thread and potentially confirmed by @tomchr's measurements. Fortunately its DIY so you can improve it yourself, just reduce the number of turns on the core. 3 would be about right. There...

Common-mode noise is normally the culprit for this and yep, its generally at a much lower level with a 'linear' supply (as opposed to an SMPSU).

Haven't had a serious listen to TDA1541A but TDA1387 is awesome for RBCD. When you factor in the price (next to nothing) they're unbeatable.

As a (somewhat pedantic) point of fact, neither TDA1541A nor TDA1387 are R2R DACs as they don't use resistors to create the bit weightings. Both of them use proprietary Philips technology.

As far as I recall it wasn't so much fixed as moved. Meaning its still there but no longer shows up at such a low level. Well, quite. A storm in a tea-cup.

As far as I'm aware, Schitt isn't using any resistor string DACs in their products but I may well be out of date. All the DAC chips they use have at least part of the DAC made up from R-2R segments. So perhaps it would be better to say that 'Schitt isn't actually manufacturing any purely R-2R DACs'.

Its 10V rather than 9V so the internal LM317 regulator will run that much warmer. Worth a try - if the audio cuts out after a while then it'll likely be due to overheating.

Good bang for the buck, especially if you love the multibit sound. Its rather sensitive to USB power quality though, there's no regulation internally of the USB bus power. Only runs at 44k1/48k over USB so no opportunity to upsample on your computer. I bought one or two for modding. Never...

Thanks, those help and they confirm that Rob Watts is indeed using S-D (he didn't say it explicitly but he talks of his 'noise shaper' and says the output from that is 6bit chunks). However just because he uses S-D doesn't make his DAC equivalent to an S-D DAC, his analog stage is way, way...

If a DAC is using PWM then it's got to have a Delta Sigma modulator in there somewhere. Although its theoretically possible to do PWM in NOS form (needs sub-nanosecond resolution on the pulsewidths i.e. an effective clock rate >1GHz) I don't believe anyone's done it yet. Happy to be proved wrong...

Going from the blurb on their site and the pics, there's no filtering (digital or analog) and they're using just resistors for I/V (no opamp).

Right (IM here being two-tone stimulus I take it). This is an interesting avenue of study. The filters in S-D DACs are in general built down to the lowest silicon area possible, which means adopting a half-band filter for the first stage upsampling (1X->2X). Half band filters are a compromise...

Yep, no disagreement there though I'd say they're biological rather than biomechanical. There we diverge, there isn't any evidence in support of this claim as far as I'm aware. Yep - I guess we diverge here because you probably think we already know all the 'laws of physics' however in my...

Yes, I agree, but they also under-estimate how sensitive we are to certain aspects of the 'music'. So for example, using Fletcher-Munson to estimate what's going to be audible and what's not, when those curves are built from the audibility thresholds of single tones, not music. To me, that's a...