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Stereophile's measurements of dCS Vivaldi DAC

Posted 9th January 2014 at 02:59 PM by abraxalito

John Atkinson's 'WOW!' (more than once) to his measurement results from the Vivaldi DAC prompted me to have a closer look at how it does for noise modulation.

The AP's FFTs shown don't come with details about the number of points in the FFTs, so noise estimates are a tiny bit tricky. However there is enough detail to make some reasonable estimates.

I've attached the plot from which I'm making my estimates - if anyone notices I've made a slip-up, please do comment and correct me.

The red line shows white noise at peak level of -4dBfs. I generated white noise in Audacity at this level to compare - with the maximum 16k point FFT and BH windowing, I got the same level of noise as on this plot - -42dBfs in 22kHz bandwidth. That suggests to me that the FFT shown has 64k points.

Another way to estimate the noise is by looking at the difference between the blue plot (19.1kHz, 0dBfs) grass and the red. To my eye, the difference in level is 76dBr...
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Ozone beta-build listening

Posted 8th January 2014 at 05:18 AM by abraxalito
Updated 8th January 2014 at 06:15 AM by abraxalito

I've had the beta build Ozone (no input stage yet, fed from my QA550 via the I2S transcoder to down-convert to 32fs) playing out 24/7 for a few days now.

Overall I'm very happy with how it sounds, just a minor gripe about sibilance on some operatic vocals which I'd like to understand better. On the upside the jump-factor (read dynamics) and soundstage stability (holographic on the right disks) are about the best yet. I'm using a couple of Decca double CDs for this - 'La Traviata' and "La Boheme'. They're about the most transparent sounding and demanding disks I have. Demanding in the sense that they have lots of emotional drama which should positively engage my attention if the DAC's really up to snuff. I never much enjoyed opera until I got into building my own NOS DACs, but now I really enjoy my dramatic fixes and these two recordings are really top of the pile. They're about 50 years old but so far I've not found anything newer which touches them (not that I've looked...
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Suffering from Audiofilia Neurosa?

Posted 2nd January 2014 at 02:18 PM by markusA

I like to read and muse on what I'm reading. Human beings are interesting and trying to delve into the psyche of humans are fascinating. Subjectivists vs. objectivists, do cables/wires have an audible character, can fuses sound different from each other, linear vs. smps... The list goes on. We can't even agree on how listening are supposed to be done ABX, long term listening, whole songs or short passages, double blind or open, known material or unfamiliar.... The only thing we seam to be able to agree on is that we're mostly disagreeing about most things.
And it's incredible how much prestige people put in their opinions defending opinions as if their life depended on it.
I love a good discussion but sometimes it's just silly.
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Rating: 2 votes, 4.00 average.

2013 Holiday Projects - Ridding the system of resistor problems

Posted 30th December 2013 at 03:35 AM by wlowes
Updated 3rd January 2014 at 02:27 AM by wlowes (add pic)

Two months ago I had great ambitions to complete a long in the planning short on execution music server by xmas. Seems I am too busy and just having too much fun listening to my system to make progress on big projects.

However, in a very low key way my system has made some stunning gains over the 2013 holiday.

My happy 6 year journey with a Lightspeed linestage finally ran afoul when an LDR packed it in. I retooled with some on hand bits while waiting for new LDRs to arrive. A snaffu with my order delayed that whole process. Meanwhile, my wonderful wife asked me what I wanted for xmas. I had been reading Arthur Salvatore's site and became interested in using an autoformer from Dave Slagle for my linestage. If your read the reviews and the technical specs, its intriguing. My system is perfect for passive. I only listen to a music server with triode ouput stage, short interconnects to OTL amps and overall have lots of gain.

On a whim...
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Old

Ultimate SQ DAC

Posted 27th December 2013 at 06:08 AM by abraxalito
Updated 30th December 2013 at 12:52 AM by abraxalito

Inspired by this thread http://www.diyaudio.com/forums/digit...-new-post.html
I've been giving a little thought for how to move beyond the 'Ozone' to a DAC able to handle more than 16bit inputs and up to 96kHz input rate. The target being 20bits and 120dB SNR (non-A weighted). The OP in that thread preferred a more marketable 'ultimate' DAC (with 192k and potentially 384k capability, along with DSD) - aims which to my way of seeing clearly conflict with a DAC having any pretentions to ultimacy.

The simplest solution - building on the digital part I already have - would be to add more TDA1545As in parallel and with a Cortex M4 direct the data to the respective chips. What's unclear though is how low the noise will go when the extra chips are added. From the DS, an A-weighted SNR is quoted of 101dB (typ) with 2mA, however this is a static noise (code = 0) and hence may well not translate to the noise achieved with bits toggling....
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Low Distortion DDS based dual channel audio synthesiser

Posted 24th December 2013 at 01:40 AM by googlyone

Well now I am on holidays over XMAS I got the time to really put in a solid chunk of time on the DDS based synthesiser.

Previous blog entries describe the PIC32MX based core to this. The thing works like a charm...

To get decent precision on the sinewave I have implemented an interpolation on a high precision Sinewave lookup table.
- The DDS references into a 12 bit "long", 24 bit "amplitude" precision sinewave LUT.
- Of itself this gives mediocre spurs, which in a DDS are heavily dependent on the frequency, but seem to result in 85-90dBc spurs. There is a fair hash of these without treatment.
- By adding a linear interpolation between samples in the Sinewave Lookup table, the spurs come out as shown below...

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- The interpolation is actually quite simple in concept:
- The top 12 bits of the DDS Phase Accumulator looks up the "Sine Sample"
...
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Old

Hakko FX-950

Posted 20th December 2013 at 10:29 AM by rjm

Earlier this year I had a really, really bad experience attempting to get a new soldering iron. This time around I made my purchase through a reputable Japanese online retailer, and am now the proud and happy owner of a Hakko FX-950 soldering station.

Its an analog unit, and was discounted quite a bit as a result. Personally I'm happier with a rotary dial temperature control anyway.

This thing rocks! I've dragged my heels on getting a decent iron for so long its ridiculous. In my defense, I could always borrow a semi-decent one from work, so the pressure to buy my own was not as great as it otherwise might have been.

Top five reasons to spend the extra cash:

1. 70W, variable, closed loop temperature control. As much heat as you need, whenever you need it: the feedback loop means that the power is proportional to the conductance load: the tip will not cool down when heating up a large thermal mass.

2. Heats up to...
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PIC32MX450F256 as DDS core driving CS4398 DAC

Posted 18th December 2013 at 09:35 AM by googlyone
Updated 18th December 2013 at 09:38 AM by googlyone

Over the last couple of months I have been playing with a PIC32MX450F256H as the DDS core, and using one of the many DAC boards I built for my DSP based crossover as the D/A element.

It has taken a while to get up and running - mainly due to me actually having commitments other than a hobby... (Bugger)

That said, getting this thing up and running also required me to get my head around the microchip XC32 compiler, and the configuration bits in the PIC32MX.

On the compiler, the most serious issue is the schemozzle they call documentation. I imagine if all you wanted to do was simple I/O and stuff you might be OK. As soon as you want to dig into the more detailed registers, the high level library documentation is borderline useless, and spread over a number of directories and the Microchip website. Very frustrating.

The other challenges I had were:
- To set up the PIC I2S interface such that there was no jitter on the LRCLK...
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Upgrading the Sapphire headphone amplifier (photos)

Posted 17th December 2013 at 10:10 PM by rjm
Updated 20th December 2013 at 10:14 AM by rjm

Straightforward transplant. Out with the old (anyone want them?) in with the new. Re-used the OPA134 op amp and my dog-eared pair of 0.47uF Multicaps.

On powering up I discovered that with the specified 10 ohms in R9,10 the output bias current was upwards of 200 mA and things were getting a bit toasty. I paralleled a second 10 ohm resistor, dropping the resistance to 5 ohms and dialing back the output bias current to about 70 mA. Latest schematic revision has R9,10 values edited to match.

Currents stable. Heatsink temperatures around 50 C. Output offsets around 15 mV. No noise or hum.

Presently giving it some burn in time.
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Old

Fix it time for PC monitor speakers

Posted 16th December 2013 at 05:23 AM by fas42
Updated 22nd June 2014 at 06:35 AM by fas42

Bummer!! After mentioning that Brad's (bcarso) units were doing very nicely I swapped CDs while they were set to max. volume, doing a good job on a classical piece. Unfortunately, the new disk was heavily compressed pop, my mind was elsewhere, and I hit the volume control a second too late - everything's OK except the right speaker has dropped about 6dB in volume, ...

I suspect that some protection circuitry has tripped, but it's not resetting. Which means, unless anyone has a good idea otherwise, that I'll have to dive inside and sort things out. But, on the other side of the equation that may be an excellent thing to do, it will give me a chance to do some more adventuresome tweaking ...

Trouble is, I'm lazy ...
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