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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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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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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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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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The coolest Taobao SD card player yet

Posted 10th December 2013 at 03:50 AM by abraxalito
Updated 21st December 2013 at 12:48 PM by abraxalito

This one rocks - it plays FLAC, WAV and mp3s. The DAC is WM8740 (not so hot) but the designer has taken the power supply very seriously. Just check out all those caps and TDK noise filter on the PCB on the right Power comes from a lithium battery behind, so its portable but there's no case - there are acrylic front and rear panels screwed on to the PCB spacers. Two 3.5mm jacks provide headphone and line out.

Its using STM32F407 to do the decoding which is a first for ARM in this sphere and the design is configured that there's an I2S link between the two PCBs. So in theory anyone could design a better sounding DAC and replace that bottom PCB whilst keeping the UI. Which I may just do.... Price is 568rmb (just under $100).

Update - I was a little curious about the PSU so I've pulled out all of those SMT 220uF caps to get a closer look. The block filter's a Murata (not TDK) BNX024 which looks like a wrong choice of part primarily because its rated for 15A. Hence...
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Superregs for your line-level projects

Posted 9th December 2013 at 07:52 AM by jan.didden
Updated 10th December 2013 at 06:02 PM by jan.didden

It’s a recurrent issue: you want to build a preamp, a DAC, a phono stage, anything that needs a nominal supply voltage between 3.3 and 15VDC, positive and/or negative polarity. Sometimes you want several supplies to isolate stages from mutual interference via the power supply. So you want a power supply regulator that approaches an ideal DC voltage source as best as possible within reasonable cost. In your search, you inevitably run into the term ‘superreg’ – so where does the name come from and what is it?

The history of very high performance low-voltage regulators is well documented on Walt Jung’s website (www.waltjung.org – look under Library|Regulators & References). An early design that attracted attention was Mike Sulzer’s, published in 1980 and 1981 in Audio Amateur. I added something to that in 1987, and then I was invited by Walt Jung to work on a further improved version. This was published in a series of four articles in Audio Amateur in 1995 by Walt (part...
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Heretical 834p mods

Posted 9th December 2013 at 12:00 AM by hbc
Updated 14th December 2013 at 05:23 PM by hbc

The EAR 834p, is a marvellous and clever circuit, in its various optimisations and design features that are often not really understood... I acquired my second one a while ago, my first one was tweaked quite successfully to make very acceptable sound by adjusting the 10pf to 5pf and changing output CF to ECC81, and removing some surplus output potential dividers, and careful valve selection. Lowest noise first, and highest gain second.

However, it went away...

The problem I have seen with these is that they sometimes suffer muddy woolly sound in the bass which tends to spoil the over all effect. The new phono box I recently got suffers this way. Now I am suspicious of feedback loops, and how they work. I suspected that the 834p was maybe running a little short of gain in the lower registers. As I enjoy heresy, and after much consideration, I decided that bootstrapping the second stage ought to give me some more gain for the feedback loop to work. See circuit...
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