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Another iteration of DACS for Crossover

Posted 26th May 2012 at 04:00 PM by googlyone

I have never been happy using DACs to implement volume control. I guess largely because of the obvious degradation in resolution at low volume levels.

On my first DSP crossover I used an AD1939 CODEC, which has 24 bit resolution - though obviously lesser precision - and my approach here was to use a mix of steeped attenuator and digitally implemented volume control.

It worked well - though pretty shortly after I built an 8 channel PGA2320 based volume control.

For my new DSP crossover I started with a simple CS4398 in the DAC output. even when I built the first boards I KNEW I would be going back to integrate a programmable attenuator.

Why didn't I just start with it? **** knows.

At lease with the modular approach all I had to do was respin my DAC board to include a PGA2320 along with the CS4398. I already had SPI to the board, sop I can sneakily use these lines for the PGA 2320, as the CS4398 is in hard wired...
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Old

6N9S / 6SL7 and DC heaters

Posted 18th May 2012 at 04:03 PM by triode_al

I have been reworking my RIAA preamp the past weeks - main effort to install a SALAS shunt in the HV.
I had some problems looking like instability of the DC. I also noted that every on/off cycle, the problem got worse. And while developing, I would switch the preamp on an off often, to see the effect of the tweaks, such as setting the shunt cuirrent.

Later I found that one 6N9S tube was 'dying', really, it went black, but intermittent.
The heater wires probably had been stretched a bit and in cold state they made some contact (measured 3-4 ohm) but when heated up it lost contact. The effect cascaded into the Vb, and was seen on both outputs similarly.

I conclude The [Russian, Reflektor brand, big logo] tube is very sensitive to the heater.

I had the two tubes running in series from a medium impedance 12 V source (IRF250, gate connected to drain via 100k resistor and a 300 uF cap: relatively slow start of 2 secs. But too fast probably...
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Old

prototype odac panels

Posted 18th May 2012 at 01:31 PM by jtktam (Newbie audio DIYer)

sweet! look at those panels!
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Old

odac

Posted 14th May 2012 at 10:37 AM by jtktam (Newbie audio DIYer)
Updated 14th May 2012 at 10:48 AM by jtktam

I had one of the first production samples in my hands for a few days and the odac sounds awesome. I have used it with my objective2, my ck2iii, my sapphire, and used it to output to my home system. it sounds so good it's hard to describe in words.

i did an informal ab test with my benchmark dac1 and the odac/o2 combo is very close in performance.

i think this will be an exciting product indeed, i can't wait for the oda to come out to complete the trifecta of objectives
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Old

3 watt ECL86 SE amp!!

Posted 12th May 2012 at 09:44 PM by hbc

It seems that random acquisitions seem to precede the direction of my inspirations. This has come in the form of a Technics SU-9011 pre amp and a pair of small infinite baffle 2 way speakers. I have no idea what they are, so please share if you do.

The active sony’s, to be honest have been getting me down, they still have a mushy quality to them. The SU-9011 seems to work but was not the happy match with them either. Enter the little 2 ways and my gain clone. Bad.

So I decided to try and power up a little EL86 record player amp which I acquired a few months ago from a friend. This seems to be a close relation to the Mullard economical 3 watt amplifier. To my slight surprise it is in good working order, so with a bit of drilling fitted some 4mm posts and some phono inputs.

With the little 2 ways and the Technics is a lovely combination, real bloom, very enjoyable, and some nice bass.
Technics has “opamps” in, so that gets...
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Old

Ceramic capacitors : who knew?

Posted 12th May 2012 at 02:15 AM by rjm
Updated 29th May 2012 at 12:51 AM by rjm

This I have been experimenting - call it a hunch - on the effects of bypassing electrolytic capcitors (Nichicon FW and KW) with 0.1 uF TDK ceramics (Mouser 810-FK28X7S2A104K) with the diamond buffer circuit used in both my B-board preamp and Sapphire headphone amplifier.

This being a mod, I had to solder the caps to the underside of the boards, attached to the leads of the Nichicon 100uF electrolyic capacitors.

I used four ceramics per channel, one per active device in the diamond buffer if you like.

I did several other changes on the B-board at the same time, so it wasn't obvious until I modded the Sapphire in the same way what was the result of the bypassing. Anyway, with both the improvement was immediate and dramatic: any sense of "transistor-like" treble glare is completely quenched. The whole top end takes a step backwards, not in extension, but in prominence.

Less audiophile detail, more swinging mojo.

Update...
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Old

Denon 103 output out of balance

Posted 8th May 2012 at 10:19 AM by tabarddn (Denon 103 History)

Hi, I have just received a 2nd hand 103, (decappitated my 1st one, yes I know I should have had it re-tipped)
Anyway the output is swung to the left. I have a 2 arm system, identical arms and a Clearaudio Beta S in the other) I use the Denon through a SUT and have swapped arms and the is no improvement. Is ther a way to rebalance the output after the SUT say with resistors. I cannot do it after the head amp as the Clearaudio uses this haed amp through a switch box.
Advice, and you thoughs please
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Old

Stepped Attenuator

Posted 8th May 2012 at 01:20 AM by rjm
Updated 8th May 2012 at 01:24 AM by rjm

I bought a stepped attenuator (actually, two of them) from ebay seller hanshare-electronics. As always with eBay, I was a little worried about what would show up.

I'm happy to report that this is a nice job. The included resistors are clearly labelled, and the documentation, while spartan, is sufficient.

The only negative is the rotary switch is a bit "clicky". Better quality units I've seen are more damped.

On the positive side, though, the resistor values are very elegantly selected, to give a smooth response of about 4 dB per step from -60 to -40 dB, and 2 dB per step from -40 to -3 dB. Having been-there, done-that, I can say that I'd happily pay the asking price to get those resistors sourced and sorted for me. Next time, I'd also pay to get it assembled. Soldering was more painful than I imagined it would be, and the pre-assembled units much neater-looking than what mine ended up as.
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Old

RJM B-board vs. 47 Labs 0247

Posted 5th May 2012 at 01:29 PM by rjm
Updated 6th May 2012 at 07:16 AM by rjm

B-board vs. 0247.

Comparison of the noise baselines, measured at the circuit output using a NI USB-6215 DAQ. Unloaded for the preamps, and with a 6 ohm load for the 0347 amplifier.
  • B-board: -139 [300Hz-100kHz] 0 dB gain (-139 - 0 = -139 dB, 110 nV sqrtHz input referred). The actual B-board output noise is below this measurement threshold.
  • 0247: -124 dB [300Hz-100kHz] 14 dB gain (-124 - 14 = -139 dB, 110 nV sqrtHz input referred).
  • 0347: -109 dB [300Hz-100kHz] 31 dB gain (-109 - 31 = -140 dB, 100 nV sqrtHz input referred).

See the attached plot for the FFT data. Note the peak at 28 Hz is an artifact of the measurement apparatus.

By way of comparison, a typical audio opamp has an input referred voltage noise figure of 3-8 nV sqrtHz (-170 ~ -160 dB) and can be expected to return this datasheet specification in most well-designed circuits. In other words the output noise is going to be about -160 dB + the circuit gain.

The 0247...
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Old

The Media Room

Posted 1st May 2012 at 02:28 PM by DrDyna

Well, I still need another coat of paint and some crown molding / baseboard, but it's coming along nicely.

The front wall is out about 25" from the foundation, I plan to install 2 Ficar IB318's in there. The EP2000 should be here tomorrow!
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