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The Double-Diamond Amplifier (DDA)

Posted 13th June 2012 at 07:09 AM by rjm
Updated 16th June 2012 at 03:57 PM by rjm

This isn't my first attempt. It's been on my mind for a while: how to coax a diamond buffer into giving voltage gain, without resorting to fronting it with a op amp.

After reading a particularly gregarious thread over in the headphone forum, I'm more and more stoked on giving this a real shot.

Despite the (catchy) name I'm thinking pre-amplifier rather than amplifier applications.

update: I have have a quick and dirty sim up and running in ltspice. Curiously, the output distortion is 15 dB lower when the buffer runs open loop than when it is included inside the feedback loop. Intrigued. Currently under investigation.

update: refined the sim slightly, achieved -85 dB distortion levels at 0 dB / 1 kHz / 600 ohms running the output buffer open loop. Bandwidth is just under 1 MHz, adjusted by changing the feedback resistance. As before, performance sims out notably worse with the buffer
inside the feedback loop.
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Project "Originality" Headphone Amplifier by Tao Kurohane

Posted 11th June 2012 at 01:35 PM by rjm
Updated 12th June 2012 at 12:32 AM by rjm

It is certainly a little bit different. One might be tempted to say "gilding the lily", but come on, headphone amplifiers are just the right place for these indulgences.

Building your own long tailed pair (LTP) to bolt in front of an IC op amp has fallen out of favor in recent years. I must admit I couldn't see the point then, and still don't.

I've seen a number of headphone amp circuits with 3 paralleled pairs of output devices. I wonder if there any real advantage over simply using one pair at 3x the current, perhaps with slightly larger transistors?
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Ultra high-end amplifier for Stax Electrostatic Headphones

Posted 9th June 2012 at 10:23 AM by dvb projekt

Because my Stax SR-404 Limited is now one year in his box without using...

Click the image to open in full size.

...i start a new project, based on the fabulous circuit from Andreas Rauenbuehler on

The Transistoramp V4.0

Click the image to open in full size.

My pcb´s are ready and now i am collecting the parts.

A set of wonderful teflon Stax Pro and Normal jacks, i´ve got from a group buy on Head Case.

Click the image to open in full size. Click the image to open in full size.

So stay tuned...

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Evolving NOS -> MOS

Posted 9th June 2012 at 08:13 AM by abraxalito

Fixing the NOS droop has the undesirable side-effect of making the imaging components worse - HF gain can't be increased up to 20kHz and then suddenly taken away above 22kHz

In the spirit of taming the near-ultrasonic emissons of a NOS DAC, I'm currently playing with an MOS design - where 'M' stands for 'minimal'. I've been wondering if the attractiveness of the NOS sound will still be preserved if I go to 2X OS in order to fix up the ultrasonics. No practical analog filter can have a sharp enough band edge so a digital one it does have to be...

A DSP implemented digital filter comes at a price - that of throwing away some bits (I'm still using only 16bit DAC chips - TDA1387) so I'm now exploring using a transversal filter (no DSP) to carry out 2X OS. The LTSpice screen grab shows the architecture I'm playing with - a 19 tap delay line feeding 19 separate DACs. The DACs are shown on the right as current sources and their individual weightings are...
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Bypassing, Goldilocks, and the Sound of Nothing

Posted 31st May 2012 at 07:28 PM by rjm
Updated 2nd June 2012 at 12:53 AM by rjm

Douglas Self writes,
The 5532 and 5534 type op-amps require adequate supply decoupling if they are to remain stable, otherwise they appear to be subject to some sort of internal oscillation that degrades linearity without being visible on a normal oscilloscope. The essential requirement is that the positive and negative rails should be decoupled with a 100 nF capacitor between them, at a distance of not more than a few millimeters from the op-amp; normally one such capacitor is fitted per package as close to it as possible.
He's someone who should know. Anyway, it doesn't take much digging on the internet to confirm beyond reasonable doubt that bypass caps should be as close to the op amp power pins as possible. So thinking about my previous experiments with bypassing the Sapphire, by adding bypass caps around the transistors I also effectively also added a bypass for the op amp, but a rather poor one as the power-pin-to-power-pin round trip loop distance is probably 10...
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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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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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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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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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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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