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Cost optimized active crossover

Posted 7th April 2015 at 07:03 AM by abraxalito

I've driven the BOM cost of this board down quite hard by choosing some 'disrespected' opamps to build it around - TL084s. They go for 0.5RMB on Taobao (about $0.08, same as a recycled TDA1387). Listening so far is positive but I've got no audiophile opamp reference to check it against. In terms of bang for the buck though, its going to be very hard to beat. All filter caps are NP0 ceramics, resistors are bog-standard thick film 0805s.

What's different about this build for me is its fully balanced and classA operation in order to cancel power supply noise. To get classA operation from TL084s means the feedback/filter networks must be very high impedance so as to draw under 100uA peak currents. Opamps aren't used as output buffers, rather I've gone for emitter followers loaded by two-transistor CCSs.

The picture is my second prototype, using the best (aka lowest ESR) caps I could get hold of - Nichicon HZ and Nippon Chemi KZE. All the copper wires sticking up around...
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Atmel plays fast and loose with its new chip's low power credentials

Posted 31st March 2015 at 02:26 AM by abraxalito
Updated 2nd April 2015 at 03:04 AM by abraxalito

On the face of it, this article gives the appearance that Atmel's raced into the lead by a substantial margin in the realm of low power ARM offerings - New ARM-powered chip aims for battery life measured in decades | Ars Technica

However a quick peek beneath the surface reveals all is not what it seems at first sight.

First a stand-out from the linked article :

Atmel, the San Jose-based microcontroller maker, today released samples of a new type of ultra-low power, ARM based microcontroller that could radically extend the battery life of small low-power intelligent devices. The new ... (MCUs) consume less than 35 microamps of power per megahertz of processing speed while active,

Radically eh? Less than 35 microamps /MHz is the claim here - wanna see how that stacks up?

Ostensibly the 35uA headline figure is a worthwhile improvement over NXP's latest offering - where NXP is claiming 55uA/MHz (the LPC5410x I posted about...
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Improving A/D perfromance of Sound Balster X-fi Music (SB1240) - and a Puzzle!!!

Posted 29th March 2015 at 12:51 PM by googlyone
Updated 7th September 2015 at 12:06 PM by googlyone

I have been playing with measuring distortion of signal sources and amplifiers a bit over the last year or two.

I am serious enough to spend some time and thought on this, but not serious enough to sink significant cash into application specific test equipment.

I have a couple of USB Sound Blaster X-fi Music (SB1240) sound cards I use for measurements. The original intent of these was for speaker test and general music. I am pressing these into use for more serious measurement.

The ADC in these is the Cirrus Logic CS5361, which is a pretty good ADC. The DAC is the AKM4396, which is a decent DAC.

When making measurements I hit a problem. The raw performance of the CS5361 is specced to be -99dBc guaranteed an -105dBc typical for THD+N. I couldn't get this.

A few things quickly went onto my list of things to try:
-1- Switching - the sound card has a lot of this - how was it implemented?
-2- Op amps...
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I've been cloned!

Posted 29th March 2015 at 12:26 PM by rjm (RJM Audio Blog)
Updated 31st March 2015 at 09:31 AM by rjm

Back at the dawn of time one of the first audio circuits I worked on was the Gainclone, followed closely by The Dac of the Klones (Oh my, the nostalgia!) and of course the Phonoclone.

The VSPS was a side-project that grew out of the Phonoclone, and actually ended up first out of the gate as a working circuit.

Apart from the general design philosophy (low parts count, simplicity, careful layout and grounding) it has no particular link to 47 Labs. While the concept of a non-inverting op amp active phonostage is nothing original the circuit is mine, particularly the configuration and values of the RIAA filter which I calculated and simulated myself. The rest is an amalgam from a dozen or so different sources, textbooks, datasheets and application notes &c. All the values are quite carefully chosen.

That said I've always put the circuits and everything else on the internet, with source attribution as I felt necessary. The boards and kits came...
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Remote tweaking

Posted 25th March 2015 at 11:13 PM by fas42

A thought has popped into my head ... I enjoy the process - well, most of the time, :D! - of refining systems so that they deliver what I call convincing sound - a quality beyond what people typically achieve with audio systems assembled and "optimised" in conventional ways. And I've been able to help others at times move in the right directions, to advance what they're currently achieving.

So, I'm curious whether there are any out there, lurking :), interested in having a one to one interaction with me in having a go at getting something better out of their systems. Before wasting any more time on pursuing a silly idea, I would be curious if anybody is interested? And if you don't like to "expose" yourself to the great unwashed, :D, just send me a PM!

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Mid-life crisis turntable purchase and speaker build and who knows what else?!

Posted 25th March 2015 at 04:14 AM by Mike94531

Not sure why, but about a month ago I decided that I wanted to buy a turntable and get into listening to albums. So I did some research and bought an old used Technics SL-BD22 and a Sansui R99-Z.

Now I have been hitting up Goodwill looking for albums and I found an actual record only store about 45 minutes from me and I bought some records from them over the weekend.

The bad news is that I don't have any decent speakers, I used to have some old Yamaha home entertainment speakers for our old CD player however I sold them at a garage sale 3 years ago or so.

How have I been listening to my new to me albums? Well, I am using my speaker setup with subwoofer that supposed to be in my office connected to my computer. My kids are not happy to be watching YouTube videos with the old stock computer speakers!

Speaking of speakers, I bought the Parts Express MTM TriTrix speaker kit...without the wood.

Below are some pictures of my stuff...
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TDA8946AJ headphone amplifier

Posted 20th March 2015 at 04:13 AM by abraxalito
Updated 23rd March 2015 at 06:40 AM by abraxalito

I built this up to see how the TDA8946AJ DC-controlled volume element sounds. According to the datasheet and comparing the figures with those for the same amp minus the volume control (TDA8946J) there's some additional THD so I was curious to hear how transparent it is.

There are transformers both on the input and the output of this. On the input to match levels (4:1 step down) and to do unbal-bal conversion. On the output again for the same reasons, except bal-unbal to drive my phones which I've not modified for 4 wire operation. The trafos are ferrite (=very cheap) RM10 for the input (under the board) and RM12 for output (behind the board). In order to be able to match a variety of phones, I've wound 4 identical secondaries so they can be combined in series or parallel.

From the pic you'll see the customary array of caps - I need to order up some lowESR (preferably NCC) 1800uF caps to do better justice to the rails. Last night I experimented with some ceramics...
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Doin' a "Gilmore" : a discrete transistor headphone amplifier

Posted 10th March 2015 at 12:17 AM by rjm (RJM Audio Blog)
Updated 13th March 2015 at 10:42 PM by rjm

Recently I spent some time updating the diamond buffer of Sapphire headphone amp circuit. Later I stumbled on Kevin Gilmore's headphone amp circuit. Well, I'd read it before, but it had slipped my mind.

On seeing the Gilmore circuit again the thought process re. a Sapphire+Gilmore went something as follows,

"Toss out op amp, convert the Gilmore dual-LTP front end to bipolar, bolt the Sapphire3 buffer stage to the back, and substitute in the Sapphire3 current sources. Wrap in a mild feedback loop."

The result is shown attached. The Vbe multiplier is still a simple resistor (R33) ... that may need to be refined to add thermal throttling. The offset servo is not shown, but the action is shown as Vadj. Alternatively a trim pot would be placed between R30 and R32 to provide a small measure of offset adjustment. Most of the open loop gain is controlled by R14,R15 ... it seems to me that some work could still be done in that area. Despite going...
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Schitt's flagship DAC uses a not-for-audio DAC chip.

Posted 7th March 2015 at 08:43 AM by abraxalito
Updated 6th May 2017 at 12:58 PM by abraxalito

The Schitt Yggy DAC has already created something of a stir over on Head-Fi amongst those who've heard pre-production prototypes. Its of interest not just because of the pre-launch buzz but also because the designer (Mike Moffat) is one of the long-time seasoned guys in the field. He says this is the best practical DAC he knows how to build. And its priced ISTM very reasonably given the amount of tech it embodies ($2300) - the DAC chips come from ADI and are $64 a piece on the manu's website. He's using 4 of them but says he had to address the glitching of the DAC without using a sample-hold which sounds like ***.

The chip is the AD5791BRUZ which ADI designed for industrial/scientific/medical applications rather than for audio. Datasheet attached.

Having looked over the DS what strikes me as interesting is that this is a 20bit DAC (1ppm) yet the 1kHz THD performance (p4) isn't anything to write home about (-97dB) and that figure is given at a very low sample rate...
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dantimax (contact information)

Posted 25th February 2015 at 03:56 PM by djg440

Was wondering if any one can help with how to contact...
I have placed a order for three remote boards and three motorized alps pots.
all of the contact links do not go through that is supplied on his sights. Hopefully someone has a email address or contact information that has worked for them and can share it.
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