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Exploring laptop sound

Posted 16th April 2015 at 11:38 PM by fas42
Updated 16th April 2015 at 11:44 PM by fas42

As mentioned elsewhere, now have a laptop with reasonable internal sound, a HP Pavillion of quite some vintage. My mainstay Dell over many years prior lost its sound many years ago, a USB port got cooked, and took down the sound circuitry at the same time; and what I was using as an interim, another Dell of nominally very good quality, had downright faulty sound, buzzed and rattled - was plain sick ...

OK, so the exercise here will be to see how good I can get the newly "installed" HP unit's sound to be, by my measures, using minimal or zero internal hardware tweaking - essentially working out what factors impact the sound, and whether the negatives can be circumvented. This gives an idea of how I go about things, what I use to "measure" with, what I'm listening for.

Trying a couple of CDs that I use often the signs were good - obviously no bass, and the volume is very restricted, but otherwise the sound was 'correct' - the music sounded like...
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Old

What's the PSRR of an emitter follower?

Posted 16th April 2015 at 01:28 AM by abraxalito

I asked this question of Yahoo and didn't find anything much - a few people mentioning the PSRR of their C-multipliers but no simulation results and no algebra. So I fired up LTspice for myself to take a look. The transistor models are the usual Gummel-Poon ones LTspice provides (one up from hybrid-pi) which look to be decent enough for this purpose.

I went for two EFs (sometimes called EF2) as that's probably a more practical arrangement in an audio amp. Some designers even prefer EF3 to get much lighter loading on the VAS/TIS. The EF load I made independent of the bias current so I could learn more about biassing. I used AC simulation to have a look at how the PSRR varied over the audio band.

Turns out the PSRR depends on at least three circuit details and one inherent characteristic of the EF transistor used. In no particular order the circuit aspects which matter are the source impedance seen by the base of the EF, secondly the load impedance seen and finally...
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Old

Are PSRR plots all they're cracked up to be?

Posted 15th April 2015 at 04:19 AM by abraxalito

My experiments last autumn with putting a transformer between a chipamp and a drive unit left me with one nagging question. Why was the sound so much clearer with the trafo than without, given that the trafo's voltage ratio was relatively low (1.5:1)? Even Frank was surprised at so much change and suggested some other effect was in play (amp instability). I've not ruled out amp instability but I have made some progress on understanding chipamp PSRR.

The first trafo experiment was done with the TDA7265 - I've since tried trafos on two other chipamps - TDA8947 and LM4766 with similar subjective results - a much clearer sound, more depth to the soundstage and so many tiny details on recordings becoming clearer that the experience has become akin to headphone listening. The trafo ratio has increased - 2.5:1 for the TDA8947 (21V rails, bridged) and 5:1 in the case of the LM4766 (again bridged), running on 62V total supply.

My current listening system is LM4766 with...
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Old

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

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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Old

I've been cloned!

Posted 29th March 2015 at 12:26 PM by rjm
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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Old

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, ! - 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, , just send me a PM!

Cheers,
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Old

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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Old

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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