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The Front End

Posted 19th November 2012 at 05:26 AM by rjm
Updated 22nd November 2012 at 06:18 AM by rjm

The most disruptive audio technology since the CD, since the advent of stereo actually, is ... the iPod. You can lump in mp3, iTunes, and digital distribution in there if you want, but itís the iPod, the physical device, which has more than anything re-defined what we think of as an audio system in the twenty first century. Shelves of physical media and a playback unit, or, if you preferred, broadcast content, has been displaced by a handheld, personal, portable jukebox. The audio component system of the 1970ís (media, sources, preamp, amp, speakers) has faded into obsolescence, replaced by powered speakers, headphone amplifiers, desktop audio, compact ďspeakers+amplifierĒ systems the ubiquitous "dock" fronting a traditional amplifier-speaker system.

Audio is missing the front end.

Because it isnít an iPod, Iím sure of that. Its day is done. No, it's pretty clear to me that the front-front end of the future is settled: Its the internet. The cloud....
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Old

My Nexus 7 Tablet

Posted 12th November 2012 at 07:54 AM by rjm
Updated 18th November 2012 at 05:03 AM by rjm

The Nexus 7 is cheap. I paid 19,800 yen for my 16 GB model, shipping and tax inc., and it came with 2,000 Yen credit to buy apps and movies and such in the online Google Play store. And yes, its plastic, even the silver metallic trim around the edge is just a silver-coated plastic part. It is solid, however; sturdy, well-built, and good-looking. The back is covered in grippy, dimpled rubber that feels like leather. The screen is a little dim, but high resolution (800x1280) ~220pi, pretty to look at and easy to read.

With a 7" screen and default portrait orientation the device is closer in spirit to a large smartphone than a small tablet. A giant, wi-fi only smartphone. It's a handy size for reading paperback-format books, comics, and news articles, but not so hot for magazine format publications and A4-formatted journal articles. Browsing the web is generally fine, but the experience varies widely depending on the individual layout of the web page. As you might expect,...
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Old

Akihabara, lost to the maids.

Posted 21st September 2012 at 12:51 AM by rjm
Updated 24th September 2012 at 12:24 AM by rjm

A maid cafe is, as far as I can make out - and wikipedia confirms - a cafe/light restaurant staffed by girls who dress up as anime characters or doll-like maid costumes. Chatting with customers is encouraged, so the atmosphere is more social than a regular cafe. Its also more expensive, and the food worse. (from what I can judge from the menus: its what my nine year old daughter might make if left alone in the kitchen...) They advertise by by having the staff stand around - in costume - on busy street corners nearby handing out small cards.

This is a phenomena that started about 5-6 years ago, or at least started to go mainstream then. Ground zero for maid cafes is the "nerd districts" where computers, comic books, and video games were sold: Akihabara in Tokyo, Nipponbashi in Osaka.

Growth appears to be exponential: every time I visit either region (I'm in Tokyo right now, staying near Akihabara) the number of maid cafes (and therefore maids on the street)...
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Old

B-board Boxer Project : A Low Voltage Headphone Amplifier for 16 ohm Loads

Posted 7th July 2012 at 01:19 AM by rjm
Updated 29th September 2012 at 03:58 AM by rjm

I always seem to end up optimizing my headphone amplifier circuits for higher impedance headphones, this mostly happens because I own a pair of 300 ohm HD-600s and it is tedious to design for both the voltage requirements of high impedance headphones and the current requirements of low impedance headphones.

Not impossible, just, for the class-A designs I seem to be building recently, increasingly large, heavy, and impractical.

Complimentary transistor circuits, however, offer the opportunity to swap voltage for current at something close to the same design cost. They are therefore a practical topology for efficient class-A power delivery into low impedance headphones. As a design experiment, my aim is to discover how far I can leverage an ultra-low-voltage, unity gain circuit for compactness without sacrificing sound quality.

Ok. Back-of-the-envelope calculations:

A typical 16 ohm in-ear-headphone has a sensitivity of 100-105...
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Old

NwAvGuy odac 24/96 DAC review

Posted 23rd June 2012 at 08:02 AM by rjm
Updated 2nd July 2012 at 05:52 PM by rjm

I cased up my odac board (NwAvGuy via jtktam) in a small aluminum project box.

The DAC is a simple two-chip affair, with a Tenor TE7022L controller fronting the ESS ES9023 DAC and integrated line driver. A couple of voltage regulators, the clock oscillator, and an eeprom chip round out the principle component list.

I compared it with my Onkyo SE-200PCI sound card. This 24/192 (115dB S/N A-weighted, 0.003% THD 0dB 1kHz) PCI card sells for about $15,000 yen and is based on the VIA Envy24HT and Wolfson WM8740.

I'm listening to 16bit 44.1kHz .wav (CD rips), though VLC [sample rate converter set to sinc, best quality, resampling quality 8]. Windows 8 release preview [default format 24/192 (onkyo), 24/96 (odac)]. Line out though Oyaide PA-02TR interconnects to the Sapphire headphone amp, and Sennheiser HD-600s.

**

So, I was planning on writing up a big 'ol review with my impressions, but, well... there's not really a...
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Old

modest base requirements for a line stage

Posted 22nd June 2012 at 07:44 AM by rjm
Updated 29th June 2012 at 06:38 AM by rjm

Copied from this post, for reference.

Quote:
Originally Posted by RNMarsh
Here are my own modest base requirements for a line stage (similar for power amp):

1. Open loop BW of 40KHz or more (-3dB)... 20KHz min.
2. IM and THD of less than .001% at 1v rms into 30 ohms for any frequency between 20Hz and 20KHz.
3. No coupling caps on input or output or in feedback path.
4. No use of dc servo circuits to track and correct dc offset and drift.
5. No more than 6-8 transistors (excluding power supply).
6. S/N ref 1 volt rms and without weighting of at least -130dB (input can be shorted or terminated).
7. No significant harmonics above the 2nd and 3rd.
8. Closed loop gain between 12 and 20 dBv
9. Low Zout (less than a fraction of an Ohm at any audio freq).
10. Distortion not be changed by source Z.
11. Transistors should be low cost and not be exotic, hard to obtain, very expensive or no longer manufactured.

There might
...
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Old

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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Old

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

http://kstlab.web.fc2.com/pro003.html

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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Old

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,
Quote:
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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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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