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Old

Akihabara, lost to the maids.

Posted 20th September 2012 at 11:51 PM by rjm
Updated 23rd September 2012 at 11:24 PM 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

modest base requirements for a line stage

Posted 22nd June 2012 at 06:44 AM by rjm
Updated 29th June 2012 at 05:38 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

Bypassing, Goldilocks, and the Sound of Nothing

Posted 31st May 2012 at 06:28 PM by rjm
Updated 1st June 2012 at 11:53 PM 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

Headphone Amplifier Gain

Posted 2nd April 2012 at 08:45 AM by rjm
Updated 2nd April 2012 at 11:43 AM by rjm

I posted this earlier today, but I think it deserves to be put in the blog - if nothing else so I can find it again next time ... and there always seems to be a next time when it comes to calculating headphone amplifier gains.

Starting at the beginning, the encoded data on a CD goes from 0 to 1 in 2^16 steps, but in a typical CD player or soundcard, the DAC output is -2.8 V to 2.8 V or 2 V rms or 6 dB. Many sources, such as phono stages and portable audio, are lower, perhaps as low as 250 mV.

How loud the sound is depends on the source signal amplitude, the position of the volume control, the circuit gain, and the impedance and sensitivity of the headphones.

As a practical matter, most people would want the volume control at the 9-10 o'clock position for "normal" listening.

For standard "line level" source, the gain required to keep the volume control at a 9-10 o'clock varies depending on the impedance...
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Old

My system (Jan 2012)

Posted 23rd January 2012 at 12:12 PM by rjm
Updated 26th January 2012 at 02:57 AM by rjm

Biggest changeover in many years.

Denon DP-2000, DA-307, DL-103 turntable/tonearm/cartridge
Phonoclone 3 with 160 VA Plitron power supply
47 Labs "Treasure" model 0247 preamplifier
47 Labs "Treasure" model 0347 amplifier
Onkyo D-605SR speakers
Cables by oyaide, mostly.
(photo: Pentax K10D, Pentax FA 31mm F1.8 AL Limited)
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Old

Five-times-bandwidth

Posted 3rd January 2012 at 04:44 PM by rjm

If we accept that conventional wisdom that the audio bandwidth extends from 20 Hz to 20 kHz, a good rule of thumb for the f(-3 dB) high and low cutoff points of the frequency response of each audio circuit element is 5x the bandwidth, or 4 Hz to 100 kHz. In practice most designs tend to shift that range a little to the higher frequencies, so perhaps 5 Hz - 200 kHz, or 4 - 250 kHz.

Personally I "tune" my circuits to 4 Hz. That is, the time constants are adjusted to about 4 ms. Capacitance is usually cheap enough to go even longer, but the influence on sonics is typically net negative.

The high frequency side is more interesting, since many circuit elements naturally run into the megahertz range, the the question is do you actively try to prevent that, and if so, where and how?

The biggest issue is bypassing: a small value electrolytic (100 uF) is probably fine up to 100 kHz or so, but quite useless at 2 Mhz. The textbook solution is...
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Old

The cost of hi-end audio: is it worth it?

Posted 20th December 2011 at 05:16 AM by rjm
Updated 20th December 2011 at 05:30 AM by rjm

Having recently actually bought some new (not used, not my own design, and relatively expensive) audio gear, and from 47 Labs no less, the following question has been occupying my thoughts of late:

How much would you pay to not have a component installed in the audio equipment you buy?

The traditional price scheme for audio equipment is [BOM-times-X], where BOM is the cost of the parts used to make it, and X is a multiple to cover fabrication and distribution costs, as well as profit for the various parties involved. My understanding is that for consumer audio "X" is about 4, though companies with strong brand recognition can get away with higher multiples. And do.

The basic problem is this: how much it costs to build and how good it sounds are not the same thing. There is some correlation: a large, high quality transformer is pretty much guaranteed to improve the sound quality, but for the rest, stuffing a pretty box with many cheap...
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