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Another package in the mail...

Posted 14th January 2012 at 11:30 AM by rjm

The 47 Labs "Treasure" stereo amplifier kit model 0367 has just arrived here at RJM Audio central command.

61,500 yen delivered, a tad more than the model 0247 headphone amplifier / DAC. Basically lose the volume control and DAC board, gain a bigger transformer and a thick aluminum bottom plate that serves as the heatsink... the amplifier circuit itself is almost identical, just with a slightly bulked-up output stage and the addition of certain safety considerations such as fine tune-able bias current and thermal protection for the output transistors.

Which makes an unusual circuit for a power amplifier: the output stage is a unity gain current buffer running open loop. For a headphone amp that's justafiable because the bias current is such that the amp will almost always be running in class A. For a power amp rated 40 W into 4 ohms, it's class AB.

Mr. Tsukahara seems pretty pleased with the result though, and I am anxious to try it...
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Old

This vs. that.

Posted 13th January 2012 at 12:41 AM by rjm
Updated 26th January 2012 at 06:42 AM by rjm

47 Labs 0247 vs. RJM Audio Sapphire

I wasn't even aware that the folks at 47 Labs were developing a headphone amplifier until after the Sapphire was finished, and I'm sure they didn't know what I was working on, so it's all the more remarkable just how similar the two designs are. Two separate answers from two separate people sharing the same general design philosophy.

Similarities:

- Solid state op amp voltage stage front end and solid state push-pull buffer running open loop for the output stage.
- Gain of 5-6x (14-16 dB)
- 20-30 mA bias current in the output stage.
- All BJT circuit** (see footnote)
- Use of "diamond buffer" circuit element. (Albeit in very different ways)
- 10 V voltage rails, split supply.

Differences:

- My voltage stage is an OPA134, or any 8 pin DIP op amp IC. 47 Labs voltage stage is a fully discrete current feedback op amp with a diamond buffer...
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Old

47 labs 0247 : done, tested, working

Posted 12th January 2012 at 01:18 PM by rjm

A few bumps along the way:

1. Soldered one of the caps in backwards. Removed and fixed, fortunately before power was applied to the board.

2. Soldered one of the transistors into the wrong place. Removed and fixed.

3. Dead channel on power up. Bad solder joint on the emitter of one the output transistors. Eyesight not what it used to be. Found on second inspection, fixed.

4. DAC board not level with cutout on front panel, had to use washers to raise it to the correct height.

Other than that, things went smoothly enough, though I spent more time with tweezers routing lead wires than is ideal for a commercially released audio kit. It's not so much difficult as it is painstaking - and I have quite a lot of experience doing these things so I imagine I had an easier time of it on the whole than most will.

The final result however is aesthetically quite pleasing, well worth the effort and expense. It is...
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Old

Progress so far

Posted 6th January 2012 at 01:02 PM by rjm
Updated 7th January 2012 at 03:00 AM by rjm

The first stage is getting the power supply installed and running. That's the little board by the transformer, which just has the diodes, main filter capacitors, and isolation resistors on the voltage rails. The case top lid is transparent plexiglass, so the internals are lit by three white LEDs to show off, and light the control labels, which are printed on the top lid rather than the front and back sides of the case.

You'll notice I have followed the instructions and removed the plastic covers on the electrolytic capacitors.

For the record I do think they sound better that way, I just normally can't be bothered as, for example, my phonoclone 3 boards have 28 of them and I consider the exposed metal surfaces a bit of a safety issue as well.
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Old

47 Labs 0247 unboxing, part deux

Posted 5th January 2012 at 11:29 AM by rjm

My kit was missing the amplifier circuit boards! So many other neat stuff distracted me from this vital fact!

So far I've wired the AC power line components, transformer, and the power supply board. It's slow progress, mainly for wanting to be sure of getting it right the first time. It's dense and fiddly, desoldering stuff in there to fix a ****-up would not be pleasant work at all.
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Old

Five-times-bandwidth

Posted 3rd January 2012 at 05:44 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

47 Labs 0247 "Treasure" unboxing

Posted 21st December 2011 at 04:33 AM by rjm
Updated 22nd December 2011 at 10:47 PM by rjm

It's here!

It came in a box the size of a small shoe box.

Curious, delightful mix of the mundane and the exotic, outwardly plain but clearly immense thought and effort has gone into the preparation.

The gorgeous hammertone finish, hand-matched transistors, and ultra-high quality machined volume/selector knobs are the little signs that immediately set it apart from the ordinary.
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Old

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

Posted 20th December 2011 at 06:16 AM by rjm
Updated 20th December 2011 at 06:30 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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Old

47 Labs "Treasure" 0247 shipping update

Posted 20th December 2011 at 12:19 AM by rjm

Scheduled to be delivered tomorrow evening!
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Old

Fascinating: SMT attenuator retrofitted into ALPs case

Posted 17th December 2011 at 03:08 AM by rjm

http://www.icl.co.jp/audio/att.htm

Less than 3,000 yen, too. Pity it's only available as 100K types, but for tube amps this is a pretty handy little part to have around.
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