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.

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...

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.

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...

Scheduled to be delivered tomorrow evening!

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.

Fancy building your own CD player with built in non-oversampling DA converter from a kit?

Look no further.

Based on a TEAC transport and ye olde Philips TDA1543 for the nonoversampling DAC

DAC is basically the Progression DAC (see DAC of ther Klones) reborn.

or salient details:

-top loading, close to the lit to automatically load the TOC.
- isolated digital and analog power supplies
- ATMEL AVR microcontroller, custom program/operating system
- simple, easy to understand display and controls
- standalone or use as a transport with external DAC
- small footprint, B5 size(W250 × H65 × D175mm)
- comes with a remote!

Although offered as a kit or pre-built, my suspicion is that all the real work has already been done: programming the microcontroller, now that's an area where most DIYers still fear to tread!

Not too many kit/home build CD players...

This is interesting.

A stereo amplifier.

Yes. Well, think of it as a bulked-up headphone amplifier. The design is one of those "ah, I should have thought of that" moments, but the details are quite tricky, as usual.

If the extend the basic "voltage stage + current buffer" topology of the 47 Labs 0147 headphone amplifier out to 40 wpc territory, you end up with the 0347.

The high power means than unlike the headphone amp design you have to run it out of class A, and that means closed loop operation.
While most people might be tempted to wrap the voltage feedback around the whole shebang, this basically ends you up with a big op amp. Op amps, with their massive negative feedback design, are not so happy driving high inductance/capacitance loads like speakers.

The trick 47 labs uses is to have two feedback pathways, with heavy "local" feedback around the op amp and a small secondary...

While I wait for the guys at 47 labs to get the Treasure 0247 together, I took a look around at some of the alternatives.

The Yulong D100 looks quite attractive and for about 2/3 the price of the 0247 kit you get a fully assembled unit!

review at head-fi

Or if you can do without a DAC, HLLY audio has your standard "transistor buffered op amp" implementation in a no-frills case:

HLLY RMK-5

It's listed at $240 but for sale on eBay for only $99 right now.

Of course there are dozens, but I single those two out as being particularly deserving of "honorable mentions". I'm still set on the 0247 though.

Just placed my order for this. I am customer no. 00028!

47 Labs web page

I figure I owed it to them. 47 Labs has been good to me, and the DIY community over the years, one way or another: gainclone, phonoclone, even the DAC-of-the-Klones.

Besides, several reasons:

1. I really want to finally hear 47 labs gear, instead of trying to reverse engineer it all the time!
2. It will be interesting to compare it against the sapphire amp.
3. I'm sure it will be fun to build and examine up close.
4. It's my Christmas present.
5. And hammertone. Finish a audio product in grey, or even better, green hammertone, and its as bees to honey...

Will blog the unboxing, building, and testing right here.