B-board vs. 0247.

Comparison of the noise baselines, measured at the circuit output using a NI USB-6215 DAQ. Unloaded for the preamps, and with a 6 ohm load for the 0347 amplifier.

• B-board: -139 [300Hz-100kHz] 0 dB gain (-139 - 0 = -139 dB, 110 nV sqrtHz input referred). The actual B-board output noise is below this measurement threshold.
• 0247: -124 dB [300Hz-100kHz] 14 dB gain (-124 - 14 = -139 dB, 110 nV sqrtHz input referred).
• 0347: -109 dB [300Hz-100kHz] 31 dB gain (-109 - 31 = -140 dB, 100 nV sqrtHz input referred).

See the attached plot for the FFT data. Note the peak at 28 Hz is an artifact of the measurement apparatus.

By way of comparison, a typical audio opamp has an input referred voltage noise figure of 3-8 nV sqrtHz (-170 ~ -160 dB) and can be expected to return this datasheet specification in most well-designed circuits. In other words the output noise is going to be about -160 dB + the circuit gain.

The 0247...

So now we have the model 0247 DAC/preamp/headphone amplifier and model 0347 power amplifier in the main system. That's the old Denon DP-2000 TT, Phonoclone 3, and Onkyo D-605SR speakers.

The gain of the 0347 is 30 dB, so with the 0247 doing duty as a preamp the overall gain is a tad high, but it's perfectly useable. I'll look at the passive preamp options (including the model 0447) at a later date.

Anyhow, the big news is it completely destroys the non-inverting LM3875 Gainclone I have been using for the last decade, so badly, in fact, I'm starting to wonder if my Gainclone was busted. In comparison with the 0347 it sounds like a distorted, uncontrolled mess.

Since my speakers are really very modest in quality (though at 82dB and 6 ohms, a bit of a rough load) I wasn't expecting much difference one way the other, so this comes as a severe shock.

Unfortunately I'm not within reach of a good reference system to give the 0347 a real evaluation....

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...

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...

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.

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.

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.

Scheduled to be delivered tomorrow evening!

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...

(regarding the Treasure 0347 stereo amplifier)

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 0147 headphone amplifier out to 40 wpc territory, you end up with the 0347.

The high power means that 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 global loop from...