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Measuring Noise

Posted 19th January 2012 at 03:28 PM by klewis
Updated 19th January 2012 at 03:32 PM by klewis

For LED's - Christer's thread http://www.diyaudio.com/forums/parts...er-diodes.html
An interesting method of grading zeners for noise, that I have used for years, is to monitor the noise across the devices with a scope while using my HP bench supply to bias them. The noise spectrum changes quite dramatically as you come into breakdown and then drops to it's minimum at it's prefered current flow. I note the current and voltage after it has settled down. I choose the ones to use by voltage match and bias them accordingly.

One other trick, if you want to know how quiet your supply is, choose a suitible coupling cap and hook the output of it up to a line input on your preamp and listen to it. Try this with and without a load and during normal operation of the supply. A good supply is dead quiet. author: MikeBettinger
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Old

A different design aesthetic.

Posted 17th January 2012 at 10:52 AM by rjm
Updated 25th January 2012 at 10:21 PM by rjm

I like the concept of appearance in high-end audio. I mean, where the look of the equipment makes a statement about what it's all about inside.

The 0347 is proportioned like a vintage tube receiver, but in miniature. It even has the lit, transparent front panel where the radio tuning strip would have resided. The heavy grey hammertone and very simple, basic hardware are reminiscent of Heathkit or Dynaco. In short, the appearance evokes the spirit of a simpler, more innocent age of vintage hifi without being a slavish replica.
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Old

Another package in the mail...

Posted 14th January 2012 at 10:30 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 12th January 2012 at 11:41 PM by rjm
Updated 26th January 2012 at 05:42 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 12:18 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

Deeper into variant one

Posted 12th January 2012 at 10:47 AM by Wolfsin (SE-BRGD a bridged mono 'wire')
Updated 12th January 2012 at 10:54 AM by Wolfsin

Will be fleshed out with image of reversed wiring for inverted channel
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Old

Mutants

Posted 11th January 2012 at 10:16 PM by Wolfsin (SE-BRGD a bridged mono 'wire')
Updated 12th January 2012 at 10:13 PM by Wolfsin (rename second variant)

When asked where frankenwires were to be filed, qusp replied

Quote:
Originally Posted by qusp View Post
file it under mutants...

...and their amplifiers
There are two variants of what I originally called the SE-BRGD frankenwire. Both start as rework boards. One gets a pair of LME49860 to replace the LME49990 using the simple surgery below. The + and - inputs to the second 49860 are reversed and resistors adjusted so the gain is equal on both sides. The effect of that reversal is to invert the signal on the second leg so it becomes a mono amp, whose differential outputs are ready to bridge one can.

The second variant, more correctly referred to as the BAL-BALM, requires no rework surgery (so could just as well not even be a rework pcb), just the addition of a tiny adapter to mount an opa1632 and leave off the 49990s. Power connection is not as clean as the first variant. It is effectively half a BAL-BAL, perfect for the audiophile with only one ear.

...
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Old

The Brush Development Co. BL-905. What is it?

Posted 9th January 2012 at 10:41 AM by tonekwest

I have what looks to be an amplifier of some sort and was wondering if any of the forum members may be familiar with what I actually have. So far, my search results have come up with nothing.
It is from the Brush Development Company. Type BL-905. Will try to post list of tubes in the unit tonight.
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Old

one small step...

Posted 8th January 2012 at 12:58 AM by cberger

... for mankind, but one giant step for me

After sucking big time in Halo, In felt like I needed some positive experience today, so I hooked up my CHR-70s to my trusted, semi-retired NAD.
Took about 1h, involving looking for my cutter to cut some old CAT5 and strip the wires, do the actual cutting and stripping, hooking up the receiver, connecting the cables and turning on the whole assembly.
And *drum roll* FM94.9 played Motorhead's "Ace Of Spades" Can it get any better???
First listening impression: sounded a bit like AM radio, but given the way the drivers are hooked up I'm not really surprised...

in other news: parts express delivered some fluff and my terminals
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Old

SouthSemi modified F2J Clone

Posted 7th January 2012 at 09:13 AM by Tea-Bag
Updated 21st November 2010 at 12:46 PM by Tea-Bag

This last weekend I replaced the IRFP240 in my F2 Clone with the R100 SouthSemi Power-JFET.

tubes-guy used psychic powers to control my mind and force me to do it.

The bias dropped off the bat. I re-biased and gave it an A-B listen to the standard channel. Seemed to be a bit 'cleaner' sounding the the default channel.

Nelson has recommended the following changes to the circuit, which I hope to implement soon. I will be re-wiring these on Peter Daniels boards.
The Peter Daniel boards are still available I believe.
http://www.diyaudio.com/forums/group...group-buy.html

Papa sayz...

The F2's that I have updated with the JFETs need the
following changes:

R6 = 47k (changed to 8.2K of FW Site)

C1 = 10 uF

Z1 removed

The potentiometer must be re-adjusted for minimum
distortion at 4.5 watts (symmetric clipping) and readjusted
...
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