diyAudio - Other Audio Things
Go Back   Home > Forums > Blogs > rjm

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Other Audio Things Audio items not from RJM Audio
Old

Stepped Attenuator

Posted 8th May 2012 at 12:20 AM by rjm
Updated 8th May 2012 at 12:24 AM by rjm

I bought a stepped attenuator (actually, two of them) from ebay seller hanshare-electronics. As always with eBay, I was a little worried about what would show up.

I'm happy to report that this is a nice job. The included resistors are clearly labelled, and the documentation, while spartan, is sufficient.

The only negative is the rotary switch is a bit "clicky". Better quality units I've seen are more damped.

On the positive side, though, the resistor values are very elegantly selected, to give a smooth response of about 4 dB per step from -60 to -40 dB, and 2 dB per step from -40 to -3 dB. Having been-there, done-that, I can say that I'd happily pay the asking price to get those resistors sourced and sorted for me. Next time, I'd also pay to get it assembled. Soldering was more painful than I imagined it would be, and the pre-assembled units much neater-looking than what mine ended up as.
Attached Thumbnails
Click image for larger version

Name:	takman50k.png
Views:	507
Size:	34.6 KB
ID:	680   Click image for larger version

Name:	takman.jpg
Views:	1437
Size:	144.3 KB
ID:	681  
rjm's Avatar
rjm
diyAudio Member
Views 1721 Comments 0 rjm is offline
Old

RJM B-board vs. 47 Labs 0247

Posted 5th May 2012 at 12:29 PM by rjm
Updated 6th May 2012 at 06:16 AM by rjm

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...
Attached Thumbnails
Click image for larger version

Name:	compiled FFT.png
Views:	531
Size:	60.7 KB
ID:	675   Click image for larger version

Name:	DSC_4078 1280.jpg
Views:	873
Size:	367.6 KB
ID:	676   Click image for larger version

Name:	DSC_0938 1280.jpg
Views:	1353
Size:	375.4 KB
ID:	677  
rjm's Avatar
rjm
diyAudio Member
Views 1308 Comments 0 rjm is offline
Old

Chigusa Modern Jazz and Coffee

Posted 28th March 2012 at 07:41 AM by rjm
Updated 28th March 2012 at 07:57 AM by rjm

I was fortunate to stumble across this place on a trip to Yokohama earlier this week.

http://g.co/maps/nzebr

I was walking around the area near Sakuragicho Stn. after dinner, and, through the windows I could make out a back wall filled with LPs, two turntables built into the bar countertop, and a pair of giant multi-way speakers. The sign out front said "Modern Jazz and Coffee". So, naturally, I went in.

First, the history of the place as it was explained to me:

First opened in 1933. Destroyed by American bombs during the war, 6000 SP records gone, re-opened, and was in business until the owners death in 1994, then taken over and run by the owners younger sister until 2007, when, at the age of 77 (!) she gave it up. Volunteers somehow managed to preserve the records and furnishings, including the sound system, and, some 5 years later, decided to relocate and reopen at a nearby location just, if I've got this right, a...
Attached Thumbnails
Click image for larger version

Name:	IMG_5938.jpg
Views:	545
Size:	31.0 KB
ID:	625  
rjm's Avatar
rjm
diyAudio Member
Views 798 Comments 0 rjm is offline
Old

Voltage regulators and ... something almost as good?

Posted 17th February 2012 at 09:55 PM by rjm
Updated 6th March 2012 at 04:21 PM by rjm

A real, honest-to-goodness voltage regulator has three parts: a fixed voltage reference, an error amplifier, and a pass element.

Most people only put eyeballs on the final, all-wrapped-up-in-a-tidy-IC-package version, typified by the LM7812, or with a couple of extra gain-set resistors, the LM317. These chips have a working bandwidth about about 2 kHz, as they are designed to 1) reduce 120 Hz ripple and 2) be rock stable no matter what abuse they are subjected to. As a result at audio frequencies and above they are pretty much noise generators...

Knowing this, many people have set out to build better regulators for audio work.

The most obvious route is to build a high performance LM7812 from discrete components. (Most excellent review here.) AD797 for the error amplifier, high stability, low noise voltage reference, etc. The trick though, is stability. The LM7812 is low bandwidth not because it's too cheap to manage anything better, but because...
Attached Thumbnails
Click image for larger version

Name:	x-reg mod2.png
Views:	1085
Size:	23.0 KB
ID:	600   Click image for larger version

Name:	TeddyReg-small mod rjm.png
Views:	2115
Size:	39.2 KB
ID:	601  
rjm's Avatar
rjm
diyAudio Member
Views 2226 Comments 0 rjm is offline
Old

"Activator 2" FET preamp for .. guitars and basses?

Posted 13th February 2012 at 10:48 PM by rjm
Updated 2nd April 2012 at 02:04 AM by rjm

I have been doing a web-dredge, searching for simple, single supply, transistor buffer/gain stages, preferably FET-based.

This one seems interesting.

The designer, Henry Nurdin, has kindly posted a full schematic.

Ignore the fact for a moment that it's designed as a tiny battery-operated module to retrofit into electric guitars, the basic circuit block with 5-6 dB non-inverting gain could be used as a front end for a headphone buffer stage like, I'm thinking especially, the Szekeres MOSFET buffer.

That's if the bandwidth is sufficient for high-end audio (should be!?) and, slightly more worrisome, acceptable gain matching between channels can be achieved without resorting to trim pots.

This circuit reminds me of something. ... Sziklai pair? Time to do some more dredging...

Ah, bingo!

Update:

And with some jiggery-pockery this is taking shape as a (yet another) headphone amplifier....
Attached Thumbnails
Click image for larger version

Name:	Activator 2.png
Views:	5722
Size:	25.4 KB
ID:	588   Click image for larger version

Name:	activator_naked.jpg
Views:	269
Size:	5.2 KB
ID:	589   Click image for larger version

Name:	activator_module.jpg
Views:	185
Size:	3.4 KB
ID:	590   Click image for larger version

Name:	aplocalypse.png
Views:	5429
Size:	18.8 KB
ID:	591   Click image for larger version

Name:	Jmo2 11a.png
Views:	788
Size:	50.5 KB
ID:	595  

Click image for larger version

Name:	DSC_3618 1280.jpg
Views:	579
Size:	380.5 KB
ID:	634  
rjm's Avatar
rjm
diyAudio Member
Views 3514 Comments 0 rjm is offline
Old

Converting Eagle printed circuit board layout files to Gerber format

Posted 10th February 2012 at 11:20 PM by rjm
Updated 26th November 2013 at 11:39 PM by rjm

File this under "things-I-should-have-learnt-to-do-many-years-ago-but-was-too-lazy-to-bother".

Many pcb fab outfits that do business with hobbyists and DIYers choose to accept Eagle .brd files, which means they do the conversion to Gerber output so you don't have to. I've relied on that for far too long, but when an error showed up in one the .pdf proofs on the last batch of boards I sent out for fabrication, they asked me to send the Gerber files instead. So I bit the bullet and after a couple of false starts managed to give them what they wanted. Looking back at it, it was easy and something I should have learnt, as I wrote up above, years ago, but, for posterity, here's how it's done:

Eagle 6.1~6.5 on Windows
  1. Make a working folder for the Gerber files.
  2. Copy the Eagle board (.brd) file to this directory.
  3. Open Eagle (version 6.1)
  4. Select menu item "file/open/CAM job"
  5. The open file dialog appears, defaulting to the Eagle
...
rjm's Avatar
rjm
diyAudio Member
Views 3904 Comments 1 rjm is offline
Old

RJM Z-reg + Pass B1

Posted 3rd February 2012 at 11:53 PM by rjm
Updated 4th February 2012 at 12:01 AM by rjm

I was asked to suggest a voltage regulator for the First Watt (Pass DIY) B1 buffer. One thing led to another and the next thing I'd sketched up a circuit board for the buffer as well as the regulator.

It's like a B-board, but with the JFET buffer instead of the diamond buffer, and with a single supply and, hence, the coupling caps front and back. Since it's using JFETs for the buffer I used a JFET for the pass device in the regulator, too.

Full credit to Nelson Pass for his design.

Eagle files do not show 2SK170 because the package is not in Eagle. All transistors 2SK170 or equivalent. Zener is 18-22V DO35 or DO41 i.e. Vishay BZX85. V++ is 5-15 V above whatever you select the Zener reference to be.
Attached Thumbnails
Click image for larger version

Name:	b1-10c-brd.png
Views:	1907
Size:	19.7 KB
ID:	586   Click image for larger version

Name:	b1-10c-sch.png
Views:	3132
Size:	21.0 KB
ID:	587  
Attached Files
File Type: zip Pass B1 RJM 10c.zip (61.8 KB, 327 views)
rjm's Avatar
rjm
diyAudio Member
Views 2548 Comments 4 rjm is offline
Old

Oh, MY!

Posted 23rd January 2012 at 06:51 AM by rjm

Denon DL-A100

Transparent DL-103 for Denon's 100th anniversary.
Attached Thumbnails
Click image for larger version

Name:	dla100_2.jpg
Views:	217
Size:	10.3 KB
ID:	577  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 815 Comments 2 rjm is offline
Old

The new system, up and running.

Posted 22nd January 2012 at 10:52 AM by rjm
Updated 25th January 2012 at 07:57 AM by rjm

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....
Attached Thumbnails
Click image for larger version

Name:	IMGP1513j 1280.jpg
Views:	763
Size:	348.1 KB
ID:	576  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 1201 Comments 1 rjm is offline
Old

47 Labs Treasure 0347 : trials and tribulations

Posted 20th January 2012 at 11:48 AM by rjm

And not even sure what a tribulation is, but I'm sure I've had at least one building this amp.

Like the 0247 it's not so much difficult as it is painstaking hard work. The output transistors have to be mounted "just so" so the boards screw to the case properly, the wiring of the thermal protection transistors and gluing them to the output devices is tricky and easy to mess up.

I triple-checked and was rewarded by, it seems, error free boards. I messed up and wired the mute switch incorrectly though (the photos show it wrong, in case you come across this blog post looking for help) and I think the switch has a fault somehow as L and R channels appear to me mixed together. Taming the offsets gave me considerable grief but I think its all OK now.

Tomorrow I'll hook it up to the speakers and see what happens.
Attached Thumbnails
Click image for larger version

Name:	DSC_3005 1280.jpg
Views:	1597
Size:	311.5 KB
ID:	569   Click image for larger version

Name:	DSC_2991 1280.jpg
Views:	2027
Size:	401.7 KB
ID:	570   Click image for larger version

Name:	DSC_2969 1280.jpg
Views:	1275
Size:	243.7 KB
ID:	571   Click image for larger version

Name:	DSC_3007 1280.jpg
Views:	2360
Size:	290.9 KB
ID:	572  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 2120 Comments 1 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 11:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2