diyAudio - RJM Audio Projects
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
RJM Audio Projects Information and announcements regarding my audio projects.
Old

Phonoclone noise measurements

Posted 3rd October 2014 at 01:40 AM by rjm
Updated 3rd October 2014 at 10:27 AM by rjm

What we are looking at here is the Fast Fourrier Transform (FFT) of the line output from my b-board buffer recorded at 24 bit, 96 kHz by an Onkyo SE-200PCI sound card. Upstream from the b-board is the Phonoclone 3 MC phono stage, connected to a Denon DL-103. The tonearm is Denon DA-307, and the deck is a Denon DP-2000.

Four recordings, taken 1) with music playing, 2) with the tonearm raised 3) with the phonoclone powered off and 4) with the b-board and all upstream components powered off.

True 24/96 data was obtained, measurements out to 48 kHz are possible, with -130 dB noise floor. (I was using Digionsound 6 to do the recording as Audacity truncates 24 bit recordings to 16 bit in Windows due to licensing issues. The FFT was generated in Audacity however.)

The soundcard's line input may have an impressive-looking low noise floor, but it's still useless for measuring line level audio devices like the b-board because the noise of the preamp/ADC...
Attached Thumbnails
Click image for larger version

Name:	phonoclone noise.png
Views:	75
Size:	65.1 KB
ID:	1395  
rjm's Avatar
rjm
diyAudio Member
Views 464 Comments 0 rjm is online now
Old

The case of the crazy Sapphire amp.

Posted 3rd April 2014 at 02:24 AM by rjm
Updated 3rd April 2014 at 12:07 PM by rjm

Case report:

A set of Sapphire boards gave the proper V+, V- voltages out of the Z-reg, providing about 10.5 and -10.5 to op amp power pins. The output offsets were unusually high however, apparently at about 2 V in one board, and somewhat less in the other. Typically the offsets are in the order of +/-15 mV.

Changing out transistors and op amps did not help, and to all inspection the passive components were installed correctly and working properly. The offset voltages were extremely temperature sensitive. Measurements for the various circuit voltages were just screwy enough to be inconclusive.

I could ask for no more tests, so requested the boards be sent back to me. I found the circuit basically worked as expected, but the offsets were indeed high on both boards, though I measured 0.6 V max rather than 2 V.

***** stop here and make a guess *****

Blowing on the board through a soda straw, the offset shot up when I blew on...
Attached Thumbnails
Click image for larger version

Name:	DSC_1611s.jpg
Views:	170
Size:	405.5 KB
ID:	1263  
rjm's Avatar
rjm
diyAudio Member
Views 418 Comments 0 rjm is online now
Old

Upgrading the Sapphire headphone amplifier (photos)

Posted 17th December 2013 at 11:10 PM by rjm
Updated 20th December 2013 at 11:14 AM by rjm

Straightforward transplant. Out with the old (anyone want them?) in with the new. Re-used the OPA134 op amp and my dog-eared pair of 0.47uF Multicaps.

On powering up I discovered that with the specified 10 ohms in R9,10 the output bias current was upwards of 200 mA and things were getting a bit toasty. I paralleled a second 10 ohm resistor, dropping the resistance to 5 ohms and dialing back the output bias current to about 70 mA. Latest schematic revision has R9,10 values edited to match.

Currents stable. Heatsink temperatures around 50 C. Output offsets around 15 mV. No noise or hum.

Presently giving it some burn in time.
Attached Thumbnails
Click image for larger version

Name:	DSC_3577 1000.jpg
Views:	390
Size:	398.6 KB
ID:	1180   Click image for larger version

Name:	DSC_3558 1000.jpg
Views:	387
Size:	303.2 KB
ID:	1181   Click image for larger version

Name:	DSC_3579 1000.jpg
Views:	265
Size:	306.7 KB
ID:	1182   Click image for larger version

Name:	DSC_3588 1000.jpg
Views:	227
Size:	311.2 KB
ID:	1183   Click image for larger version

Name:	DSC_3589 1000.jpg
Views:	174
Size:	375.9 KB
ID:	1184  

Click image for larger version

Name:	DSC_3592 1000.jpg
Views:	873
Size:	388.8 KB
ID:	1185   Click image for larger version

Name:	pcb-sapphire-20f3-sch.png
Views:	359
Size:	37.3 KB
ID:	1186  
rjm's Avatar
rjm
diyAudio Member
Views 653 Comments 0 rjm is online now
Old

Sapphire Headphone Amplifier rev. 2.0

Posted 22nd November 2013 at 12:45 AM by rjm
Updated 5th January 2014 at 09:17 AM by rjm (update schematic to 20f4)

Update: I've ordered parts for small number of Sapphire 2.0 kits. The normal price will be $125, but as an introductory offer the first batch will be available for $100. Kit includes a set of boards and all the parts for the board. You need to supply the transformers and diodes, as well as a volume control, and the chassis hardware.

Update: boards are in stock, see photo.

Original here, diyaudio thread here.

November. That time of year for finally getting around to advancing some of my audio projects a little.

The Sapphire has remained in "rev 1+" for some time now, partly because of time constraints, partly because of the lack of popularity, and partly because it was already a re-spin of the beta version and worked just fine.

There were a few housekeeping things I wanted to add though, which have been included in the 2.0 revision.

- added a dedicated ground (GND) pad to connect to chassis...
Attached Thumbnails
Click image for larger version

Name:	Sapphire20d-lt.png
Views:	443
Size:	99.0 KB
ID:	1165   Click image for larger version

Name:	DSC_0235 sm.jpg
Views:	220
Size:	323.4 KB
ID:	1179   Click image for larger version

Name:	Sapphire20f-brd-bw.png
Views:	506
Size:	26.3 KB
ID:	1206   Click image for larger version

Name:	pcb-sapphire-20f5-sch.png
Views:	347
Size:	14.1 KB
ID:	1207  
Attached Files
File Type: asc Sapphire 20.asc (3.0 KB, 167 views)
rjm's Avatar
rjm
diyAudio Member
Views 1023 Comments 3 rjm is online now
Old

J-Mo Mk. II vs. Szekeres, distortion comparison

Posted 3rd May 2013 at 09:24 AM by rjm
Updated 6th May 2013 at 12:52 AM by rjm

Two headphone amplifiers sharing the same basic MOSFET source follower output stage.

When the source current and source resistance are optimized for the given headphone load and similar maximum output power (~50 mW at 1% THD), the distortion pattern vs. output power is remarkably similar.

One plot below is simulation, the other measurements. The J-Mo 2 simulation closely matched the actual measurements, it wasn't worth my while to generate a full simulated data set when I already had the measurements on hand. No reason to suspect that the Szekeres sim is inaccurate, either.

The take home message is the distortion characteristic of a MOSFET follower is what it is, and unavoidable. Take it or leave it, as it were. However - and this is key - if you don't optimize the stage for the headphone impedance, the distortion for a given output power will increase significantly.

As an aside: Greg did his homework with the original circuit....
Attached Thumbnails
Click image for larger version

Name:	szekeres THD sim.png
Views:	177
Size:	27.4 KB
ID:	980   Click image for larger version

Name:	jmo2 thd sim.png
Views:	190
Size:	32.1 KB
ID:	981   Click image for larger version

Name:	IMGP6429 1280.jpg
Views:	239
Size:	386.1 KB
ID:	982   Click image for larger version

Name:	IMGP6436 1280.jpg
Views:	302
Size:	408.4 KB
ID:	983  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 625 Comments 0 rjm is online now
Old

X-reg voltage stabilizer LTSPICE file

Posted 15th March 2013 at 02:54 AM by rjm
Updated 20th March 2013 at 02:47 AM by rjm

I did up the X-reg circuit in LTSpice.

Results shown below, together with the LTSpice .asc file you can use to play around with this yourself.

First attached image shows FFT for the rectified DC (green), reference voltage (red) and X-reg output (blue) for the designed-for 10 mA output (top) and a more punishing 100 mA (bottom).

Second image shows an LTSpice screengrab for the LT1086 with bypassed adj pin under comparable loading. Input voltage in blue, output in green. This is a reasonable approximation of a "good" IC regulator.

Last image shows a plot of the exported LTSpice FFT data for the X-reg and the LT1086-12V (Cin 1000uF, Cout 100uF) both at nominal currents of 10 mA. The LT1086-12V is a reasonable substitute for a generic LM7812, i.e. a "bad" IC regulator.

A typical op amp will have sufficient PSRR to mop of the residual noise from the bypassed LT1086. The fixed LT1086-12V, on the...
Attached Thumbnails
Click image for larger version

Name:	xreg 01.png
Views:	1749
Size:	104.8 KB
ID:	910   Click image for larger version

Name:	LT1086.png
Views:	713
Size:	56.0 KB
ID:	912   Click image for larger version

Name:	Regulator Comparison.png
Views:	446
Size:	50.4 KB
ID:	914  
Attached Files
File Type: zip xreg 01.zip (1.9 KB, 131 views)
rjm's Avatar
rjm
diyAudio Member
Views 1641 Comments 2 rjm is online now
Old

Phonoclone boards, soldering, and Q1, Q2.

Posted 7th February 2013 at 06:34 AM by rjm

This is in response to several recent emails I've received, where people were having problems with, typically, one board having a bad V+ or V- regulated voltage output.

The number of cases relative to the number of boards shipped caused me to worry that a manufacturing error might have occurred, so at my request I had a customer return the phonoclone boards he had built to me for inspection.

I'm happy to report that the problem was traced to poor soldering technique, the boards themselves are fine. What had happened was solder had cooled before the component had fully settled, and pushing the component down to the board surface then tore the trace away from the bottom of the board, breaking the circuit.

Subsequently, thinking the transistors blown, he replaced them, doing a fair bit of damage to the pads of Q1, Q2.

Fortunately, I was able to fairly quickly set everything to rights, and the boards are now on their way back to him....
rjm's Avatar
rjm
diyAudio Member
Views 522 Comments 2 rjm is online now
Old

B-board Boxer Project : A Low Voltage Headphone Amplifier for 16 ohm Loads

Posted 7th July 2012 at 01:19 AM by rjm
Updated 29th September 2012 at 03:58 AM by rjm

I always seem to end up optimizing my headphone amplifier circuits for higher impedance headphones, this mostly happens because I own a pair of 300 ohm HD-600s and it is tedious to design for both the voltage requirements of high impedance headphones and the current requirements of low impedance headphones.

Not impossible, just, for the class-A designs I seem to be building recently, increasingly large, heavy, and impractical.

Complimentary transistor circuits, however, offer the opportunity to swap voltage for current at something close to the same design cost. They are therefore a practical topology for efficient class-A power delivery into low impedance headphones. As a design experiment, my aim is to discover how far I can leverage an ultra-low-voltage, unity gain circuit for compactness without sacrificing sound quality.

Ok. Back-of-the-envelope calculations:

A typical 16 ohm in-ear-headphone has a sensitivity of 100-105...
Attached Thumbnails
Click image for larger version

Name:	B-board Boxer AA.png
Views:	1998
Size:	26.6 KB
ID:	730   Click image for larger version

Name:	B-board Boxer AA LTSPICE.png
Views:	1303
Size:	124.7 KB
ID:	732   Click image for larger version

Name:	B-board Boxer AA 0.5 sch.png
Views:	774
Size:	19.6 KB
ID:	735   Click image for larger version

Name:	B-board Boxer AA 0.5 brd.png
Views:	611
Size:	21.7 KB
ID:	736   Click image for larger version

Name:	DSC_0083 800.jpg
Views:	246
Size:	134.3 KB
ID:	747  

Click image for larger version

Name:	DSC_0086 800.jpg
Views:	356
Size:	185.2 KB
ID:	748   Click image for larger version

Name:	DSC_0075 800.jpg
Views:	205
Size:	155.1 KB
ID:	749   Click image for larger version

Name:	DSC_0079 800.jpg
Views:	340
Size:	206.1 KB
ID:	750   Click image for larger version

Name:	DSC_0114 800.jpg
Views:	292
Size:	207.7 KB
ID:	751   Click image for larger version

Name:	DSC_0106 800.jpg
Views:	536
Size:	196.0 KB
ID:	752  

Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 2321 Comments 7 rjm is online now
Old

The Double-Diamond Amplifier (DDA)

Posted 13th June 2012 at 07:09 AM by rjm
Updated 16th June 2012 at 03:57 PM by rjm

This isn't my first attempt. It's been on my mind for a while: how to coax a diamond buffer into giving voltage gain, without resorting to fronting it with a op amp.

After reading a particularly gregarious thread over in the headphone forum, I'm more and more stoked on giving this a real shot.

Despite the (catchy) name I'm thinking pre-amplifier rather than amplifier applications.

update: I have have a quick and dirty sim up and running in ltspice. Curiously, the output distortion is 15 dB lower when the buffer runs open loop than when it is included inside the feedback loop. Intrigued. Currently under investigation.

update: refined the sim slightly, achieved -85 dB distortion levels at 0 dB / 1 kHz / 600 ohms running the output buffer open loop. Bandwidth is just under 1 MHz, adjusted by changing the feedback resistance. As before, performance sims out notably worse with the buffer
inside the feedback loop.
...
Attached Thumbnails
Click image for larger version

Name:	DDA mission patch.png
Views:	289
Size:	54.5 KB
ID:	704   Click image for larger version

Name:	DDA 0.6 FFT.png
Views:	1614
Size:	115.5 KB
ID:	709  
Attached Files
File Type: zip current feedback prototype 6 LTSPICE file.zip (1.4 KB, 150 views)
rjm's Avatar
rjm
diyAudio Member
Views 1601 Comments 2 rjm is online now
Old

Bypassing, Goldilocks, and the Sound of Nothing

Posted 31st May 2012 at 07:28 PM by rjm
Updated 2nd June 2012 at 12:53 AM by rjm

Douglas Self writes,
Quote:
The 5532 and 5534 type op-amps require adequate supply decoupling if they are to remain stable, otherwise they appear to be subject to some sort of internal oscillation that degrades linearity without being visible on a normal oscilloscope. The essential requirement is that the positive and negative rails should be decoupled with a 100 nF capacitor between them, at a distance of not more than a few millimeters from the op-amp; normally one such capacitor is fitted per package as close to it as possible.
He's someone who should know. Anyway, it doesn't take much digging on the internet to confirm beyond reasonable doubt that bypass caps should be as close to the op amp power pins as possible. So thinking about my previous experiments with bypassing the Sapphire, by adding bypass caps around the transistors I also effectively also added a bypass for the op amp, but a rather poor one as the power-pin-to-power-pin round trip loop distance is probably 10...
Attached Thumbnails
Click image for larger version

Name:	DSC_1366 1280 hack.jpg
Views:	625
Size:	313.9 KB
ID:	696   Click image for larger version

Name:	pcb-sapphire-14s1-brd-bypass.png
Views:	1256
Size:	40.6 KB
ID:	697  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 1477 Comments 0 rjm is online now
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 11:35 PM.


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