diyAudio - Other Audio Things
Go Back   Home > Forums > Blogs > RJM Audio Blog
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
If I put my notes here, I might be able to find them again later!
Other Audio Things Audio items not directly related to RJM Audio projects.
Old

Sapphire Line Preamplifier

Posted 24th July 2016 at 01:11 AM by rjm (RJM Audio Blog)
Updated Yesterday at 11:45 PM by rjm

Although the original Sapphire headphone amp can be configured as a line stage, or use as-is as a line stage, I've gone ahead and made a new circuit variant with a new set of boards.

The Sapphire Line (in development) combines the shunt-series regulator, bboard 2.0 buffer and an op amp voltage gain stage. Same basic idea as the Sapphire of course, but with a much less beefy output stage so the low noise regulator can be added and everything still fits on the board.

rev 10e - now with support for 2520 op amp modules
Attached Thumbnails
Click image for larger version

Name:	Sapphire LIne 10d LTSpice.png
Views:	18
Size:	107.4 KB
ID:	2029   Click image for larger version

Name:	sapphire line 10e brd.png
Views:	7
Size:	21.9 KB
ID:	2033   Click image for larger version

Name:	sapphire line 10e.png
Views:	15
Size:	17.5 KB
ID:	2034  
Attached Files
File Type: asc Sapphire Line 10d.asc (10.1 KB, 10 views)
rjm's Avatar
rjm
diyAudio Member
Views 39 Comments 0 rjm is offline
Old

INs and OUTs of the Asus Xonar Essence STX PCIe computer sound card

Posted 26th June 2016 at 08:12 AM by rjm (RJM Audio Blog)
Updated 18th July 2016 at 03:42 AM by rjm

Asus Xonar Essence STX, Audacity 2.1.2, VLC, Windows 10 [and DigiOnSound6 Express for 24 bit recording]

Purpose

To confirm the calibration of the sound card input and output gain. Also, to determine the relationship between the signal voltage, the recorded signal amplitude displayed in Audacity, and the signal peak and noise baseline levels in the FFT spectra.

Summary

* Setting the volume slider of the device output to 100 gives 1 V rms output for an amplitude 0.5 sine wave.
* Setting the volume slider of the device recording line input to 100 gives records a 1 V rms tone as an amplitude 0.5 sine wave, which is displayed in the frequency spectrum (FFT) as peak of magnitude 0 dB in Audacity when both channels are averaged.
* volume setting 100 needed for unity gain loopback.
* 0.5 amplitude sine wave = 0 dB FFT = 1 V rms.
* noise baseline in averaged stereo FFT is 3 dB lower than single channel measurement....
Attached Thumbnails
Click image for larger version

Name:	STX volume.png
Views:	29
Size:	13.6 KB
ID:	1998   Click image for larger version

Name:	reference FFT.png
Views:	42
Size:	23.6 KB
ID:	1999   Click image for larger version

Name:	RMAA.png
Views:	32
Size:	19.4 KB
ID:	2001   Click image for larger version

Name:	noise.png
Views:	31
Size:	4.7 KB
ID:	2002   Click image for larger version

Name:	Xonar baseline and reference tone.png
Views:	38
Size:	25.5 KB
ID:	2003  

Click image for larger version

Name:	Audacity 0.5 signal in-out.png
Views:	25
Size:	46.8 KB
ID:	2004  
Attached Files
File Type: zip RMAA report Xonar STX loop back.zip (29.2 KB, 10 views)
rjm's Avatar
rjm
diyAudio Member
Views 201 Comments 0 rjm is offline
Old

VSPSX phono stage design idea

Posted 24th June 2016 at 12:48 AM by rjm (RJM Audio Blog)
Updated 24th June 2016 at 02:54 AM by rjm

The original VSPS is getting up in years, and could do with a bit of an update.

The VSPSX adds the foursquare shunt-source voltage regulator and bboard v2.1 output buffer.

The LTSpice schematic below abbreviates the transformer, rectifiers, and filter capacitors as V1 and V2. Op amp OP27 is a placeholder.

My main concern would be fitting all this stuff on a 80x100 board. That and, well, I'm not totally convinced yet that the complexity vs. reward ratio makes its worthwhile.
Attached Thumbnails
Click image for larger version

Name:	vspsx.png
Views:	98
Size:	49.0 KB
ID:	1996  
Attached Files
File Type: asc VSPSX.asc (12.7 KB, 43 views)
rjm's Avatar
rjm
diyAudio Member
Views 132 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part 12 : The Foursquare Shunt-Source

Posted 17th June 2016 at 01:44 PM by rjm (RJM Audio Blog)
Updated 20th June 2016 at 08:37 AM by rjm

I'm not totally sure this would work as advertised, but I can't see any obvious reason why it would not...

It's pretty much the same circuit as I used in the CrystalFET, which started out in a previous blog post in the Voltage Regulators for Line Level Audio series, but here I've replaced the MOSFETs with bipolars. It is shown configured to deliver 20 mA @ 12 V, split supply. Enough to power an op amp phono stage for example, or a preamp, or the voltage gain stage of a headphone amplifier.
Attached Thumbnails
Click image for larger version

Name:	foursquare shunt regulator full.png
Views:	137
Size:	90.6 KB
ID:	1995  
Attached Files
File Type: asc foursquare shunt regulator full.asc (4.6 KB, 38 views)
rjm's Avatar
rjm
diyAudio Member
Views 209 Comments 0 rjm is offline
Old

CrystalFET Phono Stage

Posted 3rd March 2016 at 04:55 AM by rjm (RJM Audio Blog)
Updated 22nd July 2016 at 10:52 PM by rjm

Development thread here.

CrystalFET is a J113 jfet-based two-stage phono preamp, with passive equalization and on-board MOSFET-based shunt voltage regulator.

Jfets Q1 and Q3 should be matched between channels, and for best results the value of drain resistors R2 and R9 should be selected based on the jfet pinch off voltage of Q1 and Q3 respectively.

rev. 1.4e (final version) removes some unneeded resistors and tidies up the board layout a little. The resistors have been renumbered.
Attached Thumbnails
Click image for larger version

Name:	IMGP6761.jpg
Views:	106
Size:	263.9 KB
ID:	1889   Click image for larger version

Name:	IMGP6764.jpg
Views:	74
Size:	192.5 KB
ID:	1890   Click image for larger version

Name:	DSC_6236.jpg
Views:	73
Size:	262.8 KB
ID:	1897   Click image for larger version

Name:	crystalFET 1.3a response.png
Views:	58
Size:	22.7 KB
ID:	1934   Click image for larger version

Name:	pcb-crystal-14e-sch.png
Views:	24
Size:	18.3 KB
ID:	2007  

Click image for larger version

Name:	pcb-crystal-14e-brd.png
Views:	15
Size:	18.5 KB
ID:	2008   Click image for larger version

Name:	CrystalFET-14e.jpg
Views:	1
Size:	394.8 KB
ID:	2023  
Attached Files
File Type: zip pcb-crystal-14e-bom.zip (246.7 KB, 7 views)
File Type: asc Crystal 14.asc (11.2 KB, 16 views)
rjm's Avatar
rjm
diyAudio Member
Views 1115 Comments 6 rjm is offline
Old

Chromecast Audio Output Noise

Posted 26th February 2016 at 11:11 AM by rjm (RJM Audio Blog)
Updated 27th February 2016 at 12:18 AM by rjm

Measured at 24/96 with my Asus Xonar STX soundcard (~ -147 dB noise floor)

The Chromecast Audio output noise powered with the included USB wall wart supply is -130 dB at 1 kHz, rising gradually at lower frequencies and showing some switching power supply noise peaks at 4763 Hz and higher multiples, never exceeding about -120 dB.

This is respectable performance given its price point.
Attached Thumbnails
Click image for larger version

Name:	Chromecast Audio Noise Baseline.png
Views:	130
Size:	17.2 KB
ID:	1810   Click image for larger version

Name:	Chromecast Audio Noise Baseline (linear).png
Views:	126
Size:	15.9 KB
ID:	1811  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 394 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part 11 : The Crystal M Shunt

Posted 20th February 2016 at 12:49 AM by rjm (RJM Audio Blog)
Updated 22nd February 2016 at 08:35 AM by rjm

A while back I did a series of blogs on voltage regulators. Back with a new entry today: The Crystal M, configured here for 40 V DC output and a 25 mA load.

The circuit is based on two p-channel MOSFETs, the top one is a constant current source, the bottom one a constant voltage source. As the load current changes, the voltage source adjusts its current to balance.

It's lifted directly on the Salas shunt design (as reworked by me for my own jFET phono stage), but the circuit can also be considered a distant, DC-coupled relative of the Zen amp.

I trick, I discovered, to getting it to work nicely - the attached screencap shows it well-behaved while handling a full-swing output current pulse - is the source resistor R10. This resistance dials-down the current gain of the MOSFET, damping out the overshoot.

The ripple rejection is about 70 dB over the audio bandwidth. The output impedance is about 0.05 ohms over the same frequency...
Attached Thumbnails
Click image for larger version

Name:	Crystal M.png
Views:	634
Size:	48.3 KB
ID:	1805   Click image for larger version

Name:	Crystal M PSRR.png
Views:	479
Size:	51.0 KB
ID:	1806  
Attached Files
File Type: asc Crystal M.asc (2.9 KB, 343 views)
rjm's Avatar
rjm
diyAudio Member
Views 622 Comments 2 rjm is offline
Old

LTSpice filter simulation masterclass: 0 to -100dB in five easy steps!

Posted 18th February 2016 at 11:14 PM by rjm (RJM Audio Blog)
Updated 7th April 2016 at 06:58 AM by rjm

I've never put everything into a single LTSpice worksheet like this before: I find it fascinating. You can really pull apart a circuit to see what makes it tick, before solder ever hits the iron.

Power supply ripple, frequency response, gain, and crosstalk can be established. You can look at turn on and turn off transients, inrush currents, and conductance angle, and check peak currents in the filter capacitors. It's all there if you care to peek in and poke around.

I'm such a huge fan of LTSpice...

The only problem, really, is it is too perfect: all devices are perfectly matched, every part value is exact, and the temperature is always 25 C. Ground loops, wiring inductance, and thermal runaway do not exist. So no, of course there are no guarantees - but as a tool to get you 90% of the way there with the minimum of fuss and bother it is truly indispensable.

Actually I find the more experience you have the more useful LTSpice...
Attached Thumbnails
Click image for larger version

Name:	Crystal PSRR sim.png
Views:	728
Size:	476.3 KB
ID:	1801   Click image for larger version

Name:	crystalFET.png
Views:	188
Size:	28.0 KB
ID:	1891  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 495 Comments 0 rjm is offline
Old

Headphone amplifier ground. Where to make the chassis connection?

Posted 2nd February 2016 at 07:11 AM by rjm (RJM Audio Blog)
Updated 24th February 2016 at 01:02 AM by rjm

The discussion thread at the headphone forum is here, but I wanted to throw out the problem to the general blog-reading community here at diyaudio to see if anyone can nail this.

The earthed chassis (light blue) must connect to the circuit common i.e. "ground" (pale green). I do not know where the best place on the circuit ground is to tie that connection.

Suggestions please!

(COM and GND are completely equivalent pads on the circuit board, while IN- and OUT- also pads on the board but physically further away on the ground plane.)

****

Answer: as long as it connects at one point only, or the same point of both channels, it doesn't seem to matter at all. I have it connected at the ground tab of the headphone jack and that seems to be as good as anywhere.

****

The noise was in fact magnetic interference emanating from the transformers. Grounding layout changes / electrostatic...
Attached Thumbnails
Click image for larger version

Name:	Sapphire ground.png
Views:	355
Size:	32.5 KB
ID:	1775   Click image for larger version

Name:	DSC_5322b sm.jpg
Views:	568
Size:	846.7 KB
ID:	1777   Click image for larger version

Name:	DSC_5407 sm.jpg
Views:	666
Size:	748.4 KB
ID:	1780   Click image for larger version

Name:	Z-reg sim.png
Views:	248
Size:	273.4 KB
ID:	1782   Click image for larger version

Name:	IMGP6318sm.jpg
Views:	225
Size:	301.3 KB
ID:	1783  

Click image for larger version

Name:	permalloy.png
Views:	142
Size:	51.1 KB
ID:	1809  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 707 Comments 7 rjm is offline
Old

ASUS Xonar Essence STX soundcard

Posted 9th October 2015 at 10:46 PM by rjm (RJM Audio Blog)
Updated 7th November 2015 at 09:44 PM by rjm

https://www.asus.com/Essence-Hi-Fi-A...r_Essence_STX/

I admit I did not give ASUS the benefit of the doubt and seriously consider their Essence STX soundcard as a replacement for my Onkyo SE200-PCI. ASUS make nice motherboards, but unlike Onkyo have no previous expertise in high end audio.

I am happy to report - a bit late in the game, the card came out in 2009 - that they've done a really good job with it and the drivers for Windows 10, technically still in beta, work just fine.

*****

Asus updated the design recently to the STX II. The PCB has been redone, but the only visible change is the PCM1792A DAC has been moved towards the top of the card closer to the IV conversion op amps. An second LDO regulator IC, U34, empty on the STX, is now populated. A "TXCO" clock source is added next to the ASUS audio controller IC. The four film caps next to the output IC are replaced with WIMA brand. It's basically identical, so it...
Attached Thumbnails
Click image for larger version

Name:	controlpanel.jpg
Views:	244
Size:	104.2 KB
ID:	1737   Click image for larger version

Name:	DSC_8149bs.jpg
Views:	166
Size:	301.9 KB
ID:	1738   Click image for larger version

Name:	DSC_8136bs.jpg
Views:	470
Size:	318.0 KB
ID:	1739   Click image for larger version

Name:	DSC_8152bs.jpg
Views:	167
Size:	266.3 KB
ID:	1740   Click image for larger version

Name:	DSC_8136b.jpg
Views:	361
Size:	467.7 KB
ID:	1750  

Click image for larger version

Name:	DSC_0780 sm.jpg
Views:	191
Size:	151.5 KB
ID:	1751  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 863 Comments 0 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 06:08 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki