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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 Yesterday at 11:13 PM 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 magnitude of signal peak and noise baseline 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 into 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 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
* The measured performance...
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File Type: zip RMAA report Xonar STX loop back.zip (29.2 KB, 0 views)
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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.
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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.
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Old

Surprisingly Good Performance - The Amplifier of 100 Transistors

Posted 4th June 2016 at 04:42 AM by googlyone
Updated 4th June 2016 at 05:18 AM by googlyone

I finally got around to rolling out the distortion test set and the Amplifier of 100 Transistors to measure its performance.

I would like to say that I don't care - and that the whole thing is an engineering abortion. A complicated joke, and that the measurements don''t matter. The fact that I am making the measurement would however show me to be a liar - as if I didn't care, then why did I do this?

Anyway, with low distortion measurements, getting your head around the baseline of your test gear is key. With all gains / levels being equal, here is the loop-back distortion of the test system:

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Which is fine, rolls along at about 0.0003% across the band.

Then I ran a sweep of the Amplifier of 100 Transistors with NO load at 3dB below clipping:

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OK, this is saying the amplifier distortion raises it's head above the noise floor at 1KHz and is...
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Old

And then there were two... Amps of 100 Transistors

Posted 28th May 2016 at 06:39 AM by googlyone

And then there were two! A lot easier simply loading just the "output devices" and testing.

The second one initially looked super stable, but after I got it quite warm by running an almost clipping sinewave into a 4 Ohm load, I did find just a tough of oscillation on negative excursions.

The first amp had envelopes of oscillation at 3MHz. The frequency of the second amps oscillation was 13MHz.

In the end removing the capcitor between the bases of the output devices (what was it there for anyway?) tidied things up.

These Amplifiers of 100 Transistors seem to breed!

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Old

The Amplifier of 100 Transistors (output devices)

Posted 28th May 2016 at 02:18 AM by googlyone
Updated 28th May 2016 at 02:22 AM by googlyone

In my previous post I presented an idea spawned from a very bad place, primarily boredom and probably too much alcohol. Plane trips from Australia do that...

The Amplifier of 100 Transistors was the result.

Between that posting and this a few things have happened. I finished the design - adding extra decoupling and 100 Ohm base resistors to all 104 output devices. I did this because I sincerely thought I was building more of an RF oscillator than amplifier.

And I built it.

And I got it working.

This is the beast from the back before I loaded the "output devices":

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Note the ludicrous number of emitter and base resistors! Half way through I concluded that I was bonkers, and wasting several days hand building a complete folly.

Then again, even with the thing running, it is still a folly!


With the output devices loaded....
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Old

Adjustable Ultra Linear Linestage

Posted 27th May 2016 at 05:48 AM by ballpencil
Updated 27th May 2016 at 08:06 AM by ballpencil

This circuit is to fulfill my curiosity of hearing the sonic differences between pentode, ultra-linear and triode gain stage. As with any line stage, this circuit can also be the input part of a power amplifier. I'm considering a single ended amplifier where both the input and output stages have adjustable ultralinear percentage.. I'll show the output stage design on another post.

Anyway, i'm not sure there will be an audible difference between each mode other than gain.. but until i actually build this circuit, i can't really be sure.
Click the image to open in full size.

The idea is to use a pot to replace R5+R6. Dual 250K linear pot should do for both channel. You then adjust the screen feedback percentage by adjusting the ratio between R5 and R6. Here's how you obtain each mode:
1. Pentode mode is by making R5 = 200k and R6 = 0R. This will keep the screen grid at at fixed voltage regardless of plate swing.
2. Triode mode is...
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Old

Super Triode Cascode SRPP Hybrid Amplifier

Posted 26th May 2016 at 06:04 PM by ballpencil
Updated 27th May 2016 at 03:13 AM by ballpencil

Such mouthful blog title.. The idea is nothing new: to get the so-called "tube sound" from a hybrid amp. Tube sound for me comes from these two factors:
1. Triode-like linearity
2. Low to moderate damping factor
Personally, i believe number two is the main reason for tube sound. Any solid state amplifier manipulated to get a damping factor of around 1-2, instead of the typical SS amp DF that falls into the tens to hundreds, will sound like a tube amp. This is because with such low damping factor, the amp ceases to ignore the speaker impedance curve and start to become less of a voltage source and more of a current source where the bumps of speaker impedance curve will affect the amp's output.

Without further ado.. here it is:
Click the image to open in full size.

Some notes:
1. Ignore the transistor and MOSFET type. I chose them because that's what i have in LTSpice. The small signal BJT can use BC547 for...
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Old

Disclaimer

Posted 26th May 2016 at 03:25 PM by ballpencil
Updated 26th May 2016 at 03:51 PM by ballpencil

I joined diyaudio.com on Nov 2013 and that's pretty much when i started this hobby. Maybe "restarted" is a better term as i played with diy amps, tin and soldering iron back when in junior high but somehow stopped. That being said, it should be obvious that i am just a beginner and with that:
1. There will be mistakes/misinformation. Feel free to correct me. It will be much appreciated.
2. There is no guarantee any schematic shown works in real life, unless mentioned otherwise. Basically once LTSpice shows that it works, i'm 80-90% sure it should work in real life.
3. There will be updates and revisions as i learn more, hopefully with your help!
4. There will be language barrier. English is not my first language so bear with me!

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Old

The Graduates

Posted 18th May 2016 at 01:31 PM by G Speakers

Thought I'd give this blog thing a try.

I'm building a pair of bookshelf speakers for my wife as a gift. Don't worry, it's not one of those bowling ball gifts that's really for me. It will come with a record player and a few records of some of her favorites.

I recently found out my speaker configuration is actually a popular design by Carmody. Which makes me feel good about my choices, but also sets the bar high for me.

The baffle is a 1" thick walnut/maple butcher block look, with 1/2" baltic birch for the rest.

I made the mistake of comparing my PCD7 prediction with his. I noticed they are nothing alike. I got worried so I went back and re did my measurements to make sure I wasn't in a weird spot or getting a reflection. Even moving the mic all over I was pretty impressed with the consistency. The issue was - diffraction. Like 10dB of it. I beveled the corners, but it's still only a 6" wide baffle.
...
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