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Posted 26th May 2016 at 04:25 PM by ballpencil
Updated 26th May 2016 at 04:51 PM by ballpencil

I joined 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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The Graduates

Posted 18th May 2016 at 02:31 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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And now for something completely different...

Posted 14th May 2016 at 04:48 AM by googlyone
Updated 14th May 2016 at 04:53 AM by googlyone

As a kid, which depending on my wives mood could be stated to be "right now" right through to "you have never been a kid", I once made the statement that "if it can't be done with a BC549 it is not worth doing".

this statement was made in jest at the time, and probably stolen from a similar a similar assertion about the NE555. (those of you who are < 30 years old probably haven't seen these used in real anger!)

Here I am travelling, and flying from Adelaide (Australia) to the USA. This is a long, boring flight. In a fit of boredom I set myself a challenge.

So what is the challenge? Something cool and completely different for once. Hmm. Make a power amplifier using BS549's. If you have seem my play room, amplifiers are made to scare speakers and annoy the neighbours. So this can't be a lightweight 100mW job. It must be something that actually works, and is able to make real noise.

OK, it...
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Bboard buffer 2.0 (yet another version "2")

Posted 13th May 2016 at 09:22 AM by rjm (RJM Audio Blog)
Updated 27th May 2016 at 01:47 AM by rjm

A little bit of the sapphire headphone amp output stage, and a little bit of the LSK489 application note of all things (scroll down to Fig 10.).

Yes, this is probably the third "version 2" of this line buffer I've posted... I keep tossing it out and starting over. This variant looks pretty good: though the transistor count is a little high for such a basic function the performance is definitely there.

The main innovation re. the sapphire circuit is to replace the bias set resistors with diodes made out of the Vbe of transistors Q9 and Q10. This generates more voltage than is ideal, but can be handled by using largish values for the emitter resistors R13 and R14. Since this is a line stage buffer and not a headphone amplifier the output impedance of about 30 ohms and the limited output current swing are not critical flaws. It will drive 600 ohms at 0 dB with 0.001% THD. The whole circuit draws just 150 mW. The input impedance is a very high ~15 Mohms...
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The Right Preamp For My First Watt F4

Posted 11th May 2016 at 06:36 PM by oltos

Hello SY,

I have one First Watt F4 amp, so Iíd be running it stereo unbalanced to drive my speakers.

Since the Impasse debuted, have you or others implemented any revisions that I should know about?

My speakers are at least 94db sensitive, my room is 16 ft x 14 and my ears canít tolerate average SPLs much beyond ~ 60db-at least not much above the lower midrange band (i.e. allowing for the Fletcher-Munson effect). My midwoofers are cut off below 70Hz, where my pair of Rythmik 12" sealed powered subs take over.

Except for the subwoofers, my speaker system is a clone of Gary Dahlís Azurahorn 425/Radian 745 Neo Be/GPA Altec 416 system.

Are there certain tube suppliers of specific brands of 6SN7 tubes, or better sounding alternatives, that you would recommend for best performance with my speakers, such as ?
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High Sample Rate PCM

Posted 2nd May 2016 at 01:13 AM by Tam Lin
Updated 12th July 2016 at 02:38 PM by Tam Lin (corrected typo)

With delta-sigma DACs pushing insane clock rates I wondered if a traditional multi-bit DAC could not do better. The fastest multi-bit I know of is the PCM1704, which has a max BCLK rate of 25 MHz. A 32-bit sample frame can run at 768 K samples per second. That is fast but not faster than DSD64.

However, with 32 DACs per channel staggered across the sample period we get 24.576 M. That is better than DSD512. For input at or below the native rate of 768K, the DACs operate in parallel. Below the native rate, inserted nulls stretch the output sample period. Above the native rate, the DACs are staggered and the data at each point is the input sample value minus the sum of the data in the other DACs. Thus, each successive sample is the delta needed to reach the next sample point. This approach has interesting repercussions: I will let you ponder them for the time being.
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Transformers and crossfeed

Posted 15th April 2016 at 05:09 AM by abraxalito
Updated 25th April 2016 at 04:15 AM by abraxalito

Listening to headphones creates, on many recordings, an unnaturally wide soundstage. I decided to play with the idea of 'crossfeed' whereby some deliberate crosstalk is introduced between the two channels. With transformers its jolly easy to do - just create an extra winding with the right number of turns then put this winding in series with the main output of the opposite channel.

In the picture I've done this with some EP17 ferrite cores and added a DPDT changeover switch to A/B between the original and crossfed version. The crossfeed factor I've gone for is 25%. It works in practice in that there's a more natural presentation without any 'extreme' stereo effects (almost a kind of phasiness on some recordings). But sometimes I enjoy the 'all around' effect so switchable is the name of the game

Trafo winding details as follows - primary 500T of 0.1mm, two secondaries first 120T 0.21mm, second 40T 0.21mm.

Made a second one as a colleague liked...
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Understanding the J113 JFET

Posted 14th April 2016 at 02:08 PM by rjm (RJM Audio Blog)
Updated 16th April 2016 at 12:31 AM by rjm

"To fight the bug, we must understand the bug."

The J113 datasheet (Fairchild) tells you the following important information,

1. The (absolute) maximum gate-source / gate-drain voltage is 35 V.

2. The gate-source cut-off voltage (V_gs0) varies between -0.5 and -3 V.

3. The minimum zero-gate voltage drain current (I_dss) is 2 mA.

4. (from Fig. 11) the transconductance for I_ds 1-10 mA is about 10 mS largely independent of V_gs0.

5. (from Fig. 14) the voltage noise rises at low frequency and decreases with drain current, but is about 2-4 nV/sqrtHz over most of the audio bandwidth.


I bought 200 J113 off eBay, but my measurements were set back after I realized my test rig was oscillating. Fixed that, and can now say a few things in addition to the datasheet.

The first is that the transfer curve (measured at RT, V_ds 10 V) does...
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Full digital amplifier: the future is now !

Posted 11th April 2016 at 05:15 PM by globulegl
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Salas DCG-3 Preamplifier and DCSTB Power Supply

Posted 10th April 2016 at 01:26 PM by Tea-Bag
Updated 29th December 2016 at 08:37 PM by Tea-Bag

This blog is concerning ordering, parts, assembly and some brief sound review of the two new circuits designed by Salas.

The DCG-3 is a new preamplifier design. It offers 10-15db of gain, and can use several different types of input JFETs.
Here is the preliminary values in the schematic.

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Here is the prototype board

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Here is the Actual Production layout
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The DCSTB is Salas first offering of a series regulated supply. It is very easy to assemble and includes two board assemblies off one power supply. This is a somewhat 'greener' approach and requires less waste current than say it's SSLV1.1 or BIB board equivelant....
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