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Understanding the J113 JFET

Posted 14th April 2016 at 01:08 PM by rjm (RJM Audio Blog)
Updated 15th April 2016 at 11:31 PM by rjm

"To fight the bug, we must understand the bug."
--SKY MARSHALL TEHAT MERU

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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Old

Full digital amplifier: the future is now !

Posted 11th April 2016 at 04:15 PM by globulegl

https://www.homecinema-fr.com/forum/a...t30064559.html
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Old

Salas DCG-3 Preamplifier and DCSTB Power Supply

Posted 10th April 2016 at 12:26 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.

Click the image to open in full size.

Here is the prototype board

Click the image to open in full size.

Here is the Actual Production layout
Click the image to open in full size.

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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Old

Restored and modded Cambridge Audio A3i

Posted 9th April 2016 at 01:51 PM by alexcp (My DIY projects)
Updated 13th April 2016 at 03:17 PM by alexcp

The designer of Cambridge Audio A3i had talked about the amp in this forum and suggested some changes to the components that bring the performance of the amp to a new level.

When I saw a cheap A3i on eBay, I decided to try it out. One channel was DOA, but it did not matter as I was about to mod it anyway.

Here is what I've done:
  1. Replaced all rectifiers (D201-D206 on the schematic) with soft recovery diodes and removed the capacitors in paralell with the diodes;
  2. Changed the grounding scheme so that the protection circuit and the relay driver are connected directly to the star ground;
  3. Added a 30ohm resistor in series with the rectifiers of the protection circuit;
  4. Replaced the electrolytic capacitors in the amplifier (but not the protection circuit) with Nichicon KA and replaced the two large power supply capacitors with Nichicon LLS;
  5. Replaced all film capacitors with Kemet PHE426 or, where PHE426 wouldn't fit, with Kemet SMR;
  6. Replaced the rectifiers
...
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File Type: pdf A3I schematic.pdf (1,011.2 KB, 286 views)
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Old

Krell KSA-5 clone

Posted 9th April 2016 at 01:27 PM by alexcp (My DIY projects)
Updated 11th February 2017 at 03:20 PM by alexcp

When I saw the discussions of KSA-5 headphone amplifier on head-case.org and on this forum, I thought it may be a nice use for the bag of 1000uF capacitors I had at the time. This was the main motivation for putting this Krell KSA-5 clone together.

The main challenge was to drill the front panel. The 10mm aluminum panel that came with the enclosure is easy to work with, but I wanted it to be pretty and asked the people at Modushop to CNC it for me.

Although it works ok, I think it is not a very good power amplifier for loudspeakers. As a headphone amplifier, it is no match for my Musical Fidelity X-CANv8.
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File Type: zip ksa5psorig.zip (791.3 KB, 61 views)
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Old

NCore based power amplifier

Posted 9th April 2016 at 01:20 PM by alexcp (My DIY projects)
Updated 11th February 2017 at 03:25 PM by alexcp

Ever since I heard about the Hypex NCore technology, I have wanted to build a power amplifier based on Hypex NC400 modules. Here is what I got. It works very well with the preamplifier from the previous post.

I used a spare Arduino to control the SMPSes. For now, it simply allows to use a momentary push button on the front panel. I may add remote control (12V trigger or similar) later.
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File Type: pdf NC400_04xx.pdf (2.97 MB, 136 views)
File Type: pdf SMPS600_DIY_R5.pdf (1.42 MB, 58 views)
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Old

Bruno Putzeys' MicroPre

Posted 9th April 2016 at 01:14 PM by alexcp (My DIY projects)
Updated 11th April 2016 at 08:21 PM by alexcp

In April 2013, Linear Audio published in Vol.5 Bruno Putzeys' article "The G Word, or How to Get Your Audio off the Ground". Linear Audio included a free PCB for the demo project from the article: a balanced volume controller, or rather a minimalist balanced preamp with two pairs of balanced inputs.

I have been looking at balanced interconnects for some time and decided to use the free PCB and build the preamp. Here is what I built.

The enclosure used is Galaxy GX247 with front and back panels custom made by Front Panel Express. It was difficult to place a C14 power inlet on the back panel, as the space is quite limited due to the central placement of the six XLR connectors. An easy solution would be to fix the power cord permanently to the preamp, but I found a compact snap-in connector that fits the 3mm back panel of the enclosure.

I understand the article is available for download at the Hypex web site, and the PCB gerbers and a...
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Attached Files
File Type: pdf The G Word.pdf (731.5 KB, 177 views)
File Type: zip MicroPre_gerbers.zip (53.9 KB, 75 views)
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Old

My Dream System (As of Today)

Posted 9th April 2016 at 07:08 AM by museguy

Fostex T40RP mk3 with mods, including MadDog Pads $140usd

Sennheiser HD600 $377usd

Headphone Amp
Krell KSA-5 Clone

DAC
?
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Old

Print A3-sized schematics from A4 printer (Windows/OSX/Linux)

Posted 8th April 2016 at 02:10 PM by autopoiesis

The situation

1. You have a schematic in PDF format, but it's hard to read when printed on A4
2. Only A4 printer available
3. Printer drivers can't solve the problem
4. A3 size wanted (ie two sheets A4, with some overlap for taping together)
5. Following (free/OSS) programs are available:
GIMP
PosteRazor

To illustrate point 3: my printer will print multiple pages per sheet ("2 in 1" - ie reduce), or print an A4 page on (n x n) sheets (A2 - four times the area), but there's no option to double the size to A3. A4 too small; A2 too big

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About GIMP - https://www.gimp.org/
Open source image manipulation program - sort of free Photoshop, plenty of info around.

About PosteRazor - PosteRazor - Make your own poster!
PosteRazor is designed to split image files into [n by m] individual pages in a single PDF file, on whatever page size...
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Old

Mighty mite balanced SE classA headphone amp

Posted 5th April 2016 at 09:39 AM by abraxalito
Updated 25th April 2016 at 11:06 AM by abraxalito

I was going to call this amp 'fleapowered' but after doing some searching online I found fleapowered amps in general were much higher output power than this - single digit Watts typically. Whereas this one is more than a couple of orders of magnitude lower than that (under 10mW) so deserved a different moniker. Seeing as a mite is smaller than a flea, 'mighty mite' seemed to me as good as any descriptor for it.

The mighty mite started life in my imagination after I walked into a local headphones shop and tried out some cans that the shop assistant recommended to me - AT MSR7s. I'd brought my 'Buffalito' headphone buffer with me and some step down transformers for its output - fed from my mobile phone its way too loud for my AKGs and Superluxes. However the MSR7s were too loud even with the 2:1 step down trafo so I told the assistant I'd come back and listen again once I had a more suitable trafo. I figured it needed to be 4:1 step down, so I built a pair of those (PQ32/20)...
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