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CrystalFET 2 MM passive phono preamplifier with JFET amplification

Posted 21st April 2017 at 01:05 AM by rjm (RJM Audio Blog)
Updated 21st April 2017 at 04:44 AM by rjm (revised to 2.0g (capacitors C9 and C10 misslabelled))

In hindsight the original CrystalFET suffered from overreach. To obtain the 55 dB midband gain required for an MC phono stage lots of other things I might have wanted to build into the design like degenerative feedback were discarded.

Degenerative feedback as it applies to JFET amplifiers is the practice of leaving the source resistor partially or completely unbypassed. It reduces the voltage gain, but linearizes the dynamic operation of the amplifier - coercing the gain to the ratio of the source and drain resistors rather than leaving it defined by the JFET transconductance. The circuit gain can then be fixed by the designer without worrying so much about matching devices.

The CrystalFET circuit is a traditional two stage passive photo preamplifier design, the only novelty here is the addition of a second JFET configured as a source follower to each amplifier stage. To obtain above 50 dB gain no degenerative feedback could be used, and the JFETs had to be not...
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Group Buy for Salas Boards

Posted 17th April 2017 at 06:05 PM by Tea-Bag

DCG-3 preamplifier and DCSTB DC Power stabilizer purpose built for it

The boards are going to be in Matte black, like the PS on the right

Click the image to open in full size.

Threads for boards:

Building Thread

GB Thread

DCSTB Board $20
DCSTB Board $25
Transistor Kits for the DCG-3 and the DCSTB are available. Full kits are also available.
DCG-3 Transistor Kit $ 40 - includes matched transistors where needed.
DCG-3 Full Kit (includes transistor kit) $75


Note that DCSTB kits only cover half the board. Additionally, if you wish to run at a higher bias and...
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Hafler 9505 power supply capacitors for sale. IMPOSSIBLE to find!!!

Posted 11th April 2017 at 10:38 PM by wmeyer
Updated 14th April 2017 at 10:59 AM by wmeyer (forgot the caps value though members would look up supplied part #)

Would anyone be interested in purchasing Hafler 9505 PS capacitors? I am looking into acquiring brand new caps not NOS. I'm not sure what I will be charging but if I was to make a guess I would say about $100.00 each. The 9505 uses 4 of these. You can also use these in other projects as well. The small size makes it perfect for a low profile amplifier. These are very hard to find. Here is the part number, DCMX203U100CJ2B Please let me know if this works for anyone out in the diy world, Please chime in. The caps are 20,000uF 100vdc 3.635"tall x 2.5" dia with lead spacing of 1.13".
These are a direct drop in for the Hafler 9505 TransNova amplifier or this number also. i am waiting for a reply. 3186FD203T100BPA1
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Richard Allan CG10 Find - Some "New-Old-toys"

Posted 21st March 2017 at 11:49 AM by googlyone

Years ago I moved from the country back into the city. This was a move that required me to clean out heaps of stuff that I really didn't want to clear out. In our old place we had two houses on the block, one of which had been converted into an enormous studio room with NO walls, and a 14 by 14 metre shed. To say that I amassed a collection of speakers and stuff would be an understatement.

One of the things I got rid of were a pair of Richard Allan CG-10 drivers that I never got around to sticking in a box. Indeed, I never even got around to measuring their parameters.

Recently on EBAY I came across a pair of these...

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I was surprised at the condition of these - the cones look new. Needless to say they are not, the date code is 1973.

I have measured and used the CG-12, HD-15 and a bunch of other Richard Allan drivers in the past and found them...
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Did I REALLY do that?

Posted 12th March 2017 at 04:49 PM by googlyone

in my electronics workshop I have always had a stereo. Eight years ago I looked on the shelf and decided there was all the makings of an integrated preamp - DSP - Crossover and four power amplifiers.

That is the price of always making an extra board or two when I build a "thing" - you end up with a massive collection of bits.

I duly shoe-horned this lot into a case that is about 3" high. Tuned it up and didn't think a lot more.

Fast forward 8 years to two weeks ago, and there I was listening to the radio while wondering what to build next, and I thought the left tweeter sounded a bit low.

I swapped input to the amp L-R, and yep, it was. Odd - as the DSP treats L and R exactly the same, there is no balance control in there. So I swapped the speakers. Hmm, it wasn't the tweeter. It was inside the "box".

So I popped the lid, and found this...

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Removing hum from Aikido Cathode Follower (ACF-2 9-Pin)

Posted 7th March 2017 at 04:00 PM by alexcp (My DIY projects)
Updated 7th June 2017 at 09:41 PM by alexcp (Edited for brevity and, hopefully, clarity)

I purchased from Glass-Ware.com an Aikido Cathode Follower 2 (ACF-2) All-in-One 9-Pin PCB, designed by John Broskie, the editor of Tube Cad Journal (tubecad.com).

The PCB holds a pair of cathode followers, each loaded by a triode current source, and a respective power supply. In my build, a JJ E88CC with 220ohm cathode resistors shows 0.003% THD @1kHz 1Vrms with pure 2nd harmonic distortion.

As I tested my ACF, I noticed audible buzz at its outputs @0.15% THD+N - that's 1.5mVrms(!), well above the THD, and it was not a grounding problem.

A careful look at the schematic (attached), confirmed by some Spice simulation (an LTSpice model is also attached) revealed that the "Aikido" in the ACF-2 relies on the exact match of the voltages across the capacitors C18 and C19, including the hum component. These capacitors are in series for the rectifier (e.g. hum) current and, together with R4/R7, are in parallel for the signal current. In the ideal...
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File Type: asc acf-2.asc (8.0 KB, 50 views)
File Type: pdf acf-2.pdf (51.1 KB, 14 views)
File Type: pdf acf-2 one solution.pdf (51.8 KB, 17 views)
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Very Simple Phono Stage VSPS200 20th anniversary mono edition

Posted 18th February 2017 at 04:53 AM by rjm (RJM Audio Blog)
Updated 11th April 2017 at 01:02 AM by rjm (added board photo)

The classic VSPS slightly updated and fitted with a simple filtered Zener voltage regulator (Z-Reg).

Relaxed, spacious, easy to work on 80x100 double sided mono circuit boards.

The eagle .sch and .brd files, LTSpice .asc file, and Gerber zip package are all provided below.

Works fine with the NE5534A, or use whatever op amp you choose.


revision and edit history:

200a initial release
200b changed to 70x90 hole spacing
200c C3 package changed to PCM37.5, updated C3 part listing in BOM to Kemet
200d changed regulator back to the Z-reg add R9,10 to BOM
200e move C1 and C2 capacitors 90 degrees
200f further layout tweaks
200g even more layout tweaks
200h are we done with this yet?
200i - skipped -
200j - skipped -
200k removed brestrict layer and re-did the power planes using only rect/split
200l - skipped -...
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Phonoclone 4.4s (and 4.5b)

Posted 16th February 2017 at 12:11 AM by rjm (RJM Audio Blog)
Updated 16th May 2017 at 12:57 AM by rjm (added 4.5b BOM)

The Phonoclone 4 applies a major revision to the board layout, making it more logical with grouped, standardized I/O connections. The X-Reg has been replaced with the S-Reg shunt regulator circuit. Overall the BOM has been considerably simplified and the parts cost reduced.

Rev. 4.4s boards are back-compatible with earlier Phonoclone revisions, with the anachronistic 2.5"x3.5" mounting holes, so I can drop it into my existing chassis. 4.5b moves to 70x90mm mounting holes to be compatible with the Sapphire, VSPS200, and CrystalFET boards.


Build Notes

4.0b had some low level residual ripple on the output as a result of capacitive coupling or ground loop error. The boards were respun as 4.4s (special test run, limited, unsexy green color) which work as designed. The next wide release is 4.5b.

The BOM and board connectivity checks, no issues.

The Bourns trimmer, R21, comes from the factory...
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File Type: zip pcb-pc-45b1-bom.zip (222.7 KB, 28 views)
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Finally - a cheap FLAC player with digital out

Posted 8th February 2017 at 01:30 PM by abraxalito
Updated 24th May 2017 at 01:05 AM by abraxalito

I've been looking for something like this on Taobao for a few years now. A cheap player which includes a digital output so I can pair it up with one of my DACs. There have been cheap players, and there have been FLAC players but never cheap FLAC players - the cheapest prior to this one being a media player around 500rmb. This one goes into the pocket change category as its just 88rmb. What's more it includes Bluetooth. Order placed - will update after I've played with it.


Just received this - the heart of the beast is the Actions Semi ATS2825, some information about its features is available here : https://www.actions-semi.com/en/productview.aspx?id=195.
Whereas a connector for headphones (top right) is shown on the photo, this doesn't support any analog out (my board has no connector fitted there). Its purely digital output - a header for I2S and...
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iNuke received!

Posted 7th February 2017 at 09:35 PM by HumbleDeer


Just yesterday evening, I received my iNuke NU3000DSP.

I've been playing around with it for a while and I absolutely love playing with the settings. I've tried out almost everything and even as a main driver it'd sound better than my current amp.

i've made speakon connectors already, but the xlr plugs aren't working. Can someone help me set up how to connect an unbalanced source like seperate RCA's to two XLR's? Like one XLR plug with the White RCA and anothe one with the Right. The pinout is confusing as some don't state Viewed from the from or Viewed from the back.

Cheers, though. I love this amp for subwoofer duty.

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