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RJM Sapphire

Posted 4th December 2011 at 01:58 AM by jtktam (Newbie audio DIYer)

Another weekend, another project.

Started on the RJM sapphire headphone amp this weekend. Having a bit of trouble with the transformer I ordered. According to the BOM they specified a Triad 25VA unit.

I got them from Mouser and it was huge, the wires were unwieldly and I didn't think I would use them

Looking at the pics posted by RJM, they used Amveco, which is my normal brand.. DOH!

So off to digikey to order yet another set of transformers..

Also need to figure out if I would use the bridge rectifiers I already bought, or use Peter Daniels rectifier PCBs and use the MUR280 instead.. the latter will be faster and cost more.. the former might not perform but it's cheap

-joe
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Interesting blog post about fake chips

Posted 3rd December 2011 at 03:27 AM by abraxalito
Updated 5th March 2012 at 02:50 AM by abraxalito

On Counterfeit Chips in US Military Hardware bunnie's blog
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PA speakers for brothers band

Posted 30th November 2011 at 09:42 PM by googlyone

My brother was complaining about his vocals not coming through clearly in his (rather modest / amateur) band. It turned out that he was trying to use some old hifi speakers we had as kids!!!

I had a bunch of Beyma 12G125 bass drivers and some P.Audio PA-D26 compression drivers, so offered to throw some proper speakers together for him.

There were a couple of illustrations of design principles in here that are worth reiterating:
- The horn driver has a massive (and by this I mean both acoustically and electrically) resonant peakj just below 2KHz.

To use this driver and avoid horrible the resultant upper midrange peak, it is essental to put a trap on the tweeter to flatten out the impedance.

this at least gives the crossover a hope of working...

- The horn driver still has a big fat peak at 2KHz.

- The horn was CD - and needed compensation to bring the top end up to "flat".
...
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Matching Stuff

Posted 26th November 2011 at 11:24 PM by Michael Rothacher (Audiohobby.com)

The topic of JFET and MOSFET matching comes up often in the forums, so I thought I'd show you the jigs I use.

First up, is my trusty old JFET IDSS matcher.

Click the image to open in full size.

There's a 9V battery inside, and the meter probes are conneted across a 10 Ohm resistor which is connected to the JFET drain. I included a polarity switch for convenience when testing P channel parts.

It's pretty easy to connect the microclips, count to five, and take a reading.

Click the image to open in full size.

And here's what I use for the big stuff. This is my MOSFET Vgs matcher.

Click the image to open in full size.

First, I install a sample part and let it warm up for about an hour. There's a thermistor hot-glued to the heat sink,...
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new layout

Posted 25th November 2011 at 12:32 PM by jtktam (Newbie audio DIYer)

Click the image to open in full size.
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Ck2iii pics

Posted 25th November 2011 at 12:30 PM by jtktam (Newbie audio DIYer)

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Click the image to open in full size.
Click the image to open in full size.
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a10 preamp

Posted 25th November 2011 at 12:27 PM by jtktam (Newbie audio DIYer)

Haven't had a chance to update last two months.. the a10 preamp was completed with a little help from my dad and is now integral part of my setup. I even put my Linn magik up for sale.. it's that good.

Last month I started to gather the parts for the objective2 headphone amp. I got about 50-100 units worth of PCB and parts. I will start to package them as kits and sell some assembled. It will be my first try at selling here.

Last two weeks I finish building and rebuilding my Ck2iii headphone amp. The initial build was with an outboard power supply and headphone amp. The cost was running a little high since I build it using momentary switch, etc..

Then I rebuild it two days back into a single enclosure with a switch at the IEC instead. Cut cost down a lot since I no longer have to deal with umbilical cord, etc

-joe
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Recycled parts, this time, a ZX Spectrum!

Posted 22nd November 2011 at 02:51 PM by DrDyna

Re-purposed my HiVi M6A into these ZX Spectrums designed by Paul Carmody. They're a groovy little speaker with this crossover and the B&G Neo3 PDR which I am absolutely in love with now.
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RJM Audio, now on Google+

Posted 21st November 2011 at 11:06 AM by rjm (RJM Audio Blog)

I hate facebook but I'm willing to give Google+ a go. Now they have "product" pages as well as "people" pages, I have made a little port to RJM Audio.

RJM Audio Google+ page
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Old

The Von Neumann architecture is becoming the niche.

Posted 15th November 2011 at 02:50 AM by abraxalito
Updated 5th March 2012 at 02:51 AM by abraxalito

http://garysmitheda.com/paper/ARM-Techon-note.pdf

Its a single page review of ARM Techcon. At the end I think he means 'PC design' not 'PCB design' as he's written.

He says:

If Intel doesn’t do something soon this might not be much of a war.

He knows some guys at Intel read his analysis so I think he's sugaring the pill. Intel is rather like the hare in the old fable of the tortoise and the hare. The hare woke up and tried to catch up with the tortoise but it was too late. That's exactly where Intel is right now - they've become awake to the issue but they've missed the boat.
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