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RJM Audio discrete op amp (circuit schematic)

Posted 8th August 2016 at 02:06 AM by rjm (RJM Audio Blog)
Updated 8th August 2016 at 05:37 AM by rjm

This is my first op amp design which doesn't completely suck.

Now, it's a terrible op amp... don't misunderstand... (Nat Semi will not be making me any offers)... but it does perform the job I want it to do reasonably well: remain stable while providing 6-20 dB of line-level voltage amplification with low distortion, decent PSRR, and sufficient bandwidth.

The main limitation is the distortion at high frequencies rises to -70 dB. The circuit needs less open loop distortion, or more open loop gain above 10 kHz, or both.

You will note the circuit has no current sources. This is intentional. I wanted to see how far it was possible to get without them. Obviously headroom takes a big hit, but distortion and PSRR ended up better than I imagined.

This is a simulation. No guarantee it will work, and there are no safeties (current limiters, input voltage clamps, etc) shown.

PS. Frequency response in image is open loop, while...
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Standard Resistor Values for RJM Audio Projects

Posted 11th May 2015 at 09:15 AM by rjm (RJM Audio Blog)
Updated 14th May 2015 at 10:40 PM by rjm

From now on every effort will be made to consolidate to the following values, 1/4W metal film:

1, 4.75, 10, 47.5, 100, 150, 221, 475, 1000, 1500, 2210, 4750, 10000, 22100, 47500, and 100000.

Also, the 1/4W 47 ohm and 68k carbon comp. resistor is widely used as damping and bleeder functions, respectively.

Exceptions will be made for the RIAA eq. of the Phonoclone and VSPS circuits, and the business end of the X-reg, where specific, non-standard resistance values are required.

*****

On resistor selection-

I honestly don't know if one resistor sounds better than another. I do know, however, that one resistor can be more expensive than another. At Mouser your basic 1/4W metal film resistor can run between 5 cents and 2 dollars in 100 unit quantities. Setting aside sound quality, it's not at all clear that you are getting any kind of material benefit at all by getting the expensive parts. Instead, it really...
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Denon DL-103

Posted 14th October 2014 at 12:55 PM by rjm (RJM Audio Blog)
Updated 14th October 2014 at 12:57 PM by rjm

Eye candy.

My fourth. Each one comes packaged the same, with a serial number and individual calibration sheet.

This little guy is no. 2096, .39/.40 mV. Signed off by Mr. Nemoto (根本さん、ご苦労様!)
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Which soldering station should I buy?

Posted 17th May 2013 at 07:47 AM by rjm (RJM Audio Blog)
Updated 20th May 2013 at 05:20 AM by rjm

Thinking I should get a new soldering station.

I've had my eye on a Weller station for the longest time, but put off getting one for one reason or another.

Looking at the selection, I think the choice comes down to the two following models, or, indeed the equivalent made by another company:

WTCPT (link)

WES51 (link)

The main difference is in the WTCPT the tip temperature is fixed, but rigorously controlled, while the WES51 has user adjustable power but the tip temperature is left unregulated.

I'm leaning towards the WES51 as being slightly more in line with my own style of work: I'm more likely to want higher or lower temperatures depending on the job at hand than I am to require "700F" exactly.

Update 1.

A little concerned the WES51 is only 50W max. That's less than the maximum I use now for the tough stuff.

Hakko has two models in the price...
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Whither Next for RJM Audio?

Posted 26th January 2012 at 12:22 AM by rjm (RJM Audio Blog)
Updated 1st February 2012 at 08:20 AM by rjm

On the occasion of selling the 100th and last VSPS Stereo Kit, it's time to consider what direction(s) RJM Audio will take over the next little while.

A. A minor revision of the stereo VSPS board is planned. Just a point release to address feedback I received over the last couple of years. Point release on current boards (Phonoclone 3, VSPS 300, Sapphire) expected when I deplete existing stock and have to re-order.

B. Since my circuit designs are essentially modular (the voltage regulation of the Sapphire headphone amp could be used with the Phonoclone, the output stage of the Sapphire could be detached and used on the output buffer on the VSPS...) I'm going to work on bringing that vision to a concrete reality by developing "swap-in swap-out" circuit boards... like those toys where you can change out the head, body and legs of a character to make many variations.
  1. X-reg board
  2. Zener reg board
  3. basic op amp gain block board
  4. VSPS and
...
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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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VSPS Kit

Posted 3rd August 2011 at 12:21 AM by rjm (RJM Audio Blog)

My notes tell me the first VSPS Kit was shipped on July 24th 2009. Two years later, there are just over 15 of the 100 kits left unsold. This was a limited edition, once gone they are gone and at the current rate that will happen before the end of the year.

So if you had it in mind to get one...

ordering page
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Emitter resistors and diamond buffers and distortion

Posted 3rd April 2011 at 03:36 PM by rjm (RJM Audio Blog)

Plenty of helpful advice in response to my question on emitter resistors, here.

And so finally I finish my prototype Sapphire amplifier, pictured below. The case is from Chinese audio outfit hlly, and very good. I bought it on eBay.

The rest of the components are described on my web page.
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Sapphire Headphone Amplifier

Posted 28th March 2011 at 02:15 PM by rjm (RJM Audio Blog)

Since I was effectively blogging my progress with the project as a forum thread anyway, perhaps it would be better to make it a blog rather than a post. I'm open to the idea, but does anyone ever read these blogs?
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