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Old

The Z-reg

Posted 1st February 2012 at 10:58 PM by rjm (RJM Audio Blog)
Updated 2nd April 2012 at 02:02 AM by rjm

This is a followup of sorts to the X-reg, though there is nothing original about the circuit this time around.

It's just a Zener voltage regulator with a series pass transistor. I lifted this particular configuration from the Pionner C-21 preamplifier and re-tuned it for op amp applications. My main interest here is trying to make a small and convenient board layout.

I've used this circuit block already in the Sapphire amp and come away impressed.

The output is about 1 V less than the Zener voltage, and the input voltage should be about 3-6 V above the Zener reference voltage. I'm working here with 17 V unregulated supply and 12 V Zeners, but the values can be reconfigured easily enough for any output from 4-24 V

This is a low current circuit. If you are just powering a few op amps, no heatsinks are needed. Above 25 mA small heatsinks are a good idea. The circuit is not designed for output currents above 100 mA.
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Old

Current Feedback Amplifier

Posted 31st January 2012 at 05:15 AM by rjm (RJM Audio Blog)
Updated 31st January 2012 at 05:22 AM by rjm

Found this today: DC Coupled Amplifiers for Audio from an 11 year old web page by one Knut Harald Nygaard.

I've taken some minor liberties with the circuit, shown in the second, color image below. Replaced the current sources with resistors and moved the output buffer out of the feedback loop.

Note the resultant double symmetry of the dual-diamond buffer topology, highlighted in blue.
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Old

Protoamp project.

Posted 29th January 2012 at 07:52 PM by DigitalJunkie

So,I've been pondering this for a while,and I'm going to finally build it.

Basic idea- Fairly simple Push-Pull amplifier,that will deliver ~50Wpc,Using common/available tubes.
I decided to go with the 'usual' octals,since they are all a similar basing/pinout(7ac?).
This leaves us open to use 6L6,EL34,6550,KTxx,etc. for output tubes.
We'll have to have a -Vg1 supply with a wide voltage range to cover the needs of all those tubes,shouldn't be a problem.

The power transformer is a big 1kva/500W beast,used in the Tektronix 545A. (P/N 120-120)
Pete Millett was kind enough to post some data on this transformer,and a few others here:
Tek power transformers

The output transformers are rated ~100W,they came from a pair of old RCA MI-12188A amps.
They are ~3.5-4.0K (p-p) primary impedance.
There is some information on these amplifiers/transformers here:
The Shrine of the Ancient and Most Excellent RCA MI-12188A Power Amplifier...
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Old

F5

Posted 28th January 2012 at 05:39 PM by alexcp (My DIY projects)
Updated 11th April 2016 at 08:27 PM by alexcp (Added photos)

Just finished fine tuning my First Watt F5 clone.

I built it about a year ago out of parts that I had on hand back then, including a power supply reused from another project. The resulting sound was rather disappointing. Now I spent time matching transistors and tuning the feedback network. The amplifier now is very close to the performance described in the original service manual.

I am listening to F5 (the music is Tchaikovsky performed by Wiener Philharmoniker and von Karajan) and realizing that it is so good that if this was my first amplifier, I might not be interested in building anything else.

Update: after a year, this is still the best amplifier.

Update: I purchased the official F5 PCBs from the diyAudio store. I will rebuild the amplifier, hopefully with better FETs and other parts.
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Old

NOS TDA1541A double crown

Posted 27th January 2012 at 04:54 PM by dvb projekt

I am a lucky man!

Iīve got two NOS TDA1541A double crown DACīs from a friend



Click the image to open in full size.

He bought the last from Philips a long time ago...


Just now i swapped them on my Red Baron modules...

Click the image to open in full size.

What could i say.... They will never leaving the DAC modules again !!!




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Old
Rating: 2 votes, 4.50 average.

First Watt F5 Amp build

Posted 27th January 2012 at 01:53 PM by dvb projekt
Updated 13th November 2015 at 09:32 AM by dvb projekt (New photo source)

After reading so much over this amp, i will start a new project for my Hornspeaker

Letīs see if the F5 can play in the same league as my 300B monoīs



The parts


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Schaffner FN 2070 - 3A multistage EMI Filter


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Antek AS-4218 - 400VA transformer



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SST03 Softstart module from Sjostrom Audio
Design without extra transformer


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RFB03 rectifier bridge from Sjostrom Audio

Click the image to open in full size.

with IXYS DPG 60 C 200 HB
...
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Old

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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Old

My system (Jan 2012)

Posted 23rd January 2012 at 12:12 PM by rjm (RJM Audio Blog)
Updated 26th January 2012 at 02:57 AM by rjm

Biggest changeover in many years.

Denon DP-2000, DA-307, DL-103 turntable/tonearm/cartridge
Phonoclone 3 with 160 VA Plitron power supply
47 Labs "Treasure" model 0247 preamplifier
47 Labs "Treasure" model 0347 amplifier
Onkyo D-605SR speakers
Cables by oyaide, mostly.
(photo: Pentax K10D, Pentax FA 31mm F1.8 AL Limited)
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Old

Oh, MY!

Posted 23rd January 2012 at 06:51 AM by rjm (RJM Audio Blog)

Denon DL-A100

Transparent DL-103 for Denon's 100th anniversary.
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Old

op amps for audio

Posted 23rd January 2012 at 06:36 AM by rjm (RJM Audio Blog)

Douglas Self on op amps for audio, which I read before in slightly different form, on another web site somewhere, many years ago... today was a refresher course.

Excerpts from op amps in small signal audio design, by D. Self [Part 1, part 2, part 3, part 4].

I suppose I should get with the times and start using the LM4562 seeing as it is available in DIP8 now. (I had this memory that it was only SOIC, go figure...) Pity it's dual only. On the other hand, that leads to some neat ideas, like a compact version of the Sapphire amp for example, or the X-reg.

I am struck by how few choices we really have when it comes to practical op amps for audio in single DIP8 packages. There is the NE5534, TL071 and TL051, the OPA134, the OPA604, and OPA27, OPA627. Maybe the AD797 but I have yet to see the point. Given that the TL1071 and derivatives are outdated and replaced essentially by the OPA134, and given the excessive cost (and questionable sonic benefit)...
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