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The (Xross-type) X-Reg Voltage Regulator (Stabilizer)

Posted 20th December 2016 at 05:47 AM by rjm (RJM Audio Blog)
Updated 21st December 2016 at 01:52 AM by rjm

I've come this far so I might as well complete the trifecta.

This is the X-Reg circuit, with a new layout and component numbering to match the new S-Reg and Z-Reg boards. Each is a drop in replacement for the other.

Like its siblings, the X-Reg is a low current voltage regulator for line level audio. The output is about 9 V (adjustable up to 12 V) and the maximum load current is 50 mA without heatsinks, 100~150 mA with small heatsinks on Q1,2.

It is not a true regulator as there is no fixed reference and instead the output voltage is defined relative to the input voltage. The high open loop gain of the op amp is harnessed for very low noise and very high ripple rejection. It is necessarily a high feedback approach.

So, there you are: three mix-and-match power supply options for all your low voltage, low current audio needs.
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File Type: zip X-reg-16b.zip (63.6 KB, 26 views)
File Type: zip pcb-xreg-16b1-bom.zip (96.9 KB, 21 views)
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Old

The (Zener) Z-Reg Voltage Regulator

Posted 19th December 2016 at 01:55 PM by rjm (RJM Audio Blog)
Updated 21st December 2016 at 01:49 AM by rjm

Companion regulator to the S-Reg. Same board dimensions and connection layout. For line level audio.

Same idea as before rectified 2x12 VAC input, +/- 11 V output. 50 mA max output current unless the transistors are heatsinked.

There is a small amount of over-current protection afforded by R3,4 but do not short the output for all but the shortest of transients.

Eagle/Gerber files attached, so you can go get this made yourself, optinally with whatever modifications you need.

I've use this regulator circuit in my Sapphire headphone amplifier. It's a simple and modest circuit but I feel it works really well in practice as long as the audio circuitry it powers has reasonable PSRR. No feedback means no out-of-band noise or instability, even as the output impedance remains low.
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File Type: zip Z-reg-11b.zip (51.1 KB, 25 views)
File Type: zip pcb-zreg-11b1-bom.zip (73.0 KB, 25 views)
File Type: zip Z-reg-11b1-Eagle.zip (63.8 KB, 21 views)
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Old

The (Shunt-Source) S-Reg Voltage Regulator

Posted 19th December 2016 at 12:09 PM by rjm (RJM Audio Blog)
Updated Yesterday at 05:04 AM by rjm

S-reg voltage shunt-source regulator for line-level audio circuits.

This is designed to accept rectified 12x2 VAC input, producing +/-12 V output split rails.

Features soft-start and over-current protection, standard configurations for load currents up to 50 mA. High performance: 80 dB ripple rejection up to 100 kHz.
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Attached Files
File Type: asc sreg10e.asc (5.0 KB, 64 views)
File Type: zip pcb-sreg-10f2-bom.zip (90.0 KB, 23 views)
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Old

RJM Audio in 2017 [modular simplicity]

Posted 19th December 2016 at 01:11 AM by rjm (RJM Audio Blog)
Updated 28th December 2016 at 12:50 AM by rjm

The time of year where I like to draw up some plans for the next 12 months.

This years output looked something as follows,

At the end of all this I find myself sitting on four different voltage regulator circuits, several variants of the transistor output diamond buffer, five phono stages variants, and a couple of nebulous ideas about developing a discrete voltage gain amplifier.

I'm considering how to package this all up in such a way as to best appeal to diyaudio builders of widely varying application needs and skill levels while keeping a simple...
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Old

CFA audio gainblock - a second take

Posted 16th December 2016 at 02:21 AM by rjm (RJM Audio Blog)
Updated 16th December 2016 at 02:28 AM by rjm

This is either an ingenious interfacing of the output buffer and current feedback amplifier by adding second arm to the central current mirrors ... or it's another really bad idea(tm).

It simulates nicely though.

[What's happening here is current output of collector Q9 is no longer being asked to bias and drive the buffer Q16. Instead Q2 and Q17 do that job. The change lowers distortion, improves bandwidth, and even raises the PSRR a little.]
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Old

A slightly different kind of voltage amplifier

Posted 12th December 2016 at 11:44 AM by rjm (RJM Audio Blog)
Updated 21st December 2016 at 05:50 AM by rjm

(which is a current feedback amplifier)

Lately I have been looking again for a discrete transistor voltage gain amplifier for line level duty that isn't just another op amp.

I keep coming back to variations on this circuit. It's a diamond buffer input with current mirrors in the mid-section strapped around a voltage divider / feedback loop that provides the gain. This backs out into either another diamond buffer or, in the revised version below, a standard Sziklai output stage which can be more easily scaled up as needed for a headphone amp for example.

An offset bias adjust circuit could be added to trim the output offset voltage. Or use a coupling cap. It's a few hundred mV otherwise.

Circuit gain is R4/R6, approximately. The total value of R4+R6 should be kept about 20 kohms. C1 is a compensation capacitor. Circuit gain as shown is 14 dB, -3 dB at 250 kHz.

As with all CFA, the choice of the feedback resistance...
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Old

Lynx and RME Sound card pinouts

Posted 7th December 2016 at 06:28 PM by 1audio

Attached are the pinouts for a Lynx (L2 or L22) sound card and for an RME HDSP(e) sound card. The host end is a standard Dsub connector
Attached Files
File Type: zip Connector pinouts.zip (49.1 KB, 18 views)
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Old

RJM Audio desktop wallpaper

Posted 2nd December 2016 at 07:45 AM by rjm (RJM Audio Blog)

16:9 4K

rendered from VSPSX phono stage Eagle .brd output
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Old

HP 339A Mods & Upgrades

Posted 29th November 2016 at 01:42 AM by SyncTronX
Updated 1st February 2017 at 09:27 AM by SyncTronX

HP339a
Introduction


The HP339a was a state of the art (SOTA) distortion analyzer in the 1980s.
It is a full featured all-in-one product including a volt meter,
low-distortion oscillator, distortion analyzer, AM detector, and VU meter.

There was an in-depth analysis of low distortion oscillators
on DIYAudio on the following link:


<Low-disortion Audio-range Oscillator>
This was followed by a specific HP339a thread, linked here:

<HP339a>

This is a summary of those threads along with the links, conversations, and
posts, about the research and development that went into the suggested modifications to the venerable HP 339A.

Outline



Why HP 339A?

HP339A Post #78
Well, a stock 339A gives you a wide band ac voltmeter, an oscillator and analyzer. A stock one will do you pretty well as long as you have no interest in reading below...
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Old

Grundig Studio RPC 350 need help

Posted 7th November 2016 at 11:01 AM by Keepsake10

Question for transistor experts.
I recovered the amplifier module from a old Grundig studio RPC 350. This amplifier is a classical concept of the time (around 70) differential input with CCS, driver, darlington complementary finals (BDW 94 / 95) It has DC transistor protection for the output and as well a kind of thermic protection switch on the heater sink (this protection cut entirely the main if heater sink get too hot).
I changed all electrolytic Cs and checked the rest of the parts. The rectifier bridge was replaced with fast recovery rectifiers and both 10.000/30V capacitors where replaced with 18.000F/40V. Measured values as shown by Grundig are ok and the offset can be done within Grundig specifications (the old 1Kohm trimmers will be as well replaced with multi-turn ones to get much easier control).
There is one issue I cant get fixed. The original schematic show the T2004 as BD517. Actually in this place was used a small Motorola in TO92 package...
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