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Old

Project Unity Board Layout

Posted 27th December 2016 at 01:33 AM by rjm (RJM Audio Blog)
Updated 27th December 2016 at 11:11 PM by rjm

Two boards, each board configurable for line and headphone variants. Powered by nominal +12 V -12 V split regulated supply, though 9-15 V rails can be used without modification.
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File Type: zip pcb-unity-10e1-bom.zip (150.2 KB, 21 views)
File Type: zip pcb-unityB-10b1-bom.zip (98.7 KB, 17 views)
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Old

Introducing Project Unity

Posted 23rd December 2016 at 06:02 AM by rjm (RJM Audio Blog)
Updated 28th December 2016 at 12:46 AM by rjm

Following on from this post and this post, we arrive in time for the holidays with Project Unity. Merry Christmas everyone.

Four circuits: Unity, Unity H, Unity B, Unity BH. line preamp, Headphone amp, line Buffer, Headphone Buffer respectively, all derived from a common base circuit called Unity Root. Unity Root is conceptual, it exists only as a reference so you can see more clearly how the four working variants relate to each other.

It's the "all for one, and one for all" approach to diyaudio, a single research and development line applied to a range of applications, feedback from any of the applications brought back to apply to the line in general.

This simplifies not just the circuit development, similar efficiency is also brought to the documentation, board layout design, and BOM... about which I'll have more to say in a bit.
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File Type: zip Unity 10 LTSpice.zip (5.6 KB, 12 views)
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Old

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, 20 views)
File Type: zip pcb-xreg-16b1-bom.zip (96.9 KB, 15 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, 20 views)
File Type: zip pcb-zreg-11b1-bom.zip (73.0 KB, 18 views)
File Type: zip Z-reg-11b1-Eagle.zip (63.8 KB, 17 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 21st December 2016 at 05:19 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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File Type: asc sreg10e.asc (5.0 KB, 41 views)
File Type: zip pcb-sreg-10f2-bom.zip (90.0 KB, 16 views)
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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

Sapphire Line Preamplifier - My Build Notes

Posted 28th July 2016 at 04:15 AM by rjm (RJM Audio Blog)
Updated 4th December 2016 at 11:55 PM by rjm (add measurement data)

Introduction

This is my build log for relatively basic line preamplifier based on rev. 30f boards of the Sapphire3 headphone amplifier. I modified the circuit to run at lower currents (about 10 mA output bias) and adjusted the gain settings to 10/16 dB.

It is built in a Hammond 1550 cast auminum chassis, with an external Plitron 160VA 2x12VAC rectified power supply. The volume control is a 50k Goldpoint V24 stepped attenuator, while the RCA jacks are rhodium plated from Oyaide. The feature set is limited to two switchable line inputs and an output mute.

Chassis Layout Notes

Audio components are conventionally designed as rack-mounted equipment with all controls on the front panel and all connectors on the rear panel. To try and keep internal cabling to a minimum I'm modelling my preamp more like a recording console with both the controls and I/O on the top plate.

Build Notes

All components mounted...
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Attached Files
File Type: zip Sapphire Line 30f vol -10dB RMAA report.zip (32.3 KB, 77 views)
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Old

Just the buffer, ma'am.

Posted 28th July 2016 at 03:05 AM by rjm (RJM Audio Blog)
Updated 28th December 2016 at 12:46 AM by rjm (added BOM)

I've had quite a few requests for the bboard buffer circuit without the built-in regulators, so here is a bboard 2.1 standalone 2-layer board, measuring 5x8 cm. Gerber files attached in zip file.

It is designed for +/-12 V rails, but the circuit will work with anything from +/-5 V to +/-18 V. A regulated power supply is recommended.

This is a line buffer. It intended to drive cables, not headphones.

Available for $15/pair shipped. Several people have asked me about kits. I figured the BOM was so basic it wouldn't be necessary but I can send you the boards with the parts to populate them for $50/shipped. You will still need to provide the power supply.

BOM attached. (updated to 21f3 Unity B) [As a transitional step this board is being merged with Project Unity.] B-board 2.1 became the Unity B circuit, the older board is just missing the ability to convert to the Unity B H headphone driver.
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File Type: zip pcb-bb-21f3-unityB-bom.zip (88.5 KB, 5 views)
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Old

Sapphire Line Preamplifier

Posted 24th July 2016 at 02:11 AM by rjm (RJM Audio Blog)
Updated 27th July 2016 at 12:45 AM by rjm

Although the original Sapphire headphone amp can be configured as a line stage, or use as-is as a line stage, I've gone ahead and made a new circuit variant with a new set of boards.

The Sapphire Line (in development) combines the shunt-series regulator, bboard 2.0 buffer and an op amp voltage gain stage. Same basic idea as the Sapphire of course, but with a much less beefy output stage so the low noise regulator can be added and everything still fits on the board.

rev 10e - now with support for 2520 op amp modules
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