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RJM Audio Projects Information and announcements regarding my audio projects.
Old

Sapphire 4 headphone amplifier [Rev. 4.1m]

Posted 24th April 2017 at 01:02 AM by rjm (RJM Audio Blog)
Updated 21st June 2017 at 09:17 AM by rjm

Development thread starts here.

While I consider this my best work to date, the documentation trail has become hopelessly scattered so let me try to regroup in this blog post and make some sort of gateway/portal to the project. [Update: web page write up now finished.]

The followup to the Sapphire 3 started out as a generic musing on stacked diamond buffers and current mirror amplification, coalesced for a bit as the ill-fated Project Unity before becoming part of the Sapphire line initially as a temporary measure as something I could drop in my existing chassis for testing. The first iteration kept the open loop buffer of previous Sapphire iterations, but now I'm running the 4.1m boards with the buffer inside the feedback loop I realize I've ended up at just the classic, dictionary definition current feedback amplifier (CFA). Sigh. So much for originality. It sounds great though, so I'm not as upset about it as I might have been.

*****...
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File Type: zip pcb-sapphire-41m3-bom.zip (195.9 KB, 58 views)
File Type: asc Sapphire 41.asc (6.2 KB, 104 views)
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Old

CrystalFET 2 MM passive phono preamplifier with JFET amplification

Posted 21st April 2017 at 01:05 AM by rjm (RJM Audio Blog)
Updated 21st April 2017 at 04:44 AM by rjm (revised to 2.0g (capacitors C9 and C10 misslabelled))

In hindsight the original CrystalFET suffered from overreach. To obtain the 55 dB midband gain required for an MC phono stage lots of other things I might have wanted to build into the design like degenerative feedback were discarded.

Degenerative feedback as it applies to JFET amplifiers is the practice of leaving the source resistor partially or completely unbypassed. It reduces the voltage gain, but linearizes the dynamic operation of the amplifier - coercing the gain to the ratio of the source and drain resistors rather than leaving it defined by the JFET transconductance. The circuit gain can then be fixed by the designer without worrying so much about matching devices.

The CrystalFET circuit is a traditional two stage passive photo preamplifier design, the only novelty here is the addition of a second JFET configured as a source follower to each amplifier stage. To obtain above 50 dB gain no degenerative feedback could be used, and the JFETs had to be not...
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Old

Very Simple Phono Stage VSPS200 20th anniversary mono edition

Posted 18th February 2017 at 03:53 AM by rjm (RJM Audio Blog)
Updated 11th April 2017 at 01:02 AM by rjm (added board photo)

The classic VSPS slightly updated and fitted with a simple filtered Zener voltage regulator (Z-Reg).

Relaxed, spacious, easy to work on 80x100 double sided mono circuit boards.

The eagle .sch and .brd files, LTSpice .asc file, and Gerber zip package are all provided below.

Works fine with the NE5534A, or use whatever op amp you choose.


*****

revision and edit history:

200a initial release
200b changed to 70x90 hole spacing
200c C3 package changed to PCM37.5, updated C3 part listing in BOM to Kemet
200d changed regulator back to the Z-reg add R9,10 to BOM
200e move C1 and C2 capacitors 90 degrees
200f further layout tweaks
200g even more layout tweaks
200h are we done with this yet?
200i - skipped -
200j - skipped -
200k removed brestrict layer and re-did the power planes using only rect/split
200l - skipped -...
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File Type: zip VSPS200m-gerber.zip (65.9 KB, 52 views)
File Type: zip pcb-vsps200m.zip (108.0 KB, 56 views)
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Old

Phonoclone 4.4s (and 4.5b)

Posted 15th February 2017 at 11:11 PM by rjm (RJM Audio Blog)
Updated 16th May 2017 at 12:57 AM by rjm (added 4.5b BOM)

The Phonoclone 4 applies a major revision to the board layout, making it more logical with grouped, standardized I/O connections. The X-Reg has been replaced with the S-Reg shunt regulator circuit. Overall the BOM has been considerably simplified and the parts cost reduced.

Rev. 4.4s boards are back-compatible with earlier Phonoclone revisions, with the anachronistic 2.5"x3.5" mounting holes, so I can drop it into my existing chassis. 4.5b moves to 70x90mm mounting holes to be compatible with the Sapphire, VSPS200, and CrystalFET boards.

*****

Build Notes

4.0b had some low level residual ripple on the output as a result of capacitive coupling or ground loop error. The boards were respun as 4.4s (special test run, limited, unsexy green color) which work as designed. The next wide release is 4.5b.

The BOM and board connectivity checks, no issues.

The Bourns trimmer, R21, comes from the factory...
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File Type: zip pcb-pc-45b1-bom.zip (222.7 KB, 25 views)
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Old

Phono Stage Cartridge Loading Auxiliary PCB

Posted 18th January 2017 at 06:02 AM by rjm (RJM Audio Blog)
Updated 19th January 2017 at 04:33 AM by rjm

By request.

Simple 4 option loading for MC or MM cartridges. Stereo board, 80x50 mm. Part of the "useful elements" series.

Inputs are bidirectional (pass through), the signal only has to be connected to one set to function. What more loading choices? Use two boards!
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Old

Dual Bridge Rectifier PCB

Posted 18th January 2017 at 04:33 AM by rjm (RJM Audio Blog)
Updated 19th January 2017 at 04:32 AM by rjm

I'm sure there are dozens of people on diyaudio who could do up this layout, but hey, it was a super-quick modification of the cartridge loading board I was doing anyway ... so to continue the series of 50x80mm "useful elements" boards, here is a dual bridge rectifier board for a transformer with two secondaries.

It will work with just about all of my projects, or anyplace you want to have the diodes separate from the rest of the circuit.

If there is interest I may get a set made up, or make the Gerbers available.
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Old

Project Unity Board Layout

Posted 27th December 2016 at 12:33 AM by rjm (RJM Audio Blog)
Updated 27th December 2016 at 10:11 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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Old

Introducing Project Unity

Posted 23rd December 2016 at 05:02 AM by rjm (RJM Audio Blog)
Updated 27th December 2016 at 11:46 PM 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, 53 views)
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Old

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

Posted 20th December 2016 at 04:47 AM by rjm (RJM Audio Blog)
Updated 7th March 2017 at 07:09 AM by rjm (BOM 16b2 uploaded)

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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Old

The (Zener) Z-Reg Voltage Regulator

Posted 19th December 2016 at 12:55 PM by rjm (RJM Audio Blog)
Updated 7th March 2017 at 07:11 AM by rjm (BOM 11b2 uploaded)

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-11b1-Eagle.zip (63.8 KB, 42 views)
File Type: zip pcb-zreg-11b2-bom.zip (70.3 KB, 20 views)
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