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rjm rjm is offline

Richard Murdey

diyAudio Member

About Me

  • About rjm
    Canadian citizen, Japanese resident.
    Audio Circuitry
    Research Scientist
    Real Name
    Richard Murdey
  • Signature
    RJM Audio ( / G+)


Total Posts
Blog - RJM Audio Blog
  • Wiki Contributions: 0
  • Wiki Comments: 0
  • Recent Wiki Activity: rjm has no recent wiki activity
General Information
  • Last Activity: Today 11:09 AM
  • Join Date: 2nd May 2004


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View rjm's BlogRecent Entries
Latest Blog Entry

Posted 24th April 2017 at 01:02 AM by rjm Comments 3
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 closed loop I realize I've ended up at just the classic, dictionary definition current feedback amplifier. Sigh. So much for originality. It sounds great though, so I'm not as upset about it as I might have been.


I'm being loose with the "closed...

Posted 21st April 2017 at 01:05 AM by rjm Comments 0
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...

Posted 18th February 2017 at 03:53 AM by rjm Comments 0
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 -...

Posted 15th February 2017 at 11:11 PM by rjm Comments 0
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...

Posted 19th January 2017 at 10:37 PM by rjm Comments 2
Another request.

The Sapphire4 and Unity (H) boards were based on the 47 Labs Treasure 0347 amplifier circuit, and the original was not so far away that I couldn't "de-modify" the Unity (H) board back to what is essentially a 0347.

Here's what else you need to know:

Runs off 100VA or higher power transformer, 2x15 VAC secondary, bridge rectifier, 2200 uF filtering or more on the power supply rails in addition to what is on the main boards.

The outputs go to a mute toggle switch and then a 2A fast fuse before connecting to the speaker terminals.

In the original, Q9 and Q10 are taken off board and glued to the face of Q13 and Q14 packages. This provides overtemp control, as the output transistors heat up the Vbe of Q9, 10 decreases - reducing the output bias current.

C2 was not present on the original. I include this compensation capacitor as an optional tuning option, though my own tests show it shouldn't...
Recent Comments
Fair enough! I have...
Posted 25th April 2017 at 01:09 AM by needtubes needtubes is offline
I started by tabling...
Posted 24th April 2017 at 11:39 PM by rjm rjm is offline
Looks like a nice amp!...
Posted 24th April 2017 at 12:41 PM by needtubes needtubes is offline
Hi, thanks for the comment....
Posted 1st February 2017 at 12:28 AM by rjm rjm is offline
Nice to see someone...
Posted 31st January 2017 at 06:54 PM by Grasso789 Grasso789 is offline
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