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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 (phonoclone.com / G+)


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General Information
  • Last Activity: Today 04:44 AM
  • Join Date: 2nd May 2004


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Posted 22nd April 2014 at 01:40 AM by rjm Comments 2
Part of a series.

The GeminiPS is another discrete series voltage regulator, with a Zener reference and bipolar pass transistor. It's an old circuit, published in Practical Electronics in 1970-71, and written by D.S. Gibbs and I.M. Shaw. I happen to have a reprint, but there's a nice overview here.

For reference it might be worth checking back to the two transistor regulator. The GeminiPS circuit is related in the sense that it is a more sophisticated take on the same basic principle. With just a handful of components we have a stabilized, 30 W output with soft turn on and short circuit protection. The circuit can be scaled up and down relatively easily, and the complimentary (negative output) version is an easy modification.

The pass transistor (TR2/3, Q2/3) is between the circuit common and the rectifier anodes. This may seem odd, but it was relatively common back in the day when high voltage transistors were both expensive and rare. The...

Posted 11th April 2014 at 06:59 AM by rjm Comments 0
Part of a series.

I've been meaning to take up shunt regulators for some time. I've never got around to building one myself to try, so I'll have to make do by playing in simulation.

Today's circuit is the shunt analog of the Z-reg series regulator: no feedback, Zener reference, single transistor regulation. The output impedance and ripple rejection-characteristics are similar too, with about 40 dB of RR and an output impedance of just a few ohms. It can be built equivalently from either an pnp or pnp transistor. (See attached LTSpice .asc files.)

The difference between shunt and series regulation can best be explained by considering the upstream power supply: In a series regulator an increase in current demand by the load causes the regulator to increase the current to compensate. In a shunt regulator an increase in current demand by the load causes the regulator to decrease the shunt current to balance, so there is no net change in current flowing...

Posted 3rd April 2014 at 01:24 AM by rjm Comments 0
Case report:

A set of Sapphire boards gave the proper V+, V- voltages out of the Z-reg, providing about 10.5 and -10.5 to op amp power pins. The output offsets were unusually high however, apparently at about 2 V in one board, and somewhat less in the other. Typically the offsets are in the order of +/-15 mV.

Changing out transistors and op amps did not help, and to all inspection the passive components were installed correctly and working properly. The offset voltages were extremely temperature sensitive. Measurements for the various circuit voltages were just screwy enough to be inconclusive.

I could ask for no more tests, so requested the boards be sent back to me. I found the circuit basically worked as expected, but the offsets were indeed high on both boards, though I measured 0.6 V max rather than 2 V.

***** stop here and make a guess *****

Blowing on the board through a soda straw, the offset shot up when I blew on...

Posted 20th February 2014 at 11:50 PM by rjm Comments 2
Part of a series.

So you have a small handful of parts and want to build a (simple) discrete voltage regulator instead of using an IC. What to do?

For line-level audio circuits, especially op amp based (IC or discrete) preamps with high PSRR, something like the Z-reg is generally sufficient. Robust, works well, has enough ripple rejection to cut power line noise from the preamp output.

If you add just a couple more parts, however, you can add feedback to the Z-reg circuit, a simple error amplifier in the form of an additional transistor Q2, with the output-sampling voltage divider R1,R2.

The ripple rejection is not vastly superior to the circuit without the feedback unless some additional bypass capacitors are added as shown in the first version of the circuit below. The output impedance, however, improves from a few ohms to a few tenths of an ohm as a result of the feedback. Which could, in principle, be of use.


Posted 19th February 2014 at 01:44 AM by rjm Comments 0
Part of a series.

The circuit is described here.

I'm not going to spend too much time on this one. The idea is to increase the input impedance of the pass transistor by buffering it with a jFET so it will support a high-impedance passive CRCRC filter section that generates a low noise reference voltage. The reference is defined not by a Zener or diode stack, but by a simple voltage divider. There is a LM317 pre-regulator on the front, but it is traditionally configured and works independent of the following circuit so it is omited here together with the additional transistor that speeds up the charging of the reference voltage filter capacitors.

The basic problem is that lowering the noise of the reference cannot lower the output noise indefinitely. After a point the output noise is defined by the performance of the pass transistor instead.

As you can see from the simulation, the circuit has the same ripple rejection as the filtered zener-referenced one-transistor regulator,...
Recent Comments
Replace the Zener with...
Posted 23rd April 2014 at 11:14 AM by Preamp Preamp is offline
Deleted - was nonsense...
Posted 22nd April 2014 at 11:18 AM by jan.didden jan.didden is offline

Posted 8th April 2014 at 08:46 AM by SunRa SunRa is offline
Thanks for the tip....
Posted 7th April 2014 at 07:55 AM by rjm rjm is offline
Wima MKS2 XL 4.7 F...
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