Shunt-regulated 24V DC Power Supply for Preamp Modules - diyAudio
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Old 25th August 2005, 05:00 PM   #1
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Default Shunt-regulated 24V DC Power Supply for Preamp Modules

Hi,

I am using some vintage modules such as Neve, Audix and Audio Developments as preamp and they require +24 volt dc power supply. I am using LM317 series regulated p.s. to feed them. Now I want to upgrade them. Are there any designs which adopt the shunt regulated concept? Any information is greately appreciated! Thanks.
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Old 25th August 2005, 05:26 PM   #2
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You mean something like this? Select R2, R3 to get 1.25V at their junction. Add caps at the output as felt necessary.

Jan Didden
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File Type: pdf shunt reg.pdf (17.2 KB, 1697 views)
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Old 25th August 2005, 06:09 PM   #3
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Quote:
Originally posted by janneman
You mean something like this? Select R2, R3 to get 1.25V at their junction. Add caps at the output as felt necessary.

Jan Didden
Hi Jan,

Thank you for your reply. Sorry to say that I am just a layman to electronics only. What I know from shunt regulated design is from Allen Wrights' SuperReg design for the tube amp (high voltage B+). I am currently using his SuperReg boards for my tube preamp. It really sings. What I am looking for is a similar design for supplying 24 volt DC for my vintage s.s. preamp modules.

Please advise whether the design you propose suits my case. If yes, how to play around the values of R2 & R3 to get 1.25V?

Thanks.

Regards,

TC MA
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Old 25th August 2005, 06:58 PM   #4
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You could also take a look at LM431 from Texas, National and others.
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Old 26th August 2005, 09:05 AM   #5
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Not sure how sophisticated you wanna get, but I've tried out a lot of different regualtor types and settled on shunt designs myself. Even simple zener regulators sound better to me than your typical high feedback series pass regulator. But they're too noisy for most applications.

In any case, the type I've been using for the last few years uses a AD712 type opamp (required) as the control element and uses a lithium cell for the voltage reference. The shunt element is a mosfet and I use them with LC filters. No electrolytics anywhere, just chokes and quality polyprops. All copper from the diode bridge to the load. Very precise and quiet. The negative regulator is slaved to the positive with ground as its reference. Pretty simple design, and the lithium cell gets rid of the positive feedback loop that most regulators have and makes the regulator much more like a battery since the reference is truly independent. I use them on all my sources and in the power amp too. All simple off the shelf parts. The AD712 or other similar bifet input type opamps are required in order to use the lithium cell as a reference.

If interested, I can post a schematic later. Might not be what you're after, but let me know.
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Old 26th August 2005, 09:20 AM   #6
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Quote:
Originally posted by Black Heart
f interested, I can post a schematic later.
Yes please...

dave
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Old 26th August 2005, 02:44 PM   #7
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Quote:
Originally posted by Black Heart
Not sure how sophisticated you wanna get, but I've tried out a lot of different regualtor types and settled on shunt designs myself. Even simple zener regulators sound better to me than your typical high feedback series pass regulator. But they're too noisy for most applications.

In any case, the type I've been using for the last few years uses a AD712 type opamp (required) as the control element and uses a lithium cell for the voltage reference. The shunt element is a mosfet and I use them with LC filters. No electrolytics anywhere, just chokes and quality polyprops. All copper from the diode bridge to the load. Very precise and quiet. The negative regulator is slaved to the positive with ground as its reference. Pretty simple design, and the lithium cell gets rid of the positive feedback loop that most regulators have and makes the regulator much more like a battery since the reference is truly independent. I use them on all my sources and in the power amp too. All simple off the shelf parts. The AD712 or other similar bifet input type opamps are required in order to use the lithium cell as a reference.

If interested, I can post a schematic later. Might not be what you're after, but let me know.
Yes, sound very interesting and should be the one that I'm looking for. Kindly post the schematic please. THANKS.

T.C. MA
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Old 27th August 2005, 09:01 AM   #8
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Hi Blackheart,
you've dropped yourself right into it.
We all want to learn from your schematic.
Go on, post it.
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Old 27th August 2005, 04:50 PM   #9
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Quote:
Originally posted by planet10


Yes please...

dave

Quote:
Originally posted by snoopyma


Yes, sound very interesting and should be the one that I'm looking for. Kindly post the schematic please. THANKS.

T.C. MA

Quote:
Originally posted by AndrewT
Hi Blackheart,
you've dropped yourself right into it.
We all want to learn from your schematic.
Go on, post it.

Sorry for the delay guys but I've been kind of busy. I pulled the power supply stuff out of my DAC schematic into another file and am massaging it slightly and then will convert it and post it. Should definitely be sometime today. Didn't really mean to make the offer in my first post here and then be a no show and didn't know about the moderation delay in effect for newbies. Thought that I might have a schematic around of just the power supply that I could easily post, but couldn't find it on my laptop. I do have the I/V output stage of my DAC broken out since it is a separate module, and I do have the schematic for my amp module including the regulator, but the DAC regulator is closest to what snoopyma was asking for since it is set up for about +/-20 VDC. Stay tuned

Here's a simplified schematic of the DAC I/V output stage if you're interested. Power supply details to follow ... click for schematic
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Old 27th August 2005, 10:10 PM   #10
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OK, I cleaned up the power supply schematic and converted it to a gif and uploaded it to my site and you can click on it below. I'll leave it up there for a few days or so. I tend to design things a bit unorthodox, because why go to the trouble of designing something that's already been done, so if something doesn't make sense feel free to ask. This was one of my later versions that was a result of my power amp design where it is regulating about 55 VDC, so I reversed the input polarity on the opamps and used them in an inverting comparator configuration so I could power them at a low voltage and use common source shunt devices (N-channel on pos reg, P-channel on neg reg). Earlier designs used the more customary reversed common drain connection on the shunt elements with opamps configured as linear gain stages using negative feedback. Either way works OK. You can use the opamps in the "normal" mode with + to V+ and - to ground for a +24V regulator, and the opposite for -24V side. Lots of options for dealing with different voltage levels. I just wanted to develop a common design for all voltages so went with the dual stage +/-5V opamp power version since I need those voltages in the DAC anyway, and it makes for a very clean and low noise output with the opamp powered by a clean +/-5V supply

Chokes are by Hammond and the MKP caps are Sprague 735P (bought a ton while they were still available - great caps) and paper/epoxy caps are WIMA MP3-X2. Resistors are mostly precision bobbin wound.

Click here for schematic of my shunt regulator.
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