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In Reply to: RE: BDT Preamp Schematics posted by John Swenson on May 10, 2008 at 14:34:45
Being intrigued by the regulator circuit John came up with I built one up and proceeded to test, measure, and blow it up many times in the interest of learning more about the circuit.
Performance is very good the way John has it set up but there are improvements that can be made both for performance and reliability.
I changed a couple of capacitor values, one for improved stability, the other for better performance. I also added some protection circuitry and a current limit circuit.
I'm planning on building several of these into a multiple output bench supply to replace my old Tektronix Engineering power supply. The Tek supply works pretty well but is noisy, both electrically and acoustically. It also has a tendency to blow up at inopportune times as it does not have good current limiting, instead, relying on 2 watt CC resistors on the SS rectifier diodes. It let loose again today during testing of the Swenson regulator. Had to open all the windows to get that wonderful burnt CC smell out of the house. Maggie was not very impressed with the smell but enjoyed the show... It was interesting to see the meters on the power supply back lit by orange flame.
I saw John's preamp at VSAC but never found John amongst the crowds.
Anyway, take a look at me website for the info.
Follow Ups:
Hi Gary,
I read your excellent article with improvements on John Swenson's regulator and I would like to build it and give it a try. Just a couple of questions:
1. Did you use a new pcb or just modified the existing SBCCS pcb?
2. What kind of capacitor did you use for C2? Is an electrolytic OK there?
3. Also, what type of capacitors do you recommend for C1 and C5?
Regards,
Evangelos
Hi Evangelos,
The test work was done on a modified self bias CCS board. I have a board layout in the works that is mostly done. Only need to order a set of boards so I can stuff one of them and make sure it all works as planned. When all checks out good I'll put the ExpressPCB board file and a BOM in the down load section of my web page.
I've added more to the Swenson regulator page this evening with more info on setting up the regulator, the new board layout, and a picture of the test mule for entertainment.
Using the circuit designators on my schematic, C1 and C2 are film caps, C5 is a 35V electolytic. C1 and C2 need to be high performance caps, C5 is non critical.
Hi Gary,
Yes again, thank you for this inital CCS circuit & your mods to John Swenson's VR variation.
I notice a change to the value of R14 from 27K in JS's schematic to 33K in your schematic but I see no mention of it in the write-up of your mods.
Is this value significant or is it just what was on hand - I think it's purpose is to biase the gates of Q1 & Q2 with at least 20V difference? I presume with 33K the biase differential between these gates will be greater than 20V?
Evangelos,
1. I did mine point to point with Gary's mods but left out the over-current section
2. C2 is a electro 2.2uF/50V
3. C1 & C6 are 10uF & 2.2uF metallised polyester > 250V, I think?
Hi jkeny,
I think we have confused it a little: I was referring to Gary's schematic and not to John's one. I see that the numbering you ae referring to correspond to John's schematic. I also noticed that I made a mistake in my previous post: there is no C6 in Gary's schematic, I had to write C5.
Anyway, I think that a 10uF/250V metallized polyester capacitor should be quite bulky. Could I use an alectro instead?
Regards,
Evangelos
The two > 250V caps are being used as noise suppressors and carry the full output voltage accross them. I think they need to be film based for their high frequency characteristics but experts may well correct this view. Yes they are bulky!
The electro, on the other hand, doesn't carry the full ouput voltage (I measured about 100V) so 100V electro should do!
Thanks for your help.
Gary also added quite helpful information in his relative page.
Regards,
Evangelos
I agree, JS & GP are both wonderfully productive, creative & technically astute people. I'm in the final stages of building this BDT preamp & will be incorporating GP's mods to VR - looking forward to listening soon & will report back!
Has anybody built this one yet & care to share?
You and John amaze me with the things you come up with. I really want to try out this regulator now.
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