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In Reply to: RE: BDT Preamp Schematics posted by Gary P on June 01, 2008 at 20:02:55
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
Follow Ups:
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
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