CLCLC-type psu using capacitance multipliers

[Ken Moon]

I know some of you have read Merlin's psu book, so I thought you might be interested in this...

Using info learned from the book, I came up with this update to the Talon psu, which uses a CLCLC filter and a GZ34 tube rectifier.

This will let me eliminate 2 chokes and a tube rectifier, keep a similar low ripple level and very low voltage drops for the B+1/B+2 stages, like with the chokes, and still allow some sag. The Stealth rectifier diodes eliminate the possibility of any rectifier hash/schmutz (imaginary or real)

Talon schematic is here:

http://moonguitaramps.com/images/talon_schematic.png

...and here is my proposed replacement - the 47R series resistors simulate the internal resistance of the GZ34 (can use higher value R's for more sag).

The BUL312FPs have an hFE of about 9, so the equivalent capacitance for each darlington pair stage is at least 81uF (1uF x 9 x 9).

The last three B+ nodes will use traditional RC filtering (3 x 10k/22uF in this case, like the K50 preamp)

[IMG779]http://i514.photobucket.com/albums/t346 ... CLCpsu.jpg[/img]
Please let me know if you see any stupid mistakes or major problems. Positive comments are also allowed

Thanks!!

[Structo]

Interesting design Ken.

I wonder how that approach would work on an audio (Hi Fi) amp?

[Ken Moon]

Should work fine for hifi amps, or any tube amp where you see large value filter caps or chokes - each cap multiplier stage only takes up a couple of sq inches of space on a simple PCB.

Merlin presents all the math for figuring out the amount of filtering and voltage drops, so it's not too hard to come up with the equivalent to an existing design, but using the cap multipliers.

I like designs with a low voltage drop between psu stages, so I can stick to 275-0-275 and 300-0-300 PTs, which are cheaper and smaller, and also use 450V caps, which allows a much wider choice of caps.

[ToneMerc]

Looks like a style of charge pump. Just off the top of my head wouldn't the advantage of the "stealth" diodes be somewhat negated by the switching noise of the BUL312FP's?

TM

[Ken Moon]

Maybe

I don't know if the BJTs emanate any RF noise themselves - the base-collector protection diodes may also affect the switching speed of the circuit, and could throw off some crap - I may try some UF4007s or single stealth diodes in that spot if they do.

I think the only time this circuit switches is on the bottom peaks of the ripple component of the input signal - otherwise it operates as an emitter follower and doesn't switch at all - someone can slap me/correct me on that point if I've got it all wrong

I haven't made the PCB for this yet - after I gather up any more comments, I'll build it up and give youse guys a report, with scope shots and such

[David Root]

Ken, IIRC you have that right about emitter-follower operation, I just re-read the book a week ago.

I found that section very interesting myself, and it has obvious benefits in a small cramped chassis (unless you put the chokes on top of the chassis) and it is also much cheaper of course.

That Talon circuit is an oddball, it cuts the S**T out of the bass all the way thru, then resurrects it at the last moment in the 1000 uF cathode bias bypass cap. What's the rationale for that, eliminating blocking distortion in the preamp?

[Ken Moon]

Yeah, not much bass OR treble actually makes it through from the guitar itself, but very nice harmonics are generated by the triodes, and as you say, the bass is let into the party right at the end, and it has a very strong low end at the output.

And yeah, I was worried about blocking distortion at several stages, as well as trying to follow a general frequency shaping philosophy used on some super-hi-gain amps, of a huge bass cut at the input stage, and each successive stage having slightly more bass, all the way from input to output (look at the coupling cap values).

The psu supports the overall tight sound, and allows the use of cathode bias (simple) and a tube rectifier (no diode noise) without sounding mushy. The lack of any NFB helps the openness and immediacy of the amp too (wish I could find a less boo-teeky way of saying that).

This works very nicely for hard/modern rock, especially with active pickups, down tuning and fast playing, where no note smearing can be tolerated - the amp wasn't designed for a chimey jazzy clean sound, but it sounds much better than I thought it would at low volumes, and with the Express preamp it does the bloomey thing nicely when you're riding the guitar's volume knob, like expressy folks like to do