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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: Where does the current come from? posted by rage on August 26, 2012 at 16:37:28:
rage,You post this :
"I think with SE designs much of the time the large choke/caps are used to make the supply quiet enough for the driver stage and that it is a compromise to design a power supply with only ripple in mind."
- - - - - - - - - - - - -
There are TWO requirements in an amp, and they differ drastically.
The Finals stage B+ needs to be fast (50 mS. settle) and supply large instantaneous (!!!) peak amounts of unimpeded current and voltages to the Finals tube. Ripple is NOT much a problem to Finals, in most SE DHT amps, 500 mVAC at C2 is fine on > 100 dB horns. In Push Pull, a volt or more likely, two volts of AC is fine.
The Finals BEG to be dynamically correct, hence a low everything supply, to fulfill the music's need. It becomes a modern "low storage" supply. It is the best compromise we know of, to obtain full dynamic expression in the Finals stage. All else (to me) sounds "less direct", "canned", "very boring" and "processed" to hear. The music in a conventional amplifier is being played back continuously in the time-frame of the amplifier, and NOT in the time-frame of the music.
The FRONT END stage needs to be low in ripple and "rock solid". As our friend Bob Seger sings " Like a ROCK!"
A huge advantage of the two stage DC Loftin-White type amp topology is that it requires an R1/C3 after the Finals stage, to drop the B+ voltage to the Front End stage. In a well thought out design, we easily obtain about 1 mVAC of ripple to the Front End's B+, for maximum resolution and razor sharp detail. Additionally, we can use a one-part shunt regulator, to lock-in the Front End supply as it plays music (a "pull down" power resistor, B+ to ground).
So rage, the overall amp supply filter topology in your Loftin-White DC amp is L1/C1/L2/C2 (to finals) R1/C3 (to front end). KISS simple.
My point of this post is, the requirements for B+ are two-fold, and different for each supply at their point of use. Takes some very straight thinking to fulfill each requirement optimally, which Dennis Fraker applied, in 1989.
Cheers, ENJOY your DIY "kick a**" amp. A-B it at your audio friends' houses.
Jeff Medwin
Edits: 08/26/12
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Follow Ups
- RE: Where does the current come from? - drlowmu 20:28:34 08/26/12 (0)
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