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RE: SET bass issue, would appreciate insight

Posted by drlowmu (M) on January 18, 2009 at 08:54:43

In Reply to: SET bass issue, would appreciate insight posted by mwp7373 on January 17, 2009 at 16:54:59:

Hi.

The other problem no one has yet mentioned to my surprise, common in many SETs and P-P amps (which lack good solid bass response), is the amplifier's power supply.

To reproduce the bass and dynamics and inner definition inherent in the original music, requires an amplifier having the least possible series resistances in the power supply. This includes the "iron" in the supply, starting with the power transformer, the rectifiers, and particularly, the "driven" chokes, and including the resistances of the wire that hooks all this up.

The use of biamping and subwoofers adds its own peril. You have the signal degradation of going through extra parts, ie: an added active stage in the crossover.

Most crossovers use a gain stage, and put the roll offs in the negative feedback loop, which sounds like doggie-doo compared to no biamp crossover what so ever. The second bad thing is the lack of continuity, when one biamps with two dissimilar amplifiers, each has its own signature upon the music, and each has its own (differing) time frame upon the music's presentation. Its particularly bad using a triode NO negative feedback amp on top, which plays wonderfully - "in the time of the music", and using a solid state feedback amp in the bottom, which MIS-plays "in the OUT-of-time frame" of its own negative feedback loop.

In this one respect, the minimum requirement for biamping, ("ideally" - if it exists in biamping), is to have two amps, EXACTLY the same in every way, for top and bottom, and speaker wiring that is EXACTLY the same in type and length. But of course, if these amps' have stupidly poor power supplies, what is the point of the added complexity ?

So, if you want to play the purist SET game with a full deck of cards and at the highest level, I would encourage you to get a proper speaker for SET, ie HIGH efficiency - 98 dB or more, run it full range, and build a proper SET amp on your own, since very few are made ideally that you can buy.

The proper SET (or P-P) amp will start with:

1) a power transformer that has a DCR in the high voltage winding of 20 ohms or less, plate to plate. Go measure yours, it likely to be 80 ohms, four times too high to start with !! No bass, no inner definition !!

2) if tube rectified, it will have more than one rectifier tube, paralleled rectifiers, to lower the Z of the rectification process. Certain commercial tube amps in the 1950's and 60's had dual rectifiers, 99% today have ONE rectifier tube as the "accepted" standard, which is mush-city in the bass.

3) choke input supplies, with chokes having a DCR of 20 ohms or less, preferably 10 ohms or less, and two stages of filtering (L1/C1/L2/C2). Go measure the chokes on a typical amp, (measure your 805 amp!) the chokes therein are 40 to 100 ohms, four to ten times too high !! Where IS that bass, dynamic response, and inner definition, why it "got lost" my friend, in the high DCR choke windings and core !!

4) wiring inside the amp, the grounds and B+ supplies, must be short and as GOOD as possible, which means high quality and LOW in resistance...not one run of Kimber TCSS, but two in parallel is the minimum if on a budget, Siltech if not on a budget, 13 gauge approximately.

So, my advice is to get the weakest link in audio resolved, the tube amp, as a DIY project. Build one good one on your own. Remember always, the power supply is INCLUDED in the SET amp, design it for power supply inclusion, unlike PSRR in a P-P amp ! If resourceful, you can do it on your own for $2 or 3 K, no problem. Have fun, its the good battle, and I have shown you the way !! "One can not deny physics".* ..........(*CheapJack)

OK, all the above is my own opinion after many years at this........... any of the usual flamers and hecklers may now proceed.

Jeff Medwin

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

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