When I purchased my autoformers the seller sent this schematic. The L-pad is not used as a conventional L-pad but used as what the seller called it "shelving" pot.
The info I received from Werner is different:Originally Posted by gdmoore28
"The volume you can adjust, in 11 steps to each1,5 db. With the roloff pot you can adjust the starting frequency for the highrange ...the roloff pot to adjust only the under flank from high range."
WAIT a minute !!!
You know guys, 1.5 dB is a HUGE value change / adjustment step !! I think we all can easily perceive as little as .15 dB, on a good system. I'd be P.O.ed, spending money on the German design, and NOT being able to set levels as BEST as I can, due to the design !!
It seems that that is a flaw in the German chap's build, taps are too widely spaced. I have spent 40 years with adjustment pots on speakers, starting in my FMI ( Fulton Audio ) days, and the SMALLEST adjustment it totally audible, and totally needed if you want to LOCK IN levels - optimally.
I would tend to use a POT to determine values, then go FIXED -good quality SOLDERED-IN-PLACE crossover resistors !!
Low Ohms ..... Jeff Medwin
The 1.5db may be a large step but works for me better that an L-pad or fixed resistors did and allows me the flexibility of an L-pad. The following is from research on the web so not my words but I tend to concur at least to my experience with my autoformers with all 4 of the parameters below. I don't have your extensive experience or knowledge just my ageing ears witch after 50 years of chasing that elusive perfect sound are just happy to enjoy the music with my VOTTs ... still with some occasional puttering with this and that as new technology emerges or from posts such as yours and as a result, I intend on trying a fixed resistor solution and comparing the two again as my system has changed from last I tried them.
QUOTES FROM WEB
" Autoformers take performance up another notch. Unlike a resistor based volume control that throws away signal to GND when it attenuates, the autoformer attenuator uses transformer taps that step-down signal voltage in the transformer, but also step-up signal current in the process. In a sense, what you normally waste in attenuating signal with a resistor volume control, you convert to higher current with an autoformer type attenuator. The results are a sound that is:
1) Less 'anemic' sounding, better bass
2) Has more drive and an overall more dynamic sound
3) Better micro-detail
4) Even more transparent and open sounding"
If the above is true, it would seem that "throwing away signal to ground" would be something to think about with low wattage SET's.
YMMV
That is a theoretically correct statement. can't argue. I've been chasing as long, or likely longer than you have. No doubt that a autoformer will have that efficiency advantage, BUT, 99 percent of the SET amps are SO awfully poorly executed, particularly in their power supply and wiring, and 99% of the VOTTs and 604s are so poorly wired, that the difference an autoformer will make, is bettered at least ten times over, by a better / properly executed SET amp and wiring, from INSIDE the amp, forward to the voice coil wires, all ' de way. !!
Have fun, I sure am !!
Low Ohms .....Jeff
regarding the roll off pot crossover, I feel I have made a little progress, based on the comments above that the crossover frequency is likely fixed at 1200Hz. With this in mind I can adjust both the pot and the taps to see about 3Hz movement in the sound below the xo point. The pot is subtle but it does effect the lowest part of the high frequency slope.
Also, the pot has a very fine sensitivity and does effect level to a degree. So, the 1.5Hz adjustment pots can certainly be fine tuned.
Hello,
Performance for FREE.
Those two black tie wraps in the photo, on the bottom inductor, need to be cut off and thrown away!! NEVER bundle wires like that, to make it " look neat" ( and sellable to the unknowing consumer ) as it IS a sonic degrade. The degrade amount depends upon the resolution of your entire system.
So, cut off the tie wraps, and do NOT let those leads going to the terminal block, touch each other.
Amps and crossovers should NEVER employ neatly bundled wires, its the audio K.O.D. or Kiss Of Death !!
Also, when two audio wires cross each other, it is best practice to do your lay - out so they cross at right angles to each other, ( and not touching each other ) whenever possible.
Have fun, I certainly do !!!
Low Ohms ..... Jeff Medwin
Last edited by LowOhms; February 20th, 2017 at 10:43 AM.
While I disagree with pretty much 100% of your wiring opinions as super gross overkill at best, I agree pretty much 100% WRT most tube amp's power supplies being so pitiful/ not 'stiff' enough that they pretty much clip all the time for one reason or another [mostly cost] and why I'm a big fan of PassLabs' hybrid amps even if I can't afford one and now shake too bad to build a kit.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
WE can disagree on wire, I have no problem with that. I come to ALTEC using good SET amps, you certainly don't.
I have an emphasis on making a speaker GO with a 3 Watt or less two stage, directly coupled SET amp, and seek very high transfer efficiency.
Use of GOOD wire, for optimized transfer efficiency, is " the Ticket". Remember Dennis Fraker, up in Montana? Besides owning lots of VOTTs ( he was in the movie theater business most his years ) he had a JBL Paragon, at home. It would take a MINIMUM of a Jadis 30 Watt tube amp, to play in his home, and usually, a 60 Watt tube amp.
After Dennis re-engineered ALL the Paragon's wiring, ( he spent $10K, on Ensemble wire ), from the audio amp's output...all the way to the driver's voice coils, the same speakers played there hearts-out, on a 3 Watt SET amp of his design.
As to agreeing with each other on amp power supplies being bad, I bet I have a TOTALLY different set of reasons for this, than you have, engineering reasons .... as pioneered by Dennis Fraker...again !!
Years back, you helped Dennis with his MLTL GPA 604 design. He has a cool theoretical speaker question today, and wanted to talk to you about it. He asked me to get your phone number, so you two could talk. Hes not a member here, and hates to type on a computer when a phone is so much better.
BTW. the tube amps clipping is NOT what you and others think, reason -wise The too-large capacitors and too large ( and far too high in DCR ) chokes just HOG the peak currents, and do not allow the tube to reproduce the transient.
The lower Z capacitors HOGS the recharge currents from the power supply. Got that ?? !!
They dis-allow the tube from doing its thing - reproduce the music's transient properly. Dennis ( alone ) fixed that, starting in 1989 GM, with his first SET's unique design.
Low Ohms, Jeff
Last edited by LowOhms; February 20th, 2017 at 07:26 PM.
Jeff, I would love to see the voltage and current measurement traces to show the power supply's performance under load compared to traditional power supplies - actual, not simulated.
Agree that your wiring ideas are overkill for, as in this thread, crossovers. Unnecessary expense and effort but otherwise harmless.
Opinion is only as valid as its verifiable supporting evidence.
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