Does anyone care to ask an amplifier designer a technical question? My door is open.

@terry9

Are you aware that the secondary capacitance of this transformer is 800 pf and the input capacitance of the speaker panel is many times lower? If I multiply that times turns ratio squared i get a primary load of 45 Microfarads. For the transformer alone.  Are they kidding? Thats a lot to drive. The QUAD transformers are quite good and much lower capacitance. 

I dont get these Plitrons at all. Tell me what is wrong with the QUAD transformers?

The primary of the Plitron is 0.1 ohm. How low is your dc offet?

In general, your thoughts on Accuphase integrated amps? Do I need to post specs?

ramtubes OP
One thing to do is follow John Atkinson’s measurements of amplifiers. If you dont, get Stereophile its a good mag and only $12-15 a year.

This is great advise for those here, to learn and understand these Stereophile measurements, it’s crucial to giving good informed advise to others, and to selecting the right stuff for even for themselves.

As all decent manufactures use these types of measurements to design build and to test their products as well as all the EE laws that go with them. Anyone who doesn’t use or doesn’t believe in them, should be given a very wide berth as they have no idea what they’re talking about.

Cheers George

Agreed that polypropylene is best for the money. Improvements on polyp are incremental and absolutely not worth it - unless you are a hobbyist who wants to see how far he can go, just because. 

What I see in Plitron (theoretically) is two things: first, the two plates of the ESL are driven by the same core, so they can be precisely balanced; and second, they offer 75:1 step-up instead of 250:1. Since I committed to 75:1 with 25V rails, going back to 250:1 would involve re-engineering the protection circuits.

Rather than that, I would try to build high voltage amps to drive the Quads directly. Wish me luck - and long life!

What I hear (subjectively) is that the Plitron 2905's are much brighter than the remaining stock 2905, without sounding harsh. Piano on vinyl sounds quite similar to the instrument upstairs on the modified units. The unmodified unit sounds mellow but imprecise compared to the Plitronned. In fairness I must add that this was accomplished with the help of nichrome wire and a small inductor to equalize primary impedance over the frequency band, as per the Vandersteen data sheets.

My DC offset used to be 50mV or less. What it is now is a good question, one that you have prompted me to ask. Thank you.

@georgehifi 

Hey George, did you see the review of the Cary SLI-100 in the lastest issue? Why would they be so dumb to send an amp that is going to look so bad on JA's well documented test procedure? 

Read Dec, pg 91. Read pg 153 for Cary's response. In there their response they say measurements are not everything and an amplifier should sound "intoxication and emotional". "A degree of second order harmonic texture gives the midrange a certain musical.... and expands the soundstange". Pure marketing drivel. Where is Dennis Had when we need him?

The whole argument about 2nd harmonic distortion being "benign" totally ignores Intermodulation distortion which is far worse and always higher. If you are listening to a small group, singer, solo guitar a little THD isnt bad. It just creates the octave. My question is "what is the 2nd harmonic of Beethoventh's 9th:". In a full orchestra, with chorus. there is no fundamental to do much with. Some people must think the amplifier has the intelligence to go find the fundamental note and create the octave. Amplifiers arent that smart. They just amplify a time/voltage varient signal. Its not like they are following the score.  :)

All the specs on this amp are horrible, shameful, disgusting, who designed this? Please go do something else.   By John's standard this 100 watt amp reaches 1% THD as 3.2 watts, 3% at 22 watts, finally reaching its 100 watt rating at 10%. 

You all get this in addition to poor damping, noise and rising distortion even at one watt on both ends of the frequency range. 

If you want a comparson look at the review of an RM-200 II, an amp at virtually the same price.