Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
In Reply to: RE: Beveridge? posted by AJ on February 17, 2016 at 10:09:37
Sorry if this goes off-topic once again, but you probably know the answer to this question regarding the built-in woofer amplifier and electronic crossover circuits built onto the Bev 2SW amplifier chassis'. RM was kind enough to supply me with the amplifier schematics for a nominal fee, but I have never been able to obtain a full schematic that includes the crossover. I do understand that the built-in low pass filter part of the crossover is 18db/octave at 100Hz or thereabouts. But what is the slope of the high pass side of the crossover? On the amplifier schematic, a small value capacitor is shown to be in series with the input to the direct drive amplifier. If memory serves, the value is .022uF. This alone could constitute a passive first-order high pass filter in conjuction with the parallel resistance at the amplifier input, but is there upstream (active or passive) circuitry that adds to the slope of the hi-pass filter? My ohmmeter tells me that the upstream side of the .022uF capacitor is not directly connected to the RCA input jack, but beyond that I have never figured it out. Thanks for any info.
In practice, I use a restored Dahlquist electronic crossover for a low pass filter before the solid state amplifier that drives my Transmission Line woofers. I use whatever is built in to the Bev amp chassis for high pass, and I have always had the feeling I could do better, if I knew what was going on in that circuit.
Edits: 02/19/16Follow Ups:
Have you asked RM your question about the slope of the high pass filter? He should know.
I believe that the high and low pass filters on the external crossover he uses (mine is labeled Beverage RM 3 Universal Crossover) is 18 DB/octave on both sides. Roger told me he thought it important to get a lot of the bass out of the ESL panels as well as a lot of the midrange out of the woofers.
No, I have not asked RM the question. When I contacted his business in order to acquire a copy of the direct-drive amplifier schematic, I never got to talk to him directly. Once or twice I emailed him but never got an email response, either. However, his company was very prompt in providing me with the schematic, once I had sent payment.
In the pamphlet that Harold Beveridge concocted to go to purchasers of the 2SW, it does say that the low pass filter slope is 18db/octave. And I have always assumed that the high pass filter would have the same complementary slope, but that is not directly stated in the pamphlet. But I also have always wondered why there is that series capacitance in front of the amplifier input, which by itself would add a passive high pass filter with first-order kinetics. On the other hand, it does not seem to me that 6db/octave would be sufficient to sufficiently attenuate the demands upon the panels in the 2SW to produce bass response. So it is most likely a net 18db/octave slope with the gain maintained by an active element in the crossover.
I have not looked at this schematic in a long time. I am by no means an expert.
It is part of the motional feedback system Beveridge used by injecting Rf and feeding back net diaphragm displacement rf signal to crowbar or limit excursion on the line source.
He was a pretty amazing engineer. Both he and Peter Walker could put a lot of the modern types to shame I would think!
Although I responded to your PM slightly differently, on second thought, the function you are describing may be happening within the input and driver stages of the direct-drive amplifier proper, after the high pass filter, in other words. There's a 7.5M resistor that feeds back from the output stage to the driver stage, with ~1600V on one end and barely 3V on the end that is attached near the driver section. Lots of filtering going on in the input section as well. I don't pretend to understand it, but I have been able to work on it a bit only because of the tutelage of another EE Bev owner I encountered on TubeDIY. Like me, you can get the original Bev amp schematic from RM.
I quite agree, HB was at the very least a major innovator in the history of audio, if not a genius, and he gets very little credit for it, mostly because his company was so short-lived and the products are rarities. I do also think RM had a lot to do with the original dd amplifier. Every single aspect of the Model 2 or 2SW system is novel, yet the system as a whole is a smashing success. HB is easily up there with Peter Walker in my book.
Post a Followup:
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: