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In the Forum: Melquiades Amplifier
In the Thread: Super Melquiades Amplifier.
Post Subject: HF Line-level filtering mystery?Posted by Romy the Cat on: 7/23/2005
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I really do not what is gong on there and why. Thorsten's comment that line-level crossovers do not act like speakers’ level crossover confirms what I feel and what some other people suggested me. Yes, the reactance of the crossover component, the inductive reactance of the driver coils, the lack of harmonic modulations in the amplifier stages when a stage operates within a limited frequency range… all of this certainly impact the final result. So what?
The experiments with the Super Melquiades HF channel are over. I found the optimum filtering configuration (or at least it what I feel presently) and closed the amp up. To my surprise the high-pass filter at the very input of the HF amp, before the first stage, did not sounded well. It had in a way too mechanical sound. I abandoned the frequency calculations and started to use mic-feed RTA on that HF dedicated channel in order to have the identical slopes with diferent filters. i did it for the sake of more or less objective listening evaluations as evan with the very identical sloped the chanal where I had the filters at it's input sounded very thin and lean. When is puff it up with LF, moving the crossover point lower, the channel picked some “body” but still had sound very artificial and synthetic: It more sounded like “frequency pusher” instead of “normal narrow frequency sound”.
The filter between the Super Melquiades’ stages did not work due to necessity to use very low value caps against the high impedance and consequential HF roll off. However, the sound di not indicated any artificiality and was very natural, although HF channeled. Probably the first channel of the Super Milq should run full frequency. I do not know if that is the specific demand of that specific UHF rube that runs in the first stage or that is a genetic rule or perhaps something else. I know that it certainly turned out to be a rule in my case. Interpreting that in Super Melquiades’ LF channel I do have the lowpass first order filter of 65Hz sitting before the input stage… and I DO LOVE what the bass channel dose. Perhaps the problem that my frequency-limited first stage has is applicable only for HF? Or perhaps whatever the frequency-limited first stage dos at LF made me so love what the Super Melq’s LF channel does? Who knows!
Anyhow, the best, very much the best result that I was able to get form Super Melquiades’ HF channel was with the full range channel (2uF coupling cap) and the speaker level cap in series with the driver. Interestingly that when I began to lower the coupling cap I liked sound form HF channel less and less, although I it was way beyond the crossover point of driver. I was hesitant to let the output stage to operate full range, due to low inductively of the HF output transformer primary (~1-1.5H). I left between the stages .047uF that makes ~ 35Hz high-pass filter and will let it to run as is for a few weeks to see what happen next. Still, when I go with the full-blown coupling cap of 1-2uF the HF become softer and more natural. Mystery, isn’t it?
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