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Old 16th January 2013, 02:36 PM   #11
DF96 is offline DF96  England
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Quote:
Originally Posted by Salectric
I would not dismiss out of hand the "dousing" for tube selection, the wire polarity, and the resistor polarity techniques even though I haven't experienced anything like that myself. There is a lot more to audio engineering than what we can measure on a test bench.
Opening one's mind can be like opening a window: all sorts of noise and dirt floats in.
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Old 16th January 2013, 02:52 PM   #12
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Thanks, morinix, your story got me rolling on the floor.

Several years back I remotely helped someone to tune-up his HP-100 with better capacitors. Once that tantalum at the output was replaced by some film cap, the person reported that the "Hovland sound" was gone and it sounded just like any other plain vanilla preamp. Needless to say, the amp was quickly sold.
I guess they used tantalum in that location as some sort of a "harmonic synthesizer" - just look at the distortion spectrum in tantalum measurement taken by C.Bateman (below).
In the process I also reverse engineered most of the amp by looking at pictures the owner have sent me. Here's the sketch of a line stage, for those who are interested

P.S. When I saw the PCBs and all the various sorts of resistors used, my first thought was - "they must be shopping cheaply at some surplus store".
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File Type: jpg tantalum.jpg (167.8 KB, 816 views)

Last edited by elektroj; 16th January 2013 at 03:02 PM.
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Old 16th January 2013, 03:11 PM   #13
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Four coupling caps just for a linestage?? Give me a break!
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Old 16th January 2013, 03:22 PM   #14
palmas is offline palmas  Portugal
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We're the odd ones, as they sell their "mambo-jambo" expensive!
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Old 16th January 2013, 03:27 PM   #15
DF96 is offline DF96  England
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Is that really a line stage wth a gain of about 20, followed by a -12dB (x0.25) attenuator, then a source follower? Nobody would choose to design a line stage that way, as it increases distortion and reduces headroom.

My hunch is that the original design had less gain (more feedback) but they couldn't make it stable. Maybe 'dowsing' the prototype failed to modify the Bode stability plot, but that was the only technique the designer knew?

Remember, folks, this is expensive 'high end' stuff we are looking at. Presumably lots of glowing reviews and happy customers.
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Old 16th January 2013, 04:33 PM   #16
adason is offline adason  United States
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elektroj, do you know what FET is it?
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Old 16th January 2013, 04:50 PM   #17
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elektroj, do you know what FET is it?
Morinix said they used a PN4393. Nothing special, just a garden variety N-channel 40v TO-92. (post #6)
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Old 16th January 2013, 06:01 PM   #18
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I suppose in order to test transformers it was required to have them clamped in a jig that was exactly rotated so the laminations lined up with the magnetic field of the Earth in "harmony". Also, the power to test these transformers had to be generated from the alternator of a 1966 Mustang that was turned by a waterwheel fed by an artesian spring on the second Tuesday of the month only.
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Old 16th January 2013, 06:13 PM   #19
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Oh yeah, and make sure the leads are kept straight. If you bend wires it will slow down the electricity!

Its a good thing Hoveland wasn't around in the middle ages as they would have been accused of sorcery and witchcraft and burned at the stake.

Sorry, I just couldn't tsiser--i mean RESIST (wrong polarity first time).
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Old 16th January 2013, 06:42 PM   #20
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Quote:
Originally Posted by elektroj View Post
In the process I also reverse engineered most of the amp by looking at pictures the owner have sent me. Here's the sketch of a line stage, for those who are interested


You certain? Or just slandering an excellent product

It looks like a seriously misunderstood interpretation of ARC SP - 3, but at least it's easy to improve by shorting all the tubes and leaving only the fet follower. Or maybe just the tantalum cap...
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