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Old 23rd November 2006, 01:50 PM   #1
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Default A real Vendetta?

After seeing some pictures of an open Vendetta 2A and contributing a bit of imagination i ended up drawing approximate circuit diagrams. Ok, i also saw Federico Paoletti's circuit of the 2B but it didn't look too plausible. In any case they seem quite different.

Of course, not everything can be clear from photographs. Please take capacitor values and fet types as guesswork at best - they are mostly based on Mr Paoletti's values.

All the same a very interesting and unusual circuit. Unless someone spots a glaring mistake i may even attempt to build it with whatever substitutes i find.
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Old 23rd November 2006, 02:59 PM   #2
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Default Mistake ?

Unless I'm mistaken the capacitor mulipliers in SCM - 2 will not work. How are you going to charge C17 and C18?
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Old 23rd November 2006, 03:18 PM   #3
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Thanks. Missing 10k resistors between raw DC and gates. I wouldn't call them capacitance multipliers as they work similar to regulators. "Raw" dc comes from a pair of 3-terminals and the resistor divider (missing 10k and 100k) provides a fixed voltage at the gates. A better example is the input board where the resistor is replaced with a CCS.

As this is likely not the only error i'll do all corrections later.
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Old 23rd November 2006, 07:03 PM   #4
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Pretty good, Analog. I don't see any obvious problems. I might use these schematics myself for general repair, etc. They are very clear and clean.
The real problem is: Where do you get the parts today?
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Old 23rd November 2006, 07:09 PM   #5
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Thanks for the compliment JC. I'll be happy with even a pale imitation of the original. Maybe 2sk170/2sj74 and lots of matching and readjusting resistor values?
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Old 23rd November 2006, 07:54 PM   #6
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The undefined 'diodes' are 15V zeners.
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Old 23rd November 2006, 08:24 PM   #7
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SCM-2 with corrections
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Old 23rd November 2006, 09:19 PM   #8
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I also have a copy of Federico Paoletti's circuit and was planning on cloning it one day but it looks like you are going to be much faster. I'll be intrigued to see your results .

Btw., Erno Borbely still lists 2SK147/2SJ72, but at 10/15 EUR a piece, plus VAT. 2 paralleled 2sk170/2sj74 with high enough I DSS should be as close as you can get to the original jfets today, unless, off course, John Curl knows a better replacement. I believe it is generally important to have enough current through the jfets in this circuit, and to match them both for parallel and for complementary operation (I think I read such a comment from John Curl somewhere?).
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I wouldn't call them capacitance multipliers as they work similar to regulators.
Well, I would still call them cap multipliers but I am not an EE, so let's not quibble. They only "regulate" relative to the rail voltage, unlike the equivalent circuit in the MC stage, but I believe the latter are biased by JFets in order to have still lower noise and/or better line noise rejection .
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Old 24th November 2006, 12:47 AM   #9
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They are cap multipliers that are voltage controlled by a regulated supply BEFORE the multiplier. They are for noise reduction, mostly.
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Old 24th November 2006, 09:46 AM   #10
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I am still scratching my head over some of the details but that may have more to do with my head

Anyway, I think R15 should be 100K (in SCM 2). Then, R41 seems very high at 2k? And Q17 says J203 but shows an n-channel jfet, in which case it would most likely be a Kxxx (e.g. a K330)? I googled for 2SJ203 and only found a p-channel mosfet.
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