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.
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.
Mistake ?
Unless I'm mistaken the capacitor mulipliers in SCM - 2 will not work. How are you going to charge C17 and C18?
Unless I'm mistaken the capacitor mulipliers in SCM - 2 will not work. How are you going to charge C17 and C18?
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.
As this is likely not the only error i'll do all corrections later.
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?
The real problem is: Where do you get the parts today?
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?
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?).
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
.
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?).
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
.
They are cap multipliers that are voltage controlled by a regulated supply BEFORE the multiplier. They are for noise reduction, mostly.
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.
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.
Hi Martin
R15 is of course 100k, thanks for spotting it. I cut and pasted the regs from the input board and never bothered to check the values.
R41 is difficult to read from the photos as it's not colour coded. I also agree that 2k seems too high to supply the expected 3.5mA but its value will have to be tweaked anyway once you choose a FET.
Unfortunately i'm getting ready for an overseas trip as i would really like to simulate the circuit. Any idea if models for these or similar fets are available?
The j203 designation comes courtesy of Mr Paoletti. It obviously has to be an n-channel.
R15 is of course 100k, thanks for spotting it. I cut and pasted the regs from the input board and never bothered to check the values.
R41 is difficult to read from the photos as it's not colour coded. I also agree that 2k seems too high to supply the expected 3.5mA but its value will have to be tweaked anyway once you choose a FET.
Unfortunately i'm getting ready for an overseas trip as i would really like to simulate the circuit. Any idea if models for these or similar fets are available?
The j203 designation comes courtesy of Mr Paoletti. It obviously has to be an n-channel.
analog_sa said:
I think D3,4 should be in parallel rather than in series. Also, in the first diagram posted, there is a 100nF cap in parallel to 750 ohms at the output. Wonder if that 100nF is correct?
Edit: I see now that they (D3,4) have been changed to zeners, that's ok in series of course.
Jan Didden
Actually, I now found J201 - J204 N-Channel JFets (not 2SJ..), amongst others from Vishay, which are supposedly "very low noise", I presume they are the ones being used.
analog_sa,
About the IC AD 711 power supply,
could a 100 or 470 uF / 50 volts accross the 2 zeners D1 D2 remove their noise ?
Alain.
About the IC AD 711 power supply,
could a 100 or 470 uF / 50 volts accross the 2 zeners D1 D2 remove their noise ?
Alain.
