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Old 12th November 2012, 09:49 AM   #931
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Hi again Anadigit

A thought about your 'mods' question.

Although the unit 'appears' to have 'bomb-proof' RFI screening...
...in practice, this MAY not be the 'case' (sorry, no pun intended !).

It would be interesting to see, if when you test the chassis work & sardine-cans for 'continuity' with a meter...
...whether in fact there actualy IS continuity between the various aluminium chassis components.
It may be present, but of 'high resistance' also.

My experience with custom 19" aluminium chassis based electronic instalations, suggests this is VERY OFTEN not what is found.
The fact is, that many people, including numerous engineers I have met...
...do NOT appreciate that 'anodized-aluminium' does NOT conduct electricity !

Unless the anodised coating is 'scrapped back', and then earth-bonded with suitable bolts (read, high contact-pressure here) continuity between components is often poor, & SOMETIMES even non-existant.
Self-tapping chassis screws, really DON'T cut the mustard here.

This type of earth-bonding can 'spoil the look' of a nice new case...
...and I have known it to be omited on this basis alone !

Continuity can be present at manufacture...
...but subsequently 'disapear' due to oxidisation of the exposed aluminium parts...
...ie. the screw holes etc.
Also 'coated screws' of various types, or 'oily screws' present similar problems.

This is of course all well worth bearing in mind when you re-assemble the unit.

Cheers

Si.

Be carefull of that motor-run capacitor as well !!!
Un-discharged...
...It is a potential KILLER.
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Old 12th November 2012, 02:12 PM   #932
RCruz is offline RCruz  Switzerland
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Do you believe that motor run cap is in parallel with the mains ?
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Old 12th November 2012, 02:40 PM   #933
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The AC cap is across the mains. I have one plugged in, next to me, been there for years, works great in removing gross RFI on the power lines.
The IC's started out all mini dip. However, the input IC chosen is some sort of surface mount, ONLY so we first (last I looked) added an adaptor to make it into a mini-dip. There should be 3 IC's per channel. One is a low noise, transistor input, the second two are jfet input, namely 2134 and 134 respectively. The jfet input IC's only handle pre-filtered input and have it easy. The input stage takes all the cartridge signal and amplifies it, it has the most difficult job, but it has lots of dynamic headroom to work, more than most designs.
This was a difficult challenge to make something almost entirely from IC's. Scott Wurcer would disagree, but I find making great sounding products with all discrete, except for the servos, easier to get right.
For the record Scott Wurcer's AD797 was originally slated at the input IC. Later we found an equally good sounding, and quiet IC at less than 1/2 the price, so we used it, instead.
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Old 12th November 2012, 02:45 PM   #934
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Here is a early schematic for the JC-3 (what is inside each box) I cannot say that parts substitutions, omissions, etc have not been done since this is a 5 year old schematic.
Attached Files
File Type: pdf JC-3.pdf (43.7 KB, 238 views)
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Old 12th November 2012, 02:47 PM   #935
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I would assume so...

...probably an implementation of a less domestic...
...more MIL-STD (military standard) EMI filter.

Not often (if at all) found on UK domestic equipment.

A bleeder resistor probably discharges it, I would guess.

Often the only way to quickly & safely discharge some MIL-STD filter caps of similar type, is by direct relay disconnection of the mains input.
(this is what I have seen done anyhow)
It prevents a possibly LIVE capacitor appearing on the exposed mains-plug pins, when unplugging from the wall.

If the large motor-run in this unit is connected across the mains...
...and I can't see the purpose otherwise...
...It probably has a similar MIL-STD type relay or similar.

I had wondered about doing something similar on my own new preamp...
...but the potential hazard for anyone considering such a thing HAS to be delt with safely.

Cheers

Si.
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Old 12th November 2012, 02:50 PM   #936
RCruz is offline RCruz  Switzerland
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10uF ?

Looks like an EL... maybe a tin canned film cap ?
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Old 12th November 2012, 02:59 PM   #937
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The only real mod for this design is the IC's used.
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Old 12th November 2012, 03:22 PM   #938
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It could well be 50uF or even much, much higher.
Probably a polypropylene or similar film / foil type, almost certainly.
Motor-run applications, air-con, etc.

You can get some nice compact 10uF ones, intended for domestic induction cookers.
(square black type)
Or just parallel-up some mains 2.2uF say, X-class capacitors, to as large a size as you want.

The issue of the caps appearing across a pulled mains-plug IS A VERY SERIOUS ONE.

A relay, which de-energises, on pulling the wall mains-plug, is the only SAFE way for people to try a similar thing on their own gear.
PLUS bleeder resistor of course.
Domestic EMI filters normaly have a 1M Ohm resistor built in...
...but capacitance of only a fraction of a uF.

I have got some stuff on MIL-STD type EMI filters.
I might put it up on the thread about my preamp build.
It is interesting stuff (I think) for audio.
The implementation has to be right though ( safe ).

Cheers

Si.
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Old 13th November 2012, 03:57 AM   #939
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Anadigit, you made a serious mistake in buying this unit. It is NOT a Vendetta. It is adequate for the task of playing records, and many people like it. You should just sell it.
Also, please do not contact by private e-mail here. IF you have a question, put it here, so that I can explain with an answer to everyone.
What patent? For example.
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Old 13th November 2012, 04:17 AM   #940
toufu is offline toufu  United States
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anadigit. why do you have an eu flag? arent you from thailand?
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