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Old 4th March 2014, 07:00 AM   #1
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Default Difference in +V/-V -- OK?

Is it common/allowed that the voltages differs in dual voltage systems?

I was going to rip the complete power system (those parts used for RIAA stage) from Technich SA-210 but, I'm not sure if it's in good condition because of difference in DC voltage between +V/-V (+17.8V/-15.4V). There are differences in components starting from R703/R707 which are not equal but those different components does not make the voltages even (measured from the legs of the NJ4559 found in EQ where the leads end). Voltages before these resistors are equal.

My intention is to use this power 'stage' in a RIAA stage (based on op-amps) project ... if it's in condition.

Last edited by jiiteepee; 4th March 2014 at 03:09 PM. Reason: fixed the dl link to point directly to the pdf -file
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Old 4th March 2014, 07:26 AM   #2
Mooly is offline Mooly  United Kingdom
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Unbalanced supplies for DC coupled circuitry are not a problem. -10 and +15, +8 and -20, it doesn't make any difference apart from asymmetrical clipping.

Post a picture of the circuit of the regulator if you think there is a problem there.
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Old 4th March 2014, 08:07 AM   #3
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Quote:
Originally Posted by Mooly View Post
Unbalanced supplies for DC coupled circuitry are not a problem. -10 and +15, +8 and -20, it doesn't make any difference apart from asymmetrical clipping.

Thanks for the info.

Post a picture of the circuit of the regulator if you think there is a problem there.
Original schematic (as PDF) can be found through that link given in my 1st post (you find all possible information from it, component types/values etc.).

EDIT: I'm going to remove R712 because of I don't need that circuit but, is the circuit (or parts of it) where R708 leads needed (it is lower voltage circuit) ... ?

Last edited by jiiteepee; 4th March 2014 at 08:20 AM.
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Old 4th March 2014, 02:56 PM   #4
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After studying all the numerous links (at least 7 show up) from your posted link and deciding which seemed the most appropriate (the one that actually said get manual) it offered first some garbage to install... so I just declined.

Post a shot of the part of the circuit you want help with
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Old 4th March 2014, 03:27 PM   #5
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Ok.
Those sites are sometimes confusing (there are unnecessary (3rd party) links you can go wrong with). I changed the link to point directly to PDF file but, in any case here's the necessary part of the circuit (If the image doesn't show up right away just press the down arrow button (on top left) to load/open it. Blue lines seen in picture shows positions I have cut the leads because of I don't need those circuits.

Last edited by jiiteepee; 4th March 2014 at 03:34 PM. Reason: added instructions, note
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Old 4th March 2014, 03:39 PM   #6
Mooly is offline Mooly  United Kingdom
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Thanks

Looking at your picture D703/704 are different values by design... I have no idea why though. Maybe to give some better controlled start up or switch off performance (thumps and bang), just a guess though.

I doubt there is any problem with the circuitry. Measuring across the zeners directly should give a voltage equal to the zener value -/+ 10, so your values seem a little out. Again, maybe the zener values used are different to what is marked on the diagram. Manufacturers do change designs and sometimes there are quite significant differences between models intended for different destinations.
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Old 4th March 2014, 03:46 PM   #7
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Thanks!

There's connection between the -V and that "AC 6V" circuit through R708 ... can I disable the circuit by removing R708 or is it or parts of it needed for the one I leave into use?
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Old 4th March 2014, 03:57 PM   #8
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R708 and D707 is for generating a negative rail for the display. It ties the otherwise floating heater voltage to a correct voltage. So yes, you need all those parts if you want the display to work.
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