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Old 15th November 2012, 08:41 AM   #8491
Salas is offline Salas  Greece
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Quote:
Originally Posted by spartan View Post
parachuting on this thread... (having just read the main pdf file).

Is there any particular advantage of the higher voltage version on the original pdf file over the 24V version above (considering equivalent supplies)? I wonder if I can pick up from here (ie from the above schematics) with no disadvantage over what went on previously.

I suppose the Q1,2, and 5 must be matched for 6mA, right? Also, can I ask why the use of LEDs instead of regular diodes?
No disadvantage, the differences in PSU voltage are dictated by the used IDSS and resulting bias currents.

Q1 and Q2 are the most demanding, Q5 can be +/-1mA, Q6 +/- 2mA. (A Q4 is a missing designation from paralleled versions, does not exist here).

Regular diodes don't give enough voltage. They would be needed to be 3x the Leds number upping the impedance of that local current sourced shunt sub supply.
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Old 15th November 2012, 09:18 AM   #8492
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Thank you! I try to source the 6mA Idss.
Does Q3 need to be matched at a particular Idss?
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Old 15th November 2012, 09:21 AM   #8493
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If I want to use a 18V supply, would the whole circuit need to be recalculated?
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Old 15th November 2012, 09:47 AM   #8494
Salas is offline Salas  Greece
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Q3 is a bipolar transistor, not a Jfet. Thus it has Hfe, and needs no matching here. Just use a couple of the highest for Hfe in your stash for the phono channels.

For 18V it takes full recalculation and one thing sure is that it will not afford high enough load resistors to maintain its now gain. Expect 63dB total for the 24V Atupi one with a 1:10 SUT in front of it.
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Old 15th November 2012, 11:28 AM   #8495
atupi is offline atupi  Romania
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Quote:
Originally Posted by Salas View Post
They are more than enough strong for your application. Here are the modifications. You will get 5-6dB more also.
Thanks a lot Salas for customizing the schematic!
Should i change something else if i use a 0.1uf FT-3 teflon for interstage ?
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Old 15th November 2012, 11:35 AM   #8496
Salas is offline Salas  Greece
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Make the output cap 2.2uF if it will sound heavier than optimal in your system when you will do that.
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Old 16th November 2012, 11:11 AM   #8497
Doug R is offline Doug R  United States
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Question on diodes:
I have a 36-0-36 V trafo, and some 40 V Schottkys. Isn't it OK to put two diodes in series with a 220K or so resistor in parallel with each one?

Thanks
Doug
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Old 16th November 2012, 11:29 AM   #8498
Doug R is offline Doug R  United States
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Never mind! Brain F*rt

It's 18-0-18, but I still would like to know the answer
Doug
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Old 16th November 2012, 01:56 PM   #8499
Salas is offline Salas  Greece
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They were doing that in old HV equipment for equalizing diode strings, but modern diodes wouldn't mind. They are much closer in spec than their ancestors. Make them 1MegOhm to allow less ripple current crossing over if you are happy to install resistors anyway.
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Old 16th November 2012, 08:39 PM   #8500
Doug R is offline Doug R  United States
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Default MOSFET Clarification

Hi Guys,
Before I fry anything, could someone verify that I have interpreted the pins of the IRF 9540 MOSFETs (TO-220) that I am using.

Solid state stuff makes me dizzy.
Thanks
Doug
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