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Old 7th November 2012, 10:19 AM   #451
AndrewT is offline AndrewT  Scotland
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Yes,
Dual secondaries into dual bridges into a dual polarity single channel.
Your PCB suits this.
Then adding a single bridge does for the regulator.
What does the hook up wiring look like, since you say the single bridge arrangement cannot be done as I asked?
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Old 7th November 2012, 10:57 AM   #452
roender is offline roender  Romania
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Something like that? I don't think it's a good solution.
Where are you going to tap for frontend ground? If A and B points are going to be connected together in order to get the frontend ground then there is no point for dual bridge power stage.
IMHO, use a separate transformer for front end PSU
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Last edited by roender; 7th November 2012 at 11:00 AM.
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Old 7th November 2012, 11:01 AM   #453
AndrewT is offline AndrewT  Scotland
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Roender.
That arrangement does not work.
The dual secondaries demand that the extra taps must also be dual secondaries and separate. The single bridge is not compatible with the dual bridge when joined at the AC side.

I have a separate transformer for the extra 9+9Vac. That is why it is shown without the common core "|||" in the diagram.
What I don't have is a Low VA, 35+35Vac to 40+40Vac transformer.

I do have a doubler that gets the 9Vac upto 80Vdc open circuit, that falls to ~60 to 70Vdc depending on the loading. Typical droop for a doubler style circuit. Dual 9Vac secondaries + quad doublers, gets me +-80Vdc separately. I can join then at the DC side and bypass the single bridge in the reg PCB.

I'm going to post those experiments in a new Thread shortly.
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Last edited by AndrewT; 7th November 2012 at 11:06 AM.
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Old 7th November 2012, 08:37 PM   #454
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Default JFET selection and matching

Andrew, wouldn't it be easier to measure first the JFET's IDSS and Vp, pick the pairs and thereafter perform your LTP test?
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Old 8th November 2012, 09:07 AM   #455
AndrewT is offline AndrewT  Scotland
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indeed, rough batching reduces labour a lot.
Are you the Franz that posted an LTP test jig & procedure?

The equal Gate Voltage and equal Source Voltage style of LTP matching is VERY sensitive to small differences in gm. That gm difference results in difference in output current. That output current is read off across the two Drain resistors.
Three DMMs would be ideal. One across each Drain resistor and one across the Drains.
My best matches got to <0.2% of Drain current difference over a range of Id from 100% of Idss down to 20% of Idss. But the yield of these extreme matches is very low. I did get a high yield of <1% diff @ >=25%Idss. These are what I was selling to UK buyers. But most ended up getting sold to foreigners for DCB1. What a waste I kept telling my enquiring customers, but they bought anyway. Some folk have too much money.
There is a perception that dearer components play music better.
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Last edited by AndrewT; 8th November 2012 at 09:17 AM.
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Old 8th November 2012, 12:07 PM   #456
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No, as far as I can remember. Can you direct me to that post, please?
Testing each JFET separately could increase the speed of the matching process. I intend to use a HP 34907A data aquisition unit and a proper test setup for measuring and recording the data.

Last edited by franzm; 8th November 2012 at 12:20 PM.
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Old 10th November 2012, 03:42 PM   #457
scalpel is offline scalpel  United Kingdom
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Hi,Rudi,about the Reichelt Bom's.All I get when I click on them is their catalogue.What am I doing wrong
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Old 10th November 2012, 04:43 PM   #458
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Manuel: are you using the URLs of my post #446?

Best regards - Rudi

P.S.: I see: REICHELT has once more deleted the public baskets! I will do my best and re-install them!
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Old 11th November 2012, 07:39 AM   #459
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Manuel, it has been my error! I copied the URL in a wrong way.

Here they are again:

FC-100_Speaker Protection (needed twice):
https://secure.reichelt.de/index.htm...07;PROVID=2084

FC-100_Soft-Power-On (needed once):
https://secure.reichelt.de/index.htm...09;PROVID=2084

FC-100_Shunt-Regulator (needed twice):
https://secure.reichelt.de/index.htm...04;PROVID=2084

FC-100_Amplifier (needed twice):
https://secure.reichelt.de/index.htm...39;PROVID=2084

FC-100_Backend-PSU (needed twice):
https://secure.reichelt.de/index.htm...41;PROVID=2084

Not included in the carts, because Reichelt does not have the parts on stock, are:
NJL-transistors, MJE15034/MJE15035, Toshiba 2SA/2SC transistors, MKP1839 / 1F, MPC74 0R1 emitter resistors and DC blocking cap.

Best regards - Rudi_Ratlos
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Old 11th November 2012, 08:37 PM   #460
scalpel is offline scalpel  United Kingdom
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Hi Rudi,perfect!Thanks.Regards Manuel
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