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Old 23rd October 2008, 03:26 PM   #711
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Quote:
Originally posted by tryonziess
Paypal is merciless!!! I can not for the life of me figure out what kind of system -- if any -- these folks use to figure interest. Sometimes it is nothing and other times it is 3.5 to 4 percent. Go figure. I guess that is how you become a multi-billionaire. My two cents again.
...
Tad
Tad

This is what I use and so far it has been 100% correct.

PAYPAL FEE CALCULATOR

Cheers!
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Old 23rd October 2008, 03:42 PM   #712
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Thanks Tad
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Old 24th October 2008, 12:36 PM   #713
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To all,
I am receiving numerous inquiries for pcb's. All of the current supply in this group buy are spoken for. Please if you are on the wiki page confirm your order and I will send you an invoice. I wish to get boards to those who want them.

One small question to the knowledgeable. What are the differential current limiting diodes on the Jens board rated for in terms of voltage. Dr. Leach never intended for the Low TIM amp to be driven with 70 volt rails. His design has 2 - 20 volt zeners in series. Was this diode design changed to accomadate the increased rail voltages or does it need to be? I am not learned enough to answer this question.

Tad
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Old 24th October 2008, 01:10 PM   #714
AndrewT is online now AndrewT  Scotland
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The Zeners set the tail current resistor voltage. It is in effect a CCS for the LTP.
40V does not need to be changed for any PSU above +-50Vdc.
But the feed resistor to the Zener must be scaled to suit the PSU voltage. Leach gives the formula and I think Jens also gave assistance here.

If PSU <50Vdc then I suggest the Zener voltage is reduced to either 30 V or even as low as 20V.

The reasons given by Leach for choosing two sets of series diodes was to help eliminate the effect of the wide tolerance of Zener voltages. He argued it was much easier to get a pair of near 40V voltages from 4 diodes than trying to find 39V Zeners that matched. I agree, it was very easy to select twins to give matching voltages on the tail resistors.
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Old 24th October 2008, 01:19 PM   #715
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Tad,

The zeners provide a voltage reference for the front end cascodes. They are not current limiting. Notice the super amp uses the same values.

R3 and R22 change with rail voltage to limit the zener current to about 5 mA. Notice the equation for R3 and R22 is rails minus 40 - the zener stack voltage. The 8.2 denominator represents the current in the zener plus the current in three legs of the differential.

If you must , err on the low side for R3 and R22, which will increase the current in the zener stack. You want enough to regulate properly, 5 mA is sound, and 10 mA in the zener won't hurt anything. Just watch the dissipation in R2 and R22 = (V-40)^2/R
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Old 24th October 2008, 01:39 PM   #716
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I am Interested to know how Important are polar caps C21, C27 and all the C22 - C26 and C28 - C32
are these essential or just a extra
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Old 24th October 2008, 02:01 PM   #717
clm811 is offline clm811  United States
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Default Thanks, Jacco!

Quote:
The heatsinks can even run live, personally i'm not too keen of that.
Looks like that's how the 200C was configured. They're internal heat sinks, so with the cover on there's no hazard( but I'd better be careful when working on this sucker, or -ZAP!)


Quote:
If the contact surface between the bracket and the heatsink is sufficiently large and smooth enough, it saves a lot of thermal resistance.
The copper is highly polished, and it looks like they are in intimate contact with the heatsink.


[QUOTE]...Tight fitting copper rod inserts, flat end surfaces, just a weeny bit longer...put the copper angle between two lengths of large dimension solid square steel and flatten the inserts with a hammer QUOTE]

Ok I suspected that, just like my Dad used to hand-make his stuff on an anvil (Grandpa was a blacksmith)!

-chas
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Old 24th October 2008, 02:58 PM   #718
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Quote:
Originally posted by samoloko
I am Interested to know how Important are polar caps C21, C27 and all the C22 - C26 and C28 - C32
are these essential or just a extra
C21 and 27 could be eliminated or could be the only cap needed after the bridge. Jens intended them for local decoupling with a large cap bank in the PSU. If you use enough capacitance you could have a bridge feeding each channel giving some decoupling between channels sharing a common transformer.

The rest that you mentioned are optional. They provide a little decoupling right at each output device, but are not absolutely necessary. Will they have a sonic benefit? Possibly. Mouser has appropriate caps for $.25 each so I'm springing for them.
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Old 24th October 2008, 03:51 PM   #719
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Bob and Andrew,
It is nice to be able to draw in the depth of knowledge. Thanks
I was rereading - 50th time -- the information on Leach's website and came across the above. That is where the question arose.
Tad
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Old 26th October 2008, 07:14 AM   #720
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Quote:
Originally posted by BobEllis


C21 and 27 could be eliminated or could be the only cap needed after the bridge. Jens intended them for local decoupling with a large cap bank in the PSU. If you use enough capacitance you could have a bridge feeding each channel giving some decoupling between channels sharing a common transformer.

Hi Bob

would you please clear - If I got 1 pcs of transformer and 1 pcs of bridge feeding two channels - then there Is a need of C21 , C27 (all that additional caps) no mater what values are filter caps after bridge

what values do you recommend for filter caps after bridge

what have to be the feeding power supply from regulator supply board for the front ends
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