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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 2nd November 2009, 12:30 PM   #2591
RCruz is offline RCruz  Switzerland
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Simplistic NJFET RIAA
Hi massimo

The TX is smaller than spec... in the pdf I read 93mm diameter but in reality it is 87mmD

The cross section looks almost square measuring 36mm high and 30mm deep.

As I set CCS for 200mA and wanting to drop 6 volts I will need 30ohms right ?
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Old 2nd November 2009, 12:44 PM   #2592
massimo is offline massimo  Italy
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R = 6 / 0.2 = 30 Ohm, correct.
With 33 ohm (practical value), you have: V = R x I or V = 33 x 0.2 = 6.6 V drop.

Now: P = V x I or P = 6.6 x 0.2 = 1.32 W.... then x 2.5 - x 3 means a 3 W or higher reisistor .

A nice idea is to "split" this resistor for the V + and V - side and thus use a couple of 68 Ohm/2W on each side of your p.s.
Connect the V- to the chassis gnd at the second caps (you're using a CRC, aren't you?)
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Old 2nd November 2009, 12:46 PM   #2593
massimo is offline massimo  Italy
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About the Xfrm: maybe flux is on the high side, but at least they use the right "doughtnut" resulting in a perfectly "squared" toroid (beware of toroid much higher at the center).
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Old 2nd November 2009, 01:25 PM   #2594
Salas is offline Salas  Greece
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Simplistic NJFET RIAA
Because its strong ripple current there it gets lower R than predicted in my experience. Has to do with peak charging. Maybe 15R 5-10W Ricardo. Just stick some 10R there and get an indication in conjuction with your CCS setting that governs how much the Tx will sag, the charge cycle with 15mF etc. Then you can move accordingly.
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Old 2nd November 2009, 01:27 PM   #2595
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by massimo View Post
(beware of toroid much higher at the center).
The windings must overlap at the centre more than at the perimeter.
That ensures that ALL toroids are higher in the centre.
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Old 2nd November 2009, 02:27 PM   #2596
massimo is offline massimo  Italy
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Of course, Andrew, the windings overleap at the center, but in properly calculated toroids, not too much, otherwise that means that they have adopted a smaller doughnut in order to save money and/or space.
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Old 2nd November 2009, 02:35 PM   #2597
RCruz is offline RCruz  Switzerland
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If I get ir correctly I should use 10r AFTER the smoothing cap... and if it is not enough, I can use another 10r on the -V (GND in this case).

I was wondering If I could place the resistors between the rectifiers and the smoothing caps ....
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Old 2nd November 2009, 03:14 PM   #2598
disco is offline disco  Netherlands
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Ricardo,

I guess you're using two power supplies to feed your regulators. Exchanging the load one regulator is presenting to your supply for a resistor, you can experiment to hearts content with resistors, caps, coils etc. Just measure the output voltage over the load.

If I remember correctly you're set for .2A and 28V. It would take a resistor of 28/.2= 140 ohm which produces .2 x .2 x 140= 5.6W of heat. You can make a serial or parallel connection with 10W resistors, if you have some.

Placing resistors between the bridge and the cap is possible and is sometimes (if small) preferred. You can have more sections of Resistor and Capacitor but always end your filter with a cap, the largest goes last.
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Last edited by disco; 2nd November 2009 at 03:28 PM.
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Old 2nd November 2009, 03:22 PM   #2599
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by disco View Post

Placing resistors before the cap is possible and is sometimes (if small) preferred to after. You can have both but always end your filter with a cap, the largest goes last.
This answers my question !

I will try to use 10r before the capacitor.

I am using dual mono psu and Jensen 4 pole as smoother... the resistors must be before the cap.
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Old 2nd November 2009, 04:54 PM   #2600
Salas is offline Salas  Greece
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Quote:
Originally Posted by RCruz View Post
If I get ir correctly I should use 10r AFTER the smoothing cap... and if it is not enough, I can use another 10r on the -V (GND in this case).

I was wondering If I could place the resistors between the rectifiers and the smoothing caps ....
Before cap. Between bridge and cap. RC filter and drop. Think valve circuits. Don't manipulate the ground BTW.
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