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Old 13th August 2011, 04:00 PM   #221
Salas is offline Salas  Greece
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The guide writes 1K8 resistor also. Is that resistor 1K8? Anyway, add 1K instead of the Zener jumper, should give you enough conversion to reach 24V with ease.

P.S. I see you edited. The examples in the guides state they assume a certain in circuit IDSS. If a FET chances a bit weaker or stronger it takes compensation in the values.
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Old 13th August 2011, 04:04 PM   #222
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Quote:
Originally Posted by Salas View Post
Check that your Q103,203,303 are K117 JFETs and not BC transistors by mistake. Because one reason can be having no current to drive the V reference resistors and trimmers.
Q103 & Q 203 both are K117 JFETs
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Old 13th August 2011, 04:08 PM   #223
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The above quote was addressed to a Canadian member with no reference voltage. You have voltage, you just need a bit more free hand on the trimmer. Different case.
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Old 13th August 2011, 04:10 PM   #224
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Quote:
Originally Posted by Salas View Post
The guide writes 1K8 resistor also. Is that resistor 1K8? Anyway, add 1K instead of the Zener jumper, should give you enough conversion to reach 24V with ease.

P.S. I see you edited. The examples in the guides state they assume a certain in circuit IDSS. If a FET chances a bit weaker or stronger it takes compensation in the values.
Negative rail 1K805
Positive rail 1K797

Negative rail trimmer 5K42
Positive rail trimmer 5K13

I suspect JFETs I will follow your advice adding 1K resistor instead diode zener jumper
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Old 13th August 2011, 05:32 PM   #225
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Now works fine with load 270R 5W +-24Vout
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Old 13th August 2011, 05:48 PM   #226
Salas is offline Salas  Greece
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As expected. Are those sinks enough? You are burning 7.2W on the output Mosfet. 1C/W common sink for both power elements per side would look neater and surely adequate.
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Old 13th August 2011, 06:00 PM   #227
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4.5 C/W
529902B02500G Aavid Thermalloy Heatsinks

5 C/W
529801B02500G Aavid Thermalloy Heatsinks

Aren't enough?
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Old 13th August 2011, 06:29 PM   #228
Salas is offline Salas  Greece
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Long term enclosed no, I wouldn't trust them much. Given that you run 384mA @ 24V for ~90mA consumption per rail.
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Old 13th August 2011, 08:28 PM   #229
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Just remembered you told me to use these for Simplistic NJFET RIAA regs.

ABL HEATSINKS|345AB1000B|HEAT SINK, 1°C/W | Farnell España

Are also ok for the Borbely stuff, right?

P.S. Can work if I use two 4.5 C / W?

Last edited by merlin el mago; 13th August 2011 at 08:33 PM.
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Old 13th August 2011, 08:44 PM   #230
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You must always calculate the dissipation and the temperature rise at least roughly as in the guide. In this case of your 384mA @ 24V with ~90mA dummy consumption you will get 4.5C/W times 7.2W =32.4C above ambient in the output Mosfet sink. High for long term reliability. Those PCBs are designed with best layout in mind and enough dissipation. So long side or vertically parallel heatsinks, or thick metal floor are best. Small individual ones are for less than 200mA up to 15V. Get a 3 stage M3 thread taps set and make nice blind threaded holes on thick metal long sinks or make see through holes to thinner surfaces and arrange PSUs nicely and securely on good ventilation places when you will finalize constructions.
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