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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 27th Jul 2020, 4:59 pm   #21
Levente
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Default Re: TIP30 substitute for regulated -12V

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Originally Posted by snowman_al View Post
I agree a 7812 regulator makes much more sense.
Two reasons, as stated it is on the positive side of the circuit and the Pin Out is different. The tab and Pin 2 of the 78xx regs are ground. If you look at the pictures the regulator tab (and hence pin 2) is mounted on the aluminium chassis, which I guess is ground?
Hi

Thanks for your note... the regulator tab connected to the aluminium is isolated...and all the other parts are isolated...

If i swap this with the 7812 should I change anything at all or just swap exactly how the 7912 is right now?

Thanks !
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Old 27th Jul 2020, 5:07 pm   #22
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Default Re: TIP30 substitute for regulated -12V

The centre connection and tab on the 7812 must be taken to the -12V line. It is only taken to chassis when used in more conventional +12V form. Your photo seems to show the trace from that pin going nowhere!
I can't really see what that diode and output-side capacitor are doing, not much I suspect. Your choice as to leaving them in place. But I would probably remove them for now.
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Old 27th Jul 2020, 5:10 pm   #23
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Default Re: TIP30 substitute for regulated -12V

The pins on the 7812 should go in naturally to the circuit board. Tab on the bottom, insulated.
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Old 27th Jul 2020, 5:13 pm   #24
Levente
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Default Re: TIP30 substitute for regulated -12V

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Originally Posted by Pamphonica View Post
The centre connection and tab on the 7812 must be taken to the -12V line. It is only taken to chassis when used in more conventional +12V form. Your photo seems to show the trace from that pin going nowhere!
I can't really see what that diode and output-side capacitor are doing, not much I suspect. Your choice as to leaving them in place.
Thanks ... the center connection seems to end on this side but on the top side it is going into that diode + side... so bad that no one really has the schematic except one single person who wants 250USD for it ....


Thanks a million again for your help, will try and get a 7812 and see what I am getting then...
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Old 27th Jul 2020, 5:19 pm   #25
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Default Re: TIP30 substitute for regulated -12V

I keep trying to see in the photos what that extra diode and capacitor are doing. I think they are placed right across the output of the regulator. That's quite conventional in symmetrical (+ and - voltage) supplies, using a shunt diode to to protect the regulator. The cathode would go to ground, the anode to the -12V line. The capacitor is just smoothing any noise on the output. So leave them in for now, if they are across the -12V line and ground.
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Old 27th Jul 2020, 5:25 pm   #26
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Default Re: TIP30 substitute for regulated -12V

The centre pin of a 7812 definitely needs to go to -12V, not ground, and that should be the anode of the big diode (the end without a band).
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Old 27th Jul 2020, 5:28 pm   #27
Levente
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Default Re: TIP30 substitute for regulated -12V

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Originally Posted by Pamphonica View Post
I keep trying to see in the photos what that extra diode and capacitor are doing. I think they are placed right across the output of the regulator. That's quite conventional in symmetrical (+ and - voltage) supplies, using a shunt diode to to protect the regulator. The cathode would go to ground, the anode to the -12V line. The capacitor is just smoothing any noise on the output. So leave them in for now, if they are across the -12V line and ground.
Will do so...

Just looking at the pin out of the 7812...so pin 1 is V+ in, that is connected to (according to my "drawings" ) that diode cathode and digital ground.. is this correct?

the pin1 should not be connected to the the point of rectified DC? Or I am way too confused now..

will order anyway the 7812 and test it ...just afraid that i am soldering this pcb too much... might burn the thing...

thanks again Jeremy
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Old 27th Jul 2020, 5:35 pm   #28
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Default Re: TIP30 substitute for regulated -12V

I suggest that if you are worried about damaging the pcb, make up a small pcb for the -12V supply and test that outside the amplifier first so you can check the results.

Or at least disconnect the -12V line from the rest of the amplifier while you are testing.

Pin 1 (input) of the 7812 goes just to the +ve of the big 1000uF capacitor (rectified dc from the diodes), nowhere else.
Pin 2 ("ground" or common) goes to the -12V line (the other side of the 1000uF capacitor)
Pin 3 (output) goes to digital ground and diode cathode (white ring)

Just try removing the 7912 (or the transistor) and putting the 7812 exactly in its place. But make sure pin 2 (centre/tab) does somehow end up connected to the -12V line, isolated from chassis.
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