The simplistic Salas low voltage shunt regulator - Page 514

jambul · 11th July 2012, 09:24 AM

thank you salas for the explanation,
so i don't have to waste my source for the cap multiplier before your reg

regards

studiostevus · 11th July 2012, 05:24 PM

Quote:

Originally Posted by Salas

Measure IRF620's VGS. Probe at U$23's to BC collector junction on the scope. What are the results? (BIB- is for 560C, 2SK117, IRF530 other combinations I can not predict).

Vgs(MOSFET) = 820mV

U$23 is a JFET (2SK170), its Vgs = 820mV, scope G to S gives a nice flat line.

Q20 is the BC560. Scoping Q20(Collector) to U$23 gives a nice flat line.

Salas · 11th July 2012, 05:35 PM

VGS MOSFET should have been in the Volts region. It seems to me that the current follower is not open and the small BJT provides all the current it can to the load, that is why it gets hot. Can you confirm MOSFET orientation and PCB connections to original schematic please?

pidesd · 11th July 2012, 06:08 PM

i v e tried cap multiplier with bjt s (though i have not tried 2n4401 and the likes) and in the end the music sounded a little dry. that effect was reduced a lot with a mosfet cap multiplier. Still the most analogue sound is with CLC type filters, L being air core and high gauge and C a combination of cap in multiple stages.

studiostevus · 11th July 2012, 06:20 PM

Quote:

Originally Posted by Salas

VGS MOSFET should have been in the Volts region. It seems to me that the current follower is not open and the small BJT provides all the current it can to the load, that is why it gets hot. Can you confirm MOSFET orientation and PCB connections to original schematic please?

You got it. The poor BC was doing everything alone, I had wired up another JFET wrongly! The heat/stability problem is fixed now!

When measuring aroung, I noticed that both the negative regs have much more noise than they should have though (0.4mVpp).... strange !

Salas · 11th July 2012, 07:20 PM

That's nice it got solved.

When measuring noise with scope do a check with the crock end shorted to probe's nose. See what it does as a base line in the specific measurement layout and environment-time. Use 1X probe setting only. If its a DSO engage its bandwidth limit option also. That way you will know more of what's base and what's added. In general the NPN and NMOS semis are happier for self noise than their P counterparts.

studiostevus · 11th July 2012, 07:50 PM

Actually... after measuring again... the noise is actually 40mVpp, and this is not scope-related I think. It's funny, because it actually sounds pretty good to me...

I will look at it tomorrow... too tired now.

Salas · 11th July 2012, 08:03 PM

40mV pk-pk is too much. Should be near to scope's residual normally. The safe procedure is to see on dummy load, before attached to circuits, to make sure its not spectra coupling from the digital circuits.

studiostevus · 12th July 2012, 06:59 PM

Made some pictures, maybe this rings a bell?

This is the -15v reg with the tda1541a as load. Dont mind the small spikes (the fuzziness around the main shape), these are due to the clock... Scope setting is 20 mV/div

This is the same reg, unloaded (the clock is no load on this reg)

And here is the same reg with a 200r load, output voltage is still ok.

And here, the same reg loaded by a 100r resistor (which draws more than thr ccs). Max Output voltage is now obviously less... 13v.

Any ideas?

studiostevus · 07:18 PM

OOPS

12th July 2012, 06:59 PM	#5139
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Made some pictures, maybe this rings a bell? This is the -15v reg with the tda1541a as load. Dont mind the small spikes (the fuzziness around the main shape), these are due to the clock... Scope setting is 20 mV/div This is the same reg, unloaded (the clock is no load on this reg) And here is the same reg with a 200r load, output voltage is still ok. And here, the same reg loaded by a 100r resistor (which draws more than thr ccs). Max Output voltage is now obviously less... 13v. Any ideas? __________________ -------- TDA1541a-S2 / 6072a / MediaplayerDac -- Michell Gyrodec -- Aikido Preamp -- Pass F5 -- Audio Physic Tempo 2SE -- Yamamura Cabling

12th July 2012, 07:00 PM	#5140
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	OOPS __________________ -------- TDA1541a-S2 / 6072a / MediaplayerDac -- Michell Gyrodec -- Aikido Preamp -- Pass F5 -- Audio Physic Tempo 2SE -- Yamamura Cabling Last edited by studiostevus; 12th July 2012 at 07:18 PM.

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11th July 2012, 09:24 AM	#5131
jambul diyAudio Member Join Date: Mar 2011	thank you salas for the explanation, so i don't have to waste my source for the cap multiplier before your reg regards

11th July 2012, 06:08 PM	#5134
pidesd diyAudio Member Join Date: Apr 2008 Location: montreal (cotes des neiges yo!)	i v e tried cap multiplier with bjt s (though i have not tried 2n4401 and the likes) and in the end the music sounded a little dry. that effect was reduced a lot with a mosfet cap multiplier. Still the most analogue sound is with CLC type filters, L being air core and high gauge and C a combination of cap in multiple stages.

11th July 2012, 07:20 PM	#5136
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	That's nice it got solved. When measuring noise with scope do a check with the crock end shorted to probe's nose. See what it does as a base line in the specific measurement layout and environment-time. Use 1X probe setting only. If its a DSO engage its bandwidth limit option also. That way you will know more of what's base and what's added. In general the NPN and NMOS semis are happier for self noise than their P counterparts.

11th July 2012, 07:50 PM	#5137
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Actually... after measuring again... the noise is actually 40mVpp, and this is not scope-related I think. It's funny, because it actually sounds pretty good to me... I will look at it tomorrow... too tired now.

11th July 2012, 08:03 PM	#5138
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	40mV pk-pk is too much. Should be near to scope's residual normally. The safe procedure is to see on dummy load, before attached to circuits, to make sure its not spectra coupling from the digital circuits.