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Old 11th July 2012, 09:24 AM   #5131
jambul is online now jambul  Belgium
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thank you salas for the explanation,
so i don't have to waste my source for the cap multiplier before your reg

regards
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Old 11th July 2012, 05:24 PM   #5132
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Quote:
Originally Posted by Salas View Post
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.
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Old 11th July 2012, 05:35 PM   #5133
Salas is offline Salas  Greece
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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?
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Old 11th July 2012, 06:08 PM   #5134
pidesd is offline pidesd  Canada
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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.
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Old 11th July 2012, 06:20 PM   #5135
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Quote:
Originally Posted by Salas View Post
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 !
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Old 11th July 2012, 07:20 PM   #5136
Salas is offline Salas  Greece
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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.
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Old 11th July 2012, 07:50 PM   #5137
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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.
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Old 11th July 2012, 08:03 PM   #5138
Salas is offline Salas  Greece
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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.
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Old 12th July 2012, 06:59 PM   #5139
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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
Click the image to open in full size.

This is the same reg, unloaded (the clock is no load on this reg)
Click the image to open in full size.

And here is the same reg with a 200r load, output voltage is still ok.
Click the image to open in full size.

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

Any ideas?
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Old 12th July 2012, 07:00 PM   #5140
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OOPS
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Last edited by studiostevus; 12th July 2012 at 07:18 PM.
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