The simplistic Salas low voltage shunt regulator - Page 77 - diyAudio
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Old 19th July 2009, 02:19 PM   #761
Salas is offline Salas  Greece
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That's the right procedure. If the system and especially the speaker - room interface isn't tonally balanced we can not know much about the front end components. Take your time, because those comparisons have enough subtle subjective elements.
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Old 19th July 2009, 03:38 PM   #762
iko is offline iko  Canada
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Default Re: 5V Salas's Shunt Reg in B32S

Quote:
Originally posted by prakit
I installed the reg in the dac last night and left it on for burn-in. This morning I checked it and everything was in order before gave it a listen.

To answer Woodenhead about the Vreg=5.6V, yes, it's slightly high but I think it's absolutely fine. If you use the 4,7V Zener for D1, it should be closer to optimal 5V.

This listening impression is relative to the Jung/Didden reg.
Good news first. Overall the dac sounds more liquid. The mid is slightly sweeter and more fleshed out. However, the good news stops here. It sounds very dull in the hi. The bass(in which I feel is the strength of B32S) is also a bit thin and not very tight. Sorry but I have to say it doesn't sound right.

I have a feeling that some parts are not working at their optimal point. 5V is quite low. Beside the D1 that I substitute with 2xLM336-2.5, I wonder if the choice for Q3 is critical? I can't find a BC550C so I liberally use a 2SC1627A here. All JFet were chosen according to specified Idss.

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Prakit
You may want to make sure it's actually regulating. Regarding the 2sc1627a, is it an O or a Y? Both varieties are a bit low on hfe, it would make a bit of a difference for the loop gain. Dull, thin, lack of dynamic is exactly what this regulator is not about. IMHO the regulator is not working right. You may want to simplify things and make sure it works out of the whole setup right, i.e. make sure that the right shunt current goes through the shunt mosfet, that the 2sc1627a gets biased correctly (current through the reference?). You can use a simple reference such as three 1.7V or 1.8V yellow/green LEDs to test things out, and a resistor for load. Add a small resistor on the drain of the shunt mosfet and measure the voltage drop over it, then calculate the shunt current. Perhaps you've done all this, then never mind.
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Old 20th July 2009, 10:03 AM   #763
prakit is offline prakit  Thailand
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Thanks for all the advices.

I agree that somethings in my reg are not working properly. 5V doesn't leave much margin for everything so it could be very tricky to get it to work properly. Will take sometime to sort things out to find the culprit. I'll report back how it goes.

Btw, the JD's series reg is very fine but it makes things sound a bit too crisp and too sharp for my taste. I know a shunt reg can do better.

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Prakit
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Old 22nd July 2009, 09:07 PM   #764
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I am using 2 x LED + 1N4148 in series for 5V output. Less noise than Zener.
Shunting 225 mA, voltage output is 4.97V. Input is 12V. No oscillations so far.
shematic post #745.

@salas
Vgs for IRFP9240 is 4V. We are very close to margin with voltage reference at 4.3V and output at 5V.
Do you have any experience with MOSFETs with low gate treshold voltage?
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Old 22nd July 2009, 11:44 PM   #765
Salas is offline Salas  Greece
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The Vref is sitting on Vbe so it is 4.97V actually. It will be no problem if there is low input ripple, lower than 1VP-P which is normally much lower than that. Did you actually measure the Vgs of Q1? It tends to go lower than 4V at low tensions. Looks like 3.15V to me if with 5.4V CCS LED string and R1=10R, ICCS=0.225A. You applied it to a DAC already? If yes, sounds OK?
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Old 23rd July 2009, 06:59 AM   #766
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D1 as voltage reference 4.3V in my mind
Measured Vgs of Q1 = 5.3V

I am thinkink of 3.3V output, for this I need MOSFET with low gate treshold voltage.

I will test soon. No working DAC at home this moment
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Old 23rd July 2009, 07:43 AM   #767
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Maybe something like the 2SJ380, 2SJ306, 2SJ449, etc or the 2SK2391, 2SK1119, etc These are down around the 2 volt mark, I think.
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Old 23rd July 2009, 02:00 PM   #768
Salas is offline Salas  Greece
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Quote:
Originally posted by stormsonic
D1 as voltage reference 4.3V in my mind
Measured Vgs of Q1 = 5.3V

Weird number, are you sure that you did not measure Vds instead? Vgs is between pins 1 & 3.
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Old 23rd July 2009, 03:36 PM   #769
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My mistake, fingers are faster than brain
Here are measured values
Attached Images
File Type: jpg 5v_s.jpg (55.7 KB, 683 views)
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Old 23rd July 2009, 04:23 PM   #770
Salas is offline Salas  Greece
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4.12V/6R=0.68A. You said 225mA last time. Why you need so much current? Plus you show no Vgs measurements on your schematic.
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