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Old 23rd May 2008, 10:56 PM   #21
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by jkeny
So the absolute value of gate capacitance is the more important factor rather than the slope of change?

What I wanted to use this higher current/ low voltage reference for - a Panasonic SAXR57 Digital amp that uses voltage control to adjust the volume. It's range is from 10V to 40V at a max of 6A maybe. So this complicates matters I think & might make it not feasible given the gate capacitance rise at the lowest voltage

As the digital amp is a no feedback design, the quality of the PS is paramount (PSRR of zero).

I will probably give this a try after I've built up the BDT preamp & have learnt some more - thanks for your help in all this.
Keep in mind that I don't have much more experience than you do. So then:

On total cap vs. rate of change: Yes, I think so, at least as compared to something like a plate load CCS.

I don't think your application really complicates it much (but I don't know if I understand the application, cause it seems odd that a pwm amp would use input voltage to control volume -that's what pulse width is for, no?). The calculations I showed are for a 2V Vds. Vds will be lowest at the highest output setting. You could increase the bias string current at least 5x what I used as an example. You can find better FETs for the application.

You've got a bit it heat to shed, so good radiating area will be important.

Sheldon
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Old 25th May 2008, 02:29 PM   #22
jkeny is offline jkeny  Ireland
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The way this particular dig amp works is that for the first 30dB vol is controlled digitally, then it uses voltage adjustment on the output stage from 10 to 40V, then it's back to dig control.

It seems like Panasonic gave some thought to the sonic effect of digital control and opted for voltage /volume regulation in the main range of listening! Just a pity they used SMPS to do this as the sound with 12V battery is so much better! Hence the search for a high quality regulated variable PS.

P.S. - I believe John Swenson has taken the BDT preamp to VSAC this weekend - will be interested to hear feedback from anybody who heard it!
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Old 2nd June 2008, 02:55 AM   #23
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Being intrigued by the regulator circuit John came up with I built one up and proceeded to test, measure, and blow it up many times in the interest of learning more about the circuit.

Performance is very good the way John has it set up but there are improvements that can be made both for performance and reliability.

I changed a couple of capacitor values, one for improved stability, the other for better performance. I also added some protection circuitry and a current limit circuit.

I'm planning on building several of these into a multiple output bench supply to replace my old Tektronix Engineering power supply. The Tek supply works pretty well but is noisy, both electrically and acoustically. It also has a tendency to blow up at inopportune times as it does not have good current limiting, instead, relying on 2 watt CC resistors on the SS rectifier diodes. It let loose again today during testing of the Swenson regulator. Had to open all the windows to get that wonderful burnt CC smell out of the house. Maggie was not very impressed with the smell but enjoyed the show... It was interesting to see the meters on the power supply back lit by orange flame

Anyway, take a look at me website for the info.Gary P's DIY page
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Old 2nd June 2008, 03:44 AM   #24
Sheldon is offline Sheldon  United States
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Gonna cook up some boards for this baby? I'd buy a few just to have on hand.

Sheldon
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Old 2nd June 2008, 03:59 AM   #25
agent.5 is offline agent.5  United States
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Quote:
Originally posted by Sheldon
Gonna cook up some boards for this baby? I'd buy a few just to have on hand.

Sheldon

Me too.
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Old 2nd June 2008, 09:12 AM   #26
jkeny is offline jkeny  Ireland
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Moi, aussie!

The C2 10 uF is not high voltage, is it?
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Old 2nd June 2008, 02:52 PM   #27
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by jkeny
Moi, aussie!

The C2 10 uF is not high voltage, is it?
It's basically at the output voltage. So if that's high, yeah.

Sheldon
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Old 3rd June 2008, 08:49 PM   #28
jkeny is offline jkeny  Ireland
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I'm in the final stages of building a BDT preamp & while I'm waiting for Dave Slagle's trafos to arrive by post from US to Ireland (4 - 6 weeks from experience), I thought od trying these Nuvotem toroid PS trafos 3.2VA 115-0-115:22-0-22. I would have gone for 1.6VA but not in stock until end June - the higher inductance of the smaller trafo is what is needed in this case

I know nothing about this stuff so I'm relying on others to get me through this.

Do you think this trafo will work OK - it's cheap to try anyway, 20 for pair?

Has anybody built this new BDT preamp?

I will be trying the GP mods to the VR & hope all will be finished at the end of next week. WIll report back
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