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Old 2nd March 2009, 09:26 PM   #61
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Quote:
Originally posted by syn08
Guys, I agree that this little regulator is actually more complex than it appears at the first glance. There are literally hundreds of combinations you can build this, and here are a few variables I can quickly think of:

- Bipolar/MOSFET
- Polarity (NPN/PNP or Nchannel/Pchannel, with flipping the opamp inputs)
- Reference type
- Current source to feed the reference (yes, using a resistor to the output or a CCS like a JFET makes a significant difference)
- Ballast resistor or CCS
- Output cap value and ESR+ESL
- Reference bypassing cap value
- Reference bypassing connection (ground/output, yes it makes a very significant difference)
- Other bypassing (control input, like in the Minnesota shunt, yes, it makes a very significant difference).

If somebody with a simulator and enough time could try to optimize and find the best combination of the above, I would be the first to appreciate the effort.

Given the limited time I have, my intention was only to show something that works very good for me (actually probably as good or better than any discrete parallel regulator I can think of, at a fraction of complexity, size and cost).
Syn,

I don't quite understand the configuration of your reg here:

http://www.diyaudio.com/forums/attac...amp=1233846899

Why have you bypassed R296 with caps and not bypassed R242?

The Minnesota shows effectively the traditional configuration I am
suggesting.

cheers

T
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Old 2nd March 2009, 09:57 PM   #62
syn08 is offline syn08  Canada
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Quote:
Originally posted by Terry Demol


Syn,

I don't quite understand the configuration of your reg here:

http://www.diyaudio.com/forums/attac...amp=1233846899

Why have you bypassed R296 with caps and not bypassed R242?

The Minnesota shows effectively the traditional configuration I am
suggesting.

cheers

T
Compare again The minnesota uses a pnp and the opamp is flipped.. Why is the minnesota decoupling the divider up to the output?

I have posted earlier in this thread the load regulation in the two configurations. The output impedance follows the same.
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Old 2nd March 2009, 10:31 PM   #63
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Quote:
Originally posted by Terry Demol



I don't quite understand the configuration of your reg here:


Terry, i have been asking this question for a while and now have a pretty good explanation. It was probably an innocent mistake in the beginning but you are more likely to interest Syn in a root canal extraction than in admitting a mistake. So, once the question was raised he ran it through the simulator and what do you know - it's actually better (in a way) with the weird cap.

Btw, after failing to get it to work with the cap in place i tried it with bipolar outputs. No motoroboating now, so the explanation suggested by Bonsai in post #51 (the mosfet threshold voltage) was indeed correct. Tomorrow i will listen seriously with and without the cap.
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Old 2nd March 2009, 10:54 PM   #64
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Quote:
Originally posted by analog_sa



Terry, i have been asking this question for a while and now have a pretty good explanation. It was probably an innocent mistake in the beginning but you are more likely to interest Syn in a root canal extraction than in admitting a mistake. So, once the question was raised he ran it through the simulator and what do you know - it's actually better (in a way) with the weird cap.

Btw, after failing to get it to work with the cap in place i tried it with bipolar outputs. No motoroboating now, so the explanation suggested by Bonsai in post #51 (the mosfet threshold voltage) was indeed correct. Tomorrow i will listen seriously with and without the cap.
It would be worth trying the correct, ie; unity AC gain config which
should have lower noise and lower OP Z.

T
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Old 2nd March 2009, 11:22 PM   #65
jwb is offline jwb  United States
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Quote:
Originally posted by martin clark
When I've used LEDs for voltage reference purposes (at 1-3mA) I've seen impedances c.35-50ohms. Pretty low actually, and significantly better than a zener at these currents
There are zeners with substantially lower dynamic Z than LEDs these days. I just bought a box full of 6.2V zeners with 9Ω dynamic impedance at 5mA.
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Old 2nd March 2009, 11:31 PM   #66
syn08 is offline syn08  Canada
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Quote:
Originally posted by analog_sa
Terry, i have been asking this question for a while and now have a pretty good explanation. It was probably an innocent mistake in the beginning but you are more likely to interest Syn in a root canal extraction than in admitting a mistake. So, once the question was raised he ran it through the simulator and what do you know - it's actually better (in a way) with the weird cap.
I don't know how to take this. So, let me summarize:

- Me, Jan, Bonsai, others are contributing to this thread and helping you in building a parallel regulator that would match your (unknown, electrically and subjectively) requirements.
- You complain about the weird values in the schematic, again without exactly telling exactly what you need.
- Then you divert and ask about a fixed opamp gain regulator and not happy with the responses you got.
- Then you build the thing, claim motorboating, admit you have a poor grounding, and instead of fixing that you complain about the "weird" capacitor and connect it to the ground, which obviously (at least to me) degrades the performance (and you got a good explanation as of why).
- Then somebody which obviously has no clue on parallel regulators (as long as it confuses a feedback schema with a fixed gain amp) jums in and you quickly embark in that boat, criticizing something that you already admitted is working and "sounds good".
- Then you keep asking the same question about the "weird" cap and complaining about "simulation results" without offering any clue in what would be acceptable proof for you.
- Then you mentioned switching to a bipolar (and using the "weird" cap?) instead using a full swing opamp as I described above and complain about what? Still unhappy?
- You end up with insulting my efforts to help (see the quote above).
- This is not the first time - I recall a similar bitch, moan, rant attitude regarding my first version of phono amp.

I will stop short of telling what I think about your attitude... You just offered a great example of what is constantly discouraging contributions here.
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Old 2nd March 2009, 11:54 PM   #67
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Hi,
here is my sim I talked about earlier. First, the circuit. Sorry, bad drawing habits...
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File Type: gif opshunt.gif (31.6 KB, 1204 views)
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Old 2nd March 2009, 11:55 PM   #68
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leads to:
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File Type: gif output.gif (20.6 KB, 1057 views)
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Old 2nd March 2009, 11:57 PM   #69
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As you see, I've taken the AD797 which is not optimum regarding max. voltage swing. however, with a LT1115 the sim fails.

Rüdiger
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Old 3rd March 2009, 01:00 AM   #70
iko is offline iko  Canada
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Default Re: Wiring

Quote:
Originally posted by syn08
This is how I'm wiring this regulator. If the regulator is in the same case with the phono stage you may delete 3 and the shielded cable T1, and simply star the output/sense and the grounds/sense at the low noise input stage terminals.

I guarantee that using this schema will improve the performance.
Hi Syn, perhaps I'm missing something. My simulation of this circuit isn't doing very well. I do like its simplicity.
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