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Leach Super Amp  Regulated supply
Leach Super Amp  Regulated supply
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Old 18th February 2005, 02:26 PM   #11
LBHajdu is offline LBHajdu  United States
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I can’t really comment on this as I don’t have the experience. However my guess would be that the zeners hold the Vgs constant, as long as the rail doesn’t drop to low.


There is a quote from Mr. Pass here that doesn’t sound to good:



Quote:
The output impedance of this circuit is fairly low, being the inverse of the transconductance figure of the MOSFET, which for the IRFP240 is about 5 Siemens, which means that the output impedance will be about .2 ohms.

This figure is not particularly great as a regulator, and ordinarily we would look to improve on it, usually by enclosing the regulator transistor in a feedback loop to correct for this variation. If this were a higher power Class B or AB type amplifier, such an output impedance could easily result in one or two Volts of nonlinear distortion signal in the power supply, and this would bleed into the output circuit as distortion.

With a Class A amplifier, we have the advantage that the current draw from the supply is a linear function of the output current, and so no distorted "half waveform" is seen impressed on the supply voltage. This being the case, the importance of the output impedance becomes less, and we can consider using this follower without feedback.

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Old 18th February 2005, 02:27 PM   #12
Mikett is offline Mikett  Canada
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My copies of the Boak supply is unfortunately deep in storage right now. However, the aritcles were written in the early 80s in the Audio Amateur. There were a series of articles called "Measuring Power Supply output impedance" or something along those lines. In these articles it was clearly shown that regulation actually reduces measurable distortion as well. The supplies that I used was the final version of the Boak where Walter Jung had recommended some changes that improved output impedance further. What we finally did was to incorporate two boards +,-, into one board that inclluded preregulators.

The heat dissipation and transistor was not a big issue. Why? If you choose a sufficiently "stiff" transformer to begin with, you can minimize the voltage on the pass transistors by running a lower unregulated voltage and minimize the heat produced. Furthermore, since there is also preregulator, the voltages that each of the pass transistors see might be only a few volts. With this you could probably get a modern TO3/multiple palstics that could pass maybe 50+ amps and still easily stay in the SOA. I used the MJ802/4502 and recall that I was good for 50 amps.

Unlike low level signal sections, a fast unstable supply in an amp of this power could have SUPER consequences. That's probably why not many have tackled this sort of thing much. The BOAK we used was proven to be stable over several power amps and that's why I was comfortable to scale it up and use it. But I'm sure it's performance might be laughable today, but you never know.

After this amp, I have not had the desire to build another amp for over twenty years because no significant ideas have come forward..
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Old 18th February 2005, 04:22 PM   #13
LBHajdu is offline LBHajdu  United States
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Mikett,
I think your circuit may be on display at: http://www.aussieamplifiers.com/regulated.htm

Anthony has added some improvements, can you confirm if this is the circuit you used.

Leve
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Old 18th February 2005, 05:51 PM   #14
Mikett is offline Mikett  Canada
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no it was essentially a current boosted 3 terminal reg with a prereg
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Old 18th February 2005, 06:14 PM   #15
acenovelty is offline acenovelty  United States
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ALL-FET Dual low-noise regulator

2x+/-(24-40)V/200mA. Needs 2x(22-32)VAC

ONE 185.00 Euros
The EB-202/254 consists of two dual wide-band, low-noise regulators, using only FETs (JFETs and MOSFETs) as active elements. Maximum input voltage is ±45V and maximum output voltage is ±40V. Maximum output current with 5V input/output voltage difference is ±200mA.
The set-up procedure consists of adjusting the output voltage to the desired value. Connect 2x270 Ohm/5W resistors to the outputs and a DVM across one of the resistors. Connect the appropriate unregulated DC voltage to the regulator (should be approx. 5V higher than the expected output voltage) and check the output with the DVM. Adjust the output voltage to the desired value with trimpots P1/P2. If you have an oscilloscope and/or an audio µV meter, connect them across the load resistors and check the residual hum/noise. The scope should not show any ripple and the µV meter should show less then 5µV of noise over the audio bandwidth.
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Old 18th February 2005, 07:37 PM   #16
acenovelty is offline acenovelty  United States
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The Walt Jung Super-Regulator
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Old 18th February 2005, 08:38 PM   #17
LBHajdu is offline LBHajdu  United States
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acenovelty,
The Walt Jung Super-Regulator may have potential, the Borbely doesn’t it’s basically the same as the Anthony Holton circuit, but with fets and no component values. The maximum output voltage on the Borbely is way to low, and it’s allot of money to pay. You’re pay more for the intellectual property then you are for the board.

At this point the Anthony Holton circuit seems to be the best candidate. As the Pass would need feedback added or many more devices to compensate for the high resistance. The way I understand the problem is that when the amp draws instantaneous current from the regulator the voltage it outputs sags / modulates. To compensate for this the regulator with feedback senses the drop and sends even more voltage through.

Does anyone have more information on the Walt Jung Super-Regulator, the schematic does not talk about max input voltage or max output amps.

Another working circuit can be seen at LCAudio’s web site in the articles section. The only problem again is that the voltage is to low.


Leve
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Old 18th February 2005, 08:44 PM   #18
jacco vermeulen is offline jacco vermeulen  Netherlands
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Maybe Al, the Mighty Mouse, made a proper suggestion, a separate thread for a voltage regulation circuit is more obvious.

I just asked for the possibility of separated lines on the Leach layout.

The first amplifier i heard (of) with full regulation was one by ML.
That amplifier was so stable that a German mag bridged the twins and welded a couple of bras strips together with them.
You could check at MarkLev.com for the regulation circuitry.
Or ask the ML expert here, Mr John Curl, maybe he can give some info on it. The ML20, 1st or 2st ed.

Andre Schmeets in Germany made a couple of designs with simple discrete voltage regulators.
One of his designs can easily be altered for +90 volts operation,
the original is around 80 Volts in.
From memory:
1 BD139/140 and 3 BC546/556, a couple of caps and R's
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Old 18th February 2005, 09:02 PM   #19
acenovelty is offline acenovelty  United States
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http://www.alw.audio.dsl.pipex.com/jung_schematic.htm

http://www.aoselectronics.com/jungsrpcb.html
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Old 18th February 2005, 09:03 PM   #20
acenovelty is offline acenovelty  United States
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http://home.comcast.net/~walt-jung/w...ces.html-.html
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