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Old 1st October 2003, 11:47 AM   #21
ALW is offline ALW  United Kingdom
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Default A couple of clarifications

1. I didn't contact Walt before I did my PCB's, but did afterwards, primarily to say 'thank you', partly to ease my conscience (I actually had no intention of selling them, but was encouraged by popular demand).

Were I to do the same again I would ask for permission first, but since I do not make any significant income from the sale of these units (I value the feedback more than any financial gain) I felt less guilty - it's not a good excuse though!

2. As is mentioned on my website, Walt may not necessarily agree with all the component choices I made for that circuit either, certainly they are different from his original choices.

3. I think it's only polite to thank those that publish such circuits for their efforts, there's often considerable work put into such ventures that the reader may not be aware of.

My interest in the design was primarily that whilst widely recognised as offering great performance, the circuits seemed to be buried in the mists of time a bit. The constant clamour for information here, that was not served by any of the online resources I could find, swayed me to take a greater interest.

There was also a reputation for stability issues with the AD797 versions - these were addressed by Walt in his follow up 'Improved Regulator' article and in my experience the instability tag is no longer deserved.

There's an increasing number of commercial products starting to use what I strongly suspect is Walt's topology, with modification in many cases, but it seems to have taken some time for it to happen - companies such as Audiocom International who are marketing 'Super Regulators' or Trichord Research who are using Jung-type topologies in their phono stages.

I agree with Jan's comments - it's been very obvious to me, from the initial attempts by others to produce PCB's for the Jung reg's, that many seem to think that a 'PCB is simple'.

Design at this level requires serious attention to detail and Jan, like me, will have spent a long time developing that circuit board, I'm sure. Equally Walt will have expended great effort and time on the original circuit development, I am certain.

One can never assume that something doesn't matter, in audio, it often does.

Andy.
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Old 1st October 2003, 02:06 PM   #22
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Beyond individuals here at diyaudio, how about a big company like Linear Technology that might incorporate the idea into a new component say the LT1963, sell it for half the cost of ALW's PCBA, and make serious money with the idea. Who knows what is going on inside their parts. It may be an exact copy of Jung's circuit. Who in the public knows? Necessary capacitance values noted in the datasheet. I'm not saying this is the case here, but I'm sure this has happened more than once.

We on topic peranders?


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Old 1st October 2003, 02:20 PM   #23
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Don't think so. First of all, you design different when you use silicone, many transistors, current mirrors, multi emitter transistors and other "weird" parts , very few caps, etc.

Much of the new thinking has taken place in the semiconductor factories just because you can design circuits which aren't possible in an another way. This is only what I think.
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Old 1st October 2003, 02:57 PM   #24
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Wink AC?DC?NaC?

"I also wonder how long wires or pcb traces do you think is necessary in order to force use of sense wires? It's cool, but is it necessary if you talk AC performance and disregard a couple of uV is DC loss?"

The series resistance of the wires is added to the output impedance of the regulator. This is MORE OF AN ISSUE for AC than the DC drop because it affects the regulation of the voltage at the device drawing the AC current (i.e., music signal) . Remote sensing puts the wiring impedance inside the feedback loop so the regulator's low impedance appears at the load instead at the regulator output with the wiring impedance between the regulator and the load. Doing remote sensing with a regulator with a several tens of MHz GBW is very challenging engineering and beyond the scope of many analog designers. PCB layout is super critical. The error signals that the op amp in a well designed regulator is sensing in it's feedback loop are below the microvolt level. Without an absolute understanding of exactly where the signal currents run and where the feedback sense points are taken, a few millimeters of printed circuit board trace in the wrong place can greatly effect the regulation. Milliamps through Milliohms matter.

I think Andy is safe from any real competition in his design for a long time. Designing a very good regulator can be even harder than good amplifier or low noise preamp circuit. Most don't even know what the design problems are much less the solutions. This is real engineering with a vengeance at this level and why many find designing regulated supplies that sound good is a very frustrating task. Ever wonder why so many people use emitter followers and don't go very far beyond that for power supply regulators?
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Old 1st October 2003, 03:19 PM   #25
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When "Sense"-inputs come up everyone talk how important it is what AC decoupling near the regulator in order to avoid unstability. Doesn't this apply here also?
Walter Jung from the EDN article.
Quote:
If you need remote sensing, you can add the remote-sense isolation resistor R2 at the load point. Breaking the normal sense line at X enables the remote-sensing option, with C1 added to decouple the sense loop at high frequencies. A negative-output version reverses the diodes and capacitors, along with the op-amp supply pins, and substitutes complementary transistors.
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Old 1st October 2003, 03:29 PM   #26
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Default Tracking the load

Per,

It has more to do with the regulator tracking the load. The futher away the regulator is from the load the worse it tracks. Of course your right bypassing at the load is very important.
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Old 1st October 2003, 03:33 PM   #27
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It has VERY much to do with load. If you have long wires you have also "L". What happens in an amp if you put an inductor at the output and then connect feedback after this L = oscillations if you are unlucky.

So, Jim you say also that AC wise it's no (or little) use with remote sensing because you short circuit the signal near the regulator.
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Old 1st October 2003, 03:44 PM   #28
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Quote:
Originally posted by peranders
Don't think so. First of all, you design different when you use silicone, many transistors, current nmirrors, multi emitter transistors and other "weird" parts , very few caps, etc.

Much of the new thinking has taken place in the semiconductor factories just because you can design circuits which aren't possible in an another way. This is only what I think.
I agree. There are things you can do in an IC that would be impossible in discrete form. And probably vice versa.

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Old 1st October 2003, 03:50 PM   #29
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Default Re: AC?DC?NaC?

Quote:
Originally posted by Fred Dieckmann
"I also wonder how long wires or pcb traces do you think is necessary in order to force use of sense wires? It's cool, but is it necessary if you talk AC performance and disregard a couple of uV is DC loss?"

The series resistance of the wires is added to the output impedance of the regulator. This is MORE OF AN ISSUE for AC than the DC drop because it affects the regulation of the voltage at the device drawing the AC current (i.e., music signal) . Remote sensing puts the wiring impedance inside the feedback loop so the regulator's low impedance appears at the load instead at the regulator output with the wiring impedance between the regulator and the load. Doing remote sensing with a regulator with a several tens of MHz GBW is very challenging engineering and beyond the scope of many analog designers. PCB layout is super critical. The error signals that the op amp in a well designed regulator is sensing in it's feedback loop are below the microvolt level. Without an absolute understanding of exactly where the signal currents run and where the feedback sense points are taken, a few millimeters of printed circuit board trace in the wrong place can greatly effect the regulation. Milliamps through Milliohms matter.

I think Andy is safe from any real competition in his design for a long time. Designing a very good regulator can be even harder than good amplifier or low noise preamp circuit. Most don't even know what the design problems are much less the solutions. This is real engineering with a vengeance at this level and why many find designing regulated supplies that sound good is a very frustrating task. Ever wonder why so many people use emitter followers and don't go very far beyond that for power supply regulators?
Fred, I agree completely. I remember how challenging it is just to measure the Zout of this things. You need very carefull 4-wire impedance measuring techniques or you end up measuring the resistance of a piece of wire or PCB trace. I got some very nice flat traces of just 10 or 12 milliohms flat to 100kHz. Great supply? No. The supply had less than 1milliohms up til 20kHz, and rising. If you don't see the rising, you'r measuring the wrong thing, or you are a genius. I know I am not.

One of the initial problems we had to stabilise the supplies with 797's was due to remote sensing. The added inductance (and capacitance) inside the loop were just too much.

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Old 1st October 2003, 04:08 PM   #30
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Jan, if you don't pay attention to the coolness factor of remote sensing in this application, how important do you think it is really?

Note Fred, I still think Jan's and Andy's work is great.
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