A LM3886 "Stasis" Power Buffer - diyAudio
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Old 22nd April 2005, 06:01 PM   #1
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Default A LM3886 "Stasis" Power Buffer

Only for the little that go across the border inverting OPamp and non- inverting, my complete cookies.
This configurations don't see easily in the forum, because anyone has the abilities to develop usually uses it for money. I hope that some is able draw an advantage. The draw is 2 schemes. Schemes first are a circuit that I have built "the flight" to do some test, and I have thought that were able be of interest to some beginner. In practice this is an OPamp shaped in Tracking, or in degree to develop a range of tension in exit much more tall, on account of the V power floting. The second circuit is that more original. Trade of a Power current/current converter, that is it may use as buffer (unit gain) for audio circuits to ample swing. if it connects directly, without insert it in the negative feedback , himself you produce a "Stasis" amplifier. This technique has been invented and patented by Nelson Pass, and second-hand commercially. In practice, this special type of buffer "sense" the current to the load from the amplifier of tension, and from it amplifies the value, but without influence on the performances. If they use this buffer with preampli to valves to ample swing, or to discrete in class A to the results can be exceptional. For a fast evaluation, it may use the Tracking circuit enclosure. To do it works at the best the buffer, suggestion to using a Voltage amp. with Zout<10 ohms and output current +-50mA. the more experts are able modify the parameters of the buffer using the formulae take root. I hope that some does a favor to publish to forum a " Hi-end "drive circuit. I creed to have done broadly my part, and withdraw me.

Ciao and good work

Mauro Penasa
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Old 22nd April 2005, 07:05 PM   #2
homer09 is offline homer09  Canada
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mauro, i think its really amazing that you contribute this completely new and radical implimentations of the national chips. i just wish i had close to enough understanding to even be able to understand what you're talking about.

maybe your ideas will eventually trickle down into future PCB kits that i could understand a little better.

thanks mauro.
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Old 22nd April 2005, 08:00 PM   #3
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Default Thanks!

More weekend schematic rading for me! Great stuff Mauro!! Keep it coming.
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Old 23rd April 2005, 01:39 AM   #4
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It looks great Mauro!!! Stasis always sounds interesting and intriguing to me but have not built anything similar to have an opinion on it.
Would love to see others follow this road and maybe some PCB for the circuit and I might give it a try.

Did not quite understand what you said regarding the buffer and the use of a pre with this circuit, could you explain in other words?

Cheers….
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Old 23rd April 2005, 04:02 AM   #5
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Hi, Mauro,

Nice designs

Quote:
This technique has been invented and patented by Nelson Pass
Sorry, I still dont get it. Which patent? Or which Statis does it related to?
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Old 23rd April 2005, 07:45 AM   #6
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maupenas, good idea but LM3875 can't be used for this purpose because it isn't stable for gains less than 10. Have you tested your idea in real life?
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Old 23rd April 2005, 08:26 AM   #7
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Quote:
maupenas, good idea but LM3875 can't be used for this purpose because it isn't stable for gains less than 10. Have you tested your idea in real life?
The voltage gain maybe 1 (voltage buffer). But the current gain in right schematic is 100/0.1ohm=1000x. Is this making chipamp unstable?

Does this kind of "Current Amplifier" suitable for driving ordinary speakers (which is designed for voltage source amplifiers)?
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Old 23rd April 2005, 08:32 AM   #8
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So called " Stasis stage " use floating rails in power stage, not in VAS. With LM .... is this method used in professional active boxes, for example in one small box from firm KV2Audio.
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Old 23rd April 2005, 09:28 AM   #9
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Grazie Mauro!

I've been very interested in current drive and varying output impedance with LM chips ever since reading about it on Rod Elliot's site and of course all the hype with FirstWatt. Now here is something detailed to chase!
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Old 23rd April 2005, 12:43 PM   #10
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Various precise statements:
The "stasis" brevet is operational after 1978 and is in use by Threshold.
My scheme has not commercial intentions and then it is can make a will.
Datum that the "Stasis" idea is not mine, and it is broadly divulged by Pass, not time perderoes to describe it in the detail. The circuit that I have proposeded is not a "normal" buffer to unit gain voltage, but a current/current converter with input connected directly to the exit.
the Voltage amplifier that it connects to the input furnishes a tide directly to the load, but for effect of the bridge it "sees" a load with 1000 times + tall (our case) in comparison with that reality.
Datum that the circuit of tide is external a the Neg. feedback of the voltage driver amplifier, produces to all the effects the "stasis" mechanism ( is not a hypothesis,it is a certainty ). If they measure the distortion of the circuit discover that is equivalent perfectly to that of the Voltage stadium. The fact that Threshold has always used this technique with "current mirrors" and with discrete components, change the medium. If then some shows me that get it same effects of "Stasis" without respect from it the parameters, means that have invented a new system and I am able patent it.
I don't know other applications as this ( Threshold to depart ) but even for effect of the brevet, I doubt that other builders have used it.
For what concerns the doubts concern to the stability, for fortune sees that some expert takes part in explain ( better than my)
the dynamics of operation. I never don't expose circuits that doesn't work well, because this circuits have been make a will in laboratory on real prototypes. If have good bases of electronics, discover that my nets never are not banal, and itis able help you even for Your projects. in this particular case, the stability is guaranteed by R8 and C1, that I am not optional, but it creates of the pole/zero conjugated with the rest of the bridge and make it stable. this technique is second-hand ( a few ) to stabilize "on external" the no-compensateds OPamp, as LM3875 and LM3886 ( still more unstable ) and the point of work is calibrated on the prototype.

For the beginners:
For Voltage stadium I intend an amplifier to discrete or OPamp that produces the necessary voltage-gain to drive the loudspeakers ( es. 1Vin > 20Vout). If they connect my buffer to your pre-amplifier, works all well but they don't succeed to have a greater power of 5-10W. to get an amplifier in "stasis" has to build an pre-amplifier In degree to produce a voltage swing about 30Vpp and Zout<10ohm, capable of output current furnish with at least 20-50mA.
It may use a tracking circuit as what I have proposeded or other technology, as the valves circuits, or the Mosfet circuits of Pass. The output distortion and the general sound are that of the driver.

Ciao

Mauro
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