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Old 9th October 2012, 09:38 PM   #51
sreten is offline sreten  United Kingdom
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Hi,

I'm completely bored with the OP touting himself
as the arbiter regarding the original question.

rgds, sreten.
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Old 10th October 2012, 02:51 AM   #52
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Quote:
Originally Posted by sreten View Post
Hi, I'm completely bored with the OP touting himself
as the arbiter regarding the original question. rgds, sreten.
Me too! However, a schematic from phase_accurate would liven up matters considerably.
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Old 10th October 2012, 09:00 AM   #53
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I first tried simulating the classsic circuit like it is shown on page 19 of the following presentation:

http://www.electronics.dit.ie/staff/...Amplifiers.pdf

This one is really hard to get "working" in simulation (getting a good operation point in particular) and taking into account that such things are usually even trickier to get right in practice I tried a variation of the one shown on page 21. This one sets the operation point itself. The prerequisite is that the two transistors are as similar as possible (like two from the same batch or even two out of an array) and that they are thermally coupled.
In order to get it working properly the input has to be biased with a DC voltage as high as the peak voltage of the driving signal. This way it is guaranteed that you never have a negative input voltage. Instead of subtracting the offset at the output I'd suggest to use AC coupling since you would have to get rid of the fundamental frequency anyway (at least to some degree).

Regards

Charles
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Old 10th October 2012, 10:08 AM   #54
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Well, I have some BC546B and BC546C (and others) and a handy TL082 (and others). The two transistors could either be shrink wrapped together or both of them thermal glued to the op-amp, whichever method looks better to you.

It seems like an additional stereo op-amp is needed for buffer+adder. Is that right?
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Old 10th October 2012, 11:21 AM   #55
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The transistors need to be glued to each other not the transistors to the OP-AMPs.

Yes, a buffer would definitely be good. But you will need a lowpass anyway so this will act as your buffer.

Regards

Charles
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Old 13th October 2012, 05:38 AM   #56
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Bellow is a circuit I have on a breadboard.

It performs the rectifying integrator function mentioned in the Philips paper. disconnecting the capacitor gives it a plain full wave rectifier characteristic.
rcw

Last edited by rcw666; 13th October 2012 at 05:38 AM. Reason: no image
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Old 13th October 2012, 05:45 AM   #57
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Hopefully image..
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Old 15th October 2012, 10:49 PM   #58
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@rcw666
Thank you very much. I have TL082, TL062. Are they suitable?

@Elvee
Have finally sourced all of the fets except the "A" range.
Edit: RF radio parts? Aha! Just bought the "A" range from a radio repair shop in Scotland.
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Old 15th October 2012, 11:50 PM   #59
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This is the sort of thing I envisage for a stereo system, it uses a single TL 074 quad op amp.
rcw
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Old 19th October 2012, 02:28 AM   #60
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Ah, well, it looks good, but I'm sorry to say that it doesn't look quite doable with nondescript component values.
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