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Old 24th May 2011, 05:27 PM   #1
Elvee is offline Elvee  Belgium
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Default ♫♪ My little cheap Circlophoneİ ♫♪

Here is something different for a change:

It is a small, unassuming amplifier project, but with some unusual features:
It combines a circlo output topology with an active bias servo.

The servo stabilizes the quiescent current, but it goes further: it actively controls the output stage so that both sides always remain active in a "warm" class AB, having most of the attributes of the full class A, including a complete absence of crossover artifacts.

It is extremely easy to build, offers excellent performance even with 2N3055's, requires no adjustment, no matching, no thermal compensation and yet has a rock-solid thermal stability.

It is also incredibly healthy, and behaves gracefully, even with loads lower than 2R.

In short, a nice little amplifier, not in the top-class, but with excellent all round performances.

Meet the Circlophoneİ!!!
Attached Images
File Type: gif TheCirclophone.gif (25.7 KB, 17798 views)
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Old 24th May 2011, 06:20 PM   #2
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Don't mind me asz-king, but what does the "Circlo" part refer to ?
It doesn't count how one deals with winning, but how to handle a loss (İ DjT)
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Old 24th May 2011, 07:16 PM   #3
Elvee is offline Elvee  Belgium
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Originally Posted by jacco vermeulen View Post
Don't mind me asz-king, but what does the "Circlo" part refer to ?
It refers to the same-sex output transistors. It doesn't include the folklore of the original Circlotron, the floating supplies: it resembles more later versions, by Philips f.e., because there is no output transformer to worry about.
The drive is similar to that of a circlotron, and the power supplies and transistors could be rearranged in a more familiar order, but there is no advantage to be gained, rather the contrary.
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Old 25th May 2011, 12:41 AM   #4
Bigun is offline Bigun  Canada
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I likes it very much !
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 25th May 2011, 07:36 AM   #5
Elvee is offline Elvee  Belgium
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Here are some waveforms illustrating the operation and performances of the Circlophoneİ:

First, the output voltage together with the collectors currents of the output transistors: one can see that Ic never falls below ~75mA, and that the crossing current (Iq) is ~150mA (warm class AB).
Note that the "idle" transistor remains fully active: the active bias servo encompasses the whole amplifier from the input pair, and keeps all the transistors always active in a linear mode.
Next is the response to a 16V/10KHz squarewave on an infinite load impedance, followed by the same signal on a 3Ω load.
Then, there is a 16V/50KHz triangle wave, again on infinite and 3Ω loads.

Note: these pictures have been made with actual 2N3055's as output devices
Attached Images
File Type: gif CircloWFM.GIF (48.0 KB, 16480 views)
File Type: jpg 10KHzInfini[1].JPG (297.0 KB, 13471 views)
File Type: jpg 10KHz3ohm[1].JPG (338.6 KB, 15974 views)
File Type: jpg 50KHzInfini[1].JPG (327.4 KB, 14381 views)
File Type: jpg 50KHz3ohm[1].JPG (242.9 KB, 1237 views)
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Old 25th May 2011, 07:57 AM   #6
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Thumbs up goooooood

Originally Posted by Elvee View Post
Here are some waveforms

regards, Pawel
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Old 25th May 2011, 02:41 PM   #7
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It is nice to see some different topology. Nice!
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Old 26th May 2011, 08:54 AM   #8
Elvee is offline Elvee  Belgium
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Here are some additional characteristics and information:

First the clipping behaviour, see picture.

It is shown with 20V supplies, the clipping occurs to within <1.5V of either rail.
It is a simulation, but the real life waveform is strictly identical.

The supply voltage can range from 15 to 40V with no or minor modifications:
The current through R21 should ideally be kept between 1 and 1.5mA, and the total voltage of the zeners should approximately match the supply voltage.

The input resistance is ~10K, but the source impedance is preferably kept below 1K, because of the base current modulation caused by the bias servo.

Output impedance is <3mΩ @1KHz
THD @1KHz and 0.9*Vmax is <0.005%
Full power bandwidth is >100KHz
Slew rate: positive ~24V/µs, negative ~20V/µs

Here are some pics of one of the prototype:
Attached Images
File Type: gif Clipping.GIF (39.7 KB, 1770 views)
File Type: jpg CircloPic1.JPG (88.3 KB, 8201 views)
File Type: jpg Circlopic2.JPG (132.8 KB, 3658 views)
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Old 26th May 2011, 09:41 AM   #9
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Looks very nice. Are you planning a PCB?
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Old 26th May 2011, 11:02 AM   #10
parb is offline parb  United States
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It looks interesting!
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