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Old 30th May 2011, 10:48 PM   #31
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Wavebourn: But for C10 there are no caps in the signal path. Nor a transformer or tube in sight. I do not believe this design was to be used s a "classic" guitar amp.

Tekko: I understand what was ment by a Zobel, but it is Elvees design and the designer should make that addition.

To the design of a board: I was thinking of using the DIN 100x160 mm board. Anybody would like to comment on a pin-out for the 64/96 pin connector or any other aspects of the pcb layout?

Cheers, E
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Old 30th May 2011, 11:32 PM   #32
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Can we see more pics of your board?
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Old 30th May 2011, 11:36 PM   #33
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Oh boy oh boy. I've got a couple of these that have just been waiting forever for a new home!
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Old 31st May 2011, 12:05 AM   #34
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Quote:
Originally Posted by mickeymoose View Post
Wavebourn: But for C10 there are no caps in the signal path. Nor a transformer or tube in sight. I do not believe this design was to be used s a "classic" guitar amp.
Actually, I've asked the author. Your belief is irrelevant, because the question is regarding C1.
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Old 31st May 2011, 12:37 AM   #35
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Wavebourn: Enlighten us. I did not find your question about C1, or an answer to it, on this thread. Also, I did not state a belief (relevant, or not), I believe. E
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Old 31st May 2011, 12:58 AM   #36
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Quote:
Originally Posted by mickeymoose View Post
Wavebourn: Enlighten us. I did not find your question about C1, or an answer to it, on this thread. Also, I did not state a belief (relevant, or not), I believe. E
I believe the author knows what I was asking about. I did not ask you about classic guitar amps, and I did not ask silly questions about what is in the signal path.

Here is again what I asked:

Quote:
Originally Posted by Wavebourn View Post
Very nice pictures, but what about dynamic characteristics, like small signal distortions right after huge long impulses?
According to my own experience, servo in audio power amplifiers works best when it is used to correct small deviations from design center values, only and only when needed, and it have to be with as minimal as possible 2'nd order non-linearity. Otherwise envelope rectification causes modulation of working point that causes dynamic distortions that are tricky, because they cause distortions of music, but hard to spot on static measurements.
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Old 31st May 2011, 07:33 AM   #37
Zero D is offline Zero D  United Kingdom
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Lightbulb Servos

@ Wavebourn

Quote:
Otherwise envelope rectification causes modulation of working point that causes dynamic distortions that are tricky, because they cause distortions of music, but hard to spot on static measurements.
I was told some time back by someone "Skilled in the art" that servos are no good for audio. In particular, it can mess up the bass. What you said seems inline with his investigations & testing.
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Old 31st May 2011, 08:21 AM   #38
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by mickeymoose View Post
Elvee: It is your design. Show me where you would implement a Zobel so I can include it on the pcb.
Here is a modified version of the schematic.

Quote:
Can we see more pics of your board?
Here they are, plus pics of another prototype.
Note that with the ~10cm of wiring between the heatsink and the board, the transient waveforms are a shade less immaculate than the ones shown for the other prototype (they remain excellent though).

Quote:
Originally Posted by Wavebourn
Very nice pictures, but what about dynamic characteristics, like small signal distortions right after huge long impulses?

Actually, I've asked the author. Your belief is irrelevant, because the question is regarding C1.
This is a highly valid point, and when designing the bias processor, I had in mind the dismal behaviour of the Visch's topology when subjected to wide dynamic variations. See an example here:
Class B w/o crossover distortion (1975)
The Circlophone shows nothing of the sort, but there might indeed be low level issues hidden somewhere.
I will think about ways of testing this aspect.
And if you have ideas about tests that could be made, both in sim and reality, they are welcome.
Attached Images
File Type: gif TheCirclophone11.GIF (32.3 KB, 1583 views)
File Type: jpg DSCF0010.JPG (300.3 KB, 1552 views)
File Type: jpg DSCF0017.JPG (308.4 KB, 1439 views)
File Type: jpg CircloBis1.JPG (333.1 KB, 4601 views)
File Type: jpg CircloBis2.JPG (317.5 KB, 1362 views)
File Type: jpg CircloBis3.JPG (294.1 KB, 566 views)
File Type: jpg CircloBis4.JPG (343.8 KB, 533 views)
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Old 31st May 2011, 09:20 AM   #39
Elvee is offline Elvee  Belgium
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Warning:

The above schematic including the Zobel network is incorrect, it is based on a non-current version, use the version given in the first post.

The Zobel network is correct however.
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Old 31st May 2011, 09:57 AM   #40
Elvee is offline Elvee  Belgium
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Here is a first test along the lines suggested by Wavebourn.

The signal consists of 9 1KHz cycles at full power and 1 cycle with the amplitude reduced to ~1% of the maximum.

First pic shows the general outlook and the distortion: there is a marginal increase in the THD, but it remains quite gentle (LTspice calculates the THD over the last cycle of the waveform).

The second pic shows the instant of the transition magnified

The third pic is the voltage across the loop filter cap, C3 in this schematic, C1in the first schematic.

This tends to indicate (and is confirmed by the actual tests), that the servo is very clean and well behaved, and cannot be "derailed" by transient conditions the way the Visch is.
Attached Images
File Type: gif CircloDyn1.GIF (60.5 KB, 649 views)
File Type: gif CircloDyn2.GIF (56.2 KB, 459 views)
File Type: gif CircloDyn3.GIF (60.9 KB, 405 views)
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