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Old 30th June 2013, 04:09 PM   #41
dadod is offline dadod  Croatia
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This 10k step volume pot could be used as P1.
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Old 30th June 2013, 04:13 PM   #42
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Quote:
Originally Posted by mcd99uk View Post
Only thing I can add is that it is worth considering adding a low pass filter to the servo output. Another defence against high frequency nasties getting through the servo.
This servo is low pass filter.
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Old 30th June 2013, 04:19 PM   #43
mcd99uk is offline mcd99uk  United Kingdom
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This servo is low pass filter.
But does not block very high frequencies. They can still get through. Look at sallen key (I think that's the right type) filters. At high enough frequencies they start to pass the signal again.

Its only two extra components, split the 10k in to two 5ks and add a cap to ground from the middle.

Last edited by mcd99uk; 30th June 2013 at 04:23 PM.
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Old 30th June 2013, 04:32 PM   #44
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Quote:
Originally Posted by mcd99uk View Post
Its only two extra components, split the 10k in to two 5ks and add a cap to ground from the middle.
+1...I would do the same for servo input...filter any noise on the amplifier output
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Old 30th June 2013, 07:39 PM   #45
dadod is offline dadod  Croatia
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Quote:
Originally Posted by mcd99uk View Post
But does not block very high frequencies. They can still get through. Look at sallen key (I think that's the right type) filters. At high enough frequencies they start to pass the signal again.

Its only two extra components, split the 10k in to two 5ks and add a cap to ground from the middle.
What 10k resistor you are tallking about? If you mean P1 that is volume control and can't be split.
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Old 30th June 2013, 07:47 PM   #46
mcd99uk is offline mcd99uk  United Kingdom
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Originally Posted by dadod View Post
What 10k resistor you are tallking about? If you mean P1 that is volume control and can't be split.
P1 looks like the output of the DC servo. I may be being a little stupid but I'm not following how this is the volume control. With the distortion feedback I could see how it was the a gain control but this is a DC servo. Please could you explain the function of P1 to someone lacking in understanding.
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Old 30th June 2013, 09:00 PM   #47
dadod is offline dadod  Croatia
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Quote:
Originally Posted by mcd99uk View Post
P1 looks like the output of the DC servo. I may be being a little stupid but I'm not following how this is the volume control. With the distortion feedback I could see how it was the a gain control but this is a DC servo. Please could you explain the function of P1 to someone lacking in understanding.
Without DC servo P1 is connected to the ground and ratio of P1/R9 define the gain of the gain stage(current conveyor). So to maintain that when DC servo is connected it's important that servo opamp has low output impedance to play as the ground.
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Old 30th June 2013, 09:16 PM   #48
mcd99uk is offline mcd99uk  United Kingdom
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Thank you, for the explanation.

Would you be kind enough to post an .asc file of this? Looks interesting and I'd like to understand its function better.
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Old 1st July 2013, 05:49 AM   #49
dadod is offline dadod  Croatia
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Thank you, for the explanation.

Would you be kind enough to post an .asc file of this? Looks interesting and I'd like to understand its function better.
You can simulate with different P1 values, 10k is max, and you'll see haw the gain changes.
If you connect P1 to the ground instead to the DC servo output, DC servo will be off.
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Old 1st July 2013, 07:25 AM   #50
mcd99uk is offline mcd99uk  United Kingdom
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Originally Posted by dadod View Post
You can simulate with different P1 values, 10k is max, and you'll see haw the gain changes.
If you connect P1 to the ground instead to the DC servo output, DC servo will be off.
Thank you, this will be interesting!
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