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Is R10 used for setting the gain for the Sympatico? If so, can a value be suggested to set the amp gain to 15db?
Regards,
GEC
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Are you needing more or less gain than stock?
As in stock form the gain is 20db with balanced input and 14db single ended.
You can only use R10 to adjust the gain upward.
Cheers!
Russ
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Thanks Russ. I didn't know what the stock gain was. My goal is to match the voltage gain of the Sympatico to the gain of a Pass F5, which is listed as 15.3db. I will be using the Sympatico single-ended, so the stock gain may be close enough. If I need to boost the gain a little, how do I calculate for R10?
Geo
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Ok, to be accurate the stock gain is 11X(about 21db) balanced or about 6.5X(about 14.8db) single ended. So you will be very close to 15db. :)
Adjusting R10 will multiply the voltage gain by a factor of (R9+R11)/R10.
Cheers!
Russ
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Russ, one more question about the gain. Is the stock gain set with R10 open, or a value of 2K? I ask because the parts list says R10 can be either open or 2K.
thanks,
GEC
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Using the 2K resistor increases the gain by 6db.
Cheers!
Russ
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I powered both my SYMPs and everything seems to be working. I measured the voltages then tried with a speaker connected. Input is single ended with IN- shorted to IG. However, my voltage measurements indicate a gain of 26.6dB with an R10 value of 2k (0.126V in and 2.7V out). Can this be right? My understanding from below is that the gain should be 20.8dB. I seem to be off by a value of thereabout 6dB (very suspicious!) Further, I calculate (R9+R11)/R10 to be (1+1)/2 = 1. Is there another multiplicative gain component leading to an overall gain increase of 2 (i.e. 6dB)? Finally, the BOM says R10 supplied with the kit is rated at 0.6W. It looks more like a 0.25W resistor, no? Edited by user Monday, April 9, 2012 7:16:11 PM(UTC)
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.25w is fine for that position. However, the Phoenix resistor supplied is actually a .6W part.
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Brian or Russ,
would it be possible to answer/confirm my other points?
Martin
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I am not sure what answer you are expecting. :) There are two points where gain is introduced - at the instrumentation amp and at the fully differential amp. Your measurements sound correct based on the values you state.
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Based on what you previously wrote, I was expecting to measure an overall gain of 11x with a single ended input and R10 = 2k. But my measurements indicate a gain close to 22x.
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You have what you have, what do you want? I am not sure exactly what values you are using. I need to know more than R10. :)
In any case this conversation seems a bit esoteric since you know what you actual gain is. Adjust it as necessary.
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I was just trying to relate what I measured to the transfer function of the circuit in the schematic. Anyways, I figured it out with help from Wikipedia ("Instrumentation Amplifier"). The gain is (1+(R9+R11)/R10))*R3/R2. All my values are naturally as per the SYMP BOM, so I get 22x. No need to change R10, that's the gain I need.
I'm now a happy camper :)
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