I feel I have a much better understanding of the NFB after reading to the article on www.aikenamps.com, (under tech info, advanced) but I'd like to confirm one aspect:
It appears that for determining the global negative feedback, you ignore the cap and simple use the value of the presence pot to determine the value of Ri (shunt value). So if there's a shunt resistor in parallel with the presence pot, I assume that the value of Ri is the paraellel resistance of the pot and the resistor? For example, if Rs=1K and the pot is 2K, the Ri value is 667 ohms for the purpose of calculating feedback reduction gain? This would seem to be the case, but I'd like to get concensus.
OB
NFB Calculations
Moderators: pompeiisneaks, Colossal
NFB Calculations
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Re: NFB Calculations
I am by no means an expert but I believe you use the ratio of the dropping and feedback resistor and ignore the pot for the ratio calc. In effect all the pot is doing is bringing the dropping resistor into play making the NFB variable.
Someone please correct me if I am wrong
Someone please correct me if I am wrong
Re: NFB Calculations
Well that's the essesnce of my question... but here's why I think you are wrong: There are numerous implemenations (including the example on the Aikenamps site) where there is ONLY a pot, no dropping resistor. In Aiken's example, he uses the pot value to calculate the ratio. So to me it would make sense that if you add a dropping resistor, you need to consider the pot in paraellel. However, I've seen some posts on this board which would suggest the pot is being ignored.
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Re: NFB Calculations
Check your pm!
Re: NFB Calculations
Heres how I look at the tail resistor/pot/cap part of the equation:
To figure NFB depends on how your presence pot is wired. If it is in parallel to the tail resistor then you have to figure the total R first. If it is wired like a variable resistor in series with the cap and both are across the tail resistor, then you just use the tail resistor. If the pot is doing double duty as the tail R and with the cap off the wiper, you use the pot value for your calc. In all cases you can probably ignore the cap in the calculations.
To figure NFB depends on how your presence pot is wired. If it is in parallel to the tail resistor then you have to figure the total R first. If it is wired like a variable resistor in series with the cap and both are across the tail resistor, then you just use the tail resistor. If the pot is doing double duty as the tail R and with the cap off the wiper, you use the pot value for your calc. In all cases you can probably ignore the cap in the calculations.
Re: NFB Calculations
yes... all is clear now. Thank you gentlemen!
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html