What's the purpose of this resistor?
Moderators: pompeiisneaks, Colossal
What's the purpose of this resistor?
This schem is of a VHT Deliverance output power amp, and I'm wondering what the boxed 2.2K resistor is doing there. My theory is that it allows the presence control to work normally (as it would in a LTP), but prevents the 470nF from having the secondary effect of fully bypassing that stage driving the PI. Does that sounds right? I'm pretty sure the overall feedback ratio is set by the the 100K resistor and other 2.2K cathode resistor, correct?[/i]
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Re: What's the purpose of this resistor?
That resistor is there to establish a limit for the presence and resonance controls. If P9 is turned all the way so it is 0 ohms, then I suspect there might be some oscillations. I know this from experience. I think what happens is that the filter networks interact too much and due to phase shift (or maybe dilithium crystals breaking down, lol), it starts to become positive phase shift. Also, without that resistor there, and again with P9 at 0 ohms, C30 would start to act as a bypass capacitor for V5.
Or something, I guess.
Or something, I guess.
What?
Re: What's the purpose of this resistor?
It could also be that the designer liked red striped parts. 
What?
Re: What's the purpose of this resistor?
Haha, I'm sick of "2's" myself! Always finding excuses to use 39K's for some reason...
Re: What's the purpose of this resistor?
Oops, I didn't see that you'd actually tried to answer my question as well! Thanks, Jana!Jana wrote:That resistor is there to establish a limit for the presence and resonance controls. If P9 is turned all the way so it is 0 ohms, then I suspect there might be some oscillations. I know this from experience. I think what happens is that the filter networks interact too much and due to phase shift (or maybe dilithium crystals breaking down, lol), it starts to become positive phase shift. Also, without that resistor there, and again with P9 at 0 ohms, C30 would start to act as a bypass capacitor for V5.
Or something, I guess.
Yes the latter is what I was thinking, but I could see it limiting the controls as well. You'd think the amp should be stable without it, but 2.2K does seem like enough to do something (considering a traditional presence is only 5K).
Re: What's the purpose of this resistor?
Could you post the rest of the schematic?