reducing the signal to the PI on a 2204

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V2
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Re: reducing the signal to the PI on a 2204

Post by V2 »

I'm going to return to the original question in the first post. That is, would it help to add a resistor between the coupling cap and the PI? The answer is yes. Such a series R will form a voltage divider with the 1M grid leak in the PI. So if you add 1M series R, you'd drop the signal in half. The series R could be installed right on the wiper of the MV pot too (that is, it need not be added after the coupling cap. of course, adding 1M series resistance might have other effects (e.g., more resistor noise), but it's worth trying...
pdf64
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Re: reducing the signal to the PI on a 2204

Post by pdf64 »

V2 wrote:would it help to add a resistor between the coupling cap and the PI? The answer is yes. Such a series R will form a voltage divider with the 1M grid leak in the PI. So if you add 1M series R, you'd drop the signal in half
The LTP grid reference resistors are subject to local and global negative feedback; this acts to increase the effective input impedance (assuming linear conditions), maybe around x2 to x3.
So the LTP input impedance is likely to be >2M ohms.
At high frequencies, stray capacitance may act to bypass series resistors, resulting in a treble peaking circuit. With high value resistances, these high frequencies may be within the audio range.

When the LTP is overdriven, its input impedance is likely to fall.
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V2
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Re: reducing the signal to the PI on a 2204

Post by V2 »

pdf64 wrote:
V2 wrote:would it help to add a resistor between the coupling cap and the PI? The answer is yes. Such a series R will form a voltage divider with the 1M grid leak in the PI. So if you add 1M series R, you'd drop the signal in half
The LTP grid reference resistors are subject to local and global negative feedback; this acts to increase the effective input impedance (assuming linear conditions), maybe around x2 to x3.
So the LTP input impedance is likely to be >2M ohms.
At high frequencies, stray capacitance may act to bypass series resistors, resulting in a treble peaking circuit. With high value resistances, these high frequencies may be within the audio range.

When the LTP is overdriven, its input impedance is likely to fall.
Yep, and you can use those aspects of the LTPI to good effect (well, to some ears). If the usual 1M grid leaks are replaces with 470k Rs, you'll have an input impedance of around 1M. Install a pot as a variable series resistor to see if anything sounds good.
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jaysg
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Re: reducing the signal to the PI on a 2204

Post by jaysg »

Do you have a load box? Put it in parallel with whatever cab you have...same impedance. That's -3dB, or another way, your 50W amp is now a 25W. Alternately, JJ 6V6S and adjust the Z appropriately.
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