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In Reply to: RE: You're making a bigger mistake posted by Tre' on January 23, 2015 at 07:55:51
that is what I measured at the lead after the input coupling cap. :)
Follow Ups:
Yes. I'm thinking that is the value of the resistor to ground that follows the coupling capacitor.
I don't think the effective impedance to ground of the first transistor can be measured with a ohm meter and I'm thinking that impedance would only show up once the amplifier is turned on and current is flowing through the first transistor.
If I'm right, that would answer why they used such a large input coupling capacitor.
You could go about this empirically. If you replace the 330uf cap with a 1uf cap and then play the amp. Use a signal generator and measure the -3db point.
You can then do the math to calculate the impedance.
If, as an example, with a 1uf cap you find the -3db point to be 159Hz then the input impedance is 1000 ohms.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
when I took the measurement I measured from the output of the input coupling cap to ground. So that where I got the 33kohms. I'm glad I came here for help! :)
connected to and after the input coupling cap of 330uF, followed by a cap and another resistor both the cap and resistor are connected to ground. I can't see the values due to them being very small in size. I will have to get a magnifying glass to see them.
I will try my best to draw out a schematic of what I see of the input with the Long tail. This may help me do the formula for this to get a better idea. I have seen a site that had that equation for working out the Re and what size cap to use.
here's the site below.
with the other cap and resistor that is connected to ground. Sorry for not being more clear on my description.
"Sorry for not being more clear on my description."
That's OK. The bottom line, the input impedance (as explained in your link) is complicated.
That's why just simply testing it with a 1uf cap might be the easy way to go.
Once the input impedance is calculated, you can then use whatever value cap gives you the -3db point you want.
A -3db point of 2Hz will give you 20Hz with no amplitude loss or phase shift.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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