At 500 mV, no amount of gain is going to help your transistor. There
simply isn't enough voltage to bias the transistor on. You need to
change the rolloff frequency. Changing the value of the capacitor or
resistor will do that.
I couldn't figure out why I wanted a high pass filter or capacitive
coupling so I just simplified it with a level shifter. Maybe there is
a reason but no matter what, this is a great filter. It's one of my
favorites, and I get some really neat sounds with a very low
frequency.
Dave
--- In cgs_synth@yahoogroups.com, Anthony Rolando <goldenechos@...>
wrote:
is almost no amplitude. I measured the frequency and mine really
starts to lose amplitude at 20hz and is less than 500mv by 17hz.
suggested) tonight.
happening on my board. I have hard time believing that Dave and I are
the only people that have had this issue... Maybe there is something
about the way solder flows in North Carolina!
simply isn't enough voltage to bias the transistor on. You need to
change the rolloff frequency. Changing the value of the capacitor or
resistor will do that.
I couldn't figure out why I wanted a high pass filter or capacitive
coupling so I just simplified it with a level shifter. Maybe there is
a reason but no matter what, this is a great filter. It's one of my
favorites, and I get some really neat sounds with a very low
frequency.
Dave
--- In cgs_synth@yahoogroups.com, Anthony Rolando <goldenechos@...>
wrote:
> Dave, your description makes alot of sense. When I look at what ishappening on my scope I am seeing the VCO hi-pass filtered until there
is almost no amplitude. I measured the frequency and mine really
starts to lose amplitude at 20hz and is less than 500mv by 17hz.
>pass filter, right.
> The 100n cap and the 100k series R and 100k R to gnd form a high-
>solve the problem. Dave I like your fix, it is simple, works.
> Perhaps changing the value of the cap and or resistor(s) would also
>the culprit. I am going to try changing the series R to 47k (as he
> Ken has suggested that the variation in gain on the transistor is
suggested) tonight.
>circuit working, but I am still just curious about how this was
> IN ANY CASE, THANK YOU everybody for your insight. I have the
happening on my board. I have hard time believing that Dave and I are
the only people that have had this issue... Maybe there is something
about the way solder flows in North Carolina!
>so that the
> Tony
> To: cgs_synth@yahoogroups.com
> From: davebr@...
> Date: Mon, 8 Oct 2007 04:23:37 +0000
> Subject: [cgs_synth] Re: Bi N Tic question
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> It'a a high pass filter and eventually it will roll off
>15
> transistor is not ever biased on. Mine rolled off somewhere below
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> Hz. At 5 Hz the drive was 400 mV, well below Vbe required to bias
>OneCare!
> transistor. That's why I changed to a level shifter by dividing the
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> signal and clamping it to ground. Fewer parts and works to 'DC'.
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> _________________________________________________________________
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