Dave, your description makes alot of sense. When I look at what is happening 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.
The 100n cap and the 100k series R and 100k R to gnd form a high-pass filter, right.
Perhaps changing the value of the cap and or resistor(s) would also solve the problem. Dave I like your fix, it is simple, works.
Ken has suggested that the variation in gain on the transistor is the culprit. I am going to try changing the series R to 47k (as he suggested) tonight.
IN ANY CASE, THANK YOU everybody for your insight. I have the circuit working, but I am still just curious about how this was 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!
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
It'a a high pass filter and eventually it will roll off so that the
transistor is not ever biased on. Mine rolled off somewhere below 15
Hz. At 5 Hz the drive was 400 mV, well below Vbe required to bias the
transistor. That's why I changed to a level shifter by dividing the
signal and clamping it to ground. Fewer parts and works to 'DC'.
Dave
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[Non-text portions of this message have been removed]
The 100n cap and the 100k series R and 100k R to gnd form a high-pass filter, right.
Perhaps changing the value of the cap and or resistor(s) would also solve the problem. Dave I like your fix, it is simple, works.
Ken has suggested that the variation in gain on the transistor is the culprit. I am going to try changing the series R to 47k (as he suggested) tonight.
IN ANY CASE, THANK YOU everybody for your insight. I have the circuit working, but I am still just curious about how this was 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!
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
It'a a high pass filter and eventually it will roll off so that the
transistor is not ever biased on. Mine rolled off somewhere below 15
Hz. At 5 Hz the drive was 400 mV, well below Vbe required to bias the
transistor. That's why I changed to a level shifter by dividing the
signal and clamping it to ground. Fewer parts and works to 'DC'.
Dave
_________________________________________________________________
Boo! Scare away worms, viruses and so much more! Try Windows Live OneCare!
http://onecare.live.com/standard/en-us/purchase/trial.aspx?s_cid=wl_hotmailnews
[Non-text portions of this message have been removed]