I just joined this list after someone on the MOTM list posted about a
dual VCA module he built using two CSG65 PCB's. Although I decided
to do a bit more research first before I start asking questions. I'm
not familiar with directly-heated cathodes, and know extremely little
about 1J24B tubes.
If you could post the design you used for your tube VCF, perhaps I
could suggest what might be causing these unwanted oscillations.
In general, when used as amplifiers, pentodes can oscillate when they
do not have sufficient current, or when the plate capacitor and the
load (such as a speaker) form an RC network with a frequency close to
that of another RC network (such as the coupling capacitor and grid
resistors). Perhaps you could try putting different resistors in
series with the output, or changing the value of the plate capacitor,
and see what happens.
As far as impedances are concerned, adding an op-amp stage to the
input and output to provide a relatively high input impedance (eg.
20K) and a relatively low out impedance (eg. 1K), as well as match
voltage levels, might be a good idea. This way the pentode stage of
your VCF will see the same load regardless of what you connect to the
module.
On 3/10/07, kidkrazy58 put forth:
dual VCA module he built using two CSG65 PCB's. Although I decided
to do a bit more research first before I start asking questions. I'm
not familiar with directly-heated cathodes, and know extremely little
about 1J24B tubes.
If you could post the design you used for your tube VCF, perhaps I
could suggest what might be causing these unwanted oscillations.
In general, when used as amplifiers, pentodes can oscillate when they
do not have sufficient current, or when the plate capacitor and the
load (such as a speaker) form an RC network with a frequency close to
that of another RC network (such as the coupling capacitor and grid
resistors). Perhaps you could try putting different resistors in
series with the output, or changing the value of the plate capacitor,
and see what happens.
As far as impedances are concerned, adding an op-amp stage to the
input and output to provide a relatively high input impedance (eg.
20K) and a relatively low out impedance (eg. 1K), as well as match
voltage levels, might be a good idea. This way the pentode stage of
your VCF will see the same load regardless of what you connect to the
module.
On 3/10/07, kidkrazy58 put forth:
>IT makes that rumbly sound when i tune it low, what can i do to fix
>this, maybe something about loading the output, i dont know. And im
>kinda curios about something with the tube modules. Im kinda a novice
>but im wondering like, i know tubes use much difrent impendences as
>solid state. So how does that effect how i need to hook up each module
>like the vco to the vcf and then how do i hook that up to my
>amplifier. How would i figure what the impedences going in and coming
>out need to be on the vcf and the other modules, any one know and it
>allready and could give me a rough estimiate id really be glad thanx.