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cgs30 bandpass filter missing noticable resonance?

cgs30 bandpass filter missing noticable resonance?

2007-10-11 by prophei

hello all,

i just put together my first cgs30 bandpass filter (rev2), and can't seem to notice any
resonance at all. i can sweep it just fine, and there is maybe a "slight" ring in there
somewhere... but the resonance pot does nothing.

having built more complicated modules before, i immediately checked my soldering,
followed the schematic...etc to look for obvious errors. i haven't found any yet. i have also
tried 2 different pots for the resonance control, no change.

the parts list on ken's page calls out 2x 100n caps as being used, yet i only see a few 10uf
electrolitics and 22n's noted on my pcb board. there is no more room for caps on here, so
what were those called out for??

also, i am assuming that since i was not setting this up for using the "cx" cap, i just leave
that empty... and i also assume that i am supposed to add a jumper where it appears to be
indicated with 3 boxed symbols next to the beads/elec caps on the lower left side of the
pcb.

any help is greatly appreciated!

-prophei

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-11 by sasami@hotkey.net.au

>the parts list on ken's page calls out 2x 100n caps as being used, yet i
only see a few 10uf
>electrolitics and 22n's noted on my pcb board. there is no more room for
caps on here, so
>what were those called out for??

The positions for the two 100n caps are near the lower chip, to its left,
when the pots are to the right of the PCB. They are power rail decoupling.

>also, i am assuming that since i was not setting this up for using the "cx"
cap, i just leave that empty

Correct. You will notice it has a short on the back of the PCB. You would
need to cut the track if you were to install CX. It's just an option.

... and i also assume that i am supposed to add a jumper where it appears to be
>indicated with 3 boxed symbols next to the beads/elec caps on the lower
left side of the
>pcb.

There is a single jumper just below the unicorn's head.
The three "boxed" pads in the lower left are for when stacking PCBS
together, and can safely be ignored.

You do have some sort of construction error, or less likely, a part failure.
Resonance definitely works.

Ken
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-11 by Dave Kendall

Hi Prophei.

Maybe check the 4K7 resistor that goes between "RE" on the schemo and
GND?.
Yesterday I just tested an orange REV1 board using a 5K trimmer there
to see what happened... :-)
It worked fine - with a trimmer value less than around 2.7K the
resonance really got intense, but with an increasing (unpleasant)
highpass filter effect, as the resistance was lowered.
cheers,

Dave
Show quoted textHide quoted text
On 11 Oct 2007, at 14:51, prophei wrote:

> hello all,
>
> i just put together my first cgs30 bandpass filter (rev2), and can't
> seem to notice any
> resonance at all. i can sweep it just fine, and there is maybe a
> "slight" ring in there
> somewhere... but the resonance pot does nothing.
>
> having built more complicated modules before, i immediately checked
> my soldering,
> followed the schematic...etc to look for obvious errors. i haven't
> found any yet. i have also
> tried 2 different pots for the resonance control, no change.
>
> the parts list on ken's page calls out 2x 100n caps as being used,
> yet i only see a few 10uf
> electrolitics and 22n's noted on my pcb board. there is no more room
> for caps on here, so
> what were those called out for??
>
> also, i am assuming that since i was not setting this up for using
> the "cx" cap, i just leave
> that empty... and i also assume that i am supposed to add a jumper
> where it appears to be
> indicated with 3 boxed symbols next to the beads/elec caps on the
> lower left side of the
> pcb.
>
> any help is greatly appreciated!
>
> -prophei
>
>
>
>

[Non-text portions of this message have been removed]

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-11 by Jason Proctor

>You do have some sort of construction error, or less likely, a part failure.
>Resonance definitely works.

i can vouch for the bandpass filter PCB. i recently built 4 of them
100% stock with no mods and then stacked them in a parallel config as
described on the module page. i didn't do it quite as Ken suggests
but everything worked perfectly first time. the resonance isn't
extreme, but it definitely *is* there.



--
Jase is doing the AIDS ride - to sponsor him visit
http://www.aidslifecycle.org/1674

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-12 by prophei

> The positions for the two 100n caps are near the lower chip, to its left,
> when the pots are to the right of the PCB. They are power rail decoupling.

these are 2 electrolytics labeled as 10uf, unless you are referring to the 2 beads?


> There is a single jumper just below the unicorn's head.

i see no unicorn, are we looking at the same board revision?



> You do have some sort of construction error, or less likely, a part failure.
> Resonance definitely works.

i believe you about the board, this is driving me crazy trying to find =D
i will keep trying!

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-12 by prophei

>
> Hi Prophei.
>
> Maybe check the 4K7 resistor that goes between "RE" on the schemo and
> GND?.
> Yesterday I just tested an orange REV1 board using a 5K trimmer there
> to see what happened... :-)
> It worked fine - with a trimmer value less than around 2.7K the
> resonance really got intense, but with an increasing (unpleasant)
> highpass filter effect, as the resistance was lowered.
> cheers,
>
> Dave


thanks dave! this helped quite a bit. i had to go down to a 1.2k to really get anything
obvious, which is weird, but it is helping...

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-12 by sasami@hotkey.net.au

>i see no unicorn, are we looking at the same board revision?

No.

The very latest has the 100nF capacitors mounted on the back of the PCB.
There are pairs of little square pads. They are designed for surface mount
100n caps, though there is nothing to stop you attaching regular ones to them.

The only link on the board is right next to the very faint bandpass symbol
(the squiggly lines in the rectangle).

That probably makes a lot more sense to you now!

Ken
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-12 by prophei

ohhhhhh, now i get it!!

i saw those pads and wondered if they were for surface mount, but never read any
information referring to your use of them.
that was confusing! do any of your online materials for this filter mention any of this?
maybe you might want to add this =)

i will mount them there and retest tonight... much appreciate the help! i am sure this filter
will sound fine once those caps are properly added...

-michael
Show quoted textHide quoted text
--- In cgs_synth@yahoogroups.com, sasami@... wrote:
>
> >i see no unicorn, are we looking at the same board revision?
>
> No.
>
> The very latest has the 100nF capacitors mounted on the back of the PCB.
> There are pairs of little square pads. They are designed for surface mount
> 100n caps, though there is nothing to stop you attaching regular ones to them.
>
> The only link on the board is right next to the very faint bandpass symbol
> (the squiggly lines in the rectangle).
>
> That probably makes a lot more sense to you now!
>
> Ken
> _______________________________________________________________________
> Ken Stone sasami@...
> Modular Synth PCBs for sale <http://www.cgs.synth.net/>
> Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>

Re: cgs30 bandpass filter missing noticable resonance?

2007-10-12 by sasami@hotkey.net.au

>i saw those pads and wondered if they were for surface mount, but never
read any
>information referring to your use of them.
>that was confusing! do any of your online materials for this filter mention
any of this?

Some do, but I think I forgot to updated the bandpass :(

Ken
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

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