Cgs synth

just "finished" my rev 1 steiner filter finally. thanks to John
Loffink for the mods and Richard Brewster for the before & after mod
schems.

the filter works fine apart from the resonance, which seems to act as
a volume control! i wired it up so that "full" resonance would be no
resistance between the two pot terminals, seemed the right way... but
with the resonance pot all the way a/clockwise, i get a full strength
signal which sounds like no resonance, and with the pot all the way
clockwise, i get no output at all.

weird eh? the resonance circuit seems simplicity itself...

any help appreciated!

thanks,
j

It is probably a bad joint or construction error, and it is probably
elsewhere in the circuit, not directly in the resonance circuit.

Ken

thanks -- seems like there's not much to go wrong here!

so basically something on the other side of that resonance pot is
sucking harder than the cap & opamp?

i noticed that the output cap is 1uf on the board, but 10uf on the
schematic (the rev1 pre-2010 schem). probably not relevant to the
resonance problem, but otherwise significant?

>i noticed that the output cap is 1uf on the board, but 10uf on the
>schematic (the rev1 pre-2010 schem). probably not relevant to the
>resonance problem, but otherwise significant?

It's pretty insignificant - it just a coupling capacitor. Either is okay.

The resonance control does affect gain - that is its purpose. It sounds like
one of your signal paths (the feedback path?) isn't working.

Ken

>
>>It is probably a bad joint or construction error, and it is probably
>>elsewhere in the circuit, not directly in the resonance circuit.
>>
>>Ken
>>
>>>just "finished" my rev 1 steiner filter finally. thanks to John
>>>Loffink for the mods and Richard Brewster for the before & after mod
>>>schems.
>>>
>>>the filter works fine apart from the resonance, which seems to act as
>>>a volume control! i wired it up so that "full" resonance would be no
>>>resistance between the two pot terminals, seemed the right way... but
>>>with the resonance pot all the way a/clockwise, i get a full strength
>>>signal which sounds like no resonance, and with the pot all the way
>>>clockwise, i get no output at all.
>>>
>>>weird eh? the resonance circuit seems simplicity itself...
>>>
>>>any help appreciated!
>>>
>>>thanks,
>>>j
>>>
>>>
>>>
>>>
>>>------------------------------------
>>>
>>>The CGS Modular Synth home page: http://www.cgs.synth.net/
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>_______________________________________________________________________
>>Ken Stone sasami@... otherunicorn@...
>>Modular Synth PCBs for sale <http://www.cgs.synth.net/>
>>Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>>
>>
>>
>>------------------------------------
>>
>>The CGS Modular Synth home page: http://www.cgs.synth.net/
>>Yahoo! Groups Links
>>
>>
>>
>
>
>------------------------------------
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>Yahoo! Groups Links
>
>
>
>

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

Having trouble with my Bissel lag project.



When I power it up, the TL072 nearest the center of the PCB gets quite warm.



With nothing plugged into the input, the output gives out a kind of triangle wave, kind of like there's a square wave at the input (?)



I haven't yet tested various points for voltage levels... I'm scared to leave it on very long!



Maybe will Harry (Bissel) will come to our synth get-together in a couple weeks (he usually does) and take a look at it for me :)



Drew



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>When I power it up, the TL072 nearest the center of the PCB gets quite warm.

Very very bad.

Sort this out first. TL072 should stay stone cold. Somewhere you have a
power supply error, or the chip is in backwards.

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

> >i noticed that the output cap is 1uf on the board, but 10uf on the
>>schematic (the rev1 pre-2010 schem). probably not relevant to the
>>resonance problem, but otherwise significant?
>
>It's pretty insignificant - it just a coupling capacitor. Either is okay.
>
>The resonance control does affect gain - that is its purpose. It sounds like
>one of your signal paths (the feedback path?) isn't working.

well i'm back trying to sort this out. there really isn't much to go
wrong with the feedback path of this circuit, so i'm wondering --

- if there's a way to wire up the resonance pot wrong?

- if the pinout of the 2N2222 varies with package?

- what the resistance to ground should be at various points - i'm
seeing 3.7k between the wiper of the resonance point and ground.
seems a touch low... the 1k resistor in the path raises this to 4.7k.

i'd like to get this in the rack and mangling stuff -- any help appreciated!

>
>
>> >i noticed that the output cap is 1uf on the board, but 10uf on the
>>>schematic (the rev1 pre-2010 schem). probably not relevant to the
>>>resonance problem, but otherwise significant?
>>
>>It's pretty insignificant - it just a coupling capacitor. Either is okay.
>>
>>The resonance control does affect gain - that is its purpose. It sounds like
>>one of your signal paths (the feedback path?) isn't working.
>
>well i'm back trying to sort this out. there really isn't much to go
>wrong with the feedback path of this circuit, so i'm wondering --
>
>- if there's a way to wire up the resonance pot wrong?

Three leads - so yes, it is possible!

>- if the pinout of the 2N2222 varies with package?

PN2222 probably have reversed connections.

>- what the resistance to ground should be at various points - i'm
>seeing 3.7k between the wiper of the resonance point and ground.
>seems a touch low... the 1k resistor in the path raises this to 4.7k.

Not really much that can be gained doing that sort of measurement.

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

> >- if there's a way to wire up the resonance pot wrong?
>
>Three leads - so yes, it is possible!

...only two of which go to the board. aha, maybe i short the wiper to
the outer pin? that's probably it. i will try it on tonight.

>> >- if there's a way to wire up the resonance pot wrong?
>>
>>Three leads - so yes, it is possible!
>
>...only two of which go to the board. aha, maybe i short the wiper to
>the outer pin? that's probably it. i will try it on tonight.

Actually, that won't make any difference.
_______________________________________________________________________
Ken Stone sasami@... otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

> >> >- if there's a way to wire up the resonance pot wrong?
>>>
>>>Three leads - so yes, it is possible!
>>
>>...only two of which go to the board. aha, maybe i short the wiper to
>>the outer pin? that's probably it. i will try it on tonight.
>
>Actually, that won't make any difference.

any idea what *would* make a difference? :-)

if i'd reversed the transistors, i doubt i'd get any sound at all.
there's not much to go wrong in the feedback path.

>any idea what *would* make a difference? :-)
>
>if i'd reversed the transistors, i doubt i'd get any sound at all.
>there's not much to go wrong in the feedback path.

If I knew the answer, don't you think I would have told you? So far ALL of
them that have failed that I have had to fix have been construction errors.
Every last one of them.

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

> >any idea what *would* make a difference? :-)
>>
>>if i'd reversed the transistors, i doubt i'd get any sound at all.
>>there's not much to go wrong in the feedback path.
>
>If I knew the answer, don't you think I would have told you? So far ALL of
>them that have failed that I have had to fix have been construction errors.
>Every last one of them.

well you might have been leading me to make deductions myself :-)

in your position i might, teach a man to fish, all that...

well, a few months later and i'm back on the crusade to make my Steiner work.

situation: the filter works, but it has kinda low output level and
it's noisy. turning up the resonance makes the signal *quieter* until
it's completely silent at max. CV control of cutoff works fine in all
3 modes.

i have a working original rev Steiner here for reference and i put
the scope on both of them to try and track this down. i'm seeing that
the LP signal on the broken one is noticeably fuzzier after the first
cap in the chain (the 1uf). by the time the signal gets to the 2907
it's way fuzzier.

given that the 2907 tranny is involved in the main out, the feedback
path, and connects to the LP input (my understanding of this circuit
is limited!) i reckoned that swapping that out couldn't hurt, but it
made no difference. swapping out the 2222 before it made no
difference either. also swapped out the TL071 with no effect.

i was concerned that the to-92 trannies i have had different pinouts
than the metal cans, but i verified this -- and most likely CV
control etc wouldn't work without those being sorted.

not much to go wrong here, i'm scratching my head. any ideas appreciated!

of course, this always happens. as soon as i post...

turns out the 2907s i got are rogue ones with backwards pinout. swap
it out, boom! nice signal. backwards resonance pot, but i can easily
fix that...

thanks all.

Amazing how helpful forums can be, eh? :-)

I have that same thing happen to me frequently. There's something about formulating a question that sparks a different set of neurons in the brain. Just wish I could figure out how to fire them up at will.

Glad you're up and running!