Okay, I replaced the diode and with no input, the voltage at Pin 5 of the
TL072 is +4.2V. I also tried replacing the TL072, but still get the same
results.
Andrew
TL072 is +4.2V. I also tried replacing the TL072, but still get the same
results.
Andrew
On Mon, Feb 11, 2013 at 10:04 PM, A S <synthasaurus@...> wrote:
>
> Thanks Dean. I just measured the voltages. With a decreasing input
> (slowly decreasing from +5V to 0V), Pin 5 of the TL072 follows the input
> until the input drops into the 10s of Millivolts. Decreasing the input
> lower causes the voltage at Pin 5 to immediately jump to +3.74 volts. I
> disconnected the input voltage patch cord, but the +3.74 volts is still
> there. I'll try replacing the diode now to see what that does.
>
> Thanks!
> Andrew
>
>
>
> On Mon, Feb 11, 2013 at 9:42 PM, goldencardigan <dean.lowe@...>wrote:
>
>> **
>>
>>
>> Hi Andrew,
>>
>> Please ignore my last rant, it wasn't aimed at you in anyway.
>>
>> It looks like you've got your pot wiring right. Check the Diode connected
>> to Pin 5 of the TL072, next to the two 220k Resistors on the schematic.
>> With nothing connected to the Trig or Input, you should have voltage
>> present on the tranny side of the Diode, but no voltage on the side
>> connected to the TL072. If there is voltage passing from the tranny through
>> the diode, it means the diode needs to be replaced. I had a similar problem
>> with my build, although the symptoms seem to be a bit different. If you do
>> a search you should find my previous posts regarding this.
>>
>> If you haven't already, check out Tim Stinchcombes page on the VCS
>>
>> http://www.timstinchcombe.co.uk/index.php?pge=vcs
>>
>> Cheers
>> Dean
>>
>>
>> --- In cgs_synth@yahoogroups.com, sasami@... wrote:
>> >
>> > Re locking up, have you seen the modification to replace the 10n caps
>> with
>> > 1n in the cycle switching circuit? 150k also go down to 100k.
>> >
>> > Ken
>> >
>> > >Hi Dean,
>> > > Thanks very much for the reply. Regarding EG operation, I'm okay with
>> the
>> > >fact that the pots will work "in reverse" if wired with cycle mode's
>> audio
>> > >freq. in mind.
>> > >
>> > > Speaking of cycle mode, it does work as an oscillator in this mode,
>> though
>> > >I'm not sure if it works in the correct range. If I move the pots
>> clockwise
>> > >to a high freq. extreme, it will lock up. I have to toggle the cycle
>> sw.
>> > >off and on to make it work again.
>> > >
>> > > I'm ohming the pots out as I type this. CW and CCW is referenced
>> viewing
>> > >the pot from the front (shaft towards you). They are wired like this:
>> > >
>> > > Rise pot:
>> > >CW - Gnd
>> > >CCW - +15V
>> > >Wiper - RRW
>> > >
>> > >Fall Pot:
>> > >CW - Gnd
>> > >CCW - +15V
>> > >Wiper - FRW
>> > >
>> > > Rise CV:
>> > >CW - RCCW
>> > >CCW- RCW (GND)
>> > >Wiper - RW
>> > >
>> > >Fall CV:
>> > >CW - FCCW
>> > >CCW- FCW (GND)
>> > >Wiper - FW
>> > >
>> > >
>> > >The odd thing is that FCW and RCW are at ground reference, so that
>> should
>> > >be the CCW pot terminal, not CW. Unless I'm confusing myself... is the
>> > >silkscreen wrong for these two?
>> > >
>> > > Thanks again,
>> > > Andrew
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >On Mon, Feb 11, 2013 at 3:38 PM, goldencardigan wrote:
>> > >
>> > >> **
>> > >>
>> > >>
>> > >> Hi A S
>> > >>
>> > >> To me it sounds like you need to check your pot wiring. Have another
>> read
>> > >> of the wiring list and confirm your connections, as a lot of people
>> have
>> > >> had problems with this. Can you tell us which connections you have
>> used for
>> > >> the Rise, Fall and respective rate pots.
>> > >>
>> > >> Just for the record, I also want to address the claim on the 'mods'
>> page
>> > >> you listed below that the Rise and Fall connections are reversed.
>> The VCS
>> > >> is in a way an Attack/Release Envelope with a looping function. If
>> you give
>> > >> it a trigger it will respond accordingly and the Rise will control
>> the
>> > >> attack time exactly like any other envelope (the Fall acting like the
>> > >> release control). Now if you engage the looping feature, yes the
>> Rise and
>> > >> Fall pots do seem to be reversed if you compared it to a LFO. But it
>> does
>> > >> work exactly like every other envelope with a looping feature. As the
>> > >> attack and release times of the envelope decrease, the quicker the
>> > >> oscillations get.
>> > >>
>> > >> IMHO I always try to build my boards as per the designers notes and
>> make
>> > >> any mods after verifying the board is working as intended. If I do
>> have any
>> > >> probelms with the board I can gaurantee that it is a mistake I have
>> made
>> > >> and not due to a mod that I have installed.
>> > >>
>> > >> Sorry, I'll get off my soap box now. Double check your wiring and
>> let us
>> > >> know how you go.
>> > >>
>> > >> Cheers
>> > >> Dean
>> > >>
>> > >>
>> > >> --- In cgs_synth@yahoogroups.com, A S wrote:
>> > >> >
>> > >> > Hello,
>> > >> > I have a CGS75 Rev 0.0 where the Rise and Fall pots don't give
>> typical EG
>> > >> > slew rates.
>> > >> >
>> > >> > For the following symptoms, I'm using a square wave output from an
>> LFO
>> > >> set
>> > >> > about 1 Hz to the input of the VCS. The output of the VCS is
>> driving a
>> > >> VCO
>> > >> > FM input, so that I can hear what the output of the VCS is doing.
>> > >> >
>> > >> > 1. The VCS outputs the input LFO signal pretty much unaffected if
>> the
>> > >> rise
>> > >> > and fall pots are at the 9 o'clock position. If I lower either the
>> fall
>> > >> or
>> > >> > rise pot to minimum, there is a small amount of slew for each
>> function.
>> > >> >
>> > >> > 2. If I raise either (or both) pots from the 9 o'clock position, it
>> > >> doesn't
>> > >> > do anything different up to the 12 o'clock position.
>> > >> >
>> > >> > 3. If I increase the rise pot further (with the fall pot at 12
>> noon),
>> > >> > there is a positive dc offset added to the LFO input as the pot
>> level is
>> > >> > increased. There is no slew.
>> > >> >
>> > >> > 4. Conversely, if I increase the fall pot further (with the rise
>> pot at
>> > >> 12
>> > >> > noon), there is a negative dc offset added to the LFO input as the
>> pot
>> > >> > level is increased. There is no slew.
>> > >> >
>> > >> > I added the mods mentioned on this page:
>> > >> >
>> http://electro-music.com/forum/viewtopic.php?highlight=cgs75&t=54330
>> > >> >
>> > >> > and on the CGS page:
>> > >> > http://www.cgs.synth.net/modules/cgs75_vcs.html
>> > >> >
>> > >> >
>> > >> > Here are some of the check I've done....
>> > >> >
>> > >> > I tried replacing the TL074, and have checked the resistor values,
>> > >> > orientation of diodes, and transistors. All parts seem to be
>> correct
>> > >> after
>> > >> > double checking them. I've also checked the board for solder
>> shorts, and
>> > >> > have ohm'd out many of the traces from component to component.
>> > >> >
>> > >> > I checked the voltage at the base of the 2n3904 and 2n3906 (from
>> the rise
>> > >> > and fall circuits). The range as I turn the pots is from 0V min.
>> to 384mV
>> > >> > max.
>> > >> >
>> > >> > I input a manually adjusted CV at the gate input. The TL072 Pins 5
>> and 6
>> > >> > follow the gate input. Pin 7 outputs 477 mV no matter what the
>> gate input
>> > >> > voltage is. There is still 477mV if I disconnect the input cable.
>> > >> >
>> > >> > Any help would be appreciated, and I can send pics of the PCB if
>> that
>> > >> > would help.
>> > >> >
>> > >> > Thanks,
>> > >> > Andrew
>> > >> >
>> > >> >
>> > >> > [Non-text portions of this message have been removed]
>> > >> >
>> > >>
>> > >>
>> > >>
>> > >
>> > >
>> > >[Non-text portions of this message have been removed]
>> > >
>> > >
>> > >
>> > >------------------------------------
>> > >
>> > >The CGS Modular Synth home page: http://www.cgs.synth.net/
>> > >Yahoo! Groups Links
>> > >
>> > >
>> > >
>> > >
>> > __________________________________________________________
>> > Ken Stone sasami@... otherunicorn@...
>>
>> > Modular Synth PCBs for sale
>> > Australian Miniature Horses & Ponies
>> >
>>
>>
>>
>
>
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