I measured the cathode voltage of the diode. It's at +15V while an input
voltage is present. If the voltage is lowered to near zero (when Pin 5 goes
up to +4.2V), the cathode drops to +11V.
voltage is present. If the voltage is lowered to near zero (when Pin 5 goes
up to +4.2V), the cathode drops to +11V.
On Mon, Feb 11, 2013 at 10:23 PM, A S <synthasaurus@...> wrote:
>
> 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
>
>
> 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
>>> >
>>>
>>>
>>>
>>
>>
>
[Non-text portions of this message have been removed]