Fatman assembly problem.
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Author:  mackemint [ Wed Dec 21, 2011 7:24 am ]
Post subject:  Fatman assembly problem.

Hello everyone!
I have a few minor problems with my one year old Fatman.
The assembly worked quite good and I managed to get sound out of it. However, I've had some minor irregularities with the amp-ADSR.
I can't seem to get ti to work properly. The controls are very unresponsive, it seems that only Sustain and Release works the way it should.

When turning the attack knob, very little happens that of what is expected. There is a Tiny slope of volume increase but it's barely noticeable. The decay doesn't do anything at all.
When sustain is set to minimum, the tone is only exactly as long as the midi note sent, regardless of velocity.
When turning the Velocity knob down the attack of the Transient gets longer, unrelated to what the actual Attack knob is set to.
The ADSR knob acts only as a second unlinear volume knob.
Also, the Punch throw doesn't do anything but I guess that isn't so strange when the other transient shapers are inactive.

On top of it all I recently tried the CMOS sub-oscillator modification by Scott Gravenhorst.
I must have messed up something good cos it started to smell like burning and resistor 38 got charred black.
Now VCO 1 is silent. Even though the knob is turned all the way towards VCO1, VCO2 is still audible and the offset knob seems to pitch VCO2 slightly, only inversed.

If you have any suggestions to any of my problems, please help me out.

Author:  PAiA-Scott [ Fri Dec 23, 2011 1:02 pm ]
Post subject:  Re: Fatman assembly problem.

Look to be sure the wire that joins the Attack, Decay, and Release controls has good joints. It is easy to miss flowing solder to a wire when there are multiple ones on a terminal.

Compare the codes stamped on the back of the 1M potentiometers (the 1M value marking is on the side facing the panel).

If the controller sends a fixed velocity value then advancing the Velcocity cv amount to the VCA would be like instant on/off according to key down/up. Usually, a mix of VCA ADSR envelope and Velocity CV is best -- just velocity would be more abrupt.

If things look OK with the panel controls and the wires to them and their solder joints, check in the area of transistors Q10 and Q11 on the board. Maybe a joint blobbed and is causing a bridge, or, a circuit-trace and solder pad area cracked. If you don't see a break, look at the joints while gently nudging the transistor from the top side of the board watching for any movement of the solder pad. Scape away some of the coating to expose copper and solder a wire over any break.

Here are some checks and tests copied over from a previous VCA ADSR help response:

Following are some tests and checks for the VCA ADSR sections. It might help to have the illustration supplement page from the manual for the parts placement figure 1a to help with locating parts and schematics figures 5a and 5b for following through the descriptions below. Identify and examine these points and circuits on the board too--the trouble might be found just by looking at the right spot. The diagrams showing the control wiring will be useful too.

As for no R102-3 voltage (VCA ADSR Envelope CV or control voltage amount control), following are some voltages you should see. Note the first two on the uC output port line o13 and wiring point V are timed and with attack at minimum the changes will be very short duration (about 100 micro Seconds (uS)) and at maximum about 3.4 Seconds (S).

Output port line o13 (originating at the IC1 uC pin 3) runs out to resistor R88 and can be measured on the "8" end of this resistor. The jumper wire near wiring point S "points" to this resistor and the 8 end is the one towards the uC. The Key-up (Gate LED off) voltage for this line is about 1.8v. The key-down voltage drops to 0v for the duration of the VCA ADSR Attack phase (100uS to 3.4S as previously noted).

This voltage transition operates transistor Q10: When there is voltage to the transistor it is "on" and the voltage on its collector pin or Wiring point V is shunted to ground. When there is no voltage to the transistor it is off and the collector voltage (wiring point V) is there (from R90 and the connection of it to the V+ 8vdc circuit). Voltage on point V goes through D7 and via wire X to the Attack control R94 and the setting of this control varies the resistance and the time it takes the voltage to charge capacitor C19. Op-amp stage IC12:D copies this weak energy that is the charge on 19 to a stronger voltage that is the ADSR Envelope CV. So, as C19 charges, the output of IC12 follows suit.
Here's where things can go wrong as the ADSR Attack is dependent upon transistor Q10 switching and transistor Q10 switching is dependent upon the Attack phase (setting the duration of the o13 pulse). IC8:D is a comparator stage and it's job is to indicate which of its inputs is most positive. When pin11 is most positive (normally 7v Vref voltage as set by resistors R85 and R86 and shown schematically up by the VCF AR circuit), the output is 5v--when pin 10 is most positive, the output is 0v. This voltage level is a signal back to the uC as to the state of the ADSR. When it drops from 5v to 0v, the uC input port line i1 changes state from 0v to 5v with the IC7:E inverter stage on IC8's output pin 13. This i1 port line signal to the uC pin 12 starts the ADSR Decay phase and the o13 port line goes back 'high' or to 1.8v, turning 'on' transistor Q10.

Q10 zeros the voltage at point V and the setting of the Sustain control adjusts the amount of voltage the Decay control and wire W 'sees' via D6. When the control is anywhere less than maximum the charge on C19 has a path for discharge and the ADSR Envelope CV decays to this Sustain level (or just stays at a maximum 7v) for the duration of the key-press.

When all keys are up and the Gate LED is off, uC output port line o14 goes 'high' or to 3.7v from the 0v key-down level. This turns 'on' transistor Q11 which then provides a discharge path for any 'sustain' level charge remaining on C19 via the release control and wire Y through R95 and D8. The setting of the Release control R96 affects the resistance C19 'sees' as it discharges towards zero through the 'on' or conducting Q11.
The R102 VCA ADSR control provides an adjustable amount of the VCA ADSR Envelope CV that gets to the following circuit section build around op-amp IC13:C. This section converts the voltage change to a current change. Voltage measurements don't tell so much here. But if pin 1 of IC18, the current control pin has a voltage other than nearly -12v, then something is awry. Check the soldering and circuit-traces joining IC13 pins 10, 9, and 8, Q12, C24, D9, R106, R99, R103. Pin 10 should be 0v or ground/circuit-common pin 11 is V- or negative 12v and pin 4 is V+ or positive 8v.


R38 burning points to maybe a miswire with the sub-octave mod you've added. Go back and review the details to confirm you have the additions in order and that soldering for them hasn't created any bridges. The resistor might still be OK, and things would work again once the trouble is resolved, but while in there you might as well replace it.

It is normal that VCO1 Offset (and Glide) affects overall pitch slightly. Just go back and tweak pitch afterwards. The VCO anti-phase-lock modification over in this section of PAiA Talk helps minimize this with the substitution of op-amps at ICs 10 and 13.


Here's to success!

Author:  PAiA-Scott [ Wed Dec 28, 2011 11:13 am ]
Post subject:  Re: Fatman assembly problem.

The first reply that mysteriously disappeared, reappeared....

Take a look at the wiring to these controls to be sure the joints for them has flowed to both the terminal and the wire. Maybe there are multiple wires on a terminal and the solder didn't flow to one, or, with the tiny wire used now they easily break, especially if stripping knicked or broke any strands. If they're all intact and as intended, nudge them watching for any movement in the joints.

The potentiometers have their value, ie 1M for Attack and Decay marked on the side that meets the panel, but the code stamped on the back of the part would most likely match that of another 1M in the kit so you could compare this way. If during the installation of the panel controls some were put in place of others, it could affect envelope timing.

Inspect the soldering in the area of transistors Q10 and Q11. If heat during soldering caused the bond between the copper clad and the board to give way then a printed-circuit-trace might have broken. Or, the tiny pads for these transistors can be more difficult to solder without getting a blob and maybe a bridge.

The Velocity CV is a static dc level for the duration of a key down. If this control is fully advanced and the ADSR is low or at minimum, the VCA will appear to open and close instantly. Usually some of each would be sent for a combination of adsr envelope and a velocity peak. Note some controllers might only send a fixed velocity value and raising this level would just work to make the output level a bit stronger than if it had not been advanced.

To hear the Punch, set the panel controls for fast attack and decay times to a reduced sustain level and operate this switch while rapidly and repeatedly pressing keys on the controller. When on, the percussive transient will be more pronounced.

There must be something awry with the modification. R38 connects the negative twelve volt supply to IC15 of the VCO1 circuit section. It burning points to a connection between the R38-IC15pin1 node and ground or the plus supply or some other path to either of these circuits (maybe an erroneous connection to an IC pin for the added modification).

It isn't unusual to observe some interaction between the VCOs for adjustment of the VCO1 Offset control. It's the load on the Pitch CV changing slightly with the resistance between it and VCO1 changing and this lowering the pitch cv enough that it is detectable listening to the pitch of VCO2. Glide has this affect on both VCOs too, but hey, there's a knob for that and it's just a matter of tweaking Pitch to compensate.

Over in this section of PAiA Talk there are mods listed for FatMan and the VCO anti-phase-lock one has changes that minimize the interaction.


Author:  mackemint [ Sun Jan 01, 2012 12:39 pm ]
Post subject:  Re: Fatman assembly problem.

I did it! You were completely right about the potentiometers, I had mixed up the resistor for Sustain and Decay.
Now the attack and decay works good, and also the velocity and ADSR make some effect that I'm still to figure out the qualities of. ;D

Sadly, I still cannot get VCO1 to come to life. When the pot is turned all the way to 1, I only get a slightly muffled leakage from VCO2.
Do you think I have caused damage to IC15? I have unplugged all the modification components and replaced R38 with a fresh one.
I never did solder anything, just connected it with probes to the legs of the IC's.

Thanks a lot and good wishes on the new year!


Author:  PAiA-Scott [ Thu Jan 05, 2012 11:54 am ]
Post subject:  Re: Fatman assembly problem.

I am glad you have the envelope section in order!

Yes, a replacement at IC15 will probably bring VCO 1 back to life. The resistor to it burning is an indication more current than is normal flowed through and it likely took a path through the IC too.

Author:  mackemint [ Mon Jan 16, 2012 11:43 am ]
Post subject:  Re: Fatman assembly problem.

Hey Scott!
I got my replacement IC from my local provider the other day and I swapped out the old one today.
It works like a charm!
I also finally managed to put together the sub-oscillator circuit with great results. The Fatman truly makes up for his name now. ^_^

Thanks alot for your support, im moving on to further experiments.


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