Sequential prophet 5 - Page 115

7. Ready a tuning fork or if available, set up an external A-440 reference. It is not desirable to use
the Prophet's A-440 reference for filter tuning since it will tend to sync the resonating filter.
8. Key C3. trim V1-R407 FILT INIT FREQ, to resonate at A-440.
9. Key C5. trim V1-R406 FILT V/OCT. so the filter resonates exactly two octaves higher.
10. R407 and R406 interact, so repeat steps 8 and 9 until no improvement is possible.
11. Raise VOICE 2 LEVEL with its R416.
12. Zero-beat V2-R407/6 against VOICE 1 while repeating steps 8 and 9. 2 - 6 beats-per-second is
acceptable.
13. Lower VOICE 2 LEVEL and repeat steps 11 and 12 for VOICES 3-5.
With instruments, perform steps 1-5 above, then:
6. Adjust scope timebase to 440 Hz. If you sync the scope to the Prophet 440 Hz reference, be sure
to switch the reference back off.
7. With scope, probe U479-1. VI FILT BUFFER.
8. Key C3. and trim V1-R407 to display exactly one complete cycle. Use X10 magnification, if available.
9. Key C5, and trim V1-R406 to display four complete cycles.
10. R407 and R406 interact, so repeat steps 8 and 9 until no improvement is possible.
11. Probe U479-7. U486-1, U486-7. and U489-7 to trim R407/6s for VOICES 2 - 5.
4-18 OSCILLATOR TUNING
4
Although the procedure is included here for reference an oscillator's INITIAL FREQUENCY should
not have to be trimmed except when it has been replaced. These trimmers need only bring the oscil¬
lators close enough to each other for the computer to fine-tune them with the TUNE routine.
Computer tuning (auto-scaling) usually corrects sufficiently for playing. There will always be some
beating or phasing between the voices. If not excessive, these imperfections "naturalize" or "warm"
the Prophet's sound. Therefore, if the Prophet is badly out of tune, there is probably a component
failure. Carefully investigate all possible causes before retuning.
Before trimming the oscillators, you may want to check four or five of them to see if they are all flat
or sharp the same amount. If they are. then you can trim R301 DAC GAIN to change the V/OCT on
all the oscillators at one time. This could save you a lot of time with individual oscillators.
NOTE: Be careful if you decide to use this method, since trimming DAC GAIN incorrectly will mis-
adjust all CVs issued by the computer.
Start in BASIC TRIM SETUP. TABLE 4-0.
1. Switch off S221. UNISON.
2. Switch on S215, OSC B KBD.
3. Turn R206, MIX OSC B to 10.
4. Key D«3 and note pitch.
5. Key CO and adjust R203, OSC A FREQ for pitch heard in step 3. This is about 6.5 on the dial.
6. Switch on S211, OSC B SAWTOOTH.
7. Adjust R209 OSC B FREQ to same pitch as OSC A.
8. Turn R213, GLIDE, to 5.
9. Record this patch in an unused location. These procedures will refer to this patch as 5-1.
10. Press S112. EDIT.
11. Key CO and note pitch.
12. Key C2 and adjust R203 and R209. OSC A and B FREQ, for pitch heard in step 11. This is about 3
on the dial.
13. Record this patch. It will be referred to here as 5-2.
14. While holding S103. PROGRAM SELECT1. press S109. PS7. This causes all of the BIAS S/H voltages
to be set at approximately 2V. In other words, it defeats the TUNE routine.
4-9