Sequential prophet 5 - R413 Oscillator B Triangle Symmetry; R415 Final Vca Balance.4-8; Filter Tuning.4-8

4-15 R413 OSCILLATOR B TRIANGLE SYMMETRY
R413 functions similarly to R306 (para. 4-7).
Start in BASIC TRIM SETUP. TABLE 4-0. By ear:
1. Switch off S221. UNISON.
2. Switch off S215. OSC B KEYBOARD.
3. Turn R209, OSC B FREQ, to 10.
4. Switch on S212, OSC B TRIANGLE.
5. Turn R206. MIX OSC B. to 10.
6. Isolate VOICE 1 (para. 4-9) and hold a key.
7. If required, trim R413 for minimum harmonics.
8. Repeat steps 7 and 8 for VOICES 2 - 5.
With instruments, perform step 1-4 above, then:
5. Probe U457-7 with scope. Note that U457 is mounted upside down.
6. The triangle waveform should look balanced, with equal slopes (see Waveforms 4-0). Trim R413
if required to balance.
7. Probe U462-8, U462-14. U462-1 and U462-7 to trim R413s for VOICES 2 - 5.
i
4-16 R415 FINAL VCA BALANCE
R415 functions similarly to R403 (para. 4-12).
Start in BASIC TRIM SETUP. TABLE 4-0. By ear:
1. Turn R205, MIX OSC A. to 0.
2. Isolate VOICE 1 (para. 4-9).
3. Increase R105, VOL, to louder than normal.
4. While striking key repeatedly, trim R415 for minimum key dicks.
With instruments:
1. Turn R205, MIX OSC A, to 0.
2. Hold (or tape) a key.
3. With DVM, probe U490-15. VOICE 1 FIN VCA.
4. Trim R415 for 0.000-V reading.
5. Probe U491-15, U492-15, U493-15 and U494-15 to trim R415s for VOICES 2 - 5.
4»-17 FILTER TUNING
The filters are tuned at full resonance, where they oscillate with a pure sine wave. (The filters are not
temperature-compensated, so they will drift and they will nver track as well as the oscillators.)
Start in BASIC TRIM SETUP. TABLE 4-0. By ear:
4. Switch off S204, OSC A SAWTOOTH.
2. Turn R102. FILT RES. to 10.
3. With DVM. probe U350-7.
4. Adjust R101, FILT CUTOFF, for as close to ♦ 3.083-V reading as the quantized voltage steps will
allow.
5. Record this patch in an unused memory location. Verify that there is no change in the DVM
reading.
6. Isolate VOICE 1 by turning down VOICE 2 - 5 R416. VOICE LEVELS.
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