Sequential Circuits Prophet-5 Service Manual - Audiofanzine

4-19 FILTER ENVELOPE AMOUNT VCA BALANCE1. Switch PRESET off and set controls according to Figure 4-8,2. Switch FILTER KEYBOARD off.3. Probe TP303 FILT CV at hole just above U350 and adjust FILT CTF knob to read approximately 5.75V.4. Probe U433-7 VOICE 1 FILT FREQ SMR by clipping to the right end of R4145.5. Note reading (e.g., .063V), then turn FILT ENV AMTto 10. Trim R495 for same reading as with FILTENVAMT knob set too.6. Trim Voices 2 - 5 in the same way, referring to Table 4-3.Table 4-3FILTER ENVELOPE AMOUNT VCA BALANCEVOICEOTAPROBETRIMMER12345U433-7U434-14U434-1U434-7U434-8R4145R4146R4149R4154R4157R495R497R499R4101R41034-20 FILTER TUNINGNUit: 11 Rev 3.0 Software level is V.8.1, (original) and VCO SCALE TRIM has beenperformed, switch power off then back on to reset the A-*«0 port (otherwSe thCreference will be left tuned to "C"). If V.8.2 is installed, powe^reset wm ^^^rout?n?'^'^ '""'"^ '^'' '' automatically reset when exiting SCALE TRIMA scope Is required for this trim.Note that there is no computer-correction of filter tuning as there is for the oscillators, so the filters willnever track as well as the oscillators. There Is also no temperature compensation, so the filters will alwaysdrift a certain amount. For this reason, filter tuning can degrade as soon as five minutes after tuning Thefilters are gam-matched, with the set code written on PCB 4 just above U469 (e.g. 3.60 - 3.64), Include thisset code when ordering replacement filters.1. Switch PRESET off and set controls according to Figure 4-5.2. Switch UNISON on.I3. Probe TP303 FILT CV at hole just above U350 and adjust FILT CTF knob to read as close to 2 OOOV asthe quantized voltage steps will allow.4. Switch A-440 on.left end of R4498.4406. Probe U474-7 FILT output buffer by clipping on to left end of R4500.7. Alternately play A3 and A4 (highest A) while tuning R4501 INIT FREQ (OFFSET) and R4133 FILTSCALE for 440- and 880-Hz. The two trimmers Interact, so repeat until no improvement isSee Waveform 4-0.oossible8. Trim Voices 2 - 5 in the same way, referring to Table 4-4.4-14D.2