Sequential prophet 5 - R307 Master Summer Offset; Trimminc the Voices; R401 Amplifier Envelope Generator Time Constant.4-6

4-8 R307 MASTER SUMMER OFFSET
R307 (see SD312) adjusts the range of the OSC A and B MASTER SUMMERS (MSUMs). It can only be
trimmed with instruments.
Start in BASIC TRIM SETUP, TABLE 4-0.
1. With DVM. probe U377-1, A SUM CV.
2. Key CO.
3. Trim R307 so U377-1 reads -5.500V.
4-9 TRIMMING THE VOICES
As above, the following procedures are ordered as if the Prophet were going to be completely
retrimmed. But since there are 80 trimmers on PCB 4 you will probably want to avoid this situation.
Unnecessary trims can be avoided by tracing problems to specific voices. There are two ways to do
this. You can mute individual voices by turning down its R416, VOICE LEVEL, trimmer (see para. 4-20).
Then when playing in UNISON, only the unmuted voices will be heard while all the envelope gen¬
erators, for example, will be triggered simultaneously. Or, you can keep track of the voice assign¬
ments. Switch on $221, UNISON, hit a hole, then switch off S221. This resets the voice counter. The «
voices will now be assigned sequentially 1, 2, 3, 4, 5 to the first five different keys hit. The TUNE
routine also resets the voice counter.
Note that the same trimmers for separate voices have the same designator. For example, each voice
has a R401 — and the five settings should match. The procedures usually spell out the trim only for
VOICE. (VI), and VOICES 2-5 (V2 - 5) are trimmed similarly.
4-10 R401 AMPLIFIER ENVELOPE GENERATOR TIME CONSTANT
R401 adjusts the range of the AMP ENV GEN ATTACK, DECAY and RELEASE periods. It is trimmed for
comparable timing between the voices. Over periods less than 1 sec. the envelopes will closely
match. Longer ATK, DEC or REL periods normally increase differences between the voices.
Start in BASIC TRIM SETUP, TABLE 4-0.
1. Turn R112, AMP SUS, toO.
2. With DVM, probe U342-1, AMP ATK CV S/H.
3. Trigger scope from J705, SEQ TRIG OUT.
4. Set scope timebase to .1s/div.
5* With scope, probe U401-10, VOICE 1 AMP ENV GEN OUT.
6. On Prophets S/N 590 and above check for ENV GEN S/H Gain Modification (see SD313). The
modification adds IK resistors between U342-1/2. U343-1/2, U343-6/7.
7. Adjust R110, AMP ATK, so the DVM reads as close to 6.250V as the quantized voltage steps will
allows. If the S/H Gain Modification has been installed, adjust R110 for a DVM reading close
to 6.875V.
8. Key repeatedly and measure ATK period on scope.
9. Trim R401 for 0.9-sec ATK period. Note that these trimmers have a wide range and it does not
take much movement to drastically change the TC, so be careful and go slow when trimming.
10. Probe U402-10. U403-10, U404-10 and U405-10 to trim R401s for VOICES 2 - 5. If scope is dual¬
trace. VOICES 2 - 5 can be referenced to VOICE 1.
NOTE: The ATK timing will measure differently on different scopes. It is not so important that the
ATK period is absolutely 0.9 sec. as it is that the five voices match each other. Also note that the 2050s
are heat sensitive, and will drift slightly. This is usually inaudible, so don't worry about it.
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