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Elby Designs ASM-2, Construction Manual

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Elby Designs ASM-2 Construction Manual Download Page 14

ASM-2 Construction Guide

ELBY Designs - Laurie Biddulph

9 Follan Close, Kariong, NSW 2250, Australia

[email protected]

http://www.elby-designs.com

14 of 19

VCLFO - Low Frequency Oscillator

Power up, Testing and Calibration Procedures:

LFO 1 Offset Adjustment

1. Fit a jumper between JP501_2 and JP501_3.

2. Monitor TP7 with a multimeter. It will probably exhibit a tendency to drift positive or

negative, and the voltage will settle at +Ve or –Ve.

3. Reset the output voltage to zero by holding a 1K resistor between TP7 and JP502.

4. Adjust P504 until the voltage remains stable at zero volts for a period of several

seconds (without the discharge resistor in circuit).

5. Repeat steps (3) and (4), progressively switching the multimeter to more sensitive

ranges, until the drift is only a few hundred millivolts in several seconds.

6. Return jumper to JP501_1 and JP501_2

LFO 1 BEAT LED Adjustment

P505 should be adjusted so that the brightness of the LED follows the amplitude of the

triangle output, i.e. the LED brightness should be at minimum brightness when the triangle

is at its most negative, and at maximum brightness when the triangle is at its most positive.

LFO 2 Offset Adjustment

7. Fit a jumper between JP551_2 and JP551_3.

8. Monitor TP8 with a multimeter. It will probably exhibit a tendency to drift positive or

negative, and the voltage will settle at +Ve or –Ve.

9. Reset the output voltage to zero by holding a 1K resistor between TP8 and JP552.

10.Adjust P554 until the voltage remains stable at zero volts for a period of several

seconds (without the discharge resistor in circuit).

11.Repeat steps (3) and (4), progressively switching the multimeter to more sensitive

ranges, until the drift is only a few hundred millivolts in several seconds.

12.Return jumper to JP551_1 and JP551_2

LFO 2 BEAT LED Adjustment

P555 should be adjusted so that the brightness of the LED follows the amplitude of the

triangle output, i.e. the LED brightness should be at minimum brightness when the triangle

is at its most negative, and at maximum brightness when the triangle is at its most positive.

Summary of Contents for ASM-2

Page 1: ... designs bigpond com http www elby designs com 1 of 19 ASM 2 Construction Notes For PCB Rev 2 3 February 5 2020 Please note that this document is still currently under revision and we apologise for any errors or omissions Readers should feel free to email any comments to me at the address given below ...

Page 2: ...ome of the modules for testing and this will require some connecting and disconnecting to allow for easy assembly of the next stage This approach does not work with my PCB Assembly Jig and the previous method as the variations in component heights affects the height of the components on the board preventing the component retainer from working properly Option 2 may suit users with less confidence i...

Page 3: ...les and will also simplify debugging should it be needed This will result in slightly longer cable runs but this should not adversely affect the quality of the system through induced noise Colour coding of cables is not a pre requisite but once again using colour coded cables will simplify tracing faults The table below gives two examples of suggested colour schemes Cable Colour Function Red 12V B...

Page 4: ... careful with these they are unbelievably easy to blow up Component Substitutions and Your Own Modifications If you know what you re doing go for it If not stick with the recommended parts TEMPCO s The ASM kits include a TEMPCO resistor for each of the VCO s A TEMPCO can also be used in the VCF but is not included in the kit as this is less critical The ASM kits provide a 1 metal film resistor for...

Page 5: ...es Substitutes should be of a low noise high stability type The pcb footprint is for 0 2 pitch radial components 3 Capacitors below 1nF are generally 2 5 160VDC Polystyrene FCS Series but Silvered Mica will also work fine In some cases it is possible too use a high stability NPO Multilayer Ceramic capacitor The pcb footprint is for 0 2 radial components 4 Decoupling capacitors are listed as 100nF ...

Page 6: ...wired in series with S110 KCV and S101 TRANSPOSE on the panel R156 on the PCB should be replaced with a wire link R156 and an additional 100K 0 1 resistor XR149 will then be wired in series with S160 KCV and S151 TRANSPOSE on the panel R110 on the PCB should be replaced with a wire link R110 and an additional 100K resistor XR149 will then be wired in series with pots P117 PWM1 and P119 PWM2 on the...

Page 7: ... P100 P150 to give a reading of 261 626Hz 10 Remove the 5 0V on the LOG FM input 11 Confirm that the output frequency is 8 176Hz It is worth repeating these steps to ensure that the settings are stable This completes the setting up of the VCO Reconnect all control inputs The VCO can now be connected to a 1V Octave MIDI CV module and will play the correct frequency for a given MIDI Note Number as p...

Page 8: ...KHz will do Now play a note on your keyboard and then the same note an octave above Repeat this again and again and adjust the V OCT trimmer to get the filter s oscillations to jump an octave too Don t worry about the actual pitch the VCF is producing Just concentrate on getting roughly one octave difference between the low note and the high note It is a fiddly adjustment and it takes a while to g...

Page 9: ...ry C F mV DROP 16 62 70 19 67 65 22 72 60 25 77 55 28 82 50 Table 1 Correction Factor Here s a procedure without a scope The basic idea is that you use the VCF as an oscillator with Emphasis all the way up A well tuned VCO acts as a reference so the VCF should follow the VCO when CV changes Apply a control voltage CV to the VCF and a VCO Turn the Emphasis P805 pot all the way up so that the filter...

Page 10: ...alia elby designs bigpond com http www elby designs com 10 of 19 Emphasis Trim P804 and VCF Balance P803 don t have much effect You only need to adjust them when you re very picky otherwise turn P804 to minimum resistance and P803 to the mid position P807 should be set to its center position ...

Page 11: ...ith the frequency of the GATE signal 5 Adjust P406 so that the rising edge of the envelope peaks at 5V0 and that there is no overshoot or undershoot This completes the setting up for the ADSR 1 module ADSR 2 MAXIMUM ENVELOPE 1 Monitor TP11 and adjust P450 for 5V0 ATTACK PEAK 1 Set ATTACK DECAY and RELEASE to minimum and SUSTAIN to maximum 2 Set P456 fully clockwise 3 Apply a low frequency square w...

Page 12: ...dulph 9 Follan Close Kariong NSW 2250 Australia elby designs bigpond com http www elby designs com 12 of 19 VCA 1 2 Voltage Controlled Amplifier Apply xV Monitor TP13 and adjust P301 for minimum output Monitor TP14 and adjust P351 for minimum output ...

Page 13: ...up Testing and Calibration Procedures 1 Monitor the WHITE noise output 2 Adjust P601 for a nominal output of 5Vpk pk A socket should ideally be fitted for T601 so that a range of transistors can be tried to obtain optimum noise levels The white noise output should be between 2 0 and 2 8V peak to peak Different transistors should be tested along with varying the value of P601 ...

Page 14: ... LED follows the amplitude of the triangle output i e the LED brightness should be at minimum brightness when the triangle is at its most negative and at maximum brightness when the triangle is at its most positive LFO 2 Offset Adjustment 7 Fit a jumper between JP551_2 and JP551_3 8 Monitor TP8 with a multimeter It will probably exhibit a tendency to drift positive or negative and the voltage will...

Page 15: ...igns Laurie Biddulph 9 Follan Close Kariong NSW 2250 Australia elby designs bigpond com http www elby designs com 15 of 19 Glide Buffer Power up Testing and Calibration Procedures There is no calibration required for the GLIDE circuit ...

Page 16: ...ter or an audio amplifier 1 Monitor TP4 RING of the Ring Modulator 2 Apply the test signal to the CARRIER input J1601 pin 1 3 Adjust P1601 until the output signal is at minimum 4 Apply the test signal to the SIGNAL input J1601 pin 2 5 Adjust P1602 until the output signal is at minimum 6 Repeat steps 2 to 5 until no further improvement can be made The level of feed through obtained will vary betwee...

Page 17: ...SW 2250 Australia elby designs bigpond com http www elby designs com 17 of 19 Sample Hold The Sample Hold circuit has a small pcb footprint error C901 should be replaced with a resistor which can be simply stood on end to fit the board Power up Testing and Calibration Procedures ...

Page 18: ...he correct installation orientation The PCB silkscreen also indicates that the internal reference supplies are 7V this has been updated to 9V These internal reference supplies available at J3 are to be used only for the VCOs J2 is available for other panel components that require access to the main power rails 12V Power up Testing and Calibration Procedures 1 Monitor TP2 and adjust P1 7V for 9 0V ...

Page 19: ...Construction Guide ELBY Designs Laurie Biddulph 9 Follan Close Kariong NSW 2250 Australia elby designs bigpond com http www elby designs com 19 of 19 MULTIPLES These are simple 1 in to 2 out passive multiples ...

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