Arion SAD-1 - voltage to MN3102 and MN3205

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Arion SAD-1 - voltage to MN3102 and MN3205

Postby Yazoo55 » 15 Aug 2017, 14:07

I have just built the Arion SAD-1 and it's not quite right. It is difficult to tune in the bias voltage for the MN3205 and the Repeats pot is only usable for about 30% of its travel. After that the pedal goes uncontrollable.

One of the puzzles is why the voltage to the MN3102 timer chip is dropped through 2 diodes. This affects the VGG voltage supplied to the MN3205. In my build, I measure 9.1 volts on pin 5 of the MN3205 (Vdd) but 7.35 volts on pin 8 (Vgg) - as supplied from pin 8 of the MN3102. This difference seems to match a 2 diode voltage drop. The datasheet for the MN3102 states that the "most suitable Vgg voltage can be obtained when the MN3102 is used with the same supply voltage as BBD". It also recommends that Vgg be 14/15 of Vdd.

I also checked out the schematic for the Boss DM-3 which is a very similar circuit. In the Boss, both the MN3102 and the MN3205 get the same Vdd voltage.

Any advice would be very welcome.
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Re: Arion SAD-1 - voltage to MN3102 and MN3205

Postby Yazoo55 » 16 Aug 2017, 16:06

I just decided to go ahead and modify the power supply to the MN3205 chip. I added a BAT41 diode in series with the 2 1n4148 diodes to drop the VDD voltage to pin 1 of the MN3102 to 7.5 volts and lifted the pin 5 leg of the MN3205 so that I could solder a jumper lead from pin 1 on the MN3102 to give it the same 7.5 volts. It is a definite improvement. I can now set the trimpot to control the Repeats pot.

My one gripe is that there is still some distortion. I should mention I am using the V3205 Coolaudio clone of the MN3205.

The schematic is here:http://experimentalistsanonymous.com/diy/Schematics/Delay%20Echo%20and%20Samplers/Arion%20SAD-1.gif
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