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Paia 2720 rebuild advise

Posted: Mon Jun 18, 2012 6:29 pm
by orbitalgun
Thanks for having me.

I am rebuilding a Paia 2720 and have several questions I hope Paiatalk can advise on.

I've started to mount everything up and am anxious to put power to the modules, but notice the output is high by about a volt. So +10, -10, +21 VDC.

I'm concerned I may need to replace the transformers, or at least put a voltage dropping resistor before the other modules.

I know the VCO has regulation built in but what about other modules will running high voltage to them damage them?

Re: Paia 2720 rebuild advise

Posted: Thu Jun 21, 2012 9:41 am
by PAiA-Scott
It shouldn't be a problem with the power supply voltages being slightly over, and once connected to the modules, they might even drop down to the dual nine volt and positive eighteen as spec'ed.

You could also measure the current of each supply to the modules and use this to determine resistance values for added r-c filtering to the modules. For example, if it's 100mA on the 18v supply and the voltage measures 21 with the modules connected, divide the extra 3v by 0.1 for a result of 30 or the ohms to use in the r-c filter.

With the value of the resistor selected, calculate the power through the resistor (18V x 0.1A = 1.8W).

A 2W resistor will handle the power.

A 1000uF capacitor (or more) rated at 25v connected on the module side of the resistor to ground would complete the added r-c filtering / voltage optimizing circuit.

Here's to success!

Re: Paia 2720 rebuild advise

Posted: Sun Jun 24, 2012 2:29 pm
by orbitalgun
Having some pretty good luck working with this unit to get it going.

I'm trouble shooting a naughty VCA which won't be quiet.

Figuring out how to use the EG to shape waves.

Trying to install a midi to CV converter, third party.

Wondering if I should mod out the VCO's with tune/de knobs for more color and harmonics.

Switching the trigger button on the EG, think arcade.

So very much fun! Why did I wait so long to do this?

Re: Paia 2720 rebuild advise

Posted: Thu Jul 05, 2012 3:12 pm
by PAiA-Scott
See if calibrating the VCA while the EG is connected and "off" helps. Patching in some negative bias can help in addition to other control can help in other instances.

Re: Paia 2720 rebuild advise

Posted: Sun Aug 05, 2012 7:42 pm
by orbitalgun
Scott, thanks for responding and advising. Though the 2700 system is pretty straight forward expertise is a welcome commodity.

Updates include: VCA issues resolved.

Power modules corrected. EG running. (Considering using a Doepfer ADSR to "modernize" waveshaping.)

Parts for putting tuning trimpots on a faceplate now in house. Cutting acrylic faceplate today. (Boring holes tomorrow).

Trying to use a midivox arduino shield as a CV converter. I realized the VCO is not exponential. So as I am not prepared to build a keyboard from scratch please give details on the converter mentioned in other threads. I have found via web searches a Japanese version I believe was used in Korgs, around the same time, which look easy enough to perf board, but still lurking Arduino forums for programing suggestions.

Posting pictures this later week.

Here is a link to google profile up presently. ... sts?tab=wX