Thursday, November 15, 2012

Avoiding Hum From Power Supplies

If you are buying a second-hand rack, or if you already have a Doepfer modular rack with a cheap alternative (non-Doepfer) power supply you should be aware of how to avoid the (minor) transformer hum that cheap PSUs generate.

In the area near those power supplies (bottom right) no modules should be assembled that are sensitive to transformer hum.
Doepfer recommends to assemble only control voltage modules in this area (e.g. LFO, ADSR, trigger delay, clock divider/sequencer, sequencer, slew limiter, MIDI interfaces and so on)
,but no audio modules (VCO, VCF, VCA, VCP, frequency shifter, ring modulator, spring reverb and so on)
Also don't put the A-178 Theremin modules near the power supply.

Doepfer Power Supply I ( PSU I )
This matters for some of the cheap alternative non-Doepfer power supplies, and for the old Doepfer versions with PSU I 
For new A-100G3/G6 cases (with original PSU II) this does not apply. 

Find out how to distinguish the old transformer (PSU I) from the new version (PSU II) at http://patchpierre.blogspot.nl/2012/07/doepfer-power-supplies.html