[sdiy] Panels: early results

Grant Richter grichter at asapnet.net
Fri Jun 14 17:45:09 CEST 2002

> Seriously,  what is the bigga-deal with mini's?  Banana'a are great because
> they stack, but it there any sonic defficiency from a banana plug?

The stacking capability is brilliant.

Banana cables are unshielded. In synthesizers that traditionally use them
such as Serge and Buchla, the output structures are modified to so the
op-amps can "soak up" the added noise. The Buchla 200 uses a 220 ohm output
resistor with the op-amp feedback terminal connected AFTER the resistor.
This causes the op-amp to compensate for the resistor voltage drop and
lowers the AC output impedance.

Serge uses the same structure with a 330 Ohm output resistor. Also Serge
lowered the voltage range to +/- 2.5 volts to reduce crosstalk between
unshielded connectors.

The traditional 1K output resistor with the op-amp negative terminal
connector before the resistor, is designed for shielded cables. The
disadvantage with the Buchla/Serge output structure is that outputs can not
be mixed together at a multiple. Because op-amp feedback is connected after
the protection resistor, the stages will "fight" each other. With a 1K
resistor in series with the op-amp output, and the feedback before the
resistor, shorting output together simply forms a resistive mixer.

More information about the Synth-diy mailing list