Adding a Feedback Loop Adding a feedback loop expands the sonic characteristics of the SID. This modification is quite simple to implement, yet tremendously effective once installed. With the addition of a feedback loop, the SID can achieve various dirty/aggressive sound properties. feedback loop schematic I applied this mod to both of my SIDs using a stereo potentiometer. The faded portions of the schematic represent existing circuitry from previous mods. If you choose to add this mod to a single SID system, disregard the lower half of the schematic and use a regular mono pot instead. I'm still experimenting with values, but 500k seems to work rather well. I used 1/4" jacks with normally closed (NC) switch contacts. Normally, the SID audio out is routed through the switch. When a plug is inserted, SID audio out is disconnected and the SID audio input receives a signal from the plug tip. This allows me to use the audio inputs according to the original design, without any interference from the feedback mod. In addition, I could use dummy plugs as a means of disabling the feedback loop, when desired. Bass Line loop comparison: without then with feedback another version of the above While MIX IN is activated, the feedback loop creates subtle effects in P64 Bass Line. distorted bass line another distorted bass line When MIX IN is disabled, the feedback loop creates a distorted overdrive effect. (great for giving your acid lines some crunch!) bulky stereo pot With band pass (can be combined with high or low pass) filtering in P64 Mono Synthesizer, the resonance can reach self oscillation! mono synth line with increasing resonance another mono synth line with screaming resonance warbling noise with resonance set just before the threshold of self oscillation this sample demonstrates the power of self oscillating filters. All SID oscillators are disabled. This sample consists of nothing more than the filter controlled by the LFO here is a slow low/band-pass filter sweep odd tones Warning: self oscillating filters can rapidly increase output levels if you are not careful. If you’ve ever used an analog synth with good self oscillating filters, you know what I’m talking about. I recommend running your output through a compressor or limiter. This is especially advisable when using headphones or loudspeakers. I have attended too many rave parties where the Live P.A. cranks the resonance without regard to the unsuspecting audience. High decibels + high frequency = bad! By now, you already know what this is. I've added another one of my connectors. NEXT»

-AlphA

 

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