zenguru

I think you're right, moxi... in the case that the transistor really isn't conducting. And that really seems to be so. Maybe I'll just put that bc547 there and consentrate on the psu, like moxi suggested. ;) Of course, a controllable input/output would be nice... ::) By the way, what's the max amplitude of the output signal? Ok, thank's everyone!

About those "imperfections"... I believe it's the harmonics that make the moog sound so good. Although the harmonics are sometimes considered "imperfect", especially when a pure sine wave is wanted, they still give the guitar, piano, synth etc it's characteristic voice. When using transistors or vacuum tubes (or any type of components, really :) , there's always some harmonics, caused by non-linearity, and noise present. Depending on the component type, the harmonics can be "musical" or "non-musical". That's ok. What isn't so ok, is the noise. Noise is always considered a "bad thing" and an imperfection. (Well almost, some analog synths use noise sources to make different types of sounds, for example) Sources for noise are resistors and semiconductors. Noise affects the signal-to-noise-ratio, SNR, which is often expressed as desibels, dB. SNR is used in pro and often consumer audio electronics to describe the amount of the wanted audio signal compared to the not-wanted noise. I think that the BC547 in the output circuit could be replaced with BC549 or BC109. They both are "low noise general purpose" transistors. I will check it later. I don't fully understand the functionality of the original output circuit, but I will work on that... Is it just for preventing overloads (=short circuit), in normal operation the transistor doesn't conduct...? Hope someone knows better! Oh, and the input circuit looks strange too... there's basically two capacitors in series...!?! Why? The other is a coupling cap, that's for sure, for blocking DC-current. But the other one... ??? Well, as I said, I will work on that. If there's any interest, I'll be happy to share my information to others.

Hello everyone! Here is some questions from a newbie MidiBoxer... I have understood that the Audio In/Out circuitry is copied from the original design of the C64. Am I right? The Audio out uses a "general purpose" transistor BC547, which is used in a common collector (emitter follower) circuit to prevent damages caused by shorted pins. Am I right? If the transistor is replaced with a low noise audio transistor or a low noise opamp buffer, the signal will be clearer. Am I still right? ;) Also the Audio In could have an opamp buffer... Does this make any sense? Has anyone tried different component setups? Or is the amount of noise coming from the transistor so small compared to the overall noise that it can be neglected? Thanks! -zenguru-