ok i'm back to this again, i have just completed assembly on stripboard and am about to do some de-bugging, co's i know there is going to be some

http://experimentalistsanonymous.co... Synths Drum Synths and Misc Synth/Syntom.pdf

The output is from a CA3080, is this capable of powering a small 8Ω speaker, or do i need to feed the output into an audio power amp?

I don't mind going out to buy an amp/speaker combo as i will use it for all the other audio projects i intend building over the next few months, but to test can i get away with just adding the speaker to the output?

Neil.

 

The output goes through R27 (10k), RV4 (47k log pot, actually 50k), and R28, a 47k Ohm resistor. No, you won't be able to drive anything but another amplifier with that high of an impedance output.

You may actually need another FET-input opamp just to buffer that signal before going into an audio amplifier, as the impedance of the above output will be very high; anywhere from 57k to ~104k. Line level audio is supposed to have a 10k Ohm impedance.

 

can i use a crystal earpiece for testing purposes?

Neil.

 

There would not even be enough current available there to hear anything much on ordinary earphones. You might (just) hear it a bit better with a piezoelectric ("crystal") earpiece. The frequency response of these things is pretty horrid though, especially at lower frequencies which may be relevant for your drum sound.

This contraption was probably aimed at driving a sensitive high-impedance input on an amplifier meant for electric guitars or other instruments. These would typically involve lower levels and higher impedance than a line input: 1MΩ input impedance might not be out of court.

A headphone-driving amplifier with a high input impedance, such as a guitar practice amplifier might be a good choice for this. Using decent headphones, you would probably be able to hear the sound better than with anything but really excellent loudspeakers.

 

I'm dertmined to get this circuit finished along with my light modulator, so i then have time to knuckle down and study analogue electronics, a very fascinating subject with all this talk of impedance, positive feedback, negative feedback etc

thanks for the help guys.

Neil.