Hi,
I've been trying to breadboard the Keyboard Controller circuit described on this page
http://musicfromouterspace.com/inde...MAINTAB=SYNTHDIY&SONGID=NONE&VPW=1252&VPH=500
Almost all of it has been working fine, however part of it, the sample and hold section, keeps giving me troubles! It is supposed to take in a certain DC voltage (depending on what keys is pressed) and hold that voltage on a capacitor even when the key is released. This voltage is then buffered with an op amp. When I build this section however, a key is pressed and the output of the buffer initially assumes the correct voltage but then quickly ramps up to V+. I've also found that disconnecting the sample cap and buffer from the rest of the circuit still shows this behaviour, so if you just connect the capacitor from the non inverting to ground, and tie the output to the inverting, the output ramps up as well. This has really been confusing me because I can't think how the capacitor can be charging if all it's connected to is the non inverting input of the op amp. Initially i was trying this with TL074 and TL084 op amps however I've just tried it with the suggested LF444 and it's still doing the same thing. Any help as to why this is happening or how to fix it would be greatly appreciated, thankyou!
Ned
I've been trying to breadboard the Keyboard Controller circuit described on this page
http://musicfromouterspace.com/inde...MAINTAB=SYNTHDIY&SONGID=NONE&VPW=1252&VPH=500
Almost all of it has been working fine, however part of it, the sample and hold section, keeps giving me troubles! It is supposed to take in a certain DC voltage (depending on what keys is pressed) and hold that voltage on a capacitor even when the key is released. This voltage is then buffered with an op amp. When I build this section however, a key is pressed and the output of the buffer initially assumes the correct voltage but then quickly ramps up to V+. I've also found that disconnecting the sample cap and buffer from the rest of the circuit still shows this behaviour, so if you just connect the capacitor from the non inverting to ground, and tie the output to the inverting, the output ramps up as well. This has really been confusing me because I can't think how the capacitor can be charging if all it's connected to is the non inverting input of the op amp. Initially i was trying this with TL074 and TL084 op amps however I've just tried it with the suggested LF444 and it's still doing the same thing. Any help as to why this is happening or how to fix it would be greatly appreciated, thankyou!
Ned