rspangle@jarthur.Claremont.EDU (Randy Spangler) (04/11/90)
Ok, I've tapped the two wires to my speaker, with 1uF capacitors in the middle. But when I hook these (either way) into my keyboard mixer, I get this loud hum (guessing 60Hz) that swamps the actual sounds playing through the speaker. Should I have a connection to ground somewhere in here? If not, what's the cheapest and simplest way to kill the hum with a filter or the like? (from computer) BLACK YELLOW | | | | | | | +----------------||---------------- | | 1uF caps to keyboard | | (ceramic) mixer +--------------------------||---------------- | | | | (to 8-ohm .25W speaker) -- -------------------------------------------------------------------------- | Randy Spangler | The less things change, the | | rspangle@jarthur.claremont.edu | more they remain the same | --------------------------------------------------------------------------
jsm1@dukee.egr.duke.edu (J Scott McCalmont) (04/11/90)
From rspangle@jarthur.Claremont.EDU (Randy Spangler): > Ok, I've tapped the two wires to my speaker, with 1uF capacitors in the > middle. But when I hook these (either way) into my keyboard mixer, I get > this loud hum (guessing 60Hz) that swamps the actual sounds playing through > the speaker. Should I have a connection to ground somewhere in here? If > not, what's the cheapest and simplest way to kill the hum with a filter or > the like? Here's a new idea, if you have a real (old) IBM PC with the cassette interface on the back... I found that the "data out" connection on the cassette interface is tied to the same sound generator as the speaker. It's a little weird, in that when the PC is turned on (wait, wait, wait, disk light, BEEP!) the beep remains on continuously at the interface port. However, in BASIC the interface output follows the PC's speaker. The advantage here is that the cassette port can be configured for microphone-level output or line-level output. There's a set of jumpers near the front of the motherboard on my PC to make the switch. So, I just disconnected the speaker, bought a 5-pin DIN connector to connect to the cassette port, moved the jumper to line-level, added a capacitor to block the DC (although this isn't probably necessary, as most amplifiers will block DC anyway) and ran it into a stereo auxiliary input. You could also leave the jumper in the microphone position and run it into a microphone input. Since there are two ways of controlling the PC speaker (according to Peter Norton), this might not work for all applications. But it's slick, and doesn't require hacking up your PC at all. I've been waiting for a chance to post this! -- Scott McCalmont (919) 660-5244 Department of Electrical Engineering Duke University jsm1@dukee.egr.duke.edu Durham, NC 27706 ...mcnc!dukee!jsm1