Path: utzoo!utgpu!utfyzx!oscvax!utflis!wayne From: wayne@utflis.UUCP (Wayne Young) Newsgroups: comp.sys.amiga Subject: Re: Speaker for the Bridgeboard? Message-ID: <1081@utflis.UUCP> Date: Fri, 6-May-88 13:57:39 EDT References: <2915@crash.cts.com> Reply-To: wayne@flis.toronto.edu.UUCP (Wayne Young) Organization: FLIS, University of Toronto Lines: 46 Keywords: oooh, but did I ever have a time about it! Summary: Yes, I got mine to work In article <2915@crash.cts.com> artw@pnet01.cts.com (Art Weiss) writes: > > I asked this question once before and never received a response, so I >thought I'd give it another try. > Has anyone hooked up a speaker to their Bridgeboard? I have a friend who >tried but it didn't seem to work. Is there any special type os speaker that's >needed? > I'd like to have a speaker because there are times when those little beeps >would be useful. If anyone here on the net or at Commodore knows anything >about this I would appreciate their leaving me a message. > > ...Art I got my speaker hooked up, and no you don't need any special sort of speaker. I'm using a 1-1/2 inch 8-ohm speaker that's rated at about 1 watt. Read on, though. I had a devil of a time getting it to work. If you hook up you speaker and you can't get a peep out of it, then chances are you have the same problem I had. Are you handy with a soldering iron? If you aren't, get your bridgeboard repaired by somebody who isn't, like the people at Commodore. Chances are, the amplifier on the bridgeboard is busted, and you'll have to replace a few components to fix it. Look closely at the board near the two-pin speaker jack. You'll notice a discrete NPN transistor and several discrete resistors in a fairly tight cluster. The components form an emitter coupled amp. If you look closely you'll see a 100-ohm resistor (colours brown-black-brown) connected between a positive supply rail and the base of the transistor. Anything sound funny yet? You bet. This is supposed to be the bias resistor, and it's kinda small. Too small, in fact. You end up losing quite a bit of the signal since it's so small. And the transistor is improperly biased. Anyways, replace this with a friendly 3.3K resistor. Actually, you should experiment and choose a different value because this resistor sets the volume of the sound. If you can find a small 10K preset, then work that in there. Lastly, you'll probably have to replace the NPN transistor itself. Any small signal, general purpose transistor should work okay. I hope this works out for you. I had a fun time invalidating my warranty, and I'm very disappointed in Commodore for failing to properly design a simple emitter coupled amp. Can you say "Oops", guys? -- ----- {uunet,utzoo,decvax,ihnp4,allegra}!utcsri!utflis!wayne