Now killed the noise in the Pug. Thought I might warm the soldering iron up and see if this is any good. Comments welcomed. I am going to try and reduce the boominess of the factory headunit when amped. It may or may not improve things, but I want to get doing some basic electronics again for a laugh. The wife will hate this bit....

see

Go for it John!Sounds like fun.I've pondered ideas like this myself,but I've got so many irons in the fire now that I just buy the stuff pre-fab and plug it in.
I didn't realize you were so good at electronics Doc. http://bbs.scoobynet.co.uk/smile.gif

how you going to generate a nice clean +/-9V (min) supply?

Site updated after thoughts on power supply - see what you think of the voltage regulator.

I have a noise suppression filter on the headunit power supply and will take 0V and 12V (nominal of course) from that - I know it is a lot cleaner than it was before as all traces of alternator whine have now vanished since it went in.

[This message has been edited by john banks (edited 21 June 2001).]

Unfortunately the regulator doesnt work from a +ve supply. It needs a -ve supply which it will then regulate to the -ve voltage you set.

A switcher will do the trick but complicate matters in the amount of noise it will generate. You would need to filter this and pass though a linear regulator to get anywhere close to a clean supply.

I hate to say, but you're probably better off with a comercial solution.

So as Im not labelled a total killjoy, you may want to look at

Mmm, that was dawning on me that it needs a negative supply, and then your post confirmed it. Need to think a bit more. Presumably the switches charge up a capacitor and then discharge it with the connections reversed at their oscillator frequency - ie I get a horrid 10KHz overlay.

Have looked at the pdf and wondering if I can poach some ideas.

Seems like such a nice little graphic chip too... Maybe I should just buy a new headunit and save the hassle!

[This message has been edited by john banks (edited 21 June 2001).]

There's a nice little DC-DC converter chip that might just do the trick as it switches at 800KHz! Few promising leads, and folk from the uk.rec.audio.car are helping out. Hopefully sci.electronics.basics will help also. Thanks all. It is just starting to get interesting, and I hope to learn a lot.

Youre not too wrong with the description of a switcher. However, they have a knack of creating noise all over the frequency spectrum (inc. audio), so a lot of care needs to be taken in using in analogue applications.

I've always used a switcher to generate over the dc voltage I require and then filtered and linear regulated to the required voltage. You'll probably need to supply the linear reg with at least 1.5V (check data sheet - dropout voltage) more than you want it to supply. So if you want 9V feed it with 10.5V.

The other important thing to consider when using the car 12V supply is the transients it will see when things like air-con and alternators switch on/off. You need further input protection as the voltage will peak to above what most standard linear regulators will handle. You should really be looking at regulators aimed at the automotive market.