markdude

Hi, basically I want to build a very very simple bass amp on a protoboard for a project with the speaker included that is portable (so powered off small batteries). I was thinking of using a design similar to the below, but I don’t know what values of resistors and other components to use, also if I did use 12 V power supply I wouldn’t want the op amps to saturate so I going to have 2 limit my gain quiet considerably. And how would I get the – 12 V off one battery? Would I need 2?

Has anyone got any ideas on what values I should use or a better circuit design as I don’t know how this will sound. Also does anyone know the typical output from a bass guitar? I imagine it something less than 1 mV but am unsure. ops:

Thanks for any1 who replies, cheers. markdude

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Nigel Goodwin

Yes, you would need two batteries to do it that way!.

The first thing you ned to decide is how much power you want, and what sort of battery supply you are intending using.

For a first suggestion - use a 4 ohm speaker, not 8 ohm - this will provide double the power off the same voltage supply. Using a 12V supply (like a car battery) you can get 4 watts RMS in to 4 ohms, using a bridged amplifier you can get 16 watts RMS in to the same 4 ohm speaker. Using circuits designed for car radios is probably a good way for you to go.

No, it's lots more than that - I've never actually measured one, but I would guess at 50mV played very softly, and probably 500mV giving it some hammer - if I get round to it, I'll stick a scope on my daughters and measure it.

markdude

Thanks!
I will look into a bridged amplifier and find out about them first, I could use a car battery I guess but I was thinking something smaller and more practical to transport. But I prob need a hefty battery anyway to be able to power the op amps and the speaker adequately without it running flat quickly anyway.

I will look into the speaker being 4 ohms as well and reply with what I find out. Sorry about the 1 mV it was a mistake I meant 100 mV, so I think it less than 100mV output from bass, but I don't really know for sure.

Thanks for the help cheers. Markdude

markdude

I looked into the bridged amplifier but I didnt really find much else out other than it can quadrouple the wattage into a speaker, how would I wire it up so that I could keep the design similar to the one I already have (above).....

thanks for any possible help. Markdude

Nigel Goodwin

There are lots of chips which are designed as bridged amplifiers for 12V car use. Have a look at the datasheet for the (single ended) TDA2006 at http://www.videosistemas-net.com/dat...s/TDA-2006.pdf which gives an example of how to bridge it (although on +-12V).

markdude

Thanks again! I looked at using the bridged amplifier circuit on them datasheets and I think I would be able to use it and for the power gain out of the speaker I would have thought it was certainly worth it.

I still have the problem however of having a - and a + 12 V, is there any possible way of achieving both off 1 battery, it could be a standard car battery or other 12 V source?

Thanks for any help. Markdude

Nigel Goodwin

No, you would need two 12V batteries (or one 24V, with a centre tap).

The TDA2006 datasheet I mentioned was just to show you what bridging is, there are LOT'S of single IC bridge amplifiers that work off a single 12V supply - intended for car radio use - your car radio probably has at least two of them inside. The TDA2005 is a single bridged 12V amplifier, you could try searching for that one.