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Old 6th May 2012, 09:22 PM   #1
diyAudio Member
Join Date: May 2012
Default Two amplifier projects

Hello everyone,

First of all, I hope I post this in the right section. I'm fairly new to building audio equipment, though I had physics lessons in high school, which taught me how electricity works, and some ways to calculate with voltages, ohm's, etc. I also do know how to solder.

Now I have two little projects, both amplifier projects. In both cases I want to use a diy-kit from the webstore Conrad, along with some other needed parts. I will discuss the simplest first.

Mic Pre-Amp

So, I saw this diy-kit for a mic pre-amp. It contained the pre-amp pcb and the components. I also figured it would be nice to have an input jack for my mic (a 3,5mm jack), an output jack (also 3,5mm), a metal box to stuff it all in, and something to control the input volume with. So i need some kind of potmeter, but I have no idea which value I should use.
This is the link to the pcb: Mono microfoon voorversterker bouwpakket in de Conrad online shop
If you need any translation, just ask.
The purpose of this amp is to amplify a Shure Mic, which I want to use to record guitar (amp).
Please comment if you think I'm doing it all wrong, the purpose is though not to spend a lot of money.

Portable MP3-amp + speakers

Okay, this is a little bigger project. I have these Yamaha speakers, originally intended for home theater use. I once had a little mp3 amp but I lost it somewhere, but it was nice to have, so I thought: "Why can't I build one myself?". So the idea is a wooden box, to fit 2 yamaha sattelite speakers in. Both have a woofer and a tiny tweeter. The casing says the nominal input is 30 watts, peak input 110 watts. Then there should be a button on the box to power on and off, and a LED indicator to show whether it is powered or not, some kind of power source, batteries or a rechargable battery, and of course, some button to control the volume with (again potmeter of which I don't know the value).
At this point im thinking a couple of things. What should the amps voltage be? Aren't the speakers a too high wattage for the amp? What should the amps wattage be in the first place?

I was looking at this amp circuit: 2x10 Watt stereo versterker in de Conrad online shop

Please, help me out, I'd really appreciate it.

Thanks in advance,
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Old 7th May 2012, 02:40 PM   #2
diyAudio Member
Join Date: Nov 2008

For both products documentation is available under the "download-Documente" pull-downs

The Mic preamp is OK. P2 is the output level control and can be replaced with an outboard 50k Ohm log. (audio taper) pot

If you want to mary this preamp to the 2x10W amplifier you will need a buffer amp as the input to this amp is 50k Ohms and that calls for a dual (stereo) 5k audio-taper pot. Alternately just have the stereo pot on the power-amp and preset mic out level with the preamp's P2

The output wattage of the power amp depends on the supply voltag, so go for the max suggested in the data sheet. You will need the heatsink (109240-62) unless you mount the power amp onto a metal chassis.

Lastly: The wattage rating of the speakers should allways be higher than the amp driving it to avoid destroying the speaker

On the German site for the power amp is a little video worth watching

Cheers and good luck. E
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Old 7th May 2012, 07:51 PM   #3
diyAudio Member
Join Date: May 2012
Thanks for your reply Mickeymoose,

The part about the mic preamp is clear to me now, but I think you misunderstood the rest of my questions. The preamp and the 2x10W amp are two different projects. They wil not be joined together.
I was also wondering, if I let the 2x10W amp run at it maximum voltage (18 volts), won't it drain too quickly if I use, lets say, AA batteries? Isn't it a better idea to use a battery as found in mobile phones or other rechargeable devices. If so, I'll need some kind of recharge circuit, I guess.
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