Building Amp for TB 871s (1 Viewer)

[Nat Ward]

Hey guys, I've got a pair of TB 871S drivers that I'd like to turn into computer speakers. I've read around and have a decent idea of what I'd like to do for the enclosures, but I'm lost on how to power them. I want to do something stand alone so a cheap stereo reciever is out of the question. I saw on ApexJr the 12W (at 1.6ohm) JBL computer speaker amp and thought about it. But reading around, it'll drop below 6W for the 8ohm load the TB's will show it. First question......will 4W or so do me good for a computer speaker that will most of the time sit 1ft from my head? What about listening to them while watching DVDs on the laptop at the girlfriend's place from a distance of 5-10ft? If it's a viable option I'd love to hear that. Second option would be to build a small amp, specifically the 30W Velleman unit from Parts Express (part number 320-212). Only thing is that I graduated a mechanical engineer and I'm totally stupid with EE stuff . If given diagrams and instructions I'm handy enough to put it together, but designing and figuring it out on my own is tough, it just doesn't seem to sink in. Anyway, reading the PE description it appears I need a transformer, which I take as being the unit that coverts the 120V AC signal from the wall into something managable for the IC chip. My questions to anyone out there that might have built an amp or done enough research to know how it works are:

1. How do you wire up the transformer? Do you get a standard wall plug, run the wires to the input on the transformer and then from there to the R and L +/- on the Velleman circuit board?
2. Is that transformer (as recommended and sold by PE) the same type of thing that's in the "black box" you plug into the wall for commercially purchased computer speakers?
3. How do you get sound input to the circuit board? There is R/L +/-, can you somehow split a regular RCA cable into the right and left channels?
4. How should I control volume? I will be using the headphone out on my laptop (it doesn't have a line out), so I could just use the volume there, but should I wire up a potentiometer instead?

I guess I could just use some help in understanding how to build a small, somewhat simple amp like this. Or does anyone have an idea of where I could find a 10W or so amp ready to go? If there are any webpages that'll help me out I'd love to see them. I might be stupid with electronic cicuitry, but if it interests me like this I'm more than willing to learn. Thanks!
Nat Ward

 

[Bob K]

Nat,

Let me give you an offbeat suggestion: a tube amp! The 8W K-502 stereo integrated tube amp kit available from Antique Electronics Supply, http://www.tubesandmore.com , is a flat-out giant killer for a mere $140. I put one together in a morning (the amp is circuit-board based and extremely easy to build) and use it to drive a pair of single-driver Fostex speakers in my garage/igloo/shop -- simply amazing. A picture of the setup is here: http://f1.pg.photos.yahoo.com/ph/ele...p+System+2.jpg . You will want to enclose yours!

Although the TB drivers are rated 87 dB, the amp should drive them fine for nearfield computer use.

Whatever you settle on, happy listening!

Bob

Tempest Construction Pix: http://www.audiocircle.com/circles/m...view_album.php

 

[Frank Carter]

Did you happen to check out the Dual 25W sub amp from Apex Jr? I think that would be a a good option. It costs $25 w/the transformer and will give each woofer 25W.

 

[Nat Ward]

Thanks guys. I think a tube amp would be a fun project, but I'm looking to keep this project simple and small. Maybe sometime in the future. I bookmarked the page though! And thanks for the reply Frank. I guess I didn't look at the 25W amp because it was listed as a "subwoofer" amp and I didn't know if it was full range. I looked on the net and found a spec sheet which shows it 20-50k (!?) Hz, so I guess it'd work. I'll have to email ApexJR and see what they've got to say. For $25 that'd be exactly what I wanted.
Nat