Any ideas for a low-budget speaker amp?
Jul 23, 2009 at 12:27 PM Thread Starter Post #1 of 12

JamesL

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I'm at my parent's house for about 2 more weeks, and they wanted to know if I could build an amp for their in-wall speakers.

This is my first venture into a speaker amp, I have limited tools with me now, and I have limited information on the speaker requirements, so I'd really appreciate some guidance and perhaps some intuitive guesswork/estimates for what kind of power output I should be shooting for, if the heatsink looks capable enough, etc.

I couldn't find any specs on the speakers, but the previous owner noted that "50w is more than plenty". There are 4 separate volume controls and 2 woofers per control.

So far, I've scavaged a few potential cases, a hefty chunk of heatsink and a few smaller ones, switches, iec inlet & fuse, and some perfboards from broken electronics around the house.

I'm thinking of building a lm3886 or lm3875-based amp because of it's simplicity and popularity, though I'm also open to any class-D amps that may work.

If I go with a lm3886 gainclone, should I strictly follow the circuit on the datasheet? What kind of power supply is a good compromise, considering the ambiguous speaker specs and a single heatsink about yay big?
Antek has 100va toroids for $30 shipped, but I'm not sure if its sufficient. I have to buy furniture when I get back to school, so I really am on a 'starving-student' budget.
 
Jul 23, 2009 at 2:05 PM Post #3 of 12

JamesL

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Thanks nate. I haven't been to any pawnshops, but I've been cruising craigslist for anything interesting.
A lot of 1500w subwoofer amps, guitar amps, full-sized receivers.. a lot of ipod stuff, but nothing I'm really looking for.
I'll drive around though tomorrow and see what I can find.
 
Jul 23, 2009 at 3:11 PM Post #4 of 12

linuxworks

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class-T (tripath). $20 or less on ebay. 15w but its a good 15w
wink.gif
 
Jul 23, 2009 at 4:01 PM Post #6 of 12

linuxworks

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41hz site looks interesting. I had not seen that HIGH power tripath board before.

speaking of tripath, they say you can use switching power supplies with them but I got a lot of hum that way. when I went linear (12v, 1a) the hum went away. so, for some reason, switching was 'bad' for me. I plan to use a tangent TREAD or AMB s11 for this amp, I think.
 
Jul 23, 2009 at 11:45 PM Post #7 of 12

Zigis

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linuxworks, strange, maybe you unlucky have bad PS?
I use this amp board:
MKll Tripath TA2024 fully finished&tested pcb 2x15watt - eBay (item 250470450607 end time Jul-23-09 23:12:55 PDT)
with 12V 2A switching PS, wery similar to this:
12V 2A DC Universal Regulated Switching Power Supply - eBay (item 280344252845 end time Aug-08-09 18:59:18 PDT)
Very nice sound and absolutely no hum.
Amp board of course need small changes - change input caps to 2-3 uf polypropylene, Chip power caps to 470uf 16V PanasonicFM, 8600uf on power input. And preferably output DC nulling schematic.
 
Jul 24, 2009 at 2:35 PM Post #9 of 12

Heady

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Quote:

Originally Posted by linuxworks /img/forum/go_quote.gif
41hz site looks interesting. I had not seen that HIGH power tripath board before.

speaking of tripath, they say you can use switching power supplies with them but I got a lot of hum that way. when I went linear (12v, 1a) the hum went away. so, for some reason, switching was 'bad' for me. I plan to use a tangent TREAD or AMB s11 for this amp, I think.



I have an AMP6 Basic, with a switching PS and have experienced no hum. I have an AMP5 too. Both sounds good to me. I wish 41Hz has better documentation though.
 
Jul 24, 2009 at 8:25 PM Post #10 of 12

TimmyMac

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Quote:

Originally Posted by Heady /img/forum/go_quote.gif
I have an AMP6 Basic, with a switching PS and have experienced no hum. I have an AMP5 too. Both sounds good to me. I wish 41Hz has better documentation though.


I'm working on a Truepath and I know exactly what you mean.
 
Aug 24, 2009 at 5:04 PM Post #12 of 12

DKJones96

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When it comes to power output voltage is everything. Doubling voltage from +-12v to +-24v gives you a hair under 4 times the potential peak output power.

Considered just protoboarding a power amp? I paid $12 shipped for 10 pairs of IRF630/IRF9630 fets that bias easily and all else that was needed was an opamp set to a gain of 10. The most expensive part of the project easily becomes the power supply at that point. +-24v gives me ~65 watts(measured) into a 4 ohm speaker with just a single pair.
 

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