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softmoo 5th December 2012 08:28 PM

Newbie questions - are my plan and costs reasonable?
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Hi everyone,

I learned about these chipamps in makemagzine #23 - "squelette amp". This got me interested to build an LM3886 based chipamp.

The costs for a chipamp seem quite high; my plans show 220 CHF for a 2 channel chipamp in a nice case.

Is this reasonable? Does my (attached) BOM look correct? Is it worth it, say if I use JPL control 1 speakers?

What do you all think? Thanks!!

-the n00b

JMFahey 7th December 2012 12:51 AM

You are basically buying at Farnell, so the prices are normal.
Your BOM looks fine.
You are almost reaching 140Euro *just* with case, transformer. power connector and volume pot, it's your choice.
The actual amplifiers (Chip, PCB and electronic components ) cost peanuts in comparison, but that's the practical rule.
I make (guitar) amplifiers commercially, but to be competitive I have to make my own cabinets, chassis, PCBs and transformers, go figure.
In fact, I even make my own speakers !!!
Because when you buy stuff "over the counter" you must be ready to spend about the same (and sometimes more) than a commercial product.
Sad but true. :(

nigelwright7557 7th December 2012 12:58 AM

Ready built LM3886 amp pcb's are peanuts on ebay.

AndrewT 7th December 2012 11:16 AM

expect the "amplifier" cost to be ~10% of the total cost.
chassis ~30%
PSU & heatsink ~30%
amp+hardware ~30%
Adjust to make 100%.

Another unhelpful post?

Robert Kesh 7th December 2012 11:55 AM

Shaving off the pennies...

Your bleeder resistor seems expensive. Across each side of the supply, assuming it could hit 30V as a worst case, you could just use a penny 1/4 watt 8k2 resistor and be very well within rating. It doesn't have to be 2k. Parallel a few 8k2s if you like.

You can save a little money getting the NoPb version of the 3886 from Farnell at €3.41 each

And 80VA 2x18s are very cheap from Farnell, so you could buy two and use one for each chip. You'd have to double on rectifiers, but could split your capacitance across each load, though that means buying smaller caps, and the EPCOS 12000uF are a great bargain.

You have a fuse holder AND a fused inlet. But maybe you are planning to fuse the secondary side/power rail.

softmoo 12th December 2012 05:51 AM

Thanks everyone for taking the time to respond. :)

Arty 12th December 2012 07:34 AM

transformer may be purchased 2nd handed, or try to salvage one.
The case is usualy a nother hard hitter, prehaps You could visit a woddworkshop and get one for cheap, made out from wood.
The "rest" of the amplifier is as allready sayd peanuts.

sreten 12th December 2012 10:44 AM


FWIW JBL Control 1's are one of the grimmest sounding small loudspeakers
I've ever heard. They will go loud, but have no bass whatsoever, a peaky
midrange and a very bright piercing treble, they are not hifi at all IMHO.

[A friend of mine liked them, which was beyond me. Turned out later
he took a hearing test and he had terrible (for his age) hearing loss.]

In the UK here are two options you couldn't hope to build for the cost :
Used Pioneer A-300X amplifier, superb build quality for ~ 70.*
New Wharfedale CR30.4's, Richer Sounds, excellent for 100.

rgds, sreten.

* Far better than the (in)famous NAD3020 - no tone controls though.

Robert Kesh 12th December 2012 11:20 AM

JBL Control Ones are very useful as monitors for mixing music. The idea is they will present you with a worst case, just about acceptable speaker to test your mix with.

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