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Old 13th October 2006, 11:01 PM   #1
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Default My new El Cheap LM3875 PCB design.

After many attempts, I think I got it right. All I need is some more 0.1uf WIMA polypropylene caps.

The design is pretty simple; I've completed my first half-decent toner transfer onto the PCB material, and the traces are large enough that even a klutz like me can make a board that works. It's completely single-sided, although a jumper is required.

All the resistors are Vishay/Dale metal film (2% tolerance for the big Zobel resistors, 1-2% for the 22k and 680k reisistors), the capacitors are low-resistance Nichicon 100uf caps, and the 0.1uf bypass caps (soldered to bottom of PCB, directly to legs of 100uf caps) are WIMA metal film.

The total cost to populate one of these PCBs is a whopping 8$, assuming that one of the 4.7uf polypropylene caps from ApexJR is soldered P2P, and you can get LM3875's for 3$ as samples.

And, best of all, it's tiny. The cost to have one made by Olimex is about $1.20.
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Old 17th October 2006, 03:12 AM   #2
Cap_man is offline Cap_man  Thailand
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Good desing But what 's the circuit mode??
(invert , non-invet or t-network)
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Old 17th October 2006, 03:16 AM   #3
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Quote:
Originally posted by Cap_man
Good desing But what 's the circuit mode??
(invert , non-invet or t-network)

Standard gainclone. Non-inverting design following Fedde's schematic.
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Old 17th October 2006, 11:40 AM   #4
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Looks good!

Hows about some more info & Pictures!!

Tall Shadow
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Old 17th October 2006, 09:25 PM   #5
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Quote:
Originally posted by Tall Shadow
Looks good!

Hows about some more info & Pictures!!

Tall Shadow

I'll have pictures soon.

I did a bit of math: I can make a full amplifier (minus PSU) for about 25$, incl. cheapo homemade stepped attenuator, with parts ordered from Mouser and an Olimex PCB.

The homemade PCB's are almost done; I need to drill out the holes.
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Old 17th October 2006, 10:46 PM   #6
vhbaske is offline vhbaske  Puerto Rico
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Quote:
Originally posted by Spasticteapot



I'll have pictures soon.

I did a bit of math: I can make a full amplifier (minus PSU) for about 25$, incl. cheapo homemade stepped attenuator, with parts ordered from Mouser and an Olimex PCB.

The homemade PCB's are almost done; I need to drill out the holes.

BESIDES MOUSER, CHECK ALSO WHAT SOME PEOPLE OFFER AT eBay, I have bought some precision resistors there almost as a gift.
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Old 18th October 2006, 12:01 AM   #7
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Quote:
Originally posted by vhbaske



BESIDES MOUSER, CHECK ALSO WHAT SOME PEOPLE OFFER AT eBay, I have bought some precision resistors there almost as a gift.
Seeing as how 1-2% resistors are about 15-25 cents apiece, it's not that bad. Heck, an entire board (minus LM3875) is under 3$.
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Old 18th October 2006, 12:57 AM   #8
rjm is offline rjm  Japan
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Quote:
I can make a full amplifier (minus PSU) for about 25$, incl. cheapo homemade stepped attenuator, with parts ordered from Mouser and an Olimex PCB.
The bulk of Gainclone BOM has always been the PSU and chassis however, as it was with the original 47 Labs Gaincard. Leaving out these two most expensive parts and then saying "look how cheap my amp is" is misleading and if you ask me rather pointless. Heck, even the connectors alone would set you back $25 if you bought half-decent ones.

Examine the total cost, including power transformer, before deciding if PCB cost/area and resistor 1pc cost are really thnigs you need to spend time worrying over.

\R
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Old 18th October 2006, 01:17 AM   #9
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Quote:
Originally posted by rjm


The bulk of Gainclone BOM has always been the PSU and chassis however, as it was with the original 47 Labs Gaincard. Leaving out these two most expensive parts and then saying "look how cheap my amp is" is misleading and if you ask me rather pointless. Heck, even the connectors alone would set you back $25 if you bought half-decent ones.

Examine the total cost, including power transformer, before deciding if PCB cost/area and resistor 1pc cost are really thnigs you need to spend time worrying over.

\R

Heh.

Trafo cost: 15$ each. I have two.

Capacitor cost: 4$. This is for 2 12,000uf capacitors, and 4 WIMA caps to bypass them and for the snubber.

Resistor cost: Fifty cents. (Yay, Mouser!)

Power cable, small metal box: About 4.50$, thanks to my spree at a soon-to-be-closed RadioShack.

Total PSU cost: 24$, assuming I don't scrounge anything.


Gainclone:
1x two-pole 5-position rotary switch. Heloo, input selector! $1.50
1x ALPS motorized 100k pot. I found this in a sony CD player-FREE!
2x Gainclones, as above. 20$ or less.
2x 4.7uf ApexJr metal film capacitors. (The yellow winecorks.) 3$.
6x gold-plated Radio Shack RCA jacks: 5$
4x heavy-duty speaker terminals: SCROUNGED!
Metal case: Homemade from scrap copper. 10$ in parts, but free as a result of Art Metal equipment free.
Knob: Borosilicate DIY goodness!

Total cost: About 30$.


Total cost of Gainclone: 54$.

And, with the exception of the pot and LM3886's, I have parts for about four amplifiers. (However, my second one is going in a toaster.) I might also add an active class-A buffer as under Nuuk's gainclone page, adding about 8$ to the cost.

It's a great deal until you budget the 30$ I'm going to spend for a drillpress attachment for my dremel. All the caps are Nichicon or WIMA (with the exception of the input blockers), all non-PSU caps are 1-2% metal film, and the potentiometer is an ALPS, supposedly quite good.
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Old 19th October 2006, 06:23 AM   #10
rjm is offline rjm  Japan
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However, my second one is going in a toaster.
pixpls!



Scrounging, surplus, and scrap metal will certainly keep the cost down. Have fun.

/R
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