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Old 23rd October 2009, 01:03 AM   #1
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Default LM3875 Chip Amp Buffer NIGCB

I built Peter Daniel's Non-inverted chip amp kit for LM3875 and am very happy with it.

I am now looking to build a pre-amp to work very well with it, and the passive options (basically a pot or resister selector) are a compromise at best, from what I hear, due to an impedance mis-match between source and power amp.

The solution, it is said, is a buffer, and the design I hear much praise of is the Pedja Rogic j-fet buffer. He offers a kit, but I can't afford it - it's 280!!!

I have been trawling for info on how to source a schematic and shopping list and advice on building a j-fet buffer, but I'm coming up short of a good source. There's a few very techy discussions about the details and component choices, but I get lost easily, as I'm not an electronics engineer.

So, can anybody help me with a pcb source (or design) and a shopping list for a tried and tested buffer, or am I asking too much? I would prefer to be spoon-fed a lovely design and build process by an electro-genius than buy a kit, or worse, trawl and get confused...

Speaking of kits, Peter Daniels does one for $160. Is that a good option?

Many thanks
Lucas
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Old 23rd October 2009, 02:04 AM   #2
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pick up a pass B1 buffer PCB on ebay, they're $10 or so. the all-fet borbely buffer pcb is also great.

Buy the parts on Mouser, populate and solder, power and connect.
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Old 23rd October 2009, 11:32 AM   #3
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Thanks Gripracer. Have you used this board? How is it? Do you have a shopping list for me, and/or a schematic? Is there a build guide anywhere? Many thanks, Lucas
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Old 23rd October 2009, 12:03 PM   #4
ratza is offline ratza  Romania
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I'm using a preamplifier with OPA2134. If you're interesed in making the board by yourself, I can upload the design.
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Old 23rd October 2009, 12:29 PM   #5
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Tell me about OPA2134 Ratza....op-amps are just numbers to me.
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Old 23rd October 2009, 01:19 PM   #6
ratza is offline ratza  Romania
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Well, it's pretty hard to explain, as you say you're not an engineer. Shortly:
0.00008% distortion - 750 times better than LM3875,
huge bandwidth - flat output way out of audio spectrum,
low noise - I can hear a slight hiss with input disconnected and pot set to maximum but only during the night and only if I stick my ear in the tweeter. At 4 inches away there's complete silence. My speakers are 92dBm/W so this is quite impressing.

This is how the preamp looks, it has the same power supply as the LM3886.
http://i33.tinypic.com/6fv7sg.jpg
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Old 23rd October 2009, 06:05 PM   #7
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Quote:
Originally Posted by LucasAdamson View Post
Thanks Gripracer. Have you used this board? How is it? Do you have a shopping list for me, and/or a schematic? Is there a build guide anywhere? Many thanks, Lucas
The seller will send you a parts list and schematic when you buy the board. Building is very easy, you just stick the parts through the holes in the right places (marked with little pictures and numbers on the board itself), and solder. YouTube has great soldering tutorials.

About op-amps, I try to stay as far away from them as I can. "HiFi" sound, to me, should never include op-amps. Discrete>op-amp. They have many more active devices than is necessary and rely on negative feedback for their low distorion numbers. They were created to save money and space, and even the best ones are easily outperformed in terms of sound quality by any well-designed discrete stage. They will make your music sound compressed and unnatural. Op-amps are all about the spec sheet -- they look amazing on paper, but they have no place in music IMO.

Also -- if you want a good tube buffer(prebuilt, proven), there is one on eBay for under $100 including a power supply and tubes. It is based on the Musical Fidelity X10-D buffer.

Last edited by gripracer; 23rd October 2009 at 06:24 PM.
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Old 23rd October 2009, 08:58 PM   #8
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Thanks Gripracer. I've got the schematic now. A FET is an op-amp, as far as I'm aware.
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Old 24th October 2009, 01:10 AM   #9
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Quote:
Originally Posted by LucasAdamson View Post
A FET is an op-amp, as far as I'm aware.
More reading required.
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Old 24th October 2009, 07:02 AM   #10
ratza is offline ratza  Romania
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Quote:
Originally Posted by gripracer View Post
They will make your music sound compressed and unnatural. Op-amps are all about the spec sheet -- they look amazing on paper, but they have no place in music IMO.
You realize that recording studios are using lots of op-amps, don't you? And still, music plays well.
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