LM3875 Chip Amp Buffer NIGCB

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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
 
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
 
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:
More reading required. :D

Operational amplifier - Wikipedia, the free encyclopedia is where I looked and found specific mention of FETs, but I see now that I skim read, (as is usual for me with electronics, because after a while reading these threads, it can become a bit like reading algebra in Crylic.) Electronics is mostly still magic to me. I just don't get how these resistors and capacitors and fets and opamps and semiconductors make music out of electricity...
 
Last edited:
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

I've just re-read this, and it struck me: Why would it be so important to reduce total harmonic distortion so low? There's a road over at the end of my garden, and the cars going by make a permanent shhhing noise in the rain, but it gets blocked out. Furthermore, from my armchair, I've never heard hiss coming from the speakers with any amp I've had, except at ludicrous volume, which would permanently deafen my treble hearing anyway.

What I'm saying is, surely transparency is the key quality we look for in a pre-amp.
 
Last edited:
FET input means that the input impedance of the operational amplifier can be driven with very small currents, i.e. high input impedance. For me is important that the system's own noise is as low as possible. I listen sometimes during the night when is very silent and I hate to have hiss or hum audible between CD tracks.

Sound transparency is a combination of many factors, most important being the slew rate (how fast a signal can rise up) and the total distortion.
I'm not saying that harmonics do or do not sound well; I have a EL84 tube amplifier which is anything but hi-fi and yet it sounds great. So, the distortion figures aren't always that important, but that chip really sounds good and is cheap for the job it does.


P.S. Yes, it's a drunk guy who fell off with the toilet. It amuses me every time I see this picture.
 
You realize that recording studios are using lots of op-amps, don't you? And still, music plays well.

There are also op-amps in "high-end", expensive audio electronics. Op-amps are compromises in 8-pin packages, made to save space and lower power consumption.

Saying an op-amp is a better option than a discrete circuit when it comes to the absolute highest sonic performance is like picking an efficient hybrid city car over a purpose-built race car when trying to improve your lap times.

There is a place for op-amps, but they simply do not belong in any well-read enthusiast's audio system.
 
Hi jaste. The preamp uses the +/-30V rails from LM3886 power supply and this voltage is then reduced with a discrete regulator. The regulator transistors will dissipate 0.7W in case of shorted output, so there's no need for heatsinks. Here are the files for the preamp. I can provide also the details on how I calculated the values, if needed.
 

Attachments

  • OPA2134_preamp.zip
    43.3 KB · Views: 213
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.