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newbie DIYer questions

post #1 of 5
Thread Starter 
Hi, I'm an electronics technician student. I'm interested in starting my first independant project. All others have been related to school. Just a couple of questions that I need some clarification on.

I've just ordered a pair of Sennheiser 580s. I sold my mid-grade amp to get them, so I'd like to build an amp.

I'm interested in building the Meier crossfeed amp with a buffer output.

http://www.headwize.com/projects/meier_prj.htm

After speaking to a collegue with expereince in audio he recommended the OPA134/2134 for the front end and the BUF634 (TO-220) for the driver, both by Burr-Brown. I've been checking up on metal film resistors and polypropylene caps.

1. Is it better to have a small compact ciruit when it comes the headphone amps or can I spread it ot over the board without worrying about interference?

2. I plan to use an amp in the home and not for portability. Which brings me to the next question.

Would the sound quality of a larger circuit better that of a pocket amplifier or are they comparable?

3. I like listening to my records. The output on my record player is very low compared to my CD player:

Should I create a circuit with a separate phono input or will the intended circuit perform well?

Would a screw for chasis ground do the job of chasis grounding or is there someting more I need to do?

4. Does anyone know of a high frequency filter that would reduce the pops an cracks from the records?

An help would be greatly appreciated.

Matt Gregg
post #2 of 5
The Burr-brown OPA134-BUR634 is an excellent combination. A benefit of using it is it is more stable than the LM6172's used in the orignal design, which will give you more flexibility for the layout. Still it is a good idea to keep the board as small as you can, and keep all wires as short as possible. This will keep it more stable and prevent noise pickup.

The original opamps used in the article are also very good, though they are video opamps, so they are pretty well unkown to audio hobiests. Nevertheless, they are much faster and have more current output, so you could use them without the buffer. I'm not sure which one is better, i've tried both but haven't done direct comparasons. But if you use that design, definately pay attention to the layout for best performance.

2) In a home amp, the extra space shouldn't really matter, but you do have access to AC instead of batteries. As a result, you can use higher voltages and draw more current without worrying about carrying lots of batteries. But you will need to spend a lot of money on good power supply regulation/fitereing or the amp will be noisy.

3) A gain stage at the input of the amp will be enough to boost the volume. But records are equalized with an RIAA equalizaiton curve, so you will need to duplicate this filter. It would be easier just to use an existing phono preamp.

4) dunno about this one, but anything that could filter out pops and clicks would also roll off audiable frequencies... Don't think you could do that without degrading the sound.... Instead, you may want to work on your turntable to reduce pops and clicks...
post #3 of 5
In my exsperience, the filters tend to remove a portion of the signal too, and I have found that to be a bigger liability then the original noise.
post #4 of 5
Digikey now has some Buf 634's by BB in the 8 pin dip package which are easier to build a buffered amp with, plus you can change opamps and buffers later if you use this type.
Also there are several versions of Cmoy's amp using current opamp and buffers. Check out the addendums at the end of this article. Crossfeed is in another article, but is shown in several cmoy versions.
Dan
post #5 of 5
Hello,

Not much could I say when I built my first amp because I had nothing to compare to. You should just go ahead and build one. Your design is perfectly fine and it will work pretty wonderfully. Some people will suggest better buffers like EL2001 or BUF04. But then going on this tangent is not productive. ...

The size of circuit does not directly effect the performance of amplifier. What matter is how you place the parts. I can build two amp with difference size but the same quality. But you can definitely go wrong if you do "iffy" things.

Phono preamp is essentially low noise high gain amplifier. You may build your phono section with an opamp. But it has to be very low noise. Use opamp like AD797 and wire circuit extra carefully. Pull out your textbooks and the most of the important things about low noise amps should be there.

Grounding is very important. Screws do good enough. However, I prefer soldering my ground directly to my MAINS transformer ground. This is much better since screws do NOT mean perfect contact. It sometimes misbehaves.

I do not like records since these require high maintainance and I don't really want to spend time and efforts to keep them at good conditions. I understand digital signal lose some information. But for me, CDs are more convenient. ...

You may actively or passively filter out high freq with high pass filter. However, that may lose too much information. If you cut too much, you may get poorer signal than from CD. I would make my filter with a cap and variable resistor. You will never get rid of the skips and jumps but you can soften them. Getting rid of all of that you will need to process the information digitally.

Tomo
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