OPA627 + BUF634 Preamp PCB Design

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Hi!

Any comments on my PCB layout and how to improve it?
Is the grounding good enough wth the jumpers?

The pot is a Noble 50K dual log. :)
 

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I think the layout is fair but somehow I don't like your efforts to create a groundplane. Probably it will work fine but I would still suggest that you have ground under the opamps and two traces with v+ and V-, close to the IC's. I would also suggest compactness and smaller parts if possible.

Maybe you should have the BUF's close to the outputs of the opamps? Try to get the physical layout similar to the schematics.

Why don't you consider a pcb with groundplane? If you are going to make it yourself it's real easy with a groundplane. Just put brown parcel tape on the upper side. Se picture below.

An externally hosted image should be here but it was not working when we last tested it.
 
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P-A,

What do you mean by '50 ohms cable'? Surely you don't mean a cable with 50 ohms between the two conductors? Any decent opamp can drive a 50 ohms *characteristic impedance* cable, of course. It all depends on your termination resistor. If this circuit is used to drive a power amp of a couple of K or more input impedance, the buffer is pretty useless. If you want to drive say 30 ohms headphones, the buffer is a good idea, but then you wast more than half your power in R5,15. That's why I asked. It all depends om the application.

Jan Didden

Jan Didden
 
peranders said:

Did you get how I have done?

tape

etch

drill a bit with 3-4 mm drill

very easy :nod:

Yep, got it. :)


janneman said:
P-A,

What do you mean by '50 ohms cable'? Surely you don't mean a cable with 50 ohms between the two conductors? Any decent opamp can drive a 50 ohms *characteristic impedance* cable, of course. It all depends on your termination resistor. If this circuit is used to drive a power amp of a couple of K or more input impedance, the buffer is pretty useless. If you want to drive say 30 ohms headphones, the buffer is a good idea, but then you wast more than half your power in R5,15. That's why I asked. It all depends om the application.

Jan Didden

Jan Didden

I'm going to use this as a preamp for power-amps, not as a headphone amp. Should I leave R5,R15 out?
 
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No that's OK for this application.
I did note that you used the wide band connection for the buffer. That is important not because you need the bandwidth, but it puts the buffer in class A for this application. That may in fact be the advantage of having the buffer here. But for driving the power amp & cable (unless it's a lot, with high capacitance) you wouldn't really need it.

Jan Didden
 
Alcaid said:

I'm going to use this as a preamp for power-amps, not as a headphone amp. Should I leave R5,R15 out?
If you have 0-10 m cable I think a single opamp will (or can) be sufficient. BUF634 can deliver 250 mA and any good opamp can deliver quite high level into 600 ohms but I admit that a buffer is more "serious". One positive effect might be lower distortion.
 
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peranders said:

If you have 0-10 m cable I think a single opamp will (or can) be sufficient. BUF634 can deliver 250 mA and any good opamp can deliver quite high level into 600 ohms but I admit that a buffer is more "serious". One positive effect might be lower distortion.


P-A,

Surely you know that those buffers have quite higher distortion than those fantastic opamps, right? The wideband connection helps a bit by putting the buffer in class A, but it still will not come close to the opamp's performance. So, I am at a loss about your remark about the positive effect from lower distortion.

Jan Didden
 
janneman said:



P-A,

Surely you know that those buffers have quite higher distortion than those fantastic opamps, right? The wideband connection helps a bit by putting the buffer in class A, but it still will not come close to the opamp's performance. So, I am at a loss about your remark about the positive effect from lower distortion.

Jan Didden


So, what you're saying is that this preamp would be better with just the OPA627s, leaving out the buffers?
 
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