Szekeres AC-Coupled Gain Stage Layout
May 25, 2003 at 11:06 AM Post #3 of 11
Hey,

I don't like it very much. You are too concerned about aesthetic nature of the board. No parts has to be parallel to each other. That is causing strange routing messes.

Unless you can't avoid, stay on one-side only. The amp is way too simple for double sided.

The space allowed for the mosfet is too small. Remember you will need to attach a heatsink.

You will need far more space for coupling capacitors. As you upgrade your amplifiers, you will undoubtedly upgrade your couplign capacitors. In such case, you will need a lot more space.

C2 needs to be paralled with a polypropylene capacitor. (Or two)

R4 will heat up quite nicely. Just so you know.

Anyway, mainly never ever think you have to orient a part certain way, because it never is true.

Tomo
 
May 25, 2003 at 4:43 PM Post #4 of 11
Wow thanks! What are some good coupling caps? Solens? I will leave more space for the mosfet, r4, and capacitors, but i just want this as a basic layout for what i will put on a protoboard. I actually tried to put all the components on one side, but that didn't work too well with me.
 
May 25, 2003 at 6:59 PM Post #5 of 11
Quote:

Originally posted by Tomo
Hey,

....

Anyway, mainly never ever think you have to orient a part certain way, because it never is true.

Tomo


Not true, Tomo! Feng shui dictates that for harmonious signal transfer, coupling capacitors must always face north. Or is that supposed to be one's bed?

evil_smiley.gif
 
May 25, 2003 at 9:06 PM Post #6 of 11
Hello,

I did everything on one side so far. I don't see why not. Your routing is all over the place. For example, 4.7K at the ground rail shouldn't be there.

Try this: Route Szkeres stage. Then Route Opamps stage. Do it separately. Note also, first thing you do should be to lay out your parts like in schematics. Once you done that you can start rotating etc. I don't think you are doing that. Parts are all over the place.

Next, I don't see any power supply bypass capacitors. Szkeres stage will require pretty good bypassing about 1000uF or so. Bypassing for opamps are also required.

Lastly, I used Solens and Siemen. You can use several other different types, Wima, Kimber, Jensen, Multicap, etc. Good coupling caps are generally large. It makes sense to have ample space in fact capacitors themselves can take twice as much space as mosfet's with Heatsinks. (Don't forget about heatsink footprint!!!!)

T

P.S.
Hum ... Feng Shui? I thought that would improve your sex life or income.
tongue.gif
 
May 29, 2003 at 1:11 AM Post #8 of 11
Hi,

Opamp bypass can be done with a pair of very nice caps (4.7uF ~ 22uF). Note it doesn't have to be very large. On the other hand, MOSFET stage must be bypassed with something as high as 2200uF. (I used 2200uF because I had a pair o' Cerafines.)

C2 is an electrolytic. This is not a good thing. Electrolytics tend to sound loose. Looseness becomes more noticeable with higher capacitance. So I usually use the values calculated from RC low pass filter equation with R=headphone impedance and corner frequency 10~20Hz. This gives 3dB point. So pick slightly higher value than the one calculated.

Even that is optimized, high end is slightly loose. You can correct for that by bypassing C2 with good polypropylene caps. I usually use ~1uF caps. Right now, I use 4.7uF + 0.47uF. WHY? Because I got way too much of these caps. I gotta burn some.
tongue.gif


T
 
May 29, 2003 at 6:34 AM Post #10 of 11
Hello,

The schematics are illustrating an idea. We expect you to know some electronic know-how. For examples, supply bypassing should come to your mind immediately. C2 bypassing is required.

C1 can be reduced. This interstage capacitor must be high quality. Stay away from electrolytics here.

T

P.S. Sorry we don't always explain everything. But then it is that way with everything. So you gotta study up on materials. (Yeah who says this is easy.)
 
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