A GC Layout check.

S.C · 2003-07-14 4:44 am

Hi can anyone help me?
http://hk.geocities.com/solomon_choi/Mygclayout.jpg :devilr:

S.C · 2003-07-14 5:21 am

A Little changes.
http://hk.geocities.com/solomon_choi/Mygclayout02.JPG :idea:

Nuuk · 2003-07-14 8:58 am

Sorry, but what are we meant to be looking at? :scratch:

carlosfm · 2003-07-14 1:54 pm

I'm stuck here

Gotta run.
Oh...
How do I get out of here? :bawling:

S.C · 2003-07-14 4:14 pm

Try this one :bawling:

http://hk.geocities.com/solomon_choi/GC2.html

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

carlosfm · 2003-07-14 4:35 pm

That will not work.
I don't understand that signal ground. :scratch:

Take a look at Nuuk's excellent page, you'll find information there.

Nuuk · 2003-07-14 5:17 pm

That will not work.

Carlos has spoken

Actually I am not so sure. The only mistake that I can see is that pin 7 should be connected to the signal ground star.

When I originally did my GC, I connected pin 7 to the power star and got what sounded like too much bass!

Take a look at Nuuk's excellent page, you'll find information there.

Carlos has spoken again and I can't disagree with him this time

S.C · 2003-07-14 5:24 pm

My layout almost base on Nuuk's site, but we are using to different sch.http://hk.geocities.com/solomon_choi/GC2.html Plz look at the 3th pics. :scratch:

and what else is wrong, or you kind of having a bad feeling on?

Nuuk · 2003-07-14 5:32 pm

Correct me if I'm wrong but shouldn't a polarised input cap have the positive leadout facing the input? I hadn't thought about this on my GC as the Black Gate NX-Q is non-polarised.

carlosfm · 2003-07-14 6:00 pm

Nuuk said:
Correct me if I'm wrong but shouldn't a polarised input cap have the positive leadout facing the input? I hadn't thought about this on my GC as the Black Gate NX-Q is non-polarised.

I've seen if both ways in commercial products. :dodgy:

What is confusing me here is the R2 resistor, the signal ground and the input.
The sketch is a little confusing.

JOE DIRT® · 2003-07-14 6:11 pm

positive should be on the input side for the cap...atleast thats the way I`ve always arranged it

DIRT®

Nuuk · 2003-07-14 8:05 pm

What is confusing me here is the R2 resistor, the signal ground and the input.

Carlos, if you don't have a pot/attenuator as part of the GC circuit, powering it up without anything connected will cause problems.

So a resistor is soldered between the input and ground that takes the place of the ground leg of the pot/attenuator.

So, other than the ground connection from pin 7, which should go to the signal ground; and the polarity of the input cap, that circuit would seem to work fine.

If you want to refine it a bit, the input resistor could be put at an angle so that it mirrors the feedback resistor and the input cap could then be moved further up and closer to the chip, shortening the signal path.

Then R2 and the signal star ground could be moved closer to the chip as well making it possible to reduce the size of the PCB by almost half! :nod:

S.C · 2003-07-14 9:00 pm

So is this layout work, as long as I fix the Cap +/- position? :scratch:

S.C · 2003-07-14 9:05 pm

Originally posted by JOE DIRT?
positive should be on the input side for the cap...atleast thats the way I`ve always arranged it

DIRT?

Hehe, I didn't know, cuz that sketch didn't say so. Thx. :devily:

S.C · 2003-07-14 9:41 pm

Nuuk said:
Carlos, if you don't have a pot/attenuator as part of the GC circuit, powering it up without anything connected will cause problems.

So a resistor is soldered between the input and ground that takes the place of the ground leg of the pot/attenuator.

So, other than the ground connection from pin 7, which should go to the signal ground; and the polarity of the input cap, that circuit would seem to work fine.

If you want to refine it a bit, the input resistor could be put at an angle so that it mirrors the feedback resistor and the input cap could then be moved further up and closer to the chip, shortening the signal path.

Then R2 and the signal star ground could be moved closer to the chip as well making it possible to reduce the size of the PCB by almost half!

Look at the 4th one.

:nod:

Nuuk · 2003-07-15 8:32 am

S.C. have a good look at this.

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

I have shown a non-polarised cap on the input but as said before, the + side of a polarised cap is connected to the input socket.

Apart from that, you can see where the connections go to. Please note, pin 7 is connected to the signal ground.

S.C · 2003-07-15 9:23 am

OK, I had corrected the Pin 7 problem. The 4 edition was done and I put it on the same link http://hk.geocities.com/solomon_choi/GC2.html. It is exactly half of the orignial.

Still any comment, or mistake? :scratch:

carlosfm · 2003-07-15 9:38 am

JOE DIRT® said:
positive should be on the input side for the cap...atleast thats the way I`ve always arranged it
DIRT®

Me too.

Nuuk said:
Carlos, if you don't have a pot/attenuator as part of the GC circuit, powering it up without anything connected will cause problems.
So a resistor is soldered between the input and ground that takes the place of the ground leg of the pot/attenuator.
So, other than the ground connection from pin 7, which should go to the signal ground; and the polarity of the input cap, that circuit would seem to work fine.

I know, but I use the 22k resistor from the inv. input to ground (soldered to the pin) and there's where I do the signal star ground.
You can imagine the board (and the signal path) will be much shorter.
Anyway, the 22k resistor I use is there to help the stability of the chip, even with no input connected.
So, I don't use a resistor before the cap on my power amp GC.

S.C., your circuit will work, it's just not optimized.
Make the things as small as you can or you'll have humm.

Nuuk · 2003-07-15 9:40 am

Yes, that should work OK.

If you want to fine tune it though, I would move PG and MG slightly to the left (they can go under the cap if necessary) and put the input where MG is now, run R2 from input to SG (which could go up slightly ) and then connect the input to the input cap.

Nuuk · 2003-07-15 9:47 am

I know, but I use the 22k resistor from the inv. input to ground (soldered to the pin) and there's where I do the signal star ground.

Good morning Carlos. Der! I had never thought of that 22K doing the same job as the resistor to ground on the input but of course it does :ashamed:

But this is yet another reason to differentiate between the two versions of the minimised inverted GC circuit.

Now when I tried the 18K/22K to ground, the sound of my GCs was nowhere near as good as with the single resistor to ground and I couldn't understand why. Perhaps it was because I was using the 56K to ground as well! :idea:

This all goes to show that even with a circuit as simple as the minimised GC, the permutations are still vast! :nod:

A GC Layout check.

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