My_Ref Fremen Edition - need help on PCB evaluation

[soongsc]

The current PCB seems to be a nice size. Is C13 really necessary? I have never used an input cap in 30 years. If the DC gain is low enough, then this space is really a waste. If someone needed it, it's easy to connect anywhere in the input line between connector to PCB with any type you want. There are so many caps that are too big to fit on the PCB anyway.

[ClaveFremen]

Originally Posted by soongsc

The current PCB seems to be a nice size. Is C13 really necessary? I have never used an input cap in 30 years. If the DC gain is low enough, then this space is really a waste.

In this design the C13 input cap is tightly connected with C9, it can't be omitted without impacting on bass performance.

Originally Posted by soongsc

There are so many caps that are too big to fit on the PCB anyway.

Quite all... in fact the cap I recommend in my BOM will fit only outboard as in the attached picture:

[soongsc]

Originally Posted by ClaveFremen

In this design the C13 input cap is tightly connected with C9, it can't be omitted without impacting on bass performance.
...

It's my understanding that this is basically providing additional subsonic filtering (at least that is what was also previously described in the technical explanation). If it really creates a problem, then the problem would be elsewhere and system specific.
The point is, if it has to be mounted off board for best performance, why let it take up so much PCB space? All we probably need is two pads that will allow a small cap to be mounted vertically, this way we can save space for other valuable stuff.

PS. Try moving that cap in the pic around and see whether you notice a difference in sound.

[AndrewT]

move C13 off board. And use it to connect the RCA/phono/input terminal to the PCB.
Then along side you can have a DC input socket as well as the AC input socket.

[ClaveFremen]

Originally Posted by AndrewT

move C13 off board. And use it to connect the RCA/phono/input terminal to the PCB.

Probably it's a good idea to do it... I'll check

Originally Posted by AndrewT

Then along side you can have a DC input socket as well as the AC input socket.

If I understand correctly you're suggesting to place two input sockets, one that goes directly to the input net (so the coupling cap can be completely off board) and another connnected to two pads that allows mounting a tiny onboard cap, right?

[AndrewT]

no.
Look back at Jen's Leach clone.
One of the input pins bypasses the DC blocking cap.

[ClaveFremen]

Originally Posted by AndrewT

no.
Look back at Jen's Leach clone.
One of the input pins bypasses the DC blocking cap.

So a 3 pin connector...

Not much different from what I wrote but I get it

Thanks, I'll take a look.

[soongsc]

Does C9 have a across it? Seems to me not, but I just want to make sure.

[ClaveFremen]

Originally Posted by soongsc

If it really creates a problem, then the problem would be elsewhere and system specific.

Hi Soongsc,

it don't create any problem, simply it is part with C9 of the high-pass filter to avoid DC.

Originally Posted by soongsc

The point is, if it has to be mounted off board for best performance, why let it take up so much PCB space? All we probably need is two pads that will allow a small cap to be mounted vertically, this way we can save space for other valuable stuff.

I'm thinking about it.

Originally Posted by soongsc

PS. Try moving that cap in the pic around and see whether you notice a difference in sound.

I've moved the cap in the past I didn't noticed any appreciable difference.

Originally Posted by soongsc

Does C9 have a across it? Seems to me not, but I just want to make sure.

I don't get it, can you elaborate?

Or are you refferring to the black cross?

If so it's simply an handle to move the object.

[soongsc]

C9 is an electrolytic capacitor, if there is a DC offset across this cap then it's fine. If not, then I was thinking about changing it to an bipolar type electrolytic and add a bypass cap to improve it's linearity. I probably should also try it on one of my chip amps too.