Beesneez Lulu Fet - KM84 SMD mod

GraemeWoller · Sep 24, 2017

Ok, that's good to know.

I matched the trimmer that was in the original circuit, a 20k, and it's replacement was a wee surface mount job: https://goo.gl/AWDh7r

The FET is this one: https://goo.gl/iRL4zw and I just matched all the specs as close as possible with the 3819 that was in the previous board.

So, you're thinking this trimpot could be a bit lower? What sort of value are you thinking?

ln76d · Sep 25, 2017

GraemeWoller said:
Ok, that's good to know.

I matched the trimmer that was in the original circuit, a 20k, and it's replacement was a wee surface mount job: https://goo.gl/AWDh7r

The FET is this one: https://goo.gl/iRL4zw and I just matched all the specs as close as possible with the 3819 that was in the previous board.

So, you're thinking this trimpot could be a bit lower? What sort of value are you thinking?

Desoldering and soldering again smd components is unhealthy for a PCB and a brain. Try first to use 10k THT resistor for test.
Just solder it in parallel to your trimpot, check bias, set new if it is unproper, compare microphone level with second mike.

Khron · Sep 25, 2017

Parallelling a resistor with the trimpot will only lower the maximum resistance value, and/but the trimpot can "already" go down to (virtually) zero, so... What exactly would be the point of that?

GraemeWoller · Sep 25, 2017

Well, thing it made me think...

Is that if I knew the value range approx. I could get a trimpot for future boards that wasn't as wide as 0-20k and might be slightly more accurate when adjusting?

Khron · Sep 25, 2017

That's a slightly different story

GraemeWoller · Sep 25, 2017

Oh, yeah. I agree. I think it's different to what In76d is describing, for sure.

I also had a thought about doing a "hybrid" board where all the high impedance & signal path components are thru-hole and the rest of the components are SMD just to see if there is a noticeable difference...

Ah, the things I thunk...