Group order of non-inverted LM3875 pc boards? Anyone interested?

[Peter Daniel]

I think it can be used, there shouldn't be any major difference here.

[elizard]

One question - if you use a pot, you just connect the output from the pot to the "in" on the board without omitting any resistors?

[Peter Daniel]

Originally posted by hifi
I think you took the wrong riken this is the 0,5W variaty:

RIKEN- 62079 680R $2.40

But where there not also some Vishay resistors in PD:s schematic?

But then again PD might have specified a 1W Riken but it will not fit the PCB (lead spacing ~10mm)

I'm using 0.5W Riken. Also, for series 220R resistor, you might not need it, depending on your system. I'm using it only to prevent any excessive DC offset jump.

Vishay S102 is good in this position, and it seems to be more neutral than Caddock, but some people may prefer some extra touch and Caddock seem to add that extra bit of speed and dimentionality, but it could also be interpreted as edginess. The choice is yours.

[Peter Daniel]

Originally posted by elizard
One question - if you use a pot, you just connect the output from the pot to the "in" on the board without omitting any resistors?

Yes, and because I'm using 50K pot, I need 22k shunt resistor to lower input impedance (from + to ground). But if your pot is around 20k in value, you don't need 22k shunt resistor.

[digi01]

Hi,BrianGT.you do a good pcb work,the style of your PCB overall arrangement is very nice!!
Did you use Protel for that?

[elizard]

Originally posted by Peter Daniel


Yes, and because I'm using 50K pot, I need 22k shunt resistor to lower input impedance (from + to ground). But if your pot is around 20k in value, you don't need 22k shunt resistor.

no, it would be the 50k i got from you .. thank you

[BrianGT]

Originally posted by digi01
Hi,BrianGT.you do a good pcb work,the style of your PCB overall arrangement is very nice!!
Did you use Protel for that?

Yes. I used Protel for it.

--
Brian

[BrianGT]

Originally posted by elizard
One question - if you use a pot, you just connect the output from the pot to the "in" on the board without omitting any resistors?

Originally posted by Peter Daniel


Yes, and because I'm using 50K pot, I need 22k shunt resistor to lower input impedance (from + to ground). But if your pot is around 20k in value, you don't need 22k shunt resistor.

As Peter stated, if you are using a 20k pot, you do not need the shunt resistor to ground [R2]. You also might not need the 220 ohm series resistor on the input pin. I made the second pad on the R1 pad (series resistor) larger, so that the input wire can be wired directly into this pad if the 220 resistor is omitted.

--
Brian

[elizard]

Well, a little research done
www.alliedelec.com has cheap resistors!

$2.20 for the 20k in 100+ quantities (model#: 524-5575)
$1.58 for the 220R in 1+ quantity!!! (model#: 524-9996)

so that's $3.78 for these 2, plus the $2.40 for the riken .. not too bad, $6.18 for the 3 resistors ..

am i missing a resistor here?

[BrianGT]

Originally posted by elizard
Well, a little research done
www.alliedelec.com has cheap resistors!

$2.20 for the 20k in 100+ quantities (model#: 524-5575)
$1.58 for the 220R in 1+ quantity!!! (model#: 524-9996)

so that's $3.78 for these 2, plus the $2.40 for the riken .. not too bad, $6.18 for the 3 resistors ..

am i missing a resistor here?

Don't forget that you need a 20k for the negative feedback resistor, which mounts directly to the chip.

We are probably talking about $12 per board for resistors and Panasonic FC power caps, including the shipping of the components to me.

I have a prototype of the power supply board done, which is 2.5" x 1.5". 2 boards and the power supply board would make a single board that is 3.5" x 2.5".

--
Brian