Pcb for Nuuk's buffer

[endia]

i want to build nuuk's buffer for my lm3875 gainclone. i need your comments about this pcb before etching.. schematic is here;
http://myweb.tiscali.co.uk/nuukspot/...nclonepre.html

thanks.
naim

[pinkmouse]

Run separate grounds from R5/2 to a central star. I personally, would also move the bottom Q2 down below Q1/3 so it's symetrical, as well as the bottom input, then you can add another pad and run another ground trace to the star point if you find you need an input ground.

[dsavitsk]

I would leave space for PS decoupling caps close to the pins of Q1 and Q3. I would also add a space for an input resistor and couplig cap. See my edited schematic and the PCB I designed here: http://www.ecp.cc/ss-bpp.html (byt he way, there is a small bug in my boards that I have not fixed yet which is that the power groundpad is not really grounded. You have to connect to one of the output grounds instead.)

[endia]

pinkmouse, dsavitsk thanks a lot for quick replies and suggestions.. layout is more symetrical now. added input res (R6) and coupling cap, but i have to try some more to add transistors decopling caps
new layout is here..

[dsavitsk]

For the PS decoupling, since the voltages are low, you can find .1uF caps in the 50-63V range that are very small (pin spacing ~ 5mm) and should fit just fine. Look at DigiKey parts 495-1103-ND (polyester) or BC2054-ND (polypropylene -- same pin spacing but slightly fatter.) There are also some Wimas in this size that I bought from Mouser, though I don't have the part number anymore.

One other thing that can really improve performance is to make this dual mono and use dual mono power supplies. You can split V+ and V- such that 2 power supplies can be used, and then add a few pads so that they can be jumpered together if you only want to use one. Additionally, if 4 voltage regulators is too many for you, you can cheat by using a single voltage reg, then use dual TLE2426's each with their own set of rail caps. I tried this and found it to work very well -- better than just a single +/- supply. I did need about 1500uF on each rail, but if you were closer to the transistors, this would probably fall significantly. At any rate, my experience is that the quality of this circuit is all about the power supply, so it is worth some care there. Looks good so far.

[dsavitsk]

One other thing, socketing the transistors can be a good idea as different ones will alter the sound slightly. I mention this because your transistors may be too close together to get sockets in there.

[endia]

hi dsavitsk,
thank you so much, you're so helpful. i decided to build this dual mono as your suggestions. i'm planning to build Nuuk's original PS and discreete regulator, so no need to use tle22426. also i think i can use SIP sockets instead of transistor sockets for swapping

[gmphadte]

Extend ground track outside /around the tracks, nothing to loose. Do not join the loop.
Gajanan Phadte

[endia]

Gajanan, thanks.. ground track extended and ground output positioned, final layout is below. i've a question about grounding;
i'm planning to build this preamp dual mono but will use one transformer (dual secondary) for both ps regulators. should i connect this pcb grounds? if so, where? chassis ground? or is it a good idea connecting only ps grounds? thanks..

[gmphadte]

star ground at the psu cap.
don't know what it is. search in these forums, loads of explanations here

Better than that, C4 be near C3

ground current should have separate paths for signal and supply and should meet at the star point on the pcb and should not go via psu ground lead.

Gajanan Phadte