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-   -   Can someone check My PCB layout against the Schematic for mistakes please?? (http://www.diyaudio.com/forums/solid-state/102962-can-someone-check-my-pcb-layout-against-schematic-mistakes-please.html)

Minion 3rd June 2007 11:40 PM

Can someone check My PCB layout against the Schematic for mistakes please??
 
Hi Folks....

Well I found this Big 300vA 40v Power Xformer so I thought I would look for a Project that I could use it in so I came across this Fairly simple 60w Guitar amp project found here:

http://www.redcircuits.com/Page65.htm

So I did up a basic PCB design for just the power amp section and I was wondering if someone here could look at the schematic in the link above and do a quick comparison to my PCB design and see if there are any problems with it.....

The Power suply section (as well as the Preamp section) is going to be on a different PCB and much Beefier than the one in the schematic, I also didn"t include the Power on LED in the PCB design......

I would usually just go ahead and Etch the PCB and stuff it and hope for the best but I have been haveing bad luck lately with my own PCB designs so I believe it is good to have another set (or a few sets) of eyes to check it over so I don"t run into PCB mistake problems again.......


Thanx a Lot ......

:D

PS: I did a couple changes from the original design like a Much beefier Output Cap (it is a single rail supply design).....


http://i13.photobucket.com/albums/a3...0wPoweramp.jpg

Conrad Hoffman 4th June 2007 12:08 AM

I didn't check every trace, but nothing jumps out at me connection-wise. I would make a few changes to the layout. 1) The clearance between the two base traces (Q3,4) is too close. What I'd do is come off directly left from Q2, then go up, creating more space. 2) The collectors of Q3,4 should be redundant. Route the base leads below the screws, then join the two pads where the transistors attach. Guitar service is rough! 3) The R6,8 connections can be flipped to reduce the trace length. Connect C4 at the bottom of the pair, the big traces at the top. 4) I'm not sure it matters in this case, but good practice would be to connect C4 not at the bottom of R11, but at the positive lead pad of C7. 5) You've got one pad doing a lot of ground duty. Maybe establish a star point and bring several pads off it for supply return, speaker return, and input return. I assume some reasonable sized heat sink is attached, and there's enough room for it. The circuit doesn't seem to have any local bypassing of the supply, which makes me a bit nervous, but it may not matter. FWIW, your pad sizes look good- I'm constantly making boards with holes too small for the component leads!

Minion 4th June 2007 12:20 AM

Thanx for the Tips, i will do some of the Changes you suggest, But there doesn"t seem to be any Really Blatant errors in connections?? which is mostly what I wanted to know....

I was going to thicken up the Power and ground Traces anyways and I was also going to add some filter caps to the Board.....

I was going to Tie the Speaker Ground to the PSU ground which is on the PSU Board and I was going to use about 20,000uF for filtering to the PSU board as opposed to the 2200uF recomemded on the schematic, Can never have too much filtering in a PSU....

I was actually thinking of Mounting the TO-3 Transistors directly to the heatsink and just wire from the PCB to the To-3 Output devices but I"m not sure that the extra Trace/Wire length will cause problems even though I have seen it done in comercial amps (old ones)......

Thanx again.....
:D

FastEddy 4th June 2007 12:31 AM

" ... Maybe establish a star point and bring several pads off it for supply return, speaker return, and input return. I assume some reasonable sized heat sink is attached, and there's enough room for it. ..."

Yes, more ground connect pads for a star connection at Gr.
Yes, " thinking of Mounting the TO-3 Transistors directly to the heatsink and just wire from the PCB to the To-3 Output devices ..." = good idea ... and you might also add a large value cap across the power & ground connections, right on the transistor sockets on the heat sink in addition to your "20,000uF for filtering [on] the PSU board" ... (I prefer plastic MKT type caps for this ...).
Conrad is also rightly concerned about solder splash across "the two base traces (Q3,4) [==] too close ..."
You might also fatten up the traces to and from R11 & R12 ... these traces & resistors will be carrying the output power

Conrad Hoffman 4th June 2007 12:51 AM

Solder splash is certainly a concern, but beer splash was the first thing that entered my head! My recent efforts at improving an amp had a lot to do with keeping leads short. IMO, a huge supply is nice, but you have to be careful to put the star at the amp, not far away at the PS. Think in terms of all wires and traces having finite resistance and inductance, so short leads and local bypassing are the rule. I checked the pinouts on the big xsters, but not the smaller ones- be sure to check that. Top view/bottom view on data sheets has bitten me more than twice.

FastEddy 4th June 2007 01:20 AM

" ... beer splash was the first thing that entered my head! ..." :drink: :drink: :drink:

" ... keeping leads short. IMO, a huge supply is nice, but you have to be careful to put the star at the amp ..." ditto to that. :cheers:

auriches 5th June 2007 10:18 AM

maybe it's just me, but whenever i route, i never have right angles - always cut away the corners.

this is because in some electronics there can be arcs of electricity jumping at pointed junctions when being EMC tested.

FastEddy 5th June 2007 02:40 PM

" ... whenever i route [traces], i never have right angles - always cut away the corners. ..."

Always good plan ... If you have ever studied the arcing displays of very high voltage discharges, you would see that a sharp corner or "spikey" edge on a conductor is where the most glorious sparks occur, the electrostatic discharges being attracted to the sharper corners, etc., ... at much lower voltages this is not a real problem, but at the atomic level the electron flow eddy currents within the traces around a sharp trace bend can cause very interesting anamolies ... just like the ground loop phenomena ... :bigeyes:

And of course there is the esthetics of the board design ... rounded curves looking a little better than sharp corners ... IMOP.

east electronics 6th June 2007 06:05 AM

question ......
 
i wonder why so many people bother with the pcb routing and nobody noticed that the desiign its helf is almost crappy or there are not even decoupling caps on rail voltage ......

on the other hand 300va trafo @ 40v will produce almost 58 volts of dc ...is this design can work at this levels???

thats for me ..... also wonder if worth working on aproject that is not symetrical power

at this level of power something more reliable should be used

thanks sakis

FastEddy 6th June 2007 03:26 PM

sakis: " ... there are not even decoupling caps on rail voltage ..."

FastEddy above: " ... you might also add a large value cap across the power & ground connections, right on the transistor sockets on the heat sink ..."

To put more parts on the board might be a physical size question, if he wants to keep the board small ... C2 and C3 do decouple the PS rails somewhat. You may be right and the addition of few more small plastic snubbing caps might not be amiss ... :smash:


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