Hey everyone,
I am trying to route all the traces for my amplifier in FreePCB for a single sided board. I have run into a problem because it seems pretty tough to route all of these traces for 50 parts without overlapping some of them. Do you have any reccommendations for getting around this problem? One thing I know I could do is run a few jumpers to prevent the overlap. But this seems to contradict the purpose for using PCB in the first place. Any thoughts?
Thanks
Mark
I am trying to route all the traces for my amplifier in FreePCB for a single sided board. I have run into a problem because it seems pretty tough to route all of these traces for 50 parts without overlapping some of them. Do you have any reccommendations for getting around this problem? One thing I know I could do is run a few jumpers to prevent the overlap. But this seems to contradict the purpose for using PCB in the first place. Any thoughts?
Thanks
Mark
Layout the parts "a la schematic" first -- so you can see where you're going. I mean REALLY put the parts down on a piece of paper so you have a tactile feel of what you're gonna be doing.
If you're doing regular analog, you have to set your mind to two tasks -- your "0" net, i.e. GND , and V+, V- should be thought of as on the bottom of the board -- the other simultaneous (2nd) task is to mentally view horizontal traces on one plane, and vertical traces on the other -- this is how auto-routing systems work on their first pass.
If you have to "jumper" just think of a resistor with zero-ohm impedance. Unless you are going to move current at a couple of tens of Megahertz, the impedance jump and it's SWR are almost irrelevant (as Groucho said).
If you're doing regular analog, you have to set your mind to two tasks -- your "0" net, i.e. GND , and V+, V- should be thought of as on the bottom of the board -- the other simultaneous (2nd) task is to mentally view horizontal traces on one plane, and vertical traces on the other -- this is how auto-routing systems work on their first pass.
If you have to "jumper" just think of a resistor with zero-ohm impedance. Unless you are going to move current at a couple of tens of Megahertz, the impedance jump and it's SWR are almost irrelevant (as Groucho said).
Mark245 said:
Just use exactly the same pads as for your 1/4 watt resistors.
Treat the jumpers like any other components - resistors, capacitors, diodes - except you can space them much closer together, and they can be any length you want.
If you dont need close spacing, just use a 'resistor, value=0 ' in your layout.
I always save all the resistor / capacitor lead cut-offs when making boards - to use as jumpers.
Actually I have one more question. I can't seem to find a footprint for the TO-126 package. Has anyone else had this problem? I am using FreePCB and the footprint is not there and I cant find it on the internet. I guess I could just use TO-220 package and switch the pins around in Capture because the transistor pins are opposite for TO-220 and TO-126. I am trying to use the MJE340/350 in my amplifier design. Any suggestion will be appreciated.
Mark
Mark
"I am trying to route all the traces for my amplifier in FreePCB for a single sided board. I have run into a problem because it seems pretty tough to route all of these traces for 50 parts "
50 parts make enough reason to use double-side PCB. If you still want to have only one side routed, I would strongly recomend to use double-side PCB with bottom layer fully dedicated to Ground net. It is easy to make and will significantly reduce 60 Hz noise. Moreover, the routing become more simple because you will use the ground layer instead PCB traces - for GND net.
If you really need help, contact me by PM.
50 parts make enough reason to use double-side PCB. If you still want to have only one side routed, I would strongly recomend to use double-side PCB with bottom layer fully dedicated to Ground net. It is easy to make and will significantly reduce 60 Hz noise. Moreover, the routing become more simple because you will use the ground layer instead PCB traces - for GND net.
If you really need help, contact me by PM.
Thanks Grab. I might go with the double side board like you reccommend if I can fabricate boards like that at home. The reason I wanted to use single side is because I already purchased pcb with copper on only one side. I am hoping to fabricate the pc boards myself. I will be using the press-n-peel and I have bought the copper etchant also. Im not sure how the quality will come out. Has anyone used this technique before?
Mark245 said:
Most PCB software will allow you to change layer and simultaneously place a via, the track colour will change. My software just requires 2 clicks in exactly the same place. Just keep all the tracks on one side straight. You can put in a part to achieve the same effect but it's more time consuming
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Grab485 said:
One of the National Semi folks recommended avoiding the use of ground planes in audio circuits -- this was on the application note for the LM4702 amplifier. I took him up on the suggestion and began to use a ground "spider" -- with as much symmetry as possible. It does make a big difference in performance.
After a while you get used to thinking along these lines, routing as much of your power traces and ground traces along the bottom of the board as possible. Signal ground traces can be pretty thin and soon it becomes like crochet or needlepoint.
With higher frequency circuits where the supply pins have to be bypassed a ground plane is helpful -- the leads have to be as short as possible lest they become antennae radiating or receiving rfi.
It may not be pretty, but the quietest stuff I've ever built used manhattan or dead-bug construction -- and it's fast as well.
50 parts too much for a single sided board ??
91 was easy while obeying the rules..
As these are hand drawn , my basic gameplan is .. rails ,grounding and OPS first (the big stuff) , VAS and differentials with the shortest paths and best symmetry possible and not being afraid of a couple of jumpers to keep everything "right" (short).
These were completed a few weeks ago (noise floor of LTP is higher than hum). Layout was well spaced out , easily could of done 130+ components.
OS
91 was easy while obeying the rules..
As these are hand drawn , my basic gameplan is .. rails ,grounding and OPS first (the big stuff) , VAS and differentials with the shortest paths and best symmetry possible and not being afraid of a couple of jumpers to keep everything "right" (short).
These were completed a few weeks ago (noise floor of LTP is higher than hum). Layout was well spaced out , easily could of done 130+ components.
OS
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