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tool49 11th March 2005 04:38 AM

Elliot PCB questions
 
Hi there fellow DiYers, I am trying to learn the why of some things on those PCBs.

I recently bought PCBs from Mr. Elliot to build two (extended) P68.

Now a few things strike me about those PCBs and would like to know why they were made as such.

First thing, the power tracks are run straight over the output devices. And these tracks are especially widened over the output transistors. Why do so? What are the benefits of having wider traces above the transistors? Why not route them beside the transistors? (I realize this would mean a wider PCB but other reasons than that")

We can see the wider traces clearly on this picture taken from Mr. Elliot Web site: http://sound.westhost.com/p68-pic.jpg

The second thing that struck me is the size of the holes for the wire links. I could barely fit a 20 AWG wire in them. For a 500W amp, it seems too small to me. I enlarged them to fit 14 AWG. Would a 20 AWG wire been enough for chassis wiring at 5-7 amps? Where can I find info about this? (I googled and searched the forum but didn't find the info).

The last thing that also struck me is that there is no protection between the output transistor and the tracks. Can't that potentially lead to a plastic meltdown on the transistor caused by the heat of the power tracks just above? Or am I exaggerating the effects of 5-7 amps in PCB tracks?

Thanks for all your answers. Hopefully they'll give me a better understanding of the why of those choices.
Sébastien

JochenH 11th March 2005 11:12 AM

Hi,

here is what i found googling: http://www.powerstream.com/Wire_Size.htm

I think Rod did not intend to solder the wires directly into the PCB but to user solder nails (???) to connect the wires to the pcb.

Regarding the traces, beware that the screw holes reduce the width. Also i think Rod had the pcb size as well as minimized trace lengths in mind when designing the pcb.

If the tracks would warm up so much that the transistor cases melt they have to dissapate more power than the transistors themself, this will not happen. The 5-7A current is not continous.

Jochen

tool49 11th March 2005 11:37 AM

Hi Jochen, thanks for your reply.

Quote:

here is what i found googling: http://www.powerstream.com/Wire_Size.htm
Thanks for that, I'll keep it handy.

Quote:

I think Rod did not intend to solder the wires directly into the PCB but to user solder nails (???) to connect the wires to the pcb.
I've never seen anything as such, do you have any links to where I could find those. Even though their caliber would be so small to fit the hole, I doubt they could carry sufficient current for such a big amp.

Quote:

Regarding the traces, beware that the screw holes reduce the width. Also i think Rod had the pcb size as well as minimized trace lengths in mind when designing the pcb.
I realize that. But why cover the entire transistor length wize only to bypass the screw? Especially on the middle transistor, it is covered completely when the trace required to go to the left transistor is about 50 or 60 mils... Could it be anything else?

Quote:

If the tracks would warm up so much that the transistor cases melt they have to dissapate more power than the transistors themself, this will not happen. The 5-7A current is not continous.
That makes sense. I think in the case of tests using sine waves in low load resistors it could happen that the 5-7 amps would be close to continuous, but it is unlikely to happen in my case.

Thanks,
Sébastien

JochenH 11th March 2005 12:47 PM

Sébastien,

Quote:

I realize that. But why cover the entire transistor length wize only to bypass the screw? Especially on the middle transistor, it is covered completely when the trace required to go to the left transistor is about 50 or 60 mils... Could it be anything else?
Another reason could be that he wants to spread the mechanical stress from screwing the PCB onto the transitor to the whole transistor case and not only a small trace area. Because the traces have a specific height this makes a difference.

Quote:

I've never seen anything as such, do you have any links to where I could find those. Even though their caliber would be so small to fit the hole, I doubt they could carry sufficient current for such a big amp.
Unfortunately i don't know the correct English / French term for this, but i mean this http://www2.westfalia.de/shops/techn...t100_st_ck.htm

Jochen

jormajj 11th March 2005 12:59 PM

http://sound.westhost.com/pcb/ppins.htm

peranders 11th March 2005 01:14 PM

tool49, you could ask Rod yourself why he has done as he had.

It could also be that he has drawn traces but he didn't see things untill it was too late and he has ordered a heap of pcb's. Remember how many times now BrianGT has changed his Gainclone pcb.

Personally I think a 500 Watt amp needs 70 um/20 oz copper and also doublesided boards. Compare Jens' excellent looking Leach amp (and I'm sure it will work alright also).

HuntTheShunt 12th March 2005 07:42 PM

Just ask Rod ;)
 
As someone has said just ask the guy!

Rod has the best site for DIY audio I have seen.
All is circuits are backup by his reasons for creating the circuit from the ground up to the finished article.

He has patiently help me get his amps running.

In short the guy is commutative.


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