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Old 8th July 2011, 10:31 PM   #131
hurtz is offline hurtz  Germany
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I have implemented the changes in the PSU, taken from the high-cap-guide and adjusted resistor-sizes. The design is pretty similar to the guide, so this should be ok. I'm not totally sure R3/4 are enaugh with 0.25W but I think not much current will flow trough them...

Parts-list:
C1-C6: 4700uF, 35V
C7,C8,C11,C12: 100nF
C9,C10: 120nF

R1,R2: 4.7k 0.25W
R3,R4: 1R 025W

PSU+:
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Old 8th July 2011, 10:56 PM   #132
! is offline !  United States
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hurtz, your R3/C10 and R4/C9 aren't doing anything in the circuit because you have them going from ground to ground instead of from positive rail to ground and from negative rail to ground.

Also, R1` and R2 need to be larger than 0.25W, with a rail voltage at only ~35V they would exceed 0.25W dissipation and it's usually a good idea to run resistors lower than the rating, I aim for closer to half power. I'd go for a minimum of 1W or better 2W resistors there, OR increase the ohm value instead. I would also move them a little further away from capacitors since they are a constant heat source. If this board is going to have plated holes you can get away with the small traces to those resistors but otherwise I would make the trace larger (wider especially at the hole) to help deal with the heat which can delaminate the trace over time unless you're using 2oz or more copper PCB.

Also, something is wrong with the C1-C6 capacitor polarity "+", it doesn't match the output connector polarity markings.

Last edited by !; 8th July 2011 at 11:15 PM.
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Old 9th July 2011, 12:39 AM   #133
hurtz is offline hurtz  Germany
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Hi !,

whoops... too much zoom I guess..

R1/2 will only be aroud 0.144W since I only have 26V. So they should be fine.

Thanks for your corrections!

amp+:
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Old 9th July 2011, 01:38 AM   #134
! is offline !  United States
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One other thought is why remove the copper on the ground trace(s)? What I mean is, a PCB starts out entirely copper that has to be removed but only if it *needs* to be removed. It could cover everywhere on the board there isn't a positive or negative trace. What you have will work, but you could leave the entire board covered with copper and have lower impedance (leave pos & neg rails wider too). I don't know if you are making it yourself or paying for a commercial board but with DIY, one other bonus is it uses less etching acid to remove only the copper you need to, although it takes a much beefier soldering iron to solder it later, but there can be thermal reliefs around the holes to help with that.
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Old 9th July 2011, 08:35 AM   #135
hurtz is offline hurtz  Germany
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Hmm I see your point, I'm doing them myself with toner transfer. I guess I will keep it this way, since some people have reported problems with large copper pour areas. Also there will be a lot of narrow pitches which could be a problem for the DIY'ers with less accurate ways to etch.

cheers!
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Old 9th July 2011, 03:26 PM   #136
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Hi Hurtz,
Just a couple of comments. While you're technically correct that R1 and R2 will be at about 70% of rated power dissipation (assuming no more than 10% over voltage), you should realize that 1/4 watt resistors have a very small surface area too radiate heat, in this application they will run quite hot. I would recommend increasing to at least 1/2 watt rating for that reason. I also recommend that you split the trace between the two grounds at the output to keep the ground currents isolated from each other, that will prevent the positve and negative supplies from interacting with each other.

Mike
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Old 9th July 2011, 03:36 PM   #137
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Hi agian,
I meant to say split the grounds at the input side where the transformer secondaries connect, I just woke up and my old brian isn't fucntioning at it's normal 10% capacity yet.

Mike
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Old 9th July 2011, 04:18 PM   #138
hurtz is offline hurtz  Germany
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Thanks! Good point with the surface area! Have updated them to be 2W (I have better access to 2W's and there's still a lot of space left) PSU has been updated.
I wonder, if I also disconnect the Grounds on the output, and join them on the AMP, I would have a "true" star-ground, would this bring any actual advantages? Sorry if this has been discussed before, but I still have a little trouble properly imaginang how the currents behave.

cheers!

P.s. the trace-length between PSU and AMP will not exceed 10cm.
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Old 9th July 2011, 05:18 PM   #139
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Hi Hurtz,
In my last post I corrected the mistake I made in my first post when I refered to the output side of the board, I meant to say the input side, sorry about that. I'm assuming your transformer has independant secondaries with no common center tap. Obviously, if it does have a center tap you won't be able to keep the input grounds separate. It's not a huge deal, I just think it's better to keep them separate if you can.

Mike
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Old 9th July 2011, 05:54 PM   #140
hurtz is offline hurtz  Germany
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Hi Mike!

Yes I understood correctly, my transformer has two separate coils, and now the grounds join on the output of the PSU, what I meant was, what if I join those grounds on the AMP (instead of the output of the PSU)? So, seperated grounds on in- and output!

cheers!
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