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Is there anything wrong with this PS design?
Is there anything wrong with this PS design?
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Old 25th December 2017, 10:57 PM   #11
simonra is online now simonra  United Kingdom
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Quote:
Originally Posted by Keruskerfuerst View Post
For what purpose is the PSU?
Hi, I'm using this one for a phono stage I'm working on (post 35 in this thread)
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Old 25th December 2017, 11:09 PM   #12
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by simonra View Post
The component U$1 is a pot
That's how I interpreted your layout.
Quote:
IC1 is the regulator.
Yes, that's what I could see.
Quote:
Regulator input is the left red plane and output is to the right red plane.
Again,
that's what I could see.
Quote:

Looking at the layout again in the light of your comments I can see that it could have been much tighter... I'll work further on the schematic
The schematic is correct. But it is simplified to the point it is misleading you into assuming that all traces that are connected together have the same voltage at all points on any part of a trace. Similarly on a plane the simplified schematic assumes all points on the plane are at the same voltage. That is not what occurs on the PCB.
Quote:
before I get any more of these boards made up.
.......
You have to make the layout take account of these "hidden" voltage drops. The easy way is to make the important points that NEED the same voltage to be coincident on the PCB layout.
That's why
Quote:
VR pin1 + C5-ve +Zero Volts out,
should be rearranged to bring these three points/tappings together.
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Last edited by AndrewT; 25th December 2017 at 11:17 PM.
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Old 26th December 2017, 08:48 AM   #13
simonra is online now simonra  United Kingdom
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Andrew, when you talk about the VR are you referring to the IC or the sum of the components that make up the regulator? I was a bit confused by your first post:
Quote:
Originally Posted by AndrewT View Post
it appears that the top left pin of the VR is connected to the blue plane
Should I take this to mean the grounded pin of the potentiometer?
By the way, I like your comments as they force me to think about and try to understand what's going on in the circuit.
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Old 26th December 2017, 11:20 AM   #14
AndrewT is offline AndrewT  Scotland
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Variable Resistor = VR
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Old 26th December 2017, 12:03 PM   #15
simonra is online now simonra  United Kingdom
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That explains it.
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Old 28th December 2017, 08:35 PM   #16
nigelwright7557 is offline nigelwright7557  United Kingdom
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Trimmers on power supplies ? terrible way to do it.
I always used fixed voltage regulators.
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Old 28th December 2017, 10:33 PM   #17
snow1531 is offline snow1531
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You may wish to consider placing fixed resistors in series with the adjustment pots and reducing the resistance of the pots to the minimum value which will permit trimming the outputs to the desired values.
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Old 29th December 2017, 09:07 AM   #18
simonra is online now simonra  United Kingdom
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The original reason for the power supplies was to prototype so the trimmers allow for flexibility... space for fixed resistors is a good idea.
I've got to admit, I don't really understand what the negative effects of the trimmers are.
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Old 29th December 2017, 10:21 AM   #19
MorbidFractal is offline MorbidFractal
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Quote:
Originally Posted by simonra View Post
I've got to admit, I don't really understand what the negative effects of the trimmers are.
AFAIK the track is a thick film material... cermet? It is not of itself 'low noise' performance. Electrical contact is by means of metal fingers...

M43P103KB40 | Vishay 43P Series 20-Turn Through Hole Trimmer Resistor with Pin Terminations, 10kΩ +-10% 1/2W +-100ppm/degC Side Adjust | Vishay

Contact Resistance Variation (Max.) 1% or 1Ω (whichever is greater)

Might not help but presumably for audio the major concern is how that might vary with vibration. If you are playing Thrash DubJazz with your regulator sat on top of the speakers then you might lose a bit of purity and end up with Thrash DubGrunge.
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Old 29th December 2017, 11:47 AM   #20
MarcelvdG is offline MarcelvdG  Netherlands
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Use run-of-the-mill electrolytic capacitors for C4 and C7. Some brands of LM317 become unstable when the losses of the output capacitor are too small. I once connected an LM317 to two 10 uF X5R ceramic capacitors in parallel, which turned my LM317 into a sawtooth oscillator. The capacitors themselves worked as loudspeakers, so you could hear a beeping sound coming from the board. Connecting a 47 uF cheap aluminium electrolytic capacitor in parallel solved the problem.
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