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Old 5th November 2012, 10:17 AM   #1
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Default First Build PSU questions.

I'm building a smallish gain clone. On the amplifier side there seems to be a mainstream approach that I will copy. However for power supplies there seems to be a lot of contradictory advice. Pretty much every step of a PSU seems to be argued over. I'll list the things people seem to disagree on. Help me unpick fad/mojo/fairy dust from real advice.

1. X-cap over primary, yes or no?

2. Cap over secondaries. With/without series resistor?

3. Fancy diodes - if so which type - or just a solid bridge unit.

3. Caps across diodes. With/without series resistor?

4. RC filter or just big caps on their own.

5. Regulated or unregulated?

Thanks.
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Old 5th November 2012, 10:25 AM   #2
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What makes you think that asking the questions won't result in the same arguments

I'll comment on a couple....

3a. I use NXP BYV-32E's They can handle the current (if you use both in the package in parallel they can more than handle it), and IF soft recovery makes a difference then they are nice fast ones. They are not too expensive either.

4. If you go this route then you need to use low value resistors (0.5 ohms or less) or your voltage drop will be large. Voltage drop incereases proportionally to current draw. It does make a difference to ripple.

Tony.
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Old 5th November 2012, 11:08 AM   #3
AndrewT is offline AndrewT  Scotland
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For a first build stay mono and keep it simple.
A dual secondary transformer feeding a bridge rectifier, feeding two series connected capacitors. Nothing extra. Well yes, a fuse in the primary circuit.
Get it working.
Understand what you have done.
Then read more on what options can be used and WHY they might bring improvements.
I see no point in adding an option that brings NO improvement. Even worse is adding an option that actually makes performance worse. An example of this is adding polypropylene capacitors willy nilly to PSUs.
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Old 5th November 2012, 12:05 PM   #4
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Quote:
Originally Posted by wintermute View Post
What makes you think that asking the questions won't result in the same arguments
That's my intention! In one easily digestible read

Quote:
Originally Posted by wintermute View Post
3a. I use NXP BYV-32E's They can handle the current (if you use both in the package in parallel they can more than handle it), and IF soft recovery makes a difference then they are nice fast ones. They are not too expensive either.
I was weighing up either MUR8X0s, (which are close on the spec sheet to yours), or just a cheapo bridge. Whether to use a cheapo bridge or MUR8X0s/BYV-32E is the real debate. Also, surely paralleling diodes just means one will current hog, even sharing a case.

Quote:
Originally Posted by wintermute View Post
4. If you go this route then you need to use low value resistors (0.5 ohms or less) or your voltage drop will be large. Voltage drop incereases proportionally to current draw. It does make a difference to ripple.
Yes, and high wattage ones.

I'm a diy effects pedal builder, so know all these basics. It's real sonic improvement vs mojo that I'm not so knowledgeable on.

And thanks!
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Old 5th November 2012, 12:07 PM   #5
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Quote:
Originally Posted by AndrewT View Post
For a first build stay mono and keep it simple.
A dual secondary transformer feeding a bridge rectifier, feeding two series connected capacitors. Nothing extra. Well yes, a fuse in the primary circuit.
Get it working.
Understand what you have done.
Then read more on what options can be used and WHY they might bring improvements.
I see no point in adding an option that brings NO improvement. Even worse is adding an option that actually makes performance worse. An example of this is adding polypropylene capacitors willy nilly to PSUs.
Thing is I've made PSUs before for non-hi-fi audio. So want to be slightly more ambitious. It's the hi-fi mysteries that I'm really asking about, not the basics.

And I've read and read and read, and no-one seems to agree.
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Old 5th November 2012, 08:14 PM   #6
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The current sharing is an issue with discrete diodes, but as far as I know the BYV32E's being on the same die don't have this issue. If it were an issue I don't think that they would specify the current handling in the datasheet as 20A which is only possible if the diodes are paralleld as they are 10A each.

Tony.
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Old 5th November 2012, 08:53 PM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by Robert Kesh
And I've read and read and read, and no-one seems to agree.
Don't look for a recipe for success. Many of the disagreements arise from this, as people assume that something which worked well in PSU A must necessarily work well in PSU B and all others. Look for facts and understanding rather than opinions.

Quote:
1. X-cap over primary, yes or no?
Yes, it will reduce arcing on the main switch and may reduce switch-off clicks.

Quote:
4. RC filter or just big caps on their own.
Do some ripple calculations, based on the PSRR of your amp circuit.

The difference between a good PSU and a poor one can be a matter of construction details (e.g. grounding, loop size) rather than circuit details or component brands.
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Old 5th November 2012, 08:53 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

A fairly bog standard power supply with the right fusing and capacitors
wired across the bridge legs is what I'd recommend, standard stuff.

rgds, sreten.
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Old 5th November 2012, 09:20 PM   #9
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by Robert Kesh View Post
I'm building a smallish gain clone. On the amplifier side there seems to be a mainstream approach that I will copy. However for power supplies there seems to be a lot of contradictory advice. Pretty much every step of a PSU seems to be argued over. I'll list the things people seem to disagree on. Help me unpick fad/mojo/fairy dust from real advice.
Apply a logical approach and keep it simple.
Looking at the PSU design of a sensitive measuring device that I test and calibrate at work, I see the same no-nonsense approach I apply to my DIY gear.

Quote:
1. X-cap over primary, yes or no?

2. Cap over secondaries. With/without series resistor?

3. Fancy diodes - if so which type - or just a solid bridge unit.

3. Caps across diodes. With/without series resistor?

4. RC filter or just big caps on their own.

5. Regulated or unregulated?
1. Yes.
2. No.
1st 3. No, just a suitable bridge cell.
2nd 3. Yes, ceramics without series resistor.
4. Just big smoothing caps, each bypassed with ~100 nF ceramic.
5. Voltage amps regulated, power amps unregulated.
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Old 5th November 2012, 09:32 PM   #10
mcd99uk is offline mcd99uk  United Kingdom
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I tend to agree with sreten. For amps all I have used is a lot of iron, very big caps and a big basic rectifier.

The following is only personal preference which is what it all comes down to in the end.

1) Yes

2) Never done this myself.

3a) I personally like soft recovery diodes.

3b) Only bother with this if oscillations occur. I don't usually bother.

4) I don't bother.

5) Only use regulation if the circuit is intolerant of "off load" voltage rise.
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