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Old 29th June 2011, 06:21 PM   #121
! is offline !  United States
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Also, here are some snubber design tips,Ridley Engineering
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Old 29th June 2011, 06:27 PM   #122
hurtz is offline hurtz  Germany
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Thanks for your summary! I will try to implent this.
Also on the voodoo... I try to stay away from this as much as possible, since in my opinion this is ruining the whole concept of music which is mostly intended to be shared and enjoyed with many people. And this whole concept of "the more expensive the better sounding" irritates me a lot. Don't get me wrong I appreciate quality, but using a 500$ RCA cable or a copper-cooler and insisting it influences the sound is just wrong.

cheers!
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Old 29th June 2011, 06:27 PM   #123
Kay is offline Kay  Germany
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> IMO, it would be better with both on the same PCB, or
> reduction in power board size by moving at least a couple
> of those capacitors on the amp board.

so, the most important thing is,
never share Signal-GND with GND from the power supply.
I see this on the board here.
The central grounding is not on the amplifier board,
but on the power supply board

> The yet tiniest single-sided LM3886
use SMD, 1206 is not a big problem
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Old 30th June 2011, 08:00 AM   #124
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^ I was not making that point (valid or not), mine was, there is no sense in putting excessive capacitance on a PSU board remotely located, especially spending more for lower ESR caps, when what achieves the implied goal is more capacitance on the amp board.

On the PSU board, 50 to 120Hz (when AC freq is doubled through the bridge rect.) is easily managed with 10K uf or less capacitance, what remains is the current changes caused by the audio itself, current changes relative to the chipamp itself. Capacitors are filters, best placement is where the power NEEDS filtered, not on a modularized arbitrarily decided upon location.

BUT, I am speaking about electrical function, not about subjective perceptions of what sounds best - as always that requires auditioning to decide for one's self.
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Old 30th June 2011, 10:49 AM   #125
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by ! View Post
Click the image to open in full size.
using 33V and 2.4V Zeners in series.
Look at the datasheets for your chosen Zeners.
What is the maximum and minimum currents for the two different Zeners?

Is there an operating current overlap that allows both Zeners to regulate while passing the same current.
If there is then it is imperative that at all working voltages and currents that the two Zeners remain in that narrow range of regulating operating current.

Far easier and better to use two equal value Zeners (or nearly so) or just a single Zener, eg 2*18V or 18V + 20V 400mW Zeners.
Minimum regulating current ~10% * 400mW / 20v >=2mA
Maximum regulating current (worst case) 100% * 400mW / 20V <=20mA
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Old 30th June 2011, 03:59 PM   #126
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^ I am wondering if you are considering the pass transistor, that this is a transistor drive not a shunt regulator.

Those were the zeners I had, I don't recall the current now as it was a few years ago I built this, but I'm sure I checked that at the time, probably typical 500mW parts. The 430 ohm resistor limits current. Current range overlap? That's an odd concept to me for zeners when dealing within their current capability and considering rail voltage would never drop low enough that you didn't have a few mA through R1 and R2. The range doesn't seem so narrow when you are working with known values like input voltage range and a resistor value you choose based on transistor hfe, these are darlington transistors so required current is reduced, but of course it could use two separate transistors instead.

Working within a known range of voltages, two different zeners can work ok, and I didn't use a single because as I wrote I used the parts I had on hand at the time.

While I am not 100% certain, a file search in an amps project folder found 1N5257, a 500mW part. Remember this isn't a theoretical PSU (anymore), it's been powering an amp built a few years ago. I should add, this isn't the entire power rail schematic for the amp, only what is on the PSU board with an AC filter board before it and a few thousand uF bulk, and decoupling caps on the amp board.

Last edited by !; 30th June 2011 at 04:07 PM.
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Old 1st July 2011, 12:13 PM   #127
AndrewT is offline AndrewT  Scotland
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I don't think you have understood what I was trying convey.

I'll be more specific now that you have specified 500mW Zener.

The 33V Zener has a maximum current of 15.1mA.
The same Zener will start to run out of regulation at about 10% of maximum current. Some devices can get down to about 5%, but most have gone around the knee in the V vs I curve at these very low currents.
Expect your 33V Zener to have a minimum current for effective regulation of about 1.5mA.
The range of currents for the 33V Zener is ~1.5mA to 15.1mA
The 2.4V Zener has a maximum current of 208mA.
The minimum current for effective regulation will be somewhere in the range 10mA to 21mA.

The overlap in operating current for the two very different Zeners is >10mA to 15.1mA, if the 33V Zener is effectively regulating at 5% of maximum current.

There could equally well be no overlap in operating current for your two chosen very different Zeners.
You need to look up the datasheets for your Zeners, but far easier to use same Zeners for your circuit.
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Old 1st July 2011, 01:08 PM   #128
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^ Why would I do that now? It's been working for years.
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Old 1st July 2011, 02:05 PM   #129
AndrewT is offline AndrewT  Scotland
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I don't expect you to do that now.

I expect you to inform readers about your experiences and to point out any shortcomings that you should be capable of identifying so that others do not copy your mistakes.

Your circuit will operate as a crude, not particularly well regulated power source. It is not a good example of how it could or should be done.
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Old 1st July 2011, 05:04 PM   #130
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^ I wasn't trying for some kind of super regulator, and it's unneeded on chipamps with high PSRR. My point was as stated, to use parts I already had to drop voltage on a transformer with higher voltage than I wanted, within the context of building a PSU to suit one's own goals, not someone else's goals.

I don't consider it a mistake to build something that works, has higher current margin than a LM338 subcircuit would, and sounds good. If you are claiming "it could be better", sure, the same can be said about any typical gainclone, turning a simple project into more and more time, work, expense, etc. Thing is, idealizing a circuit doesn't necessarily make it sound better.
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