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Old 30th May 2005, 01:18 AM   #1
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Default Power supply performance testing? How To

Can anyone give me info on Power supply performance testing. Namley voltage regulator testing.

What test are generally usefull, how do i compare one regulator scheme VS. another perfomance wise? etc.

I have 3 regulator schematics i am interested in comparing. I have a amplifier that uses Zeners and resistors to derive +/-15vdc @ 100ma from +/-75dc rails. I want to compare the stock schem VS. using resistors to drop the voltage down to +/-30VDC then using 7815/7915 type devices or using the PASS regulator schematic.

All 3 designs should work adequitly well, but, how do i run some tests to determin which actually performs best? which would give me the cleanest power and wich would regulate the best.


Thanks


Zc
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Old 30th May 2005, 01:33 AM   #2
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if you want to test PSRR try simply observing it on osciloscope.
if you want to test output impedance feed its output with a signal thru resistor and calculate damping.
I remember someone did a comparison in power suply forum beetween 78xx/79xx and 317/337 and the latter performed much better
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Old 30th May 2005, 02:11 AM   #3
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Hi. Sounds like you're talking about the preamp supply on SWR!
I have found in my own experience that the 79xx is not very well matched to the 78xx, and the regulation gets worse very quickly once you get around 10v above the regulated voltage.
I'm not sure what advantage there would be to replacing the zeners. Here's one idea I don't know if you may have already done - is to monitor the supply lines on a scope while running the amp through it's rigor. That way you could check regulation, and alternatively you could check for other hash on the lines - which I would guess could be a greater issue than regulation.
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Old 30th May 2005, 02:47 AM   #4
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Hi adrome00, depends on the test gear you have at your disposal.

Assuming the 75V rails are on a power amplifier, what I generally do to evaluate regulator performance is to run the power amplifier at the highest safe sustainable power into a dummy load and view the regulator output on a FFT analyser for a number of spot frequencies, or sweep your AP test set through a crosstalk test using ch1 to drive the amp and ch2 on the reg supplies to see residual vs hum and noise.
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Old 30th May 2005, 05:09 AM   #5
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this is exactly on a SWR amp!!!

I dont have a FFT or and Audio precision....YET! some day.

The Zeners probably do just fine. it just seems like such a brute force way to achive the end goal. There was another post where we discussed various regulator schemes. and i found the pass labs regulator schematic and that looks like it fits the bill perfectly. But what i wanted was a rock solid, but easy way to tell if i actually gained anything by using the pass labs regulator VS stock.

the SM-900 uses Two 5 watt 1,100 ohm resistors in parallel to come up with a 550 Ohm 10 watt resistor. But, that resistor stack gets pretty warm.

and they didnt use any fuses on the secondary side of the power supply, so when one channel fails as it did on mine, it Torches the board badly! because this amp was supposed to be the ultimate amp, they didnt do or use anything they felt would hinder performance or reliability. and apparantly they felt fuses would in someway hurt performance. so the only fuse you get is the 10 amp line fuse!

I would rather have a degree of protection VS the minute amount of performance degradation So i fabbed up a small board with Four 2,200 ohm resistors in parallel to reduce the heat per resistor down some and put fuses for the B+ and B- on the board. hopefully, if a channel should fail again, it wont torch the board so badly.

Back to the regulators, now then a bass amp sits idel most of the time but with slap and pop bass there are a lot of transient demands put on the power supply. I have no idea how this effects the front end at 15vdc, how quickly do the Zeners react, is there any variance in output voltage or noise. and would the Pass regulator offer better performance or lower noise.

I thought about using a small seperate transformer, but wondered if line voltage swings and noise would actually make things worse?

I dug through some old Audio Amature mags for the old Sulzer regulator schematics, but havent found them yet, and i doubt they would work well with that big if a voltage differential anyway. The Pass labs reg seems to be the way to go.

Dang i really need to get a FFT, maybe an old HP 3580A would suffice?

Zc
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Old 30th May 2005, 05:48 AM   #6
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Sorry Zero Cool,

I addressed my post to the wrong person (my head fog). You can download a 90dB FFT "Audio Tester" which uses your soundcard and depends on it's quality. Below is my 250W/ch amp supply FFT, driven at 5W /8 ohms . See the harmonic artefacts due to AB.

I have built a low pass filter on the soundcard signal output to eliminate its harmonics giving 110dB noise floor (0.0003%).
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Old 30th May 2005, 07:14 AM   #7
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Quote:
You can download a 90dB FFT "Audio Tester"
http://www.sumuller.de/audiotester/maine.htm
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Old 30th May 2005, 04:25 PM   #8
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Quote:
Originally posted by amplifierguru
Sorry Zero Cool,

I addressed my post to the wrong person (my head fog). You can download a 90dB FFT "Audio Tester" which uses your soundcard and depends on it's quality. Below is my 250W/ch amp supply FFT, driven at 5W /8 ohms . See the harmonic artefacts due to AB.

I have built a low pass filter on the soundcard signal output to eliminate its harmonics giving 110dB noise floor (0.0003%).
I have seen these programs but how do you get the signal into the sound card? I would imagine you use the line in of course, but how do you condition the signal from speaker level and DC down to line level without effecting the results??

I have the SIA SIFT SMAART Pro software that is a FFT that i use for sound system setup. and that is a very powerfull FFT, and i have a FFT in soundforge and Wave lab. I did some testing of the crossover in my BMW's 10 channel amp with the SMAART software. that worked well enough to see the crossover slopes etc. but i had no way to calibrate the input levels etc to some reference. Any of these would work well enough to see noise and harmonics etc. but how do i connect a sound card to a power supply?? I am going to have to block the DC with a capacitor of course.

How about giving us a write up of the setup you use etc.

Zc
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Old 30th May 2005, 04:46 PM   #9
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I downloaded the software and i see it has a way to calibrate itself. will have to investigate this more.


Dave
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Old 30th May 2005, 07:46 PM   #10
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If you want to comparatively test supplies for output Z vs freq, what you do is drive a signal into the supply output through a resistor. Example: put 5V rms on a 100 ohms resistor to the supply output. That means you drive 50mA rms into the supply. You measure the residual signal at the supply. Supplose it is 1mV. You supply has an output Z of 1mV/50mA = 20mOhm.

Several caveats:
Make sure that the rms current is not higher than what the supply normally sources. Supplies cannot sink, normally. So a supply that normally delivers, say 100mA to a preamp should not be tested with more than 100mA neg peak current, so stay below 50mA rms or so.

Where do you inject the test current? Either at the point of the regulator where it's internal feedback is taken > you measure the lowest Zout; or at the point where the supply is connected to the load > you measure reality in use. Conclusion: always connect the load to the same point as the supply internal feedback point. You can easily have a 1mOhms supply connected to the load through 10mOhm of wiring. Pretty wastefull.

And oh yes, sweep the test frequency.

Jan Didden
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