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Old 10th January 2013, 07:41 AM   #31
qusp is offline qusp  Australia
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thanks, yes like I said its there, be aware of it with the choices of cap size on the output, I never use tantalum, but plenty of X7R ceramics and some allu/polymers in the range of 10mohm.

i'm just saying as yet after many uses, i'm yet to have it make any impact on the actual performance of the circuit, probably due to the fact the local decoupling caps are doing all the work. Any one where it would likely be effected i'm already using another regulator. even the NTD1 of his, based on the Pass D1, but modified, uses them and PSRR is bound to be terrible. its a simple common gate follower, but its a very constant class A load with little dynamic behaviour. I am however in the middle of designing a bipolar TPS47 based reg for it to get the size down and maybe squeeze the last drops out of the circuit, which is already pretty special, with no aberrations.

i've asked Owen if he has any impedance vs F plots of his boards. I found the ones I have, but doesnt have a Zout vs F plot, just noise vs F, some FFTs, which would give a hint you would think. i'll link him here, perhaps he'll comment. his are all adjustable regs, not sure if that makes a difference.

hes already posted these on the forum before so hopefully he wont mind.
its not like its a secret patent pending design. they are interesting anyway for their illustration of the 317 vs 337

not the last word in performance, but we all know that, good enough for a lot of loads people often discount them for though IMO
Attached Images
File Type: jpg FFT Spectrum Monitor - uV.jpg (170.2 KB, 154 views)
File Type: jpg FFT Spectrum Monitor of output - AC coupled copy.jpg (127.5 KB, 151 views)
File Type: jpg FFT Spectrum Monitor of output copy.jpg (127.6 KB, 146 views)
File Type: jpg Scope (Signal) - AC coupled copy.jpg (238.2 KB, 149 views)
File Type: jpg Scope (Signal) copy.jpg (125.6 KB, 145 views)
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Old 10th January 2013, 07:16 PM   #32
Hengy is offline Hengy  Canada
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What you guys are talking about is a little over my head.. not that I'm saying stop. It's an interesting discussion, and I read it with interest.

I ordered a few different inductors and beads from Digikey yesterday - two each of 10uH, 22uH, 47uH and a 100uH, one toroidal and one ferrite - just to experiment and see the effects of each. hopefully it also solves my problem with the smps switching noise. As I am away from my equipment this weekend , I will post the results early next week. Hopefully this will help other people in my situation.

Thanks again for the suggestions!

Hengy
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Old 14th January 2013, 12:01 AM   #33
Hengy is offline Hengy  Canada
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I have been reunited with my equipment!

I had time to try the 10uH and 22uH inductors quickly, and take a few pics for comparison. First is the 'raw' input & output. Then the 10uH (this one from Digikey) and the 22uH, all with 3500uF of input caps.
Click the image to open in full size. Click the image to open in full size. Click the image to open in full size.

The input cleans up very nicely! I can't really tell if it affects the output all that much - trying it with my amp will tell. There is very little difference between 10uH and 22uH, which doesn't surprise me. i just thought I'd play around with a few different values.

This was very quick, and when I get time - probably tomorrow - I will do a much more thorough test, and of course hook it up to my amp! I will post the results here too.

Hengy
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Old 14th January 2013, 01:16 AM   #34
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Definitely a substantial improvement on the pre reg side! It is interesting that there is very little change on the post reg side....

But the 47Khz noise spikes on the input were only around 4mV in size so it would appear that the reg is doing its job quite well at this frequency. Any residual noise you are measuring on the output could be due to measurement limitations.

Have you tried a different time base such as 2uS it may allow you to see better the shape of the noise spikes and whether there is still any residual after the reg.

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Old 14th January 2013, 11:31 AM   #35
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A couple questions -- are you using an EI transformer or a toroid, which diodes are you using, and how have you loaded the regulator?

the 47k noise could be environmental.
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Old 14th January 2013, 11:50 AM   #36
Hengy is offline Hengy  Canada
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Jackinnj, I am using a smps with a series toroid 10uH inductor and 3.5mF caps. The regulator is loaded with 150mA incandescant bulb - about a quarter of what the amp will use.

I have experienced the same noise in a few different locations.

Hengy
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Old 14th January 2013, 05:57 PM   #37
knutn is offline knutn  Norway
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Maybe this is of interest? Simple Voltage Regulators Part 1: Noise - [English]
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Old 15th January 2013, 06:51 PM   #38
Hengy is offline Hengy  Canada
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So I hooked everything up late last night, turned on the MP3 player I'm testing the amp with, plugged in some headphones...

and hum. Maybe even a bit worse! It is, however, different, which means i think the inductor did something. Also, the noise is more pronounced on one side, which I didn't notice before.

Now, I checked all the wiring, polarity, etc. I moved things around, but still, hum.

So, going back to what a few of you mentioned earlier, I think the grounding scheme I have (not so carefully) implemented is the problem. Please don't say 'I told you so'.

Tonight I plan on talking the amplifier apart and trying to implement a better grounding system - star ground to be more exact.

I must admit, I'm a bit embarrassed, wasting all the time on inductors while I really should have been paying attention to the grounding system!

Hengy
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Old 16th January 2013, 03:29 PM   #39
gootee is offline gootee  United States
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Hum could also be from having enclosed loop areas, making antennas.

Signal input and its ground must stay as close together as possible, everwhere. If wires, twist them tightly together. Or, better, use shielded twisted pair cable, with the shield connected to chassis (NOT to signal ground!) at one end only.

Also, any wire pairs with high current or highly-dynamic current could make transmitting antennas. So twist those tightly together, too. This especially includes power supply wiring.

If using pcbs, either keep ground plane over or under everything or make sure the traces are always very close together, for each type of pair.

Last edited by gootee; 16th January 2013 at 03:32 PM.
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