Starfire

Custom Power Supply for mb6582

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I've been thinking about this all morning :) Are filtering caps and/or inductors not sufficient for filtering out the HF noise from these types of PSUs? Is if the frequency that's the issue? Because I know ceramics and tantalums are typically good at HF filtering. Curious if just using some of those could help filter out the noise from the DC outputs of switchmode supplies?

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I have been talking to someone with experience on using switching PSUs in audio applications. He suggested putting coils in the path for filtering, if the HF noise would be within the audible spectrum. I have no idea if and how that would help, maybe someone who is into this matter could explain further?

Edited by NorthernLightX

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That's what I read as well, though the Wikipedia page on inductors indicates that they can actually bring in noise from other sources as well. I have read that inductors (and capacitors) are suitable for filtering HF noise so I think there is some truth to that. I don't know much about inductors to really say where to go from here, though :) I've seen inductors in PC PSU (I think anyway) so perhaps the Mean Wells already have them *shrug*

EDIT: Here is a PDF that measures filtering capabilities of tantalums up to 10kHz. The document really talks about it from an audio pipeline perspective it looks like, but there was some pretty decent information on there.

Edited by m00dawg

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I was thinking about doing exactly that. Just to clarify: you mean your MB-6582 is set up for the C64 power supply option, and you feed 12VDC into your MB6582 where it's supposed to get 9VAC, right?

I wonder if you could do the same with a C64.

Thats right.

Just like capacitors act like hp-filters when connected in series with something, coils act like lp-filters when connected in series, so it makes sense.

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I feed 12V dc into my MB6582 where it's supposed to have 9V dc. The voltage goes through the rectifying bridge (loose some voltage) smoothing caps (no change) and finally through regulator (regulated down to 9V). It works fine and doesn't seem to generate much neat (actually I think it generates less heat than the standard 9V ac way).

Exactly what I did.

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I've been thinking about this all morning :) Are filtering caps and/or inductors not sufficient for filtering out the HF noise from these types of PSUs? Is if the frequency that's the issue? Because I know ceramics and tantalums are typically good at HF filtering. Curious if just using some of those could help filter out the noise from the DC outputs of switchmode supplies?

You are thinking about it too hard.. lol..

First, you need to know what the frequency of the noise is, otherwise your shooting in the dark...

It does looks like the MeanWell ones are switching at 132Khz.

Like I mentioned before, the switching noise is above the audio spectrum (+20Khz) in modern SM powersupplies.. so, if it's there, you won't be able to hear it.. I'd doubt if your speakers or amplifier could reproduce it, and I doubt your recording interface will record it either.

Enjoy the filthyness of the SID.. that kind of audiophile thinking and SID chips don't really belong in the same sentence.. lol.

Cheers

Mike

Edited by Futureman

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132Khz is far beyond what humans can hear, yes. It's not beyond what modern samplers can do (I've seen up to 192kHz). For most applications, it's insane to go really above 96kHz. Some might say 44kHz is enough and call me out on the Nyquist Frequency Theorem but having a lower noise floor means that you can do other naughty things to audio without raising the noise floor to audible levels. One example is halving the speed of a drum loop which would cut the sampling rate in half (which ends up being 48kHz when sampling at 96kHz of course, which is still above 44kHz so no problem there). For most practical purposes, 96kHz fills those needs.

But when people want to REALLY much with the audio, 192kHz could make some sense, although at that point, your noise floor is really 132kHz when using the above power supply. I can't imagine needing 192kHz in my applications so I never record at that (I do record and highly endorse recording at 24-bit precision, even for old noisy vintage chips like the SID). So, though it's wildly pathological, filtering that noise out is in those applications might not be a bad things to look at.

So far, the only graph I have seen is the one I previously. If I am reading that correctly, we know that tantalum can attenuate 10kHz and we could infer from the graph that it can do more since the filtering was approaching zero. That's a large assumption though to go form 10kHz to 132kHz though :)

As far as the SID sound, as I said before, I know it's noisy, but it's not a distracting sort of noise and the whole point is to capture the imperfections of the SID - not the PSU :)

Long story short, for most people (likely including myself), it sounds like this switch-mode PSU is well worth it by itself without having to do any extra filtering. The exception is those with OCD :)

EDIT: Here is a another PDF describing characteristics of different capacitors when uses to attenuate HF noise from switching supplies. Figure 11 shows filtering over 100kHz (if I am reading it right, the ripple is a bit higher than that). Tantalum does indeed filter out a good chunk of the noise at those frequencies. Ceramics can also work well according to the docs, though they may introduce some noise as well (the document does not say what type of noise or at what frequency).

So, the takeaway is that, again, for pathological cases, adding a tantalum cap seems like the way to go or perhaps a ceramic. Perhaps even the two could be coupled together *shrug*. I don't even have a way to test the results at those frequencies so, again, it's all very pathological :)

Edited by m00dawg

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Why not use 2 wall warts of appropriate voltages (9VAC and 5VDC) and just wire them up?

I personally don't trust the old C64 supplies. The SID chips are worth more than the risk of burning them up when the supply fails.

--tom

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Why not use 2 wall warts of appropriate voltages (9VAC and 5VDC) and just wire them up?

Because

a. I need +5, +9, +12 and -12 volt rails so I would need 4 wallwarts with your solution.

b. Wallwarts are uncool, more than 1 wallwart is seriously uncool (IMHO). 4 wallwarts is not only insanely uncool, but also extremely impractical.

c. What's the fun in using wallwarts? I like it better if something is custom and/or expirimental. Besides, if it turns out switching PSUs aren't evil anymore per sé, lots more Midiboxers could benefit from that info, so I plan on ordering one in the very near future. Might even finish my 6582 project that way.

I personally don't trust the old C64 supplies. The SID chips are worth more than the risk of burning them up when the supply fails.

And you're exactly right to do so. (IMHO again)

Cheers, Alex.

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Because

a. I need +5, +9, +12 and -12 volt rails so I would need 4 wallwarts with your solution.

b. Wallwarts are uncool, more than 1 wallwart is seriously uncool (IMHO). 4 wallwarts is not only insanely uncool, but also extremely impractical.

c. What's the fun in using wallwarts? I like it better if something is custom and/or expirimental. Besides, if it turns out switching PSUs aren't evil anymore per sé, lots more Midiboxers could benefit from that info, so I plan on ordering one in the very near future. Might even finish my 6582 project that way.

And you're exactly right to do so. (IMHO again)

Cheers, Alex.

Display sells the t40 one for something like 34 euro. Couldn't find a local supplier for the t30.

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Display sells the t40 one for something like 34 euro. Couldn't find a local supplier for the t30.

Me likes! I didn't search very hard yet but found these 2: http://www.dil.nl/PartDetails.aspx?ProductID=ZPS30 and http://www.dil.nl/PartDetails.aspx?ProductID=ZPS4515. Have no idea about their switching freqency but one of these has been successfully used as a replacement PSU in a vintage amplifier I was told. But since those are EOL I might just go for the T40, seems to be perfectly right for what I want with it.

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Me likes! I didn't search very hard yet but found these 2: http://www.dil.nl/PartDetails.aspx?ProductID=ZPS30 and http://www.dil.nl/PartDetails.aspx?ProductID=ZPS4515. Have no idea about their switching freqency but one of these has been successfully used as a replacement PSU in a vintage amplifier I was told. But since those are EOL I might just go for the T40, seems to be perfectly right for what I want with it.

The 45-15 one is a bad idea. According to the datasheet it needs active cooling. Looking at the datasheet it does looks like a dated design. Estimated Efficiency at full load is min 65%. Which isn't very high. Could very well be that the switching frequency is quite low. But can't find what it is.

At the distributor you pay only 18.75 euro for the t-40 meanwell. Downside is they only sell to companies.

Edited by Shuriken

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The 45-15 one is a bad idea. According to the datasheet it needs active cooling. Looking at the datasheet it does looks like a dated design. Estimated Efficiency at full load is min 65%. Which isn't very high. Could very well be that the switching frequency is quite low. But can't find what it is.

At the distributor you pay only 18.75 euro for the t-40 meanwell. Downside is they only sell to companies.

I'll scrap the 45-15 then, and go for the Mean Well. Has better looks anyways.

Do you have an URL or something for the distributor's details? I'm a freelancer so I have everything needed to buy stuff directly from them, as long as I don't need to buy 10 at once anyway (in which case I might organize a bulk order :))

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I'll scrap the 45-15 then, and go for the Mean Well. Has better looks anyways.

Do you have an URL or something for the distributor's details? I'm a freelancer so I have everything needed to buy stuff directly from them, as long as I don't need to buy 10 at once anyway (in which case I might organize a bulk order :))

http://www.meanwell.nl/categories/AC-DC-POWER-SUPPLY/Enclosed/Low-cost/40-Watt-triple-output.aspx

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OK, Mean Well distributor in NL just got back to me about prices. Up to 19 units will be €18,20 per piece, when ordering more than 20 units price per piece will drop to €16,30. For standard shipping & handling they charge €25 per order.

So for example if there would be 5 midiboxers who want one, price per piece would be €18,20 + €5,00 + shipping to your home address (or come pick it up for free & a coffee).

So, is anybody interested in a bulk-order of these babies? Just shout here or PM (or mail) me, if there are a few guys interested I'll also advertise in the bulk-order section. I'm not planning on organizing a huge order though, so don't wait too long to respond but also don't jump on if you don't have the ca$h (and keep in mind that shipping in NL can be quite expensive; €7 for domestic parcels, international costs more).

Cheers, Alex.

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Due to the overwhelming amount of people who want to jump on the bandwagon (exactly 0 (zero)), I'll just go ahead and order one for myself.

:tongue:

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Hehe I was interested but I'm in the US so I figured the savings would work out for me due to shipping.

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So, the Meanwell appears to be a good solution. One more thing: should I get the T30 or T40?

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So, the Meanwell appears to be a good solution.

Some success has been reported. Still, try at your own risk :rolleyes:

One more thing: should I get the T30 or T40?

Depends on what you're going to power with it. T30 looks good enough for a 6582 with added filters and more fun, but as it is not available from the Dutch distributor (and I can't find it on meanwell.com either - discontinued maybe?) I'll go with the T40. Whichever you choose, you need the 'B' model for +5/+12/-12.

Edited by NorthernLightX

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Heads up, not all of the Mean-Well switching supplies switch at 132kHz. Some data-sheets do not list a switching frequency while others (such as the T-40) list it at 40kHz. The TP-75 was the one that had the highest switching frequency but also the highest cost :)

EDIT: Also found this off Mouser. It's not Meal-Well but meets the specs and has a documented switching frequency of 110kHz.

Edited by m00dawg

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Heads up, not all of the Mean-Well switching supplies switch at 132kHz.

Good tip. Lesson: assumption is the mother of all f***ups. I'm very glad until now I only inquired about prices because I was planning to order this morning; great timing dude! :thumbsup:

I'll go ahead and dig into some datasheets then, basically anything switching above 50KHz (I know human ears often dont go beyond 22KHz but let's assume Philips knew what they were doing when deciding that 44.1KHz was the right bandwitdh to use when they developped the CD) is out of the audible spectrum, above 94KHz is out of the recording spectrum as well and thus (theoretically) better. Aside from the guys who record at 192KHz but I don't believe any switcher is that fast. Besides, if it really adds something to your recording to go to 192KHz/32bit instead of 94KHz/32bit is a whole different discussion.

/EDIT

I found some datasheets of Mean Well supplies that deliver the required voltages:

http://www.meanwell.nl/Images/pdf/datasheets/T-40-spec.pdf

http://www.meanwell.nl/Images/pdf/datasheets/RQ-50-spec.pdf

http://www.meanwell.nl/Images/pdf/datasheets/TP-75-spec.pdf

Nowhere can I find the switching frequency. Is it hidden somewhere within another parameter?

/EDIT2

Damn I need glasses, it's at the top of each document. :whistle:

Edited by NorthernLightX

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Hmmmm, that TP-75 is not the holy grail after all I guess; this is what the datasheet says:"Fixed switching frequency at PFC:67KHz PWM:134KHz". I have no clue what that means exactly, but 67KHz does not look pretty for that price (€ 43,90) and it's quite over dimensioned even for a very full SID box.

That LPT42 @ Mouser is also a bit on the expensive side, €36 for an open frame unit.

I found this: http://www.meanwell.nl/products/Meanwell-RPT-60B---PSU-pcb-medical--plus-5V-44A---plus-12V-22A---12V-055A__RPT-60B.aspx

Features:

Open frame - oh well, we're DIY, so we'll fix something won't we?

Delivers +5v/+12v/-12v - check

Switching freq @ 100KHz - yay!

Tiny(!) - only measures 4"*2" (rougly 10cm*5cm)

Affordable - a little over €20 ex VAT

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Hah yeah I found the frequency stuff right before I was going to buy one as well - so I guess I saved us both. I sent Mean Well an e-mail asking what the fastest switching supply they had was, but I think we have already run into it (TP-75). PFC stands for power factor correction but the wikipedia article is a bit thick to read (for me anyway) in terms of what that means or if it might introduce noise.

RPT-60 looks like a winner, though it's about the same price on Mouser as the LPT42 I found. I was looking specifically at Mouser since I was ordering some encoders and things as well. I know there are places to find these types of power supplies cheaper here in the US, however.

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RPT-60 looks like a winner, though it's about the same price on Mouser as the LPT42 I found.

I believe both of them are equally suitable. The Mean Well is a little bit smaller but that's only an issue if you're tight on space. If they're no different price-wise just buy the one that's in stock :wink:

I've mailed the Dutch distributor asking about the stock of the RPT-60. If it's in stock I'll buy at least one for my 6582, and I'm considering buying one for my FM too.

BTW don't forget to buy the matching Molex connector for the primary and secondary side of the PSU.

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