m00dawg

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.

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?

If you are using 8580 or 6582A SIDs, you need to supply them with 9V so either have to figure out how to use the regulation found on the MB-6582 or build your own. I haven't looked at that part of the MB-6582 schematic in a while to know how easy that would be. Wilba made the PSU options fairly configurable though this particular setup is not one of the documented PSU options. I would like to keep heat away from the MB-6582 baseboard so if I go with this PSU option, I will likely just use a simple circuit off the PSU to supply 9VDC. Since the 12VDC supply is already a stable output, I don't need to do most of the tricks talked about in this thread (though may want the regulator protection diode. You can check out some of the spec sheets that have been passed around in this thread for what that looks like. If you go this route, you can also look at the spec sheet of the regulator you buy just to match capacitance values and such. Even when having to regulate 9V on your own, it will still end up being quite a bit less heat than going with a linear option (at least when using one transformer) - plus you get a supply that has a good amount of built in protection. Anyways hope that helps!

Yeah it's definitely $46 here (checked again just to be sure). Usually I use Allied Electronics as they are the next city over and so shipping is (usually) super fast. Didn't find these PSUs there though, and, speaking of expensive, they tend to be :) There's DigiKey as an alternative - perhaps they might have a few. For cost savings, the only thing I can think of is trying to see if people want to rock a bulk order. I was thinking of offering that for my LED matrix board I'm working on; but I don't think I'm quite ready to manage one of those things yet :) Otherwise, the prices on eBay seemed pretty reasonable so that might be an avenue as well? EDIT: One thing I did notice, though - there's no 9VDC so that will have to be regulated. I wonder, do the protection features of the PSU make having to make a simple 9VDC power supply (or using the MB6582 mainboard perhaps) negate some of the benefits of the switchmode supply?

Here's a few places I found a similar model: Mouser - $46.00 TRC Electronics - $34.29

Something definitely worth looking into. I'd save some space for my MB-SID rack. That said, I still like linear supplies just 'cause I guess. As far as SIDs being noisy, that's sort of true (they aren't THAT noisy). I find that any noise you do get from the SID is part of the character of it. I don't want to introduce noise that isn't there for sure. I'm waiting for the linear PSU peeps to voice their opinion but, yeah, it sounds like a good solution, particularly if it has built-in protection (that's a biggie because, if not, I can just as easily make a linear PSU). EDIT: Looks like it has current limiting protection according to the Spec Sheet. This could be a contender!

I doubt this tired old debate of "to switchmode or not to switchmode" will ever cease, but every-time it comes up, I learn something. I will say I am running a switching DC power supply on my sammichSID at the moment since I just haven't run into an extra AC power brick nor have I gone out and grabbed one up from Goodwill. It sounds great - I've even used it for recording, though that was because I forgot I was using a switching supply. If I had remembered, I would have swapped it out before that. I would imagine that using certain filtering caps can mitigate the noise, if not totally eliminate it. Maybe this is a place where tantalum (another fun debate) might be useful since I recall it handles HF noise fairly well. I wonder if the HF noise from these guys can be picked up on an oscope? I myself prefer a linear supply because they are fun to build; but I'll admit, having something that is "good enough" if not perfect would be good initially, particularly if it has some of the built in protection we have been discussing here. That way I can go about working on the other parts of my synthesizer. But back to the world of linear, I just found this from Allied Electronics in my inbox. First e-mail from them that might actually prove to be useful: I haven't looked at the spec sheet yet but perhaps this might be something to look at.

Ah ok...yeah I dunno if you need 3-5Amps for our purposes :) Many regulators can go 1-2A with proper heatsinking and that's likely more than you would need in most of the applications. Can't hurt though, I suppose.

Actually I think it would make more sense to put a current limiting transistor before the regulator? If you are using multiple regulators off of one transformer, for instance, you can have just one master current limiting circuit for the whole works?

No, although it would be great if you could post it here. That way those that might be searching for an answer to these questions in the future will have a place to look :)

I assume I need a diode for a negative regulator as well? I did some poking around on National's website and did not see a diode used on the 79xx datasheet, though I suspect it'd be basically the same thing?

Aha! That's super helpful, thanks! It sounds like it's only required if there's large caps on the other side, though that's certainly possible (you can use the 2200uF power cap from the MB-6582 in a custom PSU design, for instance). So, yeah, that seems like a good idea :)

The latchup I think I get (looks similar to a voltage clamp, though how those work is still a bit alien to me). But how does the diode protect the regulator exactly? I've just never seen that and it seems like it might not be a bad idea to implement which is why I'm curious :)

Gotcha. Just haven't seen that design before. Functionally, I'm not exactly sure what happens :) If the regulator fails and outputs 10V, how does the diode on the regulator help exactly? The crowbar circuits I have looked at online (and that have been discussed a bit on this thread) are based upon a voltage max that triggers the crowbar - how does this design differ (since I don't see a trigger)?

I've been reading up on the crowbar circuit and it seems to be more for voltage limiting - but isn't that the point of the regulators? If there's a short, I would have thought the thing to solve for is a large amount of current, not the voltage? As far as your design, I haven't seen a PSU design that uses diodes as you are - what exactly are they meant to do? That the ones around the regulators look to be a feedback loop of sorts?

*** C64 PSU OUTPUTS 9VAC *** As far as the circuit protector, I read up on the crowbar stuff too and I think that's the way I'm leaning. I'll have to look into using a transistor though, that sounds pretty clever, thanks!

The C64 PSU outputs 9VAC so you'd have to convert that to DC before you supply the SIDs. The standard SID module has to convert to DC on the board (as does MB6582, I think, using PSU Option A). The C64 pin-out contains a GND pin so you'd want to use that. If using a modular design (with separate CORE and SID modules), GND would be wired to the CORE module as it provides GND to the SID board via the SID connector. These may be of some help, though they are built around powering both 6581 and 8580/6582 SIDs so the incoming voltage would be higher than you need: http://ucapps.de/mbhp/mbhp_sid_c64_psu.pdf http://ucapps.de/mbhp/mbhp_4xsid_c64_psu_optimized.pdf When using the standard CORE and SID modules, however, the above would work for you.

Can you elaborate on this a bit? That sounds interesting! (Agreed by the way that the C64 PSU sucks huge infected goat balls)

Keep in mind that that vregs have some protection built in. They will generally overheat if too much current is applied or fail completely in some cases. It's probably not fast enough for an instantaneous issue on the synth side, but may be able to protect against some situations on the AC side. Also, the formula is the output of the rectified side of the transformer * 1.41. So if the transformer is outputting 12VAC, you will end up with 16.92VDC. I've verified that with my multimeter and 1.41 gets it pretty close. It comes from the fact that AC is a sign wave and that, after rectification, the average voltage is less than the peak of the wave so you end up with a bit more juice. I can't remember how to derive the number - I just remember it :) There's forum postings about how to get to that number however and SmashTV has a good link on what's going on visually though I can't find it :/ That is for full-wave, by the way. Also the input voltage on the main side of the transformer may not always be 110/220 and that will affect what voltage the transformer outputs on the other side. So you need to keep that in mind. For those really concerned, low-dropout regulators may be the answer, though I don't know if they are able to go above 1A and I have not had any experience with them myself.

I was originally going to do that with my MB-6582 too, but preferred to do all the regulation outside of the box to keep the heat down. Otherwise that's basically what a C64 PSU gives you so yeah I think that should be fine as long as you have the 5V regulator heatsinked well (and have sinks on the regulators inside the MB-6582 as well of course). I don't think you will have any problem with current draw with that setup - it's mostly making sure the 5V reg doesn't overheat, or at least that has been my experience. For my rackmount solution, the PSU will be inside the case (at least that's my idea so far) so I guess it doesn't matter where I put the regulation, though I will likely still do all that on a specialized power board/section. I can more easily cool the regulators that way - all the positive regs will likely be screwed or glued right to the chassis with the negative regulator getting it's own standard U-shaped sink (or so is my plan).

In a 1U!? Goodness I was worried about fitting everything in my 3U design :) Do you have pics of that as I would love to see how you layed things out. Are you using an MB-6582 baseboard there as well? I was planning on just using one xformer though I seem to remember reading that having an unbalanced supply can sometimes cause issues. The only thing using the -12V would be the 2044s (and the 2164's? though I am not sure I'll have those...at least not at first - I really want 2044's though :) ). I suppose if I used a smaller xformer for each that would not be so bad as an alternative though. Are there any ground issues to be worried about though when using two xformers?

A shame you didn't get it working - and a HUGE shame your MidiBox projects in the closet! Very sad! Your PSU design seems pretty solid on paper. I made a few changes (mostly with layout) but I think it's pretty good. I had a similar design for my MB-6582 (without the bi-polor option) using power resistors to bring the voltage down before the 7805 and it worked very well.

You can try Goodwill if there is one local to your area. I have found some transformers for pretty cheap there. Look for the ones that typically power amps and things (basically ones that output 10-12VAC, depending on what type of SIDs you will be stuffing in the Sammich). I would look for something around 500mA, though I doubt you would get anywhere near that with a Sammich. I thought I saw a forum post on current draw of a the Sammich not to long ago so you might want to go searching around for that. Having said that, I've run my Sammich on a switchmode PSU. It's not ideal but I haven't had as much audio issues as I thought I would have, though I wouldn't recommend using one for a long period of time or for recording.

Wilba, do you have a suggestion on heatsinks inside the Sammich? Clearance seemed to be an issue there. I have some of FuzzyLizards sinks but it didn't look like they would fit in the Sammich.