+/- 16V symetric smps?

[arjepsen]

Yes, I should get the 48V sorted also.
There's 12 mic preamps, so that would be 168mA. I do have a 50W supply at hand (stadium strontronics SRS50-48), but reading through your posts, I assume that one is way too beefy. I'm actually still debating whether I want to simply ignore the phantom power supply, since I would likely never use it - most likely I would use my MOTU 1248 if/when needing phantom power. Haven't quite made up my mind yet.

I'm not strong in the CM theory either - would you be able to give me a quick estimation for the element values for the cap, resistor and transistor for a CM on the +/- 16V supply, and/or point me to a good source that's easy to understand?

 

[Bo Deadly]

I would do something like Elliot Sound Products Project 15 Figure 3A except the rectifier isn't used of course and it does't need a 3 pole filter. You just need one RCR filter on the base. And you don't need such large tranistors. Search for my posts to user "Blissy" where I described the CM in detail. That was for a 5A supply but 2A is really not that different. I would just copy the parts talked about in that thread.

If you're not sure you'll need 48, then maybe just skip it. Otherwise I'm not sure off-the-top-of-my-head how I would integrate the shunt regulator. That would take a few days in LTSpice and I'm supposed to be writing code right now ...

 

[mjrippe]

Stop fixating on +/-16V. Seriously, +/-15V will work exactly the same in this mixer and you are driving yourself nuts for no reason.

 

[industrialarts]

Here are two options

https://capi-gear.com/catalog/product_info.php?products_id=567
http://collectivecases.com/?product=psu-cc-psu1

IMHO - This would be the way to go. It's easy and it would work. Keeping the power supply outboard of the mixer or console is a better idea - noise wise. You could add some additional filtering internally

 

[Bo Deadly]

IMHO - This would be the way to go. It's easy and it would work. Keeping the power supply outboard of the mixer or console is a better idea - noise wise. You could add some additional filtering internally

I've found that you can actually put an SMPS inside and it can be silent (as in measurably using hi-res FFT). I had one, albeit a pretty small one, literally about 5cm away from a dual THAT1510 board and it was totally noise free. The potential for noise seems to be a function of current and distance. The higher the current, the more distance is required from high-Z high-gain bits. Arjepsen said it had a PC inside it at one point. So it sounds like there should be plenty of room for two 1A supplies. If done correctly, I bet it could be completely noise free. A linear supply almost always has a mains bump.

 

[Newmarket]

I've found that you can actually put an SMPS inside and it can be silent (as in measurably using hi-res FFT)....

Yes. But the OP still has to deal with mains safety of the whole thing if changing to an internal psu.
It might not really be an issue depending on experience an knowledge.

 

[arjepsen]

Stop fixating on +/-16V. Seriously, +/-15V will work exactly the same in this mixer and you are driving yourself nuts for no reason.

Sorry for any insanity I may have been the cause of - including my own! ;-)
I do get the point, that for an opamp supply those two volts make little difference.
But the fact remains, that it must be supplying more than just opamps, because when I only supply it with +/- 15V, the desk doesn't work at all. (I did try....)

 

[arjepsen]

Sorry for any insanity I may have been the cause of - including my own! ;-)
I do get the point, that for an opamp supply those two volts make little difference.
But the fact remains, that it must be supplying more than just opamps, because when I only supply it with +/- 15V, the desk doesn't work at all. (I did try....)

AAAAAND I take it back!
previously I simply could NOT get it to work, but messing around with it now, I actually did manage to get sound supplying it with +/- 15V.
So, the issue of getting it to start up right has to be somewhere else....
I still have the issue of filtration though, which will likely lower it even further - so I might end up with only +/- 13.8V which then is a bit away from the original 16.

 

[Bo Deadly]

AAAAAND I take it back!
previously I simply could NOT get it to work, but messing around with it now, I actually did manage to get sound supplying it with +/- 15V.
So, the issue of getting it to start up right has to be somewhere else....
I still have the issue of filtration though, which will likely lower it even further - so I might end up with only +/- 13.8V which then is a bit away from the original 16.

That was probably because you need to put ~+2V into a regulator. So if you were feeding exactly 15V into your existing regulator circuit, it will not regulate and possibly just not work. Using an SMPS with CM is a completely different story. If the CM is two transistors, that a 1.2V drop. So you just need to adjust the SMPS to 16.2V to get 15V out. You don't need regulators because an SMPS is a regulator. Not nearly as good as an active regulator IC but with a CM on the output it will be good enough and quiet.

@newmaket - I don't see a problem with mains. Wiring up an ACDC SMPS is about as simple as it gets. You don't even need fuses. It's literally mains > power switch > SMPS and earth to chassis bolt. You could literally do it with a couple of wire-nuts. Although I would look closely at the power switch. If it's not a 5A+ type, I would swap it out for something beefier to account for high SMPS surge currents. Parts like that have a tendency to get banged up over the years too.

 

[arjepsen]

That was probably because you need to put ~+2V into a regulator. So if you were feeding exactly 15V into your existing regulator circuit, it will not regulate and possibly just not work. Using an SMPS with CM is a completely different story. If the CM is two transistors, that a 1.2V drop. So you just need to adjust the SMPS to 16.2V to get 15V out. You don't need regulators because an SMPS is a regulator. Not nearly as good as an active regulator IC but with a CM on the output it will be good enough and quiet.

I'm not running it through the old regulator - I'm supplying it directly to the power distribution board in the mixer.
Anyways, I think probably one of the problems I had was that I hadn't yet removed the big caps from the 5V and 12V spms'
I removed those today, and got it to work with my original +/- 15V supply.
Of course though, it has quite a bit of noise now, so I still need to try the CM circuit, and thus might still just go for the dual 15 supplies, so I can adjust both sides up.
Anyways, I was looking over the transistors you mentioned in that other thread. I would actually like to avoid smd's and also cut down on component count, so I'm thinking about using darlington transistors - problem is, I'm not certain about which specs to adjust my search for - could you advise?

 

[Bo Deadly]

Anyways, I was looking over the transistors you mentioned in that other thread. I would actually like to avoid smd's and also cut down on component count, so I'm thinking about using darlington transistors - problem is, I'm not certain about which specs to adjust my search for - could you advise?

Nah. A lot of parts are SMD-only now and the parts count for a CM is already pretty low. Not sure you're going to improve on that much.

 

[Newmarket]

@newmaket - I don't see a problem with mains. Wiring up an ACDC SMPS is about as simple as it gets. You don't even need fuses. It's literally mains > power switch > SMPS and earth to chassis bolt. You could literally do it with a couple of wire-nuts. Although I would look closely at the power switch. If it's not a 5A+ type, I would swap it out for something beefier to account for high SMPS surge currents. Parts like that have a tendency to get banged up over the years too.

Well I don't have a problem with mains wiring / safety myself - as I've designed with mains powered kit, drawn up the wiring diagrams and specs' and been responsible for regulatory compliance etc.
But I appreciate that others may not be so experienced with it - earthing / double insulation / PAT / creepage / clearance / labelling requirements for LVD compliance etc. (although I can think of a (non-audio) company that isn't so bothered about it tbh ! but that's another story).
I'd be wary of going without a fuse or other current limiting device. You need to be able to "short the secondaries" and have the kit cut out / stay safe / not catch fire. Although the meaning of "short the secondaries" can be a bit debatable wrt switching supplies.
Of course, that may be taken care of in the SMPSU but I wouldn't assume that to be the case to the standard required. The last mains powered kit I was involved with used a magnetic circuit breaker integrated into the mains switch.

 

[Bo Deadly]

I'd be wary of going without a fuse or other current limiting device. You need to be able to "short the secondaries" and have the kit cut out / stay safe / not catch fire. Although the meaning of "short the secondaries" can be a bit debatable wrt switching supplies.

You don't have to worry about any of that anymore. You don't need a fuse. I assumed we're not talking about some junk you find on aliexpress. These things are so good and cheap now, they all have those sorts of protections. It would be bazaar to find one without. LRS-35-15 is isolated, short circuit, overload, overvoltage protected, safety standards, blah, blah, blah. So SMPS actually gives you instant compliance. If anyone asks, you just point to the datasheet. If you make your own supply, THEN you have to go through all of that certification and safety hullabaloo.

 

[Newmarket]

You don't have to worry about any of that anymore. You don't need a fuse. I assumed we're not talking about some junk you find on aliexpress. These things are so good and cheap now, they all have those sorts of protections. It would be bazaar to find one without. LRS-35-15 is isolated, short circuit, overload, overvoltage protected, safety standards, blah, blah, blah. So SMPS actually gives you instant compliance. If anyone asks, you just point to the datasheet. If you make your own supply, THEN you have to go through all of that certification and safety hullabaloo.

I'd still prefer to keep an external fuse or breaker. Simple to look at a glass cartridge fuse and see how it looks if something goes wrong rather than diagnose a SMPSU. Having said that - I'm quite a fan of resettable 'Polyfuses' in the right place but not for primary mains connection. Of course, in UK we have mains fuses in the mains plug itself but it's not really the right type to guard against equipment damage.
Without going product specific, I appreciate the levels of protection that are often incorporated into SMPSUs. But having a safety standard referenced doesn't mean that a product incorporating that PSU will be compliant. eg an 'Open Frame' psu is unlikely to be compliant in itself and requires correct installation / insulation.
Similarly (from a UK/EU perspective at least), EMC compliance is not guaranteed by incorporating a PSU that has been tested to ENxxxx (can't recall the relevant standard right now). PSUs that aren't basically products in their own right (basically usable off the shelf) cannot be CE (or UKCA looking 'forward' in UK) certified.
Having said that for a DIY/One-off/Prototype there are exceptions and it's unlikely to be an issue unless it contravenes any terms of insurance or whatever.

 

[ccaudle]

still prefer to keep an external fuse or breaker

I like the power entry modules with integrated fuse, if for no other reason than peace of mind that if something chafes or cuts the insulation on the wiring connecting power entry to the power supply modules the system is still protected.

 

[Newmarket]

I like the power entry modules with integrated fuse, if for no other reason than peace of mind that if something chafes or cuts the insulation on the wiring connecting power entry to the power supply modules the system is still protected.

Yes - I'm most likely to specify that type of thing if possible.
Plus integrated EMC filter if going to use one there. One component. One panel Cut Out.

 

[arjepsen]

Nah. A lot of parts are SMD-only now and the parts count for a CM is already pretty low. Not sure you're going to improve on that much.

I finally got the parts, and have it up and running. I used the circuit from the link (Capacitance Multiplier Power Supply Filter).
The noise level is audibly less that it was with the original power supply, so that's great.
I do wonder if I can get it quiter though - there's some hiss on each channel (though again, less than before), and I imagine some of it is due to old electrolytic caps. However, there also is some whine in there, that I assume must originate from one of the smps's. Apart from the +/- 16V supply, there's a 5V and a 12V smps - and I do wonder if the whine is originating from the grounding of those other two. I do believe I've avoided ground loops, but should there be more seperation between the grounds? (I remember someone talking about putting a resistor between those seperate grounds.) I did try to make another CM for the 5V supply, but the loss of voltage is too much, and the desk becomes unstable at best.

 

[Bo Deadly]

However, there also is some whine in there, that I assume must originate from one of the smps's.

The whine is probably #2 in Bo Deadly's Guide to SMPS for Audio.

 

[arjepsen]

Yeah, I was wondering whether that would be the case. I assume it's not the +/- supply, since that seems to be loaded at a little less that 1A when idle.
So there are two other supplies: 5 and 12V, and I guess maybe noise from them could get into the audio?
The 5V seems to draw about 2.6A on average. It's an 80W supply, so that might be overdimensioned, even though it already seems to get quite hot.
The 12V might be worse though. I think it supplies the motors for the faders, 'cause it seems to draw almost no current at idle, but I got it up around 3.6A during heavy fader-work. Would it be helpful to seperate the motor-grounds from the other grounds by a cap or resistor?

 

[Bo Deadly]

The 5V seems to draw about 2.6A on average. It's an 80W supply, so that might be overdimensioned, even though it already seems to get quite hot.

Yeah, that's far too big. I thought we covered this but the SMPS has to be the right size. 80W 5V is 16A and you need 3A? You want 20W for 5V and 60W for 12V. Fortunately they're cheap.

The 12V might be worse though. I think it supplies the motors for the faders, 'cause it seems to draw almost no current at idle, but I got it up around 3.6A during heavy fader-work. Would it be helpful to seperate the motor-grounds from the other grounds by a cap or resistor?

Unfortunately for that you're going to need a shunt regulator in front of your CM probably something like this:



The series resistor would be very small like 0.1 ohm. Unfortunately, even this doesn't look like a lot of parts, in practice this is something that even I would have to fiddle with for days just to get it just right. It's also the sort of thing that if you get it wrong it could start smoking and stink up your house or worse. The shunt transistor would have to be at least 20W and mounted on a heat sink or maybe a large area of pcb heat sink (large area with pours on both sides stitched together with vias). But you can add a 10R in series with the emitter because you can limit the shunt to 1A or so. Just enough load to keep the SMPS from modulating the output.

You would definitely want to use separate grounds for anything that does not need to reference audio. You might not have to connect the motor grounds and audio grounds together at all. Just make it a separate supply and leave out the wire that is usually from the supply to the chassis bolt. Or make it a 100R resistor just to hold the floating output around the audio 0V ground potential. But 5V might need to be referenced to audio 0V because all of the controls that trigger relays might be connected to audio 0V somehow so you might not be able to put the 5V on the separate supply. Maybe you can but then connect the wire from the supply to the chassis bolt. Donno without really seeing and fiddling with it.