can't test the voltage on DC appliance

SimonH2 said:

You may be unfamiliar with the idea, but it's not rare, and for an application like this makes perfect sense.

Click to expand...

Yes, it may make sense 'in some senses'.

SimonH2 said:

.... It would certainly be possible to have a PSU made to do the whole lot in the external PSU - but it would probably be a custom model and a custom unit costs more than an off the shelf one as well as bringing various factors into play in terms of specifying the design and ensuring that the manufacturer meets it. As they've done it, the key bits that control supply quality (especially noise) are inside their own box.

Click to expand...

I still don't really understand this argument. Why couldn't an external PSU also be in something which was 'their own box', with the design and construction of the contents being entirely of their doing? Either way, they have to buy a transformer, and also have to design the rest of the power circuitry, source the components for it, and then construct it - the only difference being 'which box' they installed it in.

SimonH2 said:

But it comes down to this : whatever any of us think about it, it's how they decided to do it, and that's all that matters !

Click to expand...

Of course - but that doesn't stop me expressing my surprise, and my lack of familiarity with this approach!

Indeed, as I wrote yesterday, 'common' though that approach might be, at least for some manufacturers, there are clearly plenty of mixers out there (many of which produce a 48V 'phantom power' supply) which are powered with just (one polarity of) 12V DC from a (presumably small and light) external PSU.

SimonH2 said:

... It might even be practical to power it (for short periods) with 4off PP9 batteries to give (nominally) ±18V.

Click to expand...

Indeed, that's much the same as I recently wrote, when I suggested that it could be regarded as a bit OTT to be talking about car batteries and mains inverters to power a little bit of electronic circuitry that does not need much more than 10W!!

Kind Regards, John

JohnW2 said:

I still don't really understand this argument. Why couldn't an external PSU also be in something which was 'their own box', with the design and construction of the contents being entirely of their doing? Either way, they have to buy a transformer, and also have to design the rest of the power circuitry, source the components for it, and then construct it - the only difference being 'which box' they installed it in.

Click to expand...

I think you missed the point there.
The transformer they used may well be an off the shelf design - so all the regulatory aspects have been dealt with by someone else, and amortised over many units sold to multiple manufacturers.
The moment you design your own PSU then you have a whole raft of regulatory stuff to deal with - stuff that isn't your core business. Of course you can pay someone else do do all that - but you are still paying to have it done, and mortising those costs over a relatively small number of units. The stuff after the transformer is relatively simple, and isn't subject to a lot of the regulation that applies to the mains side.
Doing it the way they have is probably the cheapest way to do it.

Indeed, as I wrote yesterday, 'common' though that approach might be, at least for some manufacturers, there are clearly plenty of mixers out there (many of which produce a 48V 'phantom power' supply) which are powered with just (one polarity of) 12V DC from a (presumably small and light) external PSU.

Click to expand...

Well yes, as discussed, there are multiple ways of doing most things. As someone pointed out, putting a switch mode device inside a bit of audio equipment is often not the best idea - I'm sure we're all familiar with the sound from audio equipment when a mobile phone gets a bit close It's not that it can't be done - it's just another way of doing it and it has it's own downsides.

SimonH2 said:

I think you missed the point there. The transformer they used may well be an off the shelf design - so all the regulatory aspects have been dealt with by someone else, and amortised over many units sold to multiple manufacturers.

Click to expand...

I can't believe that such an application would require a bespoke transformer - surely it would be an 'off-the-shelf' one, no matter where it was destined to be located?

SimonH2 said:

The moment you design your own PSU then you have a whole raft of regulatory stuff to deal with - stuff that isn't your core business. Of course you can pay someone else do do all that - but you are still paying to have it done, and mortising those costs over a relatively small number of units.

Click to expand...

Agreed - but, with the approach we're discussing, the design and construction of the entire PSU, other than for just one component (the transformer) will have been down to 'oneself'. However, the point you seem to be making is ....

SimonH2 said:

...The stuff after the transformer is relatively simple, and isn't subject to a lot of the regulation that applies to the mains side.

Click to expand...

Given that, as above, the only component (the actual transformer) will probably be off-the-shelf, that doesn't really seem to leave a lot, or a lot of "regulation that applies to the mains side". There are countless appliances and items of equipment just in my one house that have mains electricity entering them, and the manufacturers don't seem to have bee frightened off from designing and manufacturing them.

SimonH2 said:

Doing it the way they have is probably the cheapest way to do it.

Click to expand...

I wouldn't know but, if it is, I would probably regard that as a more credible explanation than some of the other possibilities that have been suggested.

SimonH2 said:

... putting a switch mode device inside a bit of audio equipment is often not the best idea ...

Click to expand...

Agreed - but, although that's very common in 'consumer' products, I don't think any of us (certainly not I) have suggested that (as an alternative to an 'analogue' PSU utilising a wire-wound transformer) in this discussion - and, even if it had been suggested, it would entail just as much "regulation that applies to the mains side" as would any other sort of PSU.

Kind
Regards, John

JohnW2 said:

Fair enough. Some 'smoothing' (to deal with any noise) would be required in the equipment, but I would have thought that all the 'primary smoothing' )which might involve some fairly bulky components) could be done in an external PSU. As for regulation, unless we were talking about high power/current equipment (and a mixer clearly isn't that), I would again have thought that regulation within an external PSU would be adequate.
Indeed - but that, in itself, is obviously served by having the entire PSU 'external'.
Indeed, and that's why I wrote:


Kind Regards, John

Click to expand...

There is an amazing range of problems associated with power storage and transfer.
I'll try and work backwards,
One wouldn't normally put much smoothing after an analogue regulator, particularly if the load varies considerably - such as in audio equipment. Let's assume a loud crescendo sucks loads of current from the caps and pulls the voltage down to 14, the reg would have normally simply regulated it at 15V but now it has to supply extra current to recharge the cap as well as try to supply the electronics. the result my be reduced voltage unless the caps are huge and/or much larger regs and possibly rectifiers and transformers. the 15V will be modulated by the audio.

Having a regulated power supply remote from the kit will mean the varying load on the resistive losses between regs and load will 'modulate' the supply rails. additional caps at the end of the cable will create a worse scenario of the above.

Large caps in the PSU then a long lead feeding small caps and regs means A) the PSU is still split between 2 enclosures but B) now the 'wall wart' is bigger than before and C) is a bespoke device and costs considerably more to design, construct and gain approval. D) there is a (very slight) potential for the voltage prior to the regs to dip below the cut-off voltage.

Having rectification but no smoothing in the wall wart and large caps in the kit works well as the regs have instant access to the ?21V stored voltage and the recharge current is only limited by copper losses which is fairly easy to design out. There is no point in having just one component (other than the transformer) in the wall wart.

The thing about audio kit is preventing any source of distortion and allowing powerlines to affect the sound quality needs to be avoided at all costs. The ripple in a power supply is removed by a regulator, in fact properly designed regulation reduces the size of smoothing caps to maybe 10%.

JohnW2 said:

I can't believe that such an application would require a bespoke transformer - surely it would be an 'off-the-shelf' one, no matter where it was destined to be located?

Click to expand...

the point here is a manufacurer can produce a transformer in an enclosure and 'certify it', anyone else can then use that without any further 'certification' in countless other situations. For Behrenger to construct a dc psu will require a seperate 'cert' at considerable expense whereas to purchase a wallwart from sakakaki costs peanuts. For Soundcraft to construct a dc psu will require a seperate 'cert' at considerable expense whereas to purchase a wallwart from sakakaki costs peanuts. For Alto to construct a dc psu will require a seperate 'cert' at considerable expense whereas to purchase a wallwart from sakakaki costs peanuts. the considerable expense is thousands of pounds. Do you see where this is going?

SimonH2 said:

As someone pointed out, putting a switch mode device inside a bit of audio equipment is often not the best idea

Click to expand...

JohnW2 said:

Agreed - but, although that's very common in 'consumer' products, I don't think any of us (certainly not I) have suggested that (as an alternative to an 'analogue' PSU utilising a wire-wound transformer) in this discussion - and, even if it had been suggested, it would entail just as much "regulation that applies to the mains side" as would any other sort of PSU.

Click to expand...

with respect it was you John who suggested a 12V supply then something to generate the 48V phantom.

SUNRAY said:

There is an amazing range of problems associated with power storage and transfer.....

Click to expand...

Whilst I understand, and don't disagree with in concept, everything you go on to say, I can't help but wonder to what extent it is of practical relevance to a little bit of electronic circuitry (basically 'a generous handful of op-amps') which quite probably doesn't draw more than around 500 mA or so (maybe less) at ±15V?

Kind Regards, John

JohnW2 said:

Whilst I understand, and don't disagree with in concept, everything you go on to say, I can't help but wonder to what extent it is of practical relevance to a little bit of electronic circuitry (basically 'a generous handful of op-amps') which quite probably doesn't draw more than around 500 mA or so (maybe less) at ±15V?

Kind Regards, John

Click to expand...

The information I have given is based entirely on exactly the sort of device described by OP.

Back in the 70's I constructed a selection of this sort of equipment for the disco boom and I promise the problems I've described are very real

SUNRAY said:

... with respect it was you John who suggested a 12V supply then something to generate the 48V phantom.

Click to expand...

That's true, I'd forgotten that.

However, it was not really a question of "me suggesting it". Rather, I was reporting that, in my quick look, I found several (more now) of mixers which provided 48V 'phantom power' which are supply with 12V DC from an external PSU - so all of them presumably do have some sort of 'switching converter' inside them to generate the 48V (and, I would imagine, quite possibly also generating +15V and -15V, or somesuch, for the electronics).

Kind Regards, John

SUNRAY said:

The information I have given is based entirely on exactly the sort of device described by OP. Back in the 70's I constructed a selection of this sort of equipment for the disco boom and I promise the problems I've described are very real

Click to expand...

Fair enough. I obviously can't argue with your experience, even if I am surprised.

Kind Regards, John

I have had a new idea about this project (don't know if I should of started a new thread though)
If I want to power my AC device (small load remember) from an DC battery; instead of using my massive 150W Inverter
https://www.halfords.com/workshop-tools/garage-workshop/inverters/12v-150w-inverter-with-2a-usb
Can I get a really really small Inverter to do this job?
Have a look at this video, as he has made an Inverter out of a 5 pin car relay

You can get 75w inverters. Look at Screwfix item 88988.

fozzyfester said:

I have had a new idea about this project (don't know if I should of started a new thread though)
If I want to power my AC device (small load remember) from an DC battery; instead of using my massive 150W Inverter
https://www.halfords.com/workshop-tools/garage-workshop/inverters/12v-150w-inverter-with-2a-usb
Can I get a really really small Inverter to do this job?
Have a look at this video, as he has made an Inverter out of a 5 pin car relay

Click to expand...

Why not use the inverter you already have, AND already checked it works for your mixer, (Please do this as far too often the squarewave format creates noise in some kit)

fozzyfester said:

I have had a new idea about this project (don't know if I should of started a new thread though)
If I want to power my AC device (small load remember) from an DC battery; instead of using my massive 150W Inverter (here) Can I get a really really small Inverter to do this job?

Click to expand...

You could certainly use a small inverter and, as has been said, one can probably get them.

fozzyfester said:

Have a look at this video, as he has made an Inverter out of a 5 pin car relay

Click to expand...

If I understand that correctly (some commentary would be helpful!), that's essentially like an old-fashioned (non-electronic) car ignition system. As such, whilst it may well be OK to operate a light, it will produce a horrible waveform (made up on on/off 'spikes'/pulses {just like the spark plug's sparks!}) which audio equipment may very well not like at all!

Kind Regards, John

Yes, essentially the relay is just wired as a buzzer - power to the coil goes via an NC contact on the relay. Adding the capacitor will cause the circuit to ring. It would be interesting to look at the waveform.

Actually, I have all the components needed, and I have a 'scope, so time to play.

davelx said:

Yes, essentially the relay is just wired as a buzzer - power to the coil goes via an NC contact on the relay. Adding the capacitor will cause the circuit to ring. It would be interesting to look at the waveform.

Click to expand...

I think I've got a pretty good idea, even without doing the experiment!

Kind Regards, John