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Lineal VS Switching Power Supply Sound Quality
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Lineal VS Switching Power Supply Sound Quality
Socrates
Hello everybody,

Please excuse me if this question is kind of naive, but as i am quite new to many topics regarding sound quality & electronics, i would like your opinion on this. Lately i have been trying to find out the best small analogue console i could buy, i ended up with Studer 169 and few other models from the 60s & 70s as options. However, most well informed people and sellers of vintage gear i spoke to, all stressed the importance of buying a solid strong linear power supply in order to ensure the best sound quality from the console, as according to what they said, the power supply can affect a lot the sound quality, essentially giving ''cleaner'' electricity?

So, i thought that we can then assume this is the case for Eurorack systems too? Or not? Can somebody please explain if the difference is audible when using Lineal VS Switching power supply? Any other thoughts? Maybe this question is obvious to many but i would appreciate your opinions.

I see that Lineal power supplies go for good money, so i guess since they are more expensive (and bulky!) the must have something to offer.

Many thanks in advance!
daverj
There's no simple answer to your question.

Are switching supplies noisier than linear supplies? Generally yes.

Is that a problem? Sometimes.

A good circuit designer takes into account the entire system, including the power source, when designing a circuit. If a designer assumes that the power source is absolutely perfect, clean, and stable, they might make choices in the design that will cause issues when the circuit is used with a less than perfect power source.

On the other hand if the designer assumes the power source is just a source of raw power and might not be clean and stable, they will design the circuitry differently and build in protections from noisy and unstable power.

In general a switching supply has a constant flow of very thin, very high frequency spikes mixed into the DC voltage they put out. A linear supply does not. Can you hear that noise? Maybe. It depends on the design of the switching supply and the design of the circuit it is powering.

The noise on a switching supply might be a little bit above audio frequencies, or it might be a lot above. Those spikes fluctuate in size and/or frequency as the supply operates, and sometimes the filtering in the power rails can bring out very subtle fluctuations in the voltage that might be within the audio range. That still doesn't mean you can hear it. That depends on the circuitry that is powered by it, and the signal connections from that circuitry to external devices like amps and mixers.

An old audio console from the 60s or 70s was designed assuming a linear power supply. How clean and stable it was expecting that supply to be would depend on the brand and designer. There is plenty of professional audio equipment designed today that is powered from a switching power supply. And is perfectly clean.

With Eurorack there are a number of companies selling linear power supplies, and a number selling switching supplies. In many cases people owning the switching supplies have not noticed any kind of problem. But in other cases, using the same types of systems, somebody else has certainly noticed high pitched whistles and whines. Whether it's that person's attention to subtle noise, or the specific modules and external connections that caused them to hear it is not something easy to guess.

So there's no easy way to tell you if having a switching supply is going to cause you a problem. On the other hand, linear supplies generally do not ever get those high pitched whistles.

So I guess the bottom line is that if you get a linear supply you won't get high pitched digital noise in the output. If you get a switching supply, chances are you also won't get that whistle, or at least might not hear it. But you might.
Socrates
Dave, thank you a million for this extensive reply, i could not have asked for more, thanks for taking the time. Excellent information, i am sure this will be very interesting for other who might have had the same question. thumbs up

You really did put my wonder to rest. I will definitely buy a lineal power supply then, just in case. I want to make sure the highest quality electricity feeds my system. Caring about the best sound quality possible and as you said not being easy to determine the exact build quality of each module and how that might affect the overall sound, one would't like to leave it to chance regarding those high pitched whistles, which might or might not interfere of degrade the audio somehow. Do you recommend any one particularly?

If anybody has actually had some experience and noticeably heard the audi quality change when using lineal please let us know. Of if anybody had been able to A/B a sine wave or other audio with switching/lineal power supplies please do come forward!
Just me
One thing I have noticed over the years. Take it as just some old guy's subjective spew.
Switching power supplies, even inexpensive ones, for me have always had much more stable (voltage regulation wise) outputs than anything but the best and with biggest ultra high slewing rate transformer linear supplies.
If the linear doesn't have superb filtering and regulation, it will play hell with oscillators and sometimes filters. This can be designed out of the picture if rail voltages are higher than the module uses and the module is regulating and filtering the rails.
When linear supplies fail, they just go undervolt and then die. Usually. When switching supplies fail they can spike the hell out of the output. Sometimes.
slow_riot
I am a 100% firm believer that power supply, being the foundation of every signal in an audio system, is absolutely worth critical thinking about. Crucially, is that the quality of the system is matched to the PSU, a lot of expensive eurorack systems are being powered by throwaway PSUs.

However, in order to best look at the picture, you need to make your measurements absolutely objective, and rather than "sound quality", it is better to consider the role of the PSU in the overall system, and how well suited it is to satisfying the particular objectives that are required of it. Safety is perhaps even more critical than low noise and high ability to drive loads without loss of regulation. These last 2 points can be measured, BTW, and an honest manufacturer will tell you their specs.

I am currently maintaining/repairing a 40 amp switching power supply which is technically excellent, although really far too complex to be appropriate for a music system and has been so badly physically designed that I have thought about just ditching it for a new one. So it is theoretically possible that a switching supply can compete regarding noise (hint: you will need perhaps as many inductors as you do transformers in a linear supply), but I don't know if one is on the market yet.
Rex Coil 7
I've been exposed to what most folks would say is an unusual amount of power supply issues. Stompbox designs are subjected to the world's worst power supply systems. Often times stompboxes end up being powered by PSUs made for video games, cell phone chargers, and calculators ... masked by some trusted and known name. More times than I can remember I've heard someone tell me that the circuit I designed for them was junk ... I politely ask them to test the device using a 9v batt .. magically the "junk" pedal suddenly sounds like diamond plated golden angel's voices. Usually the person will then say something like "I figured since my power supply had brand name ~X~ on it that it could be trusted".

Not. Unfortunately.

Linear power supplies do have their issues, no doubt. However, a ~crappy~ switching PSU sounds WAY worse than a bad linear PSU. While some circuit designers prefer to design-in certain protections and filters, it should be noted that these filters and protections can (and do) "suck tone" from certain circuit types in certain applications.

In the guitar stompbox world, "tone suck" is a big deal. It's usually caused by impedance issues loading the guitar's pickups. But it is also caused by underpowered stompbox circuits. How did they become "underpowered"? Well, they're not actually "underpowered" per se, but they'd work FAR better if they had a couple more volts available for processing the sound. Those couple of volts can be found in power filters in many cases. For instance, when you're only working with 9vdc, cutting the available power by 1.2 volts (from using a polarity protection diode) isn't helping the "tone suck" issue at all. So, designing in fewer protections and power filters can create a for more "pure" tone (depending on the circuit and it's application).

In the end, using shitty power makes no more sense than putting crappy tires on that 800hp 200mph $Million+ ~Supercar~. It's like my flight chief told me when I was a teenage punk in the US Military ..... "Those boots cost you $80 bucks .... make them look like $80 boots!" (in reference to keeping a better shine on my boots). Well, the same goes for your audio processing system. You spend SERIOUSLY BIG CASH on these systems, yet so many of them are powered by crap (as has been mentioned already in this thread).

I owned/operated an RV Auxiliary Generator repair station for fifteen+ years. I saw that same bad attitude in that arena as well. People that owned $10k+ diesel generators in $Million+ RVs that don't regularly service that auxiliary power generator as it should be, and when they want it to perform it fails. Then they get pissed off because their $10k gen doesn't work. Clue .... get one. Some people's children.

Do yourself a favor ... put the best tires available on that Ferrari ... shine those $80 boots and show them the respect they deserve ... and buy good linear power for your synth (that probably cost more than the used car you own). Don't take it for granted that a "trusted" name brand is on the PSU ... many companies buy globally certified PSUs to jump over the cost of certifying their own power supplies (I can't blame them, it costs fat stacks to certify your own PSU all over the planet ..... FAAAAR less expensive to use a PSU that is already been given all of those World Certs .... just look at a decent wall wart sometime, it's slathered with certification logos...). Anyhow, many companies take it for granted that the PSU that they sell for THEIR devices is clean power and it will not create problems for other devices on the same power bus. Don't make the same mistake (I sure have!) of taking it for granted that because brand name "X" is on the PSU that it is assured to work with everything. You can end up chasing your tail trying to "fix" something in your modular system that isn't actually broken to begin with ... it's just crappy power causing the troubles.

I run in to this situation all the time. I must not be a "good circuit designer" because I refuse to make compromises in my processors to deal with crappy power. I insist that my customers use "clean power" ... and in the long run they are better off for it.

That said, I think it's clear that you have to use clean power, there are many other (hard headed) circuit designers out there like myself that place audio performance above "mission compromising protections" ... heheh. smile

If you want to put the worries of adding problems to your already very complex audio processor (your modular synth) to rest ... invest in solid power. Linear is heavier (physically heavier ... those transformers are dense and solid, made of iron laminates and copper windings on the best of them), they need to warm-up a bit before they'll become stable, and they throw off excess voltage as heat (they can be pretty inefficient) ... so yea, they come with some hassles ... but they also tend to provide the least problematic power.

This has been my experience on the issue.
listentoaheartbeat
The following thread turned into a very interesting (and heated) debate about power supplies. Worth reading if you are interested in this:

https://www.muffwiggler.com/forum/viewtopic.php?t=105030

Similar discussions here, mainly dealing with the question whether or not linear power supplies are worth it, and what the available options are:

https://www.muffwiggler.com/forum/viewtopic.php?t=117460

https://www.muffwiggler.com/forum/viewtopic.php?t=134371

The SNR and performance (tuning stability, headroom) of my synth improved significantly when I switched to a linear power supply and solid bus bar distribution system by Hinton. It's shown and discussed in two of the above threads. It's been running perfectly for 1,5 years now, couldn't be happier!
Rex Coil 7
Another thing to keep in mind is to clean up the input power that feeds the system. In the USA we use 115 volts AC to power our lives. I use a Belkin power strip that is "lightning protected" for up to 3KV and filtered as well. Then the power is routed to a Furman power conditioner/distributor (PL-8C).

The idea being to give the modular synth system as many clean power advantages as possible. Using a PSU that provides clean secondary is all well and good, but let's not forget to help it along by providing that PSU with clean primary power ... or at least as clean as possible primary.

Another primary power issue is bussing. Many times if you use a wall outlet that is on the same power bus as some other noisy contraption (perhaps a microwave oven) that WILL cause primary power issues. I've gone to the trouble of mapping out which outlets are connected to which main power bus in my home's main breaker box. There are several outlets in my studio that share the same main power bus as some rather noisy things. So I have to avoid using those outlets for things like power amps.

Every home/business in the USA that uses single phase power has two busses (two "hot legs") and a neutral leg ... mapping which hot leg is powering which outlet can save you TONS of headache and money chasing down a simple problem that is within your home/studio and NOT within your music system. Just using a different power outlet to plug your system in to can completely change the situation ... depending on what else you are powering with that same electrical system.

So do what you can to filter and condition the input power before it ever reaches your sound gear and you'll create fewer problems. And if you feel you need to, take the time to map out your hot legs and breaker busses in your studio. There's only two legs, and knowing which outlet is connected to which ~thing~ inside your home or studio can really help to eliminate these types of issues. I just used a Sharpie to mark the outlet wall covers with a "I" or a "II" ... that way I know which outlets are on which leg. I make sure to keep my sensitive stuff on the opposite leg of our microwave oven and other noisy digital devices (like that home entertainment center, some DVD players are racket makers!) Digitally controlled lighting is also a hell-maker .... lights that use digital/switching power systems to provide dimming. LED lights (such as Christmas lights and certain types of "light strings") are another problematic source ... keep all of that on one dedicated power leg, and the stuff that is sensitive to that crap ... amplifiers and such ... on the other power leg.

smile
mrand
reviewing this old thread with interest, and figure it's as good a place as any to put a question out there:

There are many tin-box +/-15 switchmodes available from china for low cost. I'm wondering if anyone has chosen to regulate this down to 12v for a cleaner source for their euroracks.

Will the regulators at least remove 2v worth of switching-noise? Or perhaps HFspikes somehow persists right through the 12v regulators?
luchog
mrand wrote:
reviewing this old thread with interest, and figure it's as good a place as any to put a question out there:

There are many tin-box +/-15 switchmodes available from china for low cost. I'm wondering if anyone has chosen to regulate this down to 12v for a cleaner source for their euroracks.

Will the regulators at least remove 2v worth of switching-noise? Or perhaps HFspikes somehow persists right through the 12v regulators?


Down-regulating voltage will not turn a crappy switched-mode power supply into a good one. Even if doing so can smooth out the average power, you're still going to be dealing with ripple issues, intermittent spikes and troughs due to poor-quality components, and higher failure rates. And the cost of the components necessary to compensate for a bad power supply will rapidly add up to the cost of a good power supply.

You're better off starting with the best power supply you can afford, which is rated for the amount of power your system is expected to require, plus a reasonable buffer. If you're putting together a rack with $5000 worth of modules, you're doing yourself a grave disservice trying to power it with a $50 power supply.
Graham Hinton
mrand wrote:
There are many tin-box +/-15 switchmodes available from china for low cost. I'm wondering if anyone has chosen to regulate this down to 12v for a cleaner source for their euroracks.


You can, but what you are essentially doing is building a linear PSU and replacing the transformer with a SMPSU. If everything else is equal this costs more, has more problems and requires EMC certification for resale. If I thought it was a good idea I'd be doing it.

This technique is used in a lot of 1U outboard equipment, I first saw it in the SPX-90 and guess what? There are thousands of broken SPX-90s out there and it's always the SMPSU that has blown, usually the capacitors due to the stress.
mrand
Thanks for the replies!

Graham Hinton wrote:

This technique is used in a lot of 1U outboard equipment


I think this is where I got thinking about it from. Another idea is to distribute the power to each synth case as AC, say 18VAC. I have some ashly gear that does something like this, though can't remember the name of their standard. Also I have some biamp gear that uses 27VAC. I presume this gets rectified/regulated to +/-15 or 12v in the box, but haven't opened them up to see how.

Does distributing power to each case as AC present any advantages? I suppose heat dissipation is spread out more thinly across more places.

Perhaps I should note that I'm not building eurorack, though they are 12v. My cases are smaller (~2u) 19"rack units, each requiring something like 150ma per rail, so far, but I'd like to design to accommodate greater current draw... no idea how high to set that ceiling yet though.

Any tips/suggestions welcome!
SynthBaron
I have never had audio chain issues that involved a linear power supply, but have had many caused by switching power supplies.
Graham Hinton
mrand wrote:
Does distributing power to each case as AC present any advantages?


It keeps the modules isolated from each other, but there are many disadvantages. 50 or 60Hz at several amps going everywhere is going to create non-audio friendly magnetic fields. Power is best distributed to point of use at high ac voltage and low current. Mains is fine for equipment. Transformering it down to low voltage/high current loses the advantage.


Quote:

I suppose heat dissipation is spread out more thinly across more places.


You still have to get the same total out of the case.

The Tektronix TM500 series test modules used a regulator per module scheme, but they only had up to eight modules in a frame and only sizes below six didn't have noisy fans. Several inches at the back of each module were lost to regulation and the frames were around 17" to 20" deep. The frame provided power transistors on heatsinks for each module which used up connector pins and made it difficult to work on the modules for calibration/repair.

Quote:

Perhaps I should note that I'm not building eurorack, though they are 12v. My cases are smaller (~2u) 19"rack units, each requiring something like 150ma per rail, so far, but I'd like to design to accommodate greater current draw... no idea how high to set that ceiling yet though.


Any reason why you don't want a small linear mains PSU per unit?
mrand
Graham Hinton wrote:
Power is best distributed to point of use at high ac voltage and low current. Mains is fine for equipment. Transformering it down to low voltage/high current loses the advantage.


Ahhh, thank you.

Quote:
Any reason why you don't want a small linear mains PSU per unit?


hmmm, I guess I thought that it was best practice to keep the transformer away from the audio circuits, but I see now that that was probably incorrect. Also, I imagined that bulky mains cabling from the back of each unit would be cumbersome.

My final, perhaps worst reason, was simply that I didn't want incur the cost of sourcing many small transformers. I have a couple large doughnut types from a pair of adam a7x monitors that I fancied putting into use. Trouble is I cant find a datasheet, so don't know their current ratings. I was advised by a PEng and ex-electrician to "just draw current till I felt it getting hot". Not sure about that one.

But this seems like it might be a great strategy. If there is a PSU failure, it doesn't shut the whole system down for repairs. Also, it would let me take advantage of economies of scale - these would be easy, low cost builds.
mrand
I did some searching for a north american supply of transformers and came across this NOS/surplus outlet with a few promising looking selections. Others may be interested:
www.surplussales.com/class/inductor/lowvolt-13to29v-Secondary.html

For example this unit is around $5 each:
• Secondary: 14/28 volts
• Two 14v @ 350mA (Parallel 14V @ 700ma or Series 28V @ 350mA)
• Apparent Power: 10 VA
• Dimensions: 1.686"L x 1.347"W x 1.3"H

I'm wondering, would a transformers like this installed right up close to the synth circuits require shielding? It would be low current draw from the PSUboard, maybe 100ma per rail. I'm thinking a shallow 19" rack unit, maybe 10-15cm deep with right angle/panel mount PCBs at the front and transformer/PSU attached on the interior at the back. Comments welcome.
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