| Jay |
I have plenty of switching power supply units. It seems that they have noise issues. But my computer is silent and can produce good sound. And so do newer commercial DVD players. So what is the real problem here?
Recently I took out a switching power supply which is also used to power up computer monitor. I guess the voltage and current is suitable for at least providing B+ for a tube preamp. Anybody know if this is possible or not? |
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| Robski666 |
Jay,
SMPS and so called Iron PSU's all get built for a cost which means there either good ok or rubbish, that said I have a pre-amp which runs from an smps and it is very clean. I think it all depends what your preference is and what you can get.
There is no reason a well designed SMPS can't be as good as a conventional PSU. Having said that I wouldn't say that computer smps's are always good examples of state of the art electronics.
But I have heard of people modifying them to supply other voltage/current then what they were designed to.
I think it really becomes a personal taste aspect and what your comfortable wit.
Robert |
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| Jay |
5V is very common with SMPS. I have tried this for DAC. While dynamics is outstanding, I do hear unacceptable noise.
Like most of my SMPS, it was well built. I took them from expensive electronic devices. There are at least 5 panasonic chokes on it (and a 3-layers PCB) but still noisy. |
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| Geek |
I did some R&D on SMPS for automotive tube audio use and found it as good as a SS bench linear supply.
The only think to remember is careful shielding and proper bypassing. I double-shielded (with gap to avoid a ground-loop), looped the wire a couple of times through an RFI toroid and finally out through feedthrough capacitors. |
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| rascal101 |
| The noise from an SMPS is just too high to be acceptable for audio. Ripple & Noise, conducted and radiated emi, switching noise etc. |
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| sagarverma |
| quote: | Originally posted by rascal101
The noise from an SMPS is just too high to be acceptable for audio. Ripple & Noise, conducted and radiated emi, switching noise etc. |
switching noise:xeye: .do u have 'audiophile' ears?30khz is inaudible to humans! |
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| nickds1 |
| quote: | Originally posted by rascal101
The noise from an SMPS is just too high to be acceptable for audio. Ripple & Noise, conducted and radiated emi, switching noise etc. |
This is a bit of a sweeping statement, aka generalisation.
SMPSs, like all PSUs, are built to spec. Most digital systems can tolerate a certain amount of noise at 50kHz etc, but not so for audio. So, audio SMPSs are heavily filtered and are run at non-audio frequencies. I have built many many SMPSs, a couple of which I use for valve audio use. These are not hack designs, but are high-end systems.
Basically, for the average person, its far easier to build a quiet non-SMPS that an SMPS system - SMPSs are tricky to get right. However, if you do get it right, they are cheap, small, light, highly efficient and very effective. Noise is barely measurable on a good system.
When I use an SMPS for audio use, I use good filters on both input and output e.g. MuRata BNP002-03 and encase the SMPS in a shielding box (as used for small RF projects - you can also use a box made from soldered pieces of single or double sided PCB - another Ham Radio trick).
Nick |
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| cerrem |
I design SMPS for a living and yes if you use the standard run of the mill designs used in the last 20 years, you will not get good performance in audio...
I have designed switchers that switch as high as 2 Mhz and and produce little noise...
ALso , the use of quasi-resonant/resonant SMPS circuits are very low with EMI ....
There is a place for SMPS in audio, I would recomend switching above 450kHz and also using a resonant topology...
Chris |
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| janneman |
Hi Chris,
I guess you are familiar with the Vicor units, which I think are quasi-resonant (or zero-current switching). I have used a few (the 150W 2nd generation units) in audio designs with good results, but that may have been luck ;) .
What is your opinion on the Vicors for audio use? They also have a RAM (Ripple Attenuation Module) available to further decrease output noise by some 20dB, but the final price gets steep so I am not sure it would be worthwhile.
Jan Didden |
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| serengetiplains |
Chris, further to Jan's post, can you name a few brands of switchers you think give good performance for audio use? Would much appreciate your opinion. I've been looking on the internet, but cannot seem to latch onto proper figures of merit to guide my search.
Any opinions on Tamura switchers? For instance, this one. |
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| kevinkr |
I currently design semiconductor ATE for a living, and due to space and power consumption constraints mostly use SMPS for my raw dc supplies. Simple external filters using a single common mode choke, a couple of inductors and some low ESR capacitors can knock down conducted noise by several orders of magnitude or more.
For suitable chokes and inductors take a look at http://www.coilcraft.com
You can also use high performance linears after the SMPS for somewhat improved noise performance and to define a low source impedance at audio frequencies. (Note most linears do not have enough loop bandwidth to effectively remove noise above 100kHz. Linear Tech has several specified at 100kHz that do work well.)
Noise levels of much less than 50uVrms over a 100kHz bw are achievable with some care using the above techniques.
Shielding to reduce electrostatic coupling is also very important. Look at some of the other posts for more on this.
ATE applications often require measurement accuracies of 10ppm or better, including the noise contribution. No audio device is even close.
Kevin
Edit: Link is correct URL but does not seem to work correctly in firefox, copy and paste into your browser address bar if the link is misdirected. Might be some problem with the webserver as well. |
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| EC8010 |
| kevinkr: An interesting post - thanks. (The link worked fine with my Firefox.) |
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| cerrem |
I really don't won't to give my opinions on VICOR and such....
Tell me what your voltage, power requirements are and then I can recommend something or I can suggest specs you should be looking for...
Chris |
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| ilimzn |
| quote: | Originally posted by kevinkr
[B]I currently design semiconductor ATE for a living, and due to space and power consumption constraints mostly use SMPS for my raw dc supplies... ATE applications often require measurement accuracies of 10ppm or better, including the noise contribution. No audio device is even close.
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Great post. I once designed a preamp for a capacitor microphone (Bruel & Kjaer) which was portable, so necessitated the use of SMPS to get all the required voltages. An ordinary flyback was used, the real stuff is in careful control of all current paths, and proper magnetic shielding - very much like what you describe. It proved much more troublesome to provide amp noise performance that was lower than the SMPS injected noise. Anyone who knows what these microphones are capable of, knows what I mean. |
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| serengetiplains |
| quote: | Originally posted by cerrem
I really don't won't to give my opinions on VICOR and such....
Tell me what your voltage, power requirements are and then I can recommend something or I can suggest specs you should be looking for...
Chris |
Hi Chris, I have use for two voltages:
* 12VDC in the range of 5A to 10A
* 90VDC @ 5A (or larger, but that's getting big).
Thanks!
Tom |
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| rascal101 |
I didn't make a sweeping statement when I said that SMPS do not have a home in high end audio. This is due to my experience working with switchers for the past 8 years. Ripple, & Noise and conducted/radiated emi (not audible yes but imagine the noise from the switcher coupling to the audio electronics - you need very good shielding).
Have also done auditions on vintage amplifiers using switchers. |
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| serengetiplains |
I'm not sure ripple and EMI are the most important factors for judging the sonic worth of a power supply. I might speculate that a power supply's ability to track changes in load current without generating spurious voltages in the process + a power supply's ability to reject mains grunge might be more important. I'm running a pair of Charlize amps via a cheap $25 switcher, and it sounds very good. Makes me wonder what a good switcher could do.
The highly rated and lovely sounding Emm Labs digital gear uses switchers. |
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| rascal101 |
I believe you are referring to transient response. SMPS should have better transient response than linear power supplies.
Speaking of ripple and noise I still have to see ripple and noise figures in the 1mV range for SMPS.
Speaking of sound, this is purely subjective. If you don't hear it then SMPS is good for you. |
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| serengetiplains |
| quote: | Originally posted by rascal101
I believe you are referring to transient response. |
Yes, and what might be called dynamic noise, ie, non-signal voltages created in response to amplifying the signal. One example of this, in a linear supply, is voltage variations created by current spikes filling capacitor banks. |
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| rascal101 |
Sir Serengetiplains,
Transient response refers to the response of the SMPS PSU to load changes eg from 10% load to 50% load or from 90% load to 40% load. Typically SMPS companies design power supplies for a step load of 50%. Power supply must maintain regulation and get back to nominal output within a specified settling time.
Transient response is a measure of the responsiveness of the feedback loop and also gives you an idea of the phase margin - stability.
What we do to minimize noise from the FET switch is minimize the loop area, use a star connection for the ground, avoid low voltage PCB tracks passing through high voltage tracks, capacitor layout at edge of tracks to ensure filter action, use copper shield at transformer etc. Despite this you still have EMI (albeit passing CISPR or FCC requirements).
To offset this for audio application is to isolate SMPS from the audio electronics itself and to use a lot of low esr e-caps to minimize ripple & noise.
Despite this I still do not want any SMPS for audio application. The effort and time required to equal the quietness of a linear power supply is not worth it. It is quite possible but it will very very difficult using an ordinary SMPS topology (eg flyback, forward, 2 FET forward - you would have to go half bridge or full bridge). |
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| rascal101 |
Sir Serengetiplains,
I have nothing against SMPS. Understand the rationale - efficiency, area and weight (the transformer is smaller). However, unless its designed by reputable SMPS designers I wouldn't be going that route just yet. I don't expect an audio electronics company to be good at designing SMPS also. Very different field.
Rascal101 |
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| richwalters |
| quote: | Originally posted by rascal101
The noise from an SMPS is just too high to be acceptable for audio. Ripple & Noise, conducted and radiated emi, switching noise etc. |
Come on.......that statement requires modification...In defence... I use and design switchmode technology in audio... ....Ripple and noise aren't issues anymore with good components and designs. Some switching mode topologies have noisy reputations but it is simple to choose another. It may more costly to produce.
I use a 75Khz 1 kW boostmode power factor corrector as the 530V B+ supply in my tube power amps, also a push-pull low voltage converter ....both are far quieter in terms of emitted pollution than the poorly screened flyback psu used in most satellite down receivers and other consumer products from the far east.
Commercially made units may just scrape through compliance to EMI standards but since much of todays music goes through circuits using similiar technology, i.e digital processing and oversampling algorithms....one can't avoid switchmode anymore.
richj |
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| jackinnj |
Check this switcher out: LT1683 -- Jim Williams at Linear has also written several good apnotes AN70 stands out -- on converters and noise control.
btw, Linn uses a switcher in one of their amplifiers. |
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| rascal101 |
| quote: | | Come on.......that statement requires modification...In defence... I use and design switchmode technology in audio... ....Ripple and noise aren't issues anymore with good components and designs. Some switching mode topologies have noisy reputations but it is simple to choose another. It may more costly to produce. |
I said that SMPS do not have a home at high end audio because I don't believe a good number of people who design audio amps are also good at SMPS. Insofar as SMPS companies, there are hundreds all over the world. But it doesn't mean these companies produce a good design. I come from an SMPS company and I do see the designs. While I have not designed a full power supply yet (just pieces eg PFC, inrush ckt etc), I noticed that even seasoned design engineers are not completely familiar with all parts of the power supply. We have a consultants for magnetics, DC-DC, PFC, EMI etc. Depends on the output power - higher output = more consultants. Typically we have 1 in a typical project depending on the need.
Speaking of SMPS in audio application, yes its true we're seeing more and more and it will just be a matter of time. However, I don't believe it is this time just yet. |
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| richwalters |
ok rascal....too true....to design a smps with all protective features takes alot of practical and theorical experience in physics and magnetics and most of todays engineers lack both in depth and magnetics (sadly) is still a black art subject. I'm from the old school of thought when a university degree was worth something, not like the ones obtainable now.
richj |
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| Tony |
sometime in the 80's SONY came out with an smps psu type power supply. can seem to recall the model number now, but it was done before, no reason not to be able to do it today.
there is even a mosfet power amp being sold as kit whith a full bridge smps psu. |
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| janneman |
| quote: | Originally posted by Tony
sometime in the 80's SONY came out with an smps psu type power supply. can seem to recall the model number now, but it was done before, no reason not to be able to do it today.
there is even a mosfet power amp being sold as kit whith a full bridge smps psu. |
The SONY TA-N86 and TA-N88 both had smps's. The TA-N88 was itself a switch-mode amp (class D avant la lettre!).
Jan Didden |
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| ilimzn |
| Jan, there was a number of them both before and after, in their high-end lineup as well as the regular consumer stuff. I've seen and heared a number of them, and in fact own a TA-N88B. The switchmode power supply used in them is not as advanced as todays designs (and all discrete), but it does the job very well. It is an extensively shileded (has it's own sealed box) two step design, with a buck regulator in front of a self-oscillating push-pull cpnverter. I did however notice the propensity to produce acustical noise rather than electrical, a faint hiss perceptible only in very quiet conditions (like in the middle of the night). There were some issues with reliability, though - due to much worse filter cap technology, compared to what is obtainable today - anyone who ever designed a SMPS already knows what I'm talking about. |
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| janneman |
| quote: | Originally posted by ilimzn
Jan, there was a number of them both before and after, in their high-end lineup as well as the regular consumer stuff. I've seen and heared a number of them, and in fact own a TA-N88B. The switchmode power supply used in them is not as advanced as todays designs (and all discrete), but it does the job very well. It is an extensively shileded (has it's own sealed box) two step design, with a buck regulator in front of a self-oscillating push-pull cpnverter. I did however notice the propensity to produce acustical noise rather than electrical, a faint hiss perceptible only in very quiet conditions (like in the middle of the night). There were some issues with reliability, though - due to much worse filter cap technology, compared to what is obtainable today - anyone who ever designed a SMPS already knows what I'm talking about. |
Yes indeed, my experiences with the -88 are similar to yours. In fact, I got two, both broken (the smps part). One I was able to repair and is functional, the other one is still waiting for me to find a quiet day to trouble shoot. Probably Wednesday morning 2007... ;)
The case is a study in RF and EMI engineering and I find the same metal "finger" seals I saw when working on Air defense radars many moons ago.
Jan Didden |
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| jackinnj |
| quote: | Originally posted by janneman
The case is a study in RF and EMI engineering and I find the same metal "finger" seals I saw when working on Air defense radars many moons ago.
Jan Didden |
fwiw == you can purchase the finger stock at Surplus Sales of Nebraska: http://www.surplussales.com/ (they also have a huge assortment of polystyrene caps). |
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| janneman |
Just to put something tangible to the discussion: the attached is from the Vicor website. Output ripple from smps, top is from supply itself, bottom after going through a R(ipple) A(ttenuation) M(odule). Bottom one is 1.5mV RMS. Not bad at 10A load, eh! If it just was a tad less expensive and/or I were a millionaire....;)
Jan Didden |
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| cerrem |
| quote: | Originally posted by richwalters
ok rascal....too true....to design a smps with all protective features takes alot of practical and theorical experience in physics and magnetics and most of todays engineers lack both in depth and magnetics (sadly) is still a black art subject. I'm from the old school of thought when a university degree was worth something, not like the ones obtainable now.
richj |
Rich I agree with you 100%.....
I don't mean to sound arogant but at all the companies I worked at doing SMPS design...their design gurus were morons....they had basic understanding of things with no understanding of advanced magnetics and physics and I would try to explain control loop theory to these guys 100 times and it wouldn't sink in....SOme of these guys are afraid of math and can't follow some second order diff equations... I scratch my head thinking how did this shmuck get a degree....
I am venting here, because in many cases I wind up doing all the work while these guys screw around in the lab contributing very little... Some of these companies are pretty big names....
cerrem |
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