Folks,
I've been building my own power amps for a long time, probably over 35 years, and usually associated with live musical performance (guitar amps, PA amps, Monitors, etc). Not total "from scratch" circuits, mind you, there seem to be plenty of good designs around I certainly don't have the skills to improve on. But from the beginning my biggest headache and expense has always been the power supply.
All my work these days is with solid state circuits with Bi-Polar supplies. Thankfully filter caps with huge ratings have continually gotten cheaper, smaller and lighter, but not so with transformers. Because of that, power supplies for amplifiers designed for true power in the 100w - 300w category routinely cost me more to build than any other part of the project, and of course they are big and add a lot of weight. The occasional good buy on a torrid on e-bay is a fleeting comfort. Maybe eventually Class-D will be an alternative, but obviously the theoretical maximum benefit there is only a 50% reduction in required PS capacity.
SO... all this to say... what about switchers? I keep hearing why switchers are bad for power amps, but a lot of the explanations don't seem to make sense. And too often these days I've found that a so called 800 watt PA head at someone's performance certainly does not weigh enough to be sporting the copper and iron to make a brute force supply worthy of the numbers. OK, we all know power can be rated many ways, but I suspect some of these numbers are honest, and that some manufacturers are using switchers. Does anyone have any experience with using switchers for higher power amp applications they can share with me?
I've been building my own power amps for a long time, probably over 35 years, and usually associated with live musical performance (guitar amps, PA amps, Monitors, etc). Not total "from scratch" circuits, mind you, there seem to be plenty of good designs around I certainly don't have the skills to improve on. But from the beginning my biggest headache and expense has always been the power supply.
All my work these days is with solid state circuits with Bi-Polar supplies. Thankfully filter caps with huge ratings have continually gotten cheaper, smaller and lighter, but not so with transformers. Because of that, power supplies for amplifiers designed for true power in the 100w - 300w category routinely cost me more to build than any other part of the project, and of course they are big and add a lot of weight. The occasional good buy on a torrid on e-bay is a fleeting comfort. Maybe eventually Class-D will be an alternative, but obviously the theoretical maximum benefit there is only a 50% reduction in required PS capacity.
SO... all this to say... what about switchers? I keep hearing why switchers are bad for power amps, but a lot of the explanations don't seem to make sense. And too often these days I've found that a so called 800 watt PA head at someone's performance certainly does not weigh enough to be sporting the copper and iron to make a brute force supply worthy of the numbers. OK, we all know power can be rated many ways, but I suspect some of these numbers are honest, and that some manufacturers are using switchers. Does anyone have any experience with using switchers for higher power amp applications they can share with me?
SMPS are nice, but require much more engineering to give good results. There are lots of different topologies from tough to simple with corresponding results. PCB layout is for better designs pretty critical for best performance. Require usually custom parts like inductors that you have to wind on your own. SMPS work with rectified mains voltage so not for the faint of heart, beginners should stay away anyway.
If one can handle all of that, SMPS may be a good solution if weight is of top priority - which it isn't for most people.
Have fun, Hannes
If one can handle all of that, SMPS may be a good solution if weight is of top priority - which it isn't for most people.
Have fun, Hannes
Thanks. Well its really the combination of weight, footprint, and especially cost that makes me curious. So many times I'm surprised to see cases where complex technology is cheaper than the simpler solution, when the simpler one is bigger and heavier and more costly. I wouldn't venture to try to roll my own, but I suppose I was hoping that with all the cheap switchers for PCs out there, some manufacturer might be targeting solid state audio amplifier products, with some good off the shelf offerings. With a good torriadal transformer often osting over $100, well.. you can surely see why I keep hoping.
MAny if not most commercial pro audio OEMs have switcher based power amps. It works well and reliably. That is how you get a 1000watt power amp that weighs only 20 pounds.
And there is a whole series of recent Crate guitar tube amps using SMPS for the B+, the heaters, bias, and the low voltage rails.
But Peavey or Crest or QSC or whoever don't buy those supplies off the shelf from some power supply maker. They engineer their own. SO if you are looking for some ready made SMPS you may have to look for a while.
But look through the surplus outlets, and who knows what you might find. I used to shop for linear supplies and small switchers at places like MP Jones, and they had pages and pages. And while you may need a split supply, there is nothing wrong with stacking two single voltage SMPSs to get the two rails.
And there is a whole series of recent Crate guitar tube amps using SMPS for the B+, the heaters, bias, and the low voltage rails.
But Peavey or Crest or QSC or whoever don't buy those supplies off the shelf from some power supply maker. They engineer their own. SO if you are looking for some ready made SMPS you may have to look for a while.
But look through the surplus outlets, and who knows what you might find. I used to shop for linear supplies and small switchers at places like MP Jones, and they had pages and pages. And while you may need a split supply, there is nothing wrong with stacking two single voltage SMPSs to get the two rails.
reply
Switch Mode Power Supply circuits can greatly reduce the size, weight and cost of high current, high voltage supply rails in audio power amplifiers. But since many switching regulators are made to function in the 20 to 50kHz region, they have the possibility of putting switching noise, harmonics and/or intermodulation products into the audio frequency signal path. To examine this hypothesis, a Switch Mode Power was constructed using a popular control IC and applied to an amplifier of known quality. Measurements on the output line of the amplifier revealed only a small number of harmonics, only minimally related to the switching frequency of the power suppply. These were approximately 70dB below a 1 watt reference level, and well outside the audio frequency range.
Switch Mode Power Supply circuits can greatly reduce the size, weight and cost of high current, high voltage supply rails in audio power amplifiers. But since many switching regulators are made to function in the 20 to 50kHz region, they have the possibility of putting switching noise, harmonics and/or intermodulation products into the audio frequency signal path. To examine this hypothesis, a Switch Mode Power was constructed using a popular control IC and applied to an amplifier of known quality. Measurements on the output line of the amplifier revealed only a small number of harmonics, only minimally related to the switching frequency of the power suppply. These were approximately 70dB below a 1 watt reference level, and well outside the audio frequency range.
Well funny you should mention good 'ol Marlin P Jones. Here's a recent 200W stereo amp project of mine, for driving stage monitor speakers. The first photo shows the fairly nice-n-pretty finished project. But the second shows the ugly inside. Note the 4 transformers (courtesy Marlin P Jones" bolted together. The combination of 4 provide two split supplies for the two amp circuits, hardly visible. The empty space on the left past the transformers is where the filter caps were installed.
I hope you get a kick out of it, but you can see where I sure would be happier with some neat little (and light!) switcher! 🙂
My amp with Vicor modules kicks a$$.
http://dsl.mine.nu/galleri/misc/miniamp/mini5.jpg
But of course, they are not cheap.. also in a bigger amp I use 4wire to the circuitboard, it's not changing many millivolts..
.
Yep, it's that small..
http://dsl.mine.nu/galleri/misc/miniamp/mini5.jpg
But of course, they are not cheap.. also in a bigger amp I use 4wire to the circuitboard, it's not changing many millivolts..
.
Yep, it's that small..
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switching power supply link
Look at the following link from the switching power supply forum of a commercial switching power supply for amps that a member has apparently tested for switching noise. http://www.diyaudio.com/forums/powe...o-amplifiers-why-audio.html?highlight=dps-400. I haven't found one for sale, and have found offbrand assembled PC power supplies to be hit and miss on reliability (mostly miss, although the current one is more than a year old). However, it looks a lot smaller than your setup. Have you considered golf-cart charger transformers?- 36V CT, not shielded for hum, but finding a surplus steel box would be easier than what you have done with your 4 transformers.
About switching PS commercial amplifiers. When got onto this forum I had found a CarvXX 2.0T power amp on craigslist and was looking around to see what people thought of it. Somebody said it produced 87? KHz transients visible on a scope on the output lines, and had a turn on whump that was going to take a relay mod and timer to get rid of. I didn't buy it, upgraded a dynakit ST-120 instead. But an $80 switcher at 400W might get me started on a project to upgrade my HD TV sound.
Look at the following link from the switching power supply forum of a commercial switching power supply for amps that a member has apparently tested for switching noise. http://www.diyaudio.com/forums/powe...o-amplifiers-why-audio.html?highlight=dps-400. I haven't found one for sale, and have found offbrand assembled PC power supplies to be hit and miss on reliability (mostly miss, although the current one is more than a year old). However, it looks a lot smaller than your setup. Have you considered golf-cart charger transformers?- 36V CT, not shielded for hum, but finding a surplus steel box would be easier than what you have done with your 4 transformers.
About switching PS commercial amplifiers. When got onto this forum I had found a CarvXX 2.0T power amp on craigslist and was looking around to see what people thought of it. Somebody said it produced 87? KHz transients visible on a scope on the output lines, and had a turn on whump that was going to take a relay mod and timer to get rid of. I didn't buy it, upgraded a dynakit ST-120 instead. But an $80 switcher at 400W might get me started on a project to upgrade my HD TV sound.
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I have Carver pm2.0t which uses Switch Mode Power supply. It produce +-120v top rails. It has SM frequency of 21khz but it produce 1/2 harmonic and is audible. By design it is soft start - no thumps, no relay. My opinion on low SM frequency(21khz) is because no available high speed high current rectifier at that time (1980)(?). In theory, if you can park your SM frequency 100khz or higher, you can at least reduce SMPS noise. My 0.02.
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