Hello everybody , there is one thing I would like to try and thats using cheap power supply pcbs from china which are available at both 24 volts at 6 amps and at 36 volts at 5 amps. Of course they cannot compare to a supply using a toroidal transformer but they do save a lot of money and they are stabilized.
Plus they are small and compact at a cost of only a few dollars........
But , as far as I know , they have a nasty ripple on their output which needs to be filtered out.
Can anyone enlighten me on this subject please?
Plus they are small and compact at a cost of only a few dollars........
But , as far as I know , they have a nasty ripple on their output which needs to be filtered out.
Can anyone enlighten me on this subject please?
Hi,
I believe I have such SMPS you talk about. "Only a few dollars" is a matter of your definition of "few". Around 12-14 $. There are some cheaper 100-120W SMPS looking rather similar but they are not worth the savings.
My SMPS work and I have successfully used them with class D amplifiers. I put 10000uF extra power line decoupling before the amplifier, that reduces the ripple a lot. If you want even better you can use a linear post regulator.
If they are for a some shorter experiments they are OK. For permanent constructions, I would spend a little more on Meanwell SMPS which many here use.
I believe I have such SMPS you talk about. "Only a few dollars" is a matter of your definition of "few". Around 12-14 $. There are some cheaper 100-120W SMPS looking rather similar but they are not worth the savings.
My SMPS work and I have successfully used them with class D amplifiers. I put 10000uF extra power line decoupling before the amplifier, that reduces the ripple a lot. If you want even better you can use a linear post regulator.
If they are for a some shorter experiments they are OK. For permanent constructions, I would spend a little more on Meanwell SMPS which many here use.
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I use a 36V 5A supply for the heaters of 36LW6 tubes... I don't detect any noise worth correcting...
Post from Faux-French:
yes thats about right but 24 dollars for two of those is cheap when considering that I have a dual voltage supply at 2x 36 volts and 5 amps , regulated and totalling 360 watts max. plus 4 dollars for a DC-detector that only connects the amps when both voltages are truly present. The kind used for speaker-protection can be used to disconnect the supply if one of them fails........
But I have doubts how they react to adding a 10000uf capacitor directly to their output for one as I read somewhere that that can sooner or later cause them to blow ?? someting about the modified esr influencing the control feedback?
A coil to pass the DC but filters at the switching frequency should both avoid that and make the output at the 10000uf a lot cleaner.
Post from kodabmx:
used for heater circuits it is not relevant at all I guess but I want to use it to supply anaudio amp with it
yes thats about right but 24 dollars for two of those is cheap when considering that I have a dual voltage supply at 2x 36 volts and 5 amps , regulated and totalling 360 watts max. plus 4 dollars for a DC-detector that only connects the amps when both voltages are truly present. The kind used for speaker-protection can be used to disconnect the supply if one of them fails........
But I have doubts how they react to adding a 10000uf capacitor directly to their output for one as I read somewhere that that can sooner or later cause them to blow ?? someting about the modified esr influencing the control feedback?
A coil to pass the DC but filters at the switching frequency should both avoid that and make the output at the 10000uf a lot cleaner.
Post from kodabmx:
used for heater circuits it is not relevant at all I guess but I want to use it to supply anaudio amp with it
yes thats about right but 24 dollars for two of those is cheap when considering that I have a dual voltage supply at 2x 36 volts and 5 amps , regulated and totalling 360 watts max. plus 4 dollars for a DC-detector that only connects the amps when both voltages are truly present. The kind used for speaker-protection can be used to disconnect the supply if one of them fails........
I have never tried to stack them. For symmetrical use I have traditional transformer supplies, some of them with linear regulator.
But I have doubts how they react to adding a 10000uf capacitor directly to their output for one as I read somewhere that that can sooner or later cause them to blow ?? someting about the modified esr influencing the control feedback?
It depends on their current limit protection and if they start to oscillate. I did not do a scientific study but tried on a whim. And, it worked with repeated start-up. Extra output capacitance influences stability.
A coil to pass the DC but filters at the switching frequency should both avoid that and make the output at the 10000uf a lot cleaner.
If you add a coil, in particular if the resulting resonance frequency is not sufficiently damped, you risk worsening the stability more than with just a capacitor. I know that in theory an LC filter will do the job but with a dynamic loads it is not always that simple.
I have never tried to stack them. For symmetrical use I have traditional transformer supplies, some of them with linear regulator.
But I have doubts how they react to adding a 10000uf capacitor directly to their output for one as I read somewhere that that can sooner or later cause them to blow ?? someting about the modified esr influencing the control feedback?
It depends on their current limit protection and if they start to oscillate. I did not do a scientific study but tried on a whim. And, it worked with repeated start-up. Extra output capacitance influences stability.
A coil to pass the DC but filters at the switching frequency should both avoid that and make the output at the 10000uf a lot cleaner.
If you add a coil, in particular if the resulting resonance frequency is not sufficiently damped, you risk worsening the stability more than with just a capacitor. I know that in theory an LC filter will do the job but with a dynamic loads it is not always that simple.
hello again,
the parts I have bought and am experimenting with are these:
Electronico 36V 5A 180W 50/60HZ AC-DC Interruptor Fuente de Alimentacion Modulo | eBay
8.50 euros is just under 10 dollars no shipping fee.
I want to use two of these for a symmetric supply. The idea is to connect their outputs to a relay of a speaker-protection-module which will only pass the supply-voltages directly to the amps when both supply-voltages are present as otherwise the dc-imbalance detected by that module will not actuate the realay. The relay contacts will be bridged by two large 33 ohm resistors to allow the caps of the amps to be charged up with a limited inrush- current to allow the smps to start up normally and to limit the output current to about 1,1 amp in case of a short at the amps. The start delay of the module should be about 2 to 3 seconds for that and can be adjusted easily by just changing the corresponding resistor. A second protection module at the output of the amps will have a delay of about 5 seconds so the speakers are only conected once everything is stabilyzed and ready to go.
I think this about covers the general idea with a cost of only aroung 25 dollars for a well protected power-supply as described further up....
Any input , info on this will be more than welcome.
Greets Michael
the parts I have bought and am experimenting with are these:
Electronico 36V 5A 180W 50/60HZ AC-DC Interruptor Fuente de Alimentacion Modulo | eBay
8.50 euros is just under 10 dollars no shipping fee.
I want to use two of these for a symmetric supply. The idea is to connect their outputs to a relay of a speaker-protection-module which will only pass the supply-voltages directly to the amps when both supply-voltages are present as otherwise the dc-imbalance detected by that module will not actuate the realay. The relay contacts will be bridged by two large 33 ohm resistors to allow the caps of the amps to be charged up with a limited inrush- current to allow the smps to start up normally and to limit the output current to about 1,1 amp in case of a short at the amps. The start delay of the module should be about 2 to 3 seconds for that and can be adjusted easily by just changing the corresponding resistor. A second protection module at the output of the amps will have a delay of about 5 seconds so the speakers are only conected once everything is stabilyzed and ready to go.
I think this about covers the general idea with a cost of only aroung 25 dollars for a well protected power-supply as described further up....
Any input , info on this will be more than welcome.
Greets Michael
For 20 bucks, try it and see. Mine is providing 1.8A without fan cooling inside a chassis, and it runs around 75c. I wouldn't try asking them for 5A without using a fan.
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I wiil of course mount them so that their heatsinks are in vertical position for best air circulation. But a slow turning 12 cm pc-style fan at 7 volts is inaudible so I will consider that.
In addition to the possible resoncance problem that FauxFrench mentioned, a series inductor will increase the output impedance.
Cheap power supplies like those are quite likely to produce a lot of common-mode noise. You can mitigate that by connecting the 0V output to earth as directly as possible. If that's not enough, then you might need a common-mode choke followed by a capacitor before the earth connection (one per PSU if you're using a pair in series for a symmetric supply)
Cheap power supplies like those are quite likely to produce a lot of common-mode noise. You can mitigate that by connecting the 0V output to earth as directly as possible. If that's not enough, then you might need a common-mode choke followed by a capacitor before the earth connection (one per PSU if you're using a pair in series for a symmetric supply)
Thanks for the info. I am planning to enclose them in a wire-mesh to shield them anyways. In addition I will see what might be necesary to eliminate as much ripple and noise as possible from the outputs. if the choke is for a frequency of say 1000Hz it should attenuate at the switching-frequencies. Correct me if wrong please
This is a Trial and Error project for me as the only measuring instruments I have are a 60Mhz dual trace scope ( HAMEG ) and two reasonable multimeters
🙂
🙂
Sometimes a cheap SMPS can be much quieter than a linear toroidal supply. I used a CRC filter with a snubber.
See the difference here Strange Forest of Noise with Linear PSU
One issue with SMPS is that they self protect by shutting off if you drive a cap bank directly. In which case, a slow or soft start mechanism is needed. I use a cap Mx which ramps up slowly.
Putting a CLC (with R parallel L) in between SMPS and cap Mx then followed by linear regulator can be a good option.
Like this:
GB for Simple Cap-Mx Regulated Low-Noise PSU
See the difference here Strange Forest of Noise with Linear PSU
One issue with SMPS is that they self protect by shutting off if you drive a cap bank directly. In which case, a slow or soft start mechanism is needed. I use a cap Mx which ramps up slowly.
Putting a CLC (with R parallel L) in between SMPS and cap Mx then followed by linear regulator can be a good option.
Like this:
GB for Simple Cap-Mx Regulated Low-Noise PSU
When we talk about this noise in a psu, is it even audible/ detrimental to the music, or purely an objective measurement thing?
Edit.....assuming a psu for a power amp...and not for delicate digital circuits
Edit.....assuming a psu for a power amp...and not for delicate digital circuits
Hello jimk04
cannot say yet as I am building the amps but as soon as I have it all up and running and some result I will post it here.
So far I will test these to see what they can deliver and how hot do they get loading them with a dummy load . Couple of car headlight bulbs, using three of those in series will give me a load of a little more than 4 amps continuos load and if they take that without overheating and during 24 hours nonstop I then can proceed to test them with an amp. I am not going to risk blowing an amp without this test first. While doing this I will connect a scope to what ripple there is at a 4 amp load as well.
Greetings Michael
cannot say yet as I am building the amps but as soon as I have it all up and running and some result I will post it here.
So far I will test these to see what they can deliver and how hot do they get loading them with a dummy load . Couple of car headlight bulbs, using three of those in series will give me a load of a little more than 4 amps continuos load and if they take that without overheating and during 24 hours nonstop I then can proceed to test them with an amp. I am not going to risk blowing an amp without this test first. While doing this I will connect a scope to what ripple there is at a 4 amp load as well.
Greetings Michael
oh and one more thing : Probably I will have to build some softstart mechanism as without that I doubt they will start up normally when connected to 10000 or more uf capacitors. Their overload protection will probably see to that unfortunately........
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I have been using several different ones of thes for quite a while now and IÄwould like to shre my experiences with them.
First to say and agree with former posts one should not expect more than about 60% of their max output if they are to last. so a 5 amp one can deliver 3 amps for a long time without problems provided the enclosure is well enough ventilated , and that in case of audio can be 3 amps RMS.
The weak point of these modules are the capacitors as is no surprise so it is not a bad idea to change those for good low ESR ones . this alone doubles and triples their life-expectancy . so far only one out of 8 I am using died beyond repair on me in about two years I am using the things because a leaking cap caused shorts in the ic control chip so after that I changed all the caps on the secondary side and since that no problems.
with two others which I use to power an amp for test purposes I had a faint noise in the tweeters but that disappeared adding two 1uf caps on the electrolytic power caps on the amp-board. This test amp is based on an LM3886-chip so is a class AB amp.
First to say and agree with former posts one should not expect more than about 60% of their max output if they are to last. so a 5 amp one can deliver 3 amps for a long time without problems provided the enclosure is well enough ventilated , and that in case of audio can be 3 amps RMS.
The weak point of these modules are the capacitors as is no surprise so it is not a bad idea to change those for good low ESR ones . this alone doubles and triples their life-expectancy . so far only one out of 8 I am using died beyond repair on me in about two years I am using the things because a leaking cap caused shorts in the ic control chip so after that I changed all the caps on the secondary side and since that no problems.
with two others which I use to power an amp for test purposes I had a faint noise in the tweeters but that disappeared adding two 1uf caps on the electrolytic power caps on the amp-board. This test amp is based on an LM3886-chip so is a class AB amp.
MalleeMike, apart from one cap fault (without any assessment of why it failed), all i see you say are ifs and maybes. Perhaps if you use the module and amass some test results that aren't subjective and then report back, then this thread will have some value imho.
