connect the smps to the amplifier, the amplifier to an artifical load, big power resistor with minimal impedance which the amplifier can accept, inject a variable amplitude sine wave, let's say 1khz, increase the ampltude untill the amp enter in clip mode, and measure the output power, and voltage rails. also measure the time while the smps can deliver this power untill will enter in protection mode, or the output voltage will drop.
That selection procedure does not make it worth buying a possible candidate SMPS, for audio, because your test procedure ignores what a speaker requires as transient current supply/demand.
Let's take an example.
100W into 8r0 amplifier with an 8r0 load on it driven to maximum power will output 40Vpk and 5Apk.
At first sight an SMPS that can supply +-45Vdc @ 5Apk from either supply rail would seem to meet this current demand requirement.
that +-45V @5Apk indicates a 450VA smps for a 100W amplifier supplying a purely resistive load.
But we know that the speaker can demand ~ three times the current that a resistive load = nominal speaker impedance.
How can we determine, before purchase, whether a 200VA/400VA/800VA/1500VA SMPS can meet both the short term continuous power demand and the transient current demand of that hypothetical 100W amplifier?
I know from reading this Forum how to assemble an unregulated linear supply that can do this adequately.
Let's take an example.
100W into 8r0 amplifier with an 8r0 load on it driven to maximum power will output 40Vpk and 5Apk.
At first sight an SMPS that can supply +-45Vdc @ 5Apk from either supply rail would seem to meet this current demand requirement.
that +-45V @5Apk indicates a 450VA smps for a 100W amplifier supplying a purely resistive load.
But we know that the speaker can demand ~ three times the current that a resistive load = nominal speaker impedance.
How can we determine, before purchase, whether a 200VA/400VA/800VA/1500VA SMPS can meet both the short term continuous power demand and the transient current demand of that hypothetical 100W amplifier?
I know from reading this Forum how to assemble an unregulated linear supply that can do this adequately.
How do we do this?
AndrewT said:
100W at 8ohms means 28.8V rms, 40V peak. correct untill now. but let's not make a confusion. you didn't mention anything about the amplifier class, topology or efficiency. the 450W peak wich you mention before is the maximum peak load, which last miliseconds. the energy stored in the capacitors is enough to sustain this peaks. the average power is much less than 450W, in most of the cases is not more than 90W for a 90% efficient amplifier.
AndrewT said:
how come will take 3 times ? that 3 times is not acctual 3 times, maximum 2 times. why ? a speaker with 8 ohms impedance has about 5.5Ohms resitance. and is supplied with AC, not DC we not speak about resistance anymore.
but let's say that is like you said. if we multiply the 450W with 3 we will get 1350W. so the SMPS must provide 13.5 times the amplifier rated power ??? please show me one single smps which can do this. including in pro-audio field.
very curious, i know many PA amps which deliver 2x2000W and draw 10-12 A from 110V mains. but they use to play music, not pure sine wave.
give us the answer in stages if you prefer.
What is a sensible SMPS rating for a 100W into 8r0 amplifier?
What is a sensible SMPS rating for a 100W into 8r0 amplifier?
please formulate the question with proper terms, so i can understand-it correctly. otherwise i can't give you the answer which are you waiting for.
If we have a hypothetical 100W into 8r0 amplifier and an 8ohm speaker, what rating (+-Vdc & VA) of SMPS would you recommend?
what class, topology, efficiency ?
assuming that your answer is ClassD, 90%, i would say a SMPS which can deliver at least 100W continuous, infinite time, 120-160W continuous for 1 minute and at least two times more peak power. the capacitors should be at least 10mF on each rail. and surprisingly, will work.
assuming that your answer is ClassD, 90%, i would say a SMPS which can deliver at least 100W continuous, infinite time, 120-160W continuous for 1 minute and at least two times more peak power. the capacitors should be at least 10mF on each rail. and surprisingly, will work.
As i know lot of very expensive "digital" (Class D amplifiers with SMPS) amplifier who cannot make its rated power for long time. (they usually can make it for 1-2 minute, the quarter power for 2 hours, and tenth power for infinite). So are they bad amplifiers then? And then why they use them for every big stage and outdoor concert id their SMPSs are only rated for lower power contionously for long term?
Last time my band played together with a trash metal band. When I watched the peak idicator of my amplfiers I could see, that my band (prog-rock) had a 30dB peak-average difference. Even the trash metal band had at least 10dB (although they used diode-cipping distortion effects for bass, guitar and even vocals).
So the" rated power continously for long term" is not important for me at least. Over-designing something don't always mean it will last forever.
Last time my band played together with a trash metal band. When I watched the peak idicator of my amplfiers I could see, that my band (prog-rock) had a 30dB peak-average difference. Even the trash metal band had at least 10dB (although they used diode-cipping distortion effects for bass, guitar and even vocals).
So the" rated power continously for long term" is not important for me at least. Over-designing something don't always mean it will last forever.
Do you have TA3020 based amps, which can be fitted onto a heatsink? The one attached will be too small if used in a 4 ohm bridged eq'ed sub. Can the fets be moved to the other side of the board or - alternatively what are your thoughts regarding a solid aluminium block the height of the toroids and the capacitors that can be mounted on the external heatsink instead.
a small 60x60 mm fan can be attached onto the existing heatsink if higher power is required, or the heatsink can be replaced with a bigger one, same profile, just longer size. if you want to install the amplifier on an existing heatsink, an aluminium block can be used instead of the heatsink with extension under the pcb to have good contact with the bigger heatsink. this can be made on request, but i need about one week to order the Al pieces.
i suggested 1.5 times this
after you updated with class AB. i tought that is obvious.
cnx said:
after you updated with class AB. i tought that is obvious.
Hi,
now to the second part.
How do we assess that the SMPS we have identified will work with the ClassAB amplifier when we modify it by adding +-10mF to the output rails?
now to the second part.
How do we assess that the SMPS we have identified will work with the ClassAB amplifier when we modify it by adding +-10mF to the output rails?
Hi AndrewT,
Are you contemplating a gainclone powered by CNX SMPS? Sounds like an interesting project.
col.
Are you contemplating a gainclone powered by CNX SMPS? Sounds like an interesting project.
col.
third part:
Dear Andrew, i don't want you to feel irritated by my last post, but i have the feeling that you see the things a little different than i do. maybe that's why you addressed me with that supperior attitude. but i'm affraid that, either due to emotions, or "skin effect" knowledges, you made 2 major mistakes:
fascinating, but the amplifier will not draw those 5A from both rails in the same time. and the peak current consumption will be 5A on each rail at a time. this because when one transistor is opened the other one is closed, so no current draw. so how did you got 450VA ?
did you check the cables, maybe there is a shortcircuit somewhere
Dear Andrew, i don't want you to feel irritated by my last post, but i have the feeling that you see the things a little different than i do. maybe that's why you addressed me with that supperior attitude. but i'm affraid that, either due to emotions, or "skin effect" knowledges, you made 2 major mistakes:
AndrewT said:
fascinating, but the amplifier will not draw those 5A from both rails in the same time. and the peak current consumption will be 5A on each rail at a time. this because when one transistor is opened the other one is closed, so no current draw. so how did you got 450VA ?
AndrewT said:
did you check the cables, maybe there is a shortcircuit somewhere
no,
CNX on the one hand tells us it's simple to select an SMPS to power a power amplifier and then tells us we can screw it all up by selecting the wrong type and/or miss-connecting it.
I would like Cnx to explain how we do the job correctly.
I don't believe it can be done simply nor cheaply. He has different views.
I certainly have no intention of buying random SMPS without some expert guidance. I know that I know nothing about SMPS, except that they alone cannot cheaply meet the peak current requirements of a power amplifier.
CNX on the one hand tells us it's simple to select an SMPS to power a power amplifier and then tells us we can screw it all up by selecting the wrong type and/or miss-connecting it.
I would like Cnx to explain how we do the job correctly.
I don't believe it can be done simply nor cheaply. He has different views.
I certainly have no intention of buying random SMPS without some expert guidance. I know that I know nothing about SMPS, except that they alone cannot cheaply meet the peak current requirements of a power amplifier.
yes, alternate current draw from either supply rail.cnx said:
To me +-45Vdc, each capable of 5Apk comes out at 45*5 + 45*5 = 450VA.
The other difference in opinion we have is that speakers are/are not resistors.
That 5Apk is what an amplifier driving an 8r0 resistor with a 40Vpk sinewave would have to deliver.
The speaker load is reactive and that reactance demands much more current. Regularly twice what a resistor load would demand and occasionally three times.
There is a report on the Forum that shows that both moderate and severe reactance speakers when driven with real music signals can draw upto five times the nominal current that an equivalent resistor would draw.
Let's just settle for three times and identify where the 15Apk can come from an unmodified SMPS that is either 150VA ot 450VA. You choose.
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