Hi Gurus,
Sorry for this newbie question.
I am trying to build a class ab amp powered by SMPS sold in Aliexpress as I want to try SMPS to power the mono amp.
It uses 2 pairs of to3 output and im currently using 600va transformer.
Given that the transformer has 35-0-35ac after bridge rectifier estimate: +49, -49Vdc, then can tap to 0 ground from transformer center tap to amp board ground.
I just wanted to check if this SMPS attached will work?
What do I need to ask the seller? Should I ask for a +50vdc, -50vdc, with 0 ground or should a go a little bit higher like 53-55+/-vdc,+0 ground?
Will it just be a direct connection to the amp circuit board? just connect +50vdc, -50vdc, then the 0 from SMPS to ground of the board?
Thanks in advance.
Sorry for this newbie question.
I am trying to build a class ab amp powered by SMPS sold in Aliexpress as I want to try SMPS to power the mono amp.
It uses 2 pairs of to3 output and im currently using 600va transformer.
Given that the transformer has 35-0-35ac after bridge rectifier estimate: +49, -49Vdc, then can tap to 0 ground from transformer center tap to amp board ground.
I just wanted to check if this SMPS attached will work?
What do I need to ask the seller? Should I ask for a +50vdc, -50vdc, with 0 ground or should a go a little bit higher like 53-55+/-vdc,+0 ground?
Will it just be a direct connection to the amp circuit board? just connect +50vdc, -50vdc, then the 0 from SMPS to ground of the board?
Thanks in advance.
The difference in perceived output or loudness will be negligible comparing -/+45 or -/+55 volt rails. Lower is often better unless you can make a good case for not doing so.
You do indeed just connect the -, the + and ground as you describe. Yu need to check that you have not got excessive capacitance on the rails, remember SMPS is totally different and large caps are not usually needed and can in many cases cause problems.
Hi Jan,
Thanks for your reply. The amp that Im currently using works perfectly and I would just like to try the smps power supply. maybe ill just stick to 50vdc+- which is working well and stable and able to power low impedance driver.
Hi Mooly,
Thanks for your reply.
I'll just stick to 50vdc+,-.
My current supply is 600va with 2pc 4700uf wire in series in the bridge -> secondary 0v tap to the series connection of the caps, then tap to amp ground.
Can I just check how would I know/check if I got excessive capacitance on the rails?
Does SMPS require me to use my existing smoothing caps?
Sorry for the dumb questions.
You would have to consult the SMPS data sheets as this is something that different SMPS react differently to.
Conventional PSU's use big (like your 4700uF) caps because the ripple frequency is low (100 or 120 Hz depending on mains frequency of 50 or 60 Hz). So these need big value caps. The SMPS runs at many kHz and so the ripple frequency is very high. Values as small as 47uF or 100uF can be used.
If you load an SMPS with to much capacitance then they can sometimes have problems starting and also problems regulating against changes in load current. That is one to ask the manufacturer of the SMPS as to what they recommend.
HI Oldiy,
Thank for the response.
for 50vdc+ and 50vdc- cooler meaning heatsink or fan? thanks
Hi Mooly,
Thanks again for your response.
Just to double check if I understood what you mentioned, so I would need to check with the seller what is the capacitance of their smps on the secondary side right? So if it's around 47uf to 100uf it will be suitable?
Also, do SMPS power supplies able to handle low impedance loads like 4-2ohms? Or that would depend on the amp design? As currently this amp able to handle low impedance driver.
Thanks in advance.
That all depends on the amp. After that you have to be sure that the power supply (SMPS or conventional) can deliver the current that the amp needs for any given level and load. The amp will draw the same current for a given output no matter what PSU is used.
The SMPS manufacturer/distributor should be able to advise on how much capacitance it can have added.
I found this from a few years ago:
https://www.diyaudio.com/community/threads/adding-capacitance-to-smps.332247/
Hi Mooly,
Thanks again for your kind assistance and for directing me to the link above.
The insights that you have shared helped me to understand smps supply better.
I will check with the seller and ask for data sheet, hopefully they can provide. Will also check with them the capacitance of their 600watt and if it's possible to add if needed just in case. (also the current capability of the smps supply)
Thanks
Hi Mooly,
Sorry to trouble you again.
May I just check if this capacitance is ok?
It's on their store it's using 80v 1200uf by default.
Tia
Sorry to trouble you again.
May I just check if this capacitance is ok?
It's on their store it's using 80v 1200uf by default.
Tia
It depends as much on the power supply as it does the amplifier. The problem with class AB amps is that they draw 3.14X (that’s right pi times) the average current at the PEAK of every cycle. If an SMPS goes into a limiting condition with this load you will reduce the amp’s output power. Period. Output capacitance can be used to supply this current - it does in conventional supplies. All SMPS’s have some output capacitance - they all lave LC filters designed for the switching frequency. Those “filters” in conventional supplies are designed for 120 Hz, and it doesnt take that much extra capacitance to be good enough down to 40 or even 20 (20,000 uF is all you ever need). But SMPSs don’t like that much capacitance because they take too long to charge initially and THAT draws too much current. Most SMPSs will take a short term overload above rated continuous current. But how much and how long could be anything. Might be enough for full power at 20 Hz, but don’t count on it (Because the bean counters are counting beans). If you use a supply RATED for 3X the average current draw (at full power, lowest impedance) you would not run into any limiting mechanism OR require any output capacitance. But that might be one big, expensive supply. It’s quite practical for smaller amplifiers, though. Just not 200 watt per channel ones unless you’ve got money to spend.
hi Wg_ski,
Thanks for your reply.
Given that in currently running my amp with 600va transformer with 50vdc+- will the smps above rated at 600watt suffice? It also say 18-20amp since im only using 2 pairs output should i mame it 3-4pairs or just keep it at 2pairs?
Tia
Putting some answers together, since you jump from subject to subject and it gets confusing.
1) you are asking about 150W 8 ohm amplifier, fed from +/-49V rails, and we are answering that, period, please do not add new variables such as different voltages, load impedances, etc.
Your original question has not been answered in full (yet) because you keep changing the goalposts.
2) from those shown by you, closest is +/-48V "600VA" so stick to it.
Note: I am rounding all voltages to 50V for easier Math.
3) by the way, they claim 600VA input ; so it´s reasonable to count with 500VA output.
4) 8 ohm speaker load will "look" like 2*PI*8 ohm rail to rail (same as PI*8 ohm rail to ground as Wgski mentioned above) so equivalent 50 ohm so will pull average 100V/50r=2A
But peak will still be 50V/8 ohm=6.25A
All assuming ideal conditions, zero voltage drop across transistors, etc.... which is fine because we are estimating heaviest possible load.
If real world load is slightly lighter, call it a (small) safety margin 🙂
5) and SMPS is capable of putting out 500VA/100V=5A
Looks insufficient, BUT we are saved because load is not simultaneous on both rails, at any given moment amp is pulling current from either one rail or the other, so its peak current capability feeding this split rail class AB amplifier is 500VA/50V=10A.
So you see it´s fine feeding this amp as specified, not so sure if you lower load to 4 ohm (it might but real close), forget 2 ohm.
6) do NOT add extra capacitance, supply (supposedly) meets its specs and does not need anything besides what it already has.
You can add smallish decoupling caps .say 50-100uF rail to ground, at the powr amp board itself, for stability, their small size will not bother SMPS.
Old style supplies are "elastic" and forgiving and if overloaded they just drop voltage, period; SMPS are OCD afflicted tightly regulated with tons of feedback, and get crazy if loaded beyond their comfort zone.
Best case, they turn OFF or clamp down output drastically.
PS: your amp is capable of 120W RMS into 8 ohm.
Why?
1) you are asking about 150W 8 ohm amplifier, fed from +/-49V rails, and we are answering that, period, please do not add new variables such as different voltages, load impedances, etc.
Your original question has not been answered in full (yet) because you keep changing the goalposts.
2) from those shown by you, closest is +/-48V "600VA" so stick to it.
Note: I am rounding all voltages to 50V for easier Math.
3) by the way, they claim 600VA input ; so it´s reasonable to count with 500VA output.
4) 8 ohm speaker load will "look" like 2*PI*8 ohm rail to rail (same as PI*8 ohm rail to ground as Wgski mentioned above) so equivalent 50 ohm so will pull average 100V/50r=2A
But peak will still be 50V/8 ohm=6.25A
All assuming ideal conditions, zero voltage drop across transistors, etc.... which is fine because we are estimating heaviest possible load.
If real world load is slightly lighter, call it a (small) safety margin 🙂
5) and SMPS is capable of putting out 500VA/100V=5A
Looks insufficient, BUT we are saved because load is not simultaneous on both rails, at any given moment amp is pulling current from either one rail or the other, so its peak current capability feeding this split rail class AB amplifier is 500VA/50V=10A.
So you see it´s fine feeding this amp as specified, not so sure if you lower load to 4 ohm (it might but real close), forget 2 ohm.
6) do NOT add extra capacitance, supply (supposedly) meets its specs and does not need anything besides what it already has.
You can add smallish decoupling caps .say 50-100uF rail to ground, at the powr amp board itself, for stability, their small size will not bother SMPS.
Old style supplies are "elastic" and forgiving and if overloaded they just drop voltage, period; SMPS are OCD afflicted tightly regulated with tons of feedback, and get crazy if loaded beyond their comfort zone.
Best case, they turn OFF or clamp down output drastically.
PS: your amp is capable of 120W RMS into 8 ohm.
Why?
- 48V rails
- substract 4V power transistor drop=44V, which is your peak voltage
- so 31V RMS so 120W RMS into 8 ohm.
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Just note, the SMPS has a regulated voltage output. Any overload or short at the outputs will cause fold back and set output voltages to near zero..
How much overload (in amps) is by the SMPS design, usiually +10% of the rated current.
Where as conventional transformer rectifier type usually do not protect on overload or short circuit. They supply large currents until everything gets burnt.
Regards.
How much overload (in amps) is by the SMPS design, usiually +10% of the rated current.
Where as conventional transformer rectifier type usually do not protect on overload or short circuit. They supply large currents until everything gets burnt.
Regards.