Good Day everyone.. I have a couple of power amp modules good for 100 watts output as well a couple of power supply boards that I can use to set up a good power supply. I had planned on doing a power supply for each module but now would like to use a single torroid/ chassis mount transformer. The modules need +- 42 volts to push 100 watts output. How big a transformer do I need and what secondary voltage should it be.. The toroidal ones use a vamp rating not amps.. I figure 30 volts CT @ 5-6 amps should be enough.. Can someone guide me in this respect and let me know how to calculate this in future.. Thanks for your help Cheers Wayne
start with your total maximum output power.
For domestic duty the transformer VA should be roughly one to two times the total maximum output power.
If you have two 100W into 4ohms amplifiers, then the total maximum power is 200W. That would suit a transformer of 200VA to 400VA.
For maximum flexibility buy a dual secondary transformer. Each secondary can be used to feed a bridge rectifier + smoothing capacitor.
Alternatively the dual sec can be very easily converted to Centre Tapped and the three output wires feed into a single bridge rectifier + two smoothing capacitors connected in series.
ESP and TNT have good webpages that explain all this.
For domestic duty the transformer VA should be roughly one to two times the total maximum output power.
If you have two 100W into 4ohms amplifiers, then the total maximum power is 200W. That would suit a transformer of 200VA to 400VA.
For maximum flexibility buy a dual secondary transformer. Each secondary can be used to feed a bridge rectifier + smoothing capacitor.
Alternatively the dual sec can be very easily converted to Centre Tapped and the three output wires feed into a single bridge rectifier + two smoothing capacitors connected in series.
ESP and TNT have good webpages that explain all this.
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Someone will soon be along to complicate matters with calculations allowing for mains voltage variations, in reality any good amplifier design should be able to handle these variations.
The simple maths behind AC to DC conversion is quite simple.
Let's start with the required DC voltage, in your case 42VDC.
The diodes in the bridge rectifier will drop about 0.7V each, with two in play at any one moment that is 1.4V. So we want to start with 43.4VDC.
Divide that figure by 1.414 gives you 30.69VAC.
Your 30V transformer will be ideal for the task.
As AndrewT has stated above, this needs to be between 2 x 3 times the power for your amplifiers (2 x 100W). So you really ought to be looking at 400VA or greater.
The simple maths behind AC to DC conversion is quite simple.
Let's start with the required DC voltage, in your case 42VDC.
The diodes in the bridge rectifier will drop about 0.7V each, with two in play at any one moment that is 1.4V. So we want to start with 43.4VDC.
Divide that figure by 1.414 gives you 30.69VAC.
Your 30V transformer will be ideal for the task.
As AndrewT has stated above, this needs to be between 2 x 3 times the power for your amplifiers (2 x 100W). So you really ought to be looking at 400VA or greater.
Power supply
Thanks for your help on this.. Ordered up the transformer and once arrived will look for a case for this thing.. I have a line on a defunct Dynaco Stereo 80 that appears big enough.. Seller only wants $30 so seems like a good deal.. I will get back to everyone and let you know the story.. Once up and tested I will post some pictures.. Hopefully there will be no smoke on the Canadian horizon
Thanks again for the help Cheers Wayne
Thanks for your help on this.. Ordered up the transformer and once arrived will look for a case for this thing.. I have a line on a defunct Dynaco Stereo 80 that appears big enough.. Seller only wants $30 so seems like a good deal.. I will get back to everyone and let you know the story.. Once up and tested I will post some pictures.. Hopefully there will be no smoke on the Canadian horizon
Thanks again for the help Cheers Wayne
Good morning everyone. Thanks for all the replies with regard to the power supply.. I have everything in place just waiting on the large filter caps to arrive to do the mock up and see what this amp will do.. I have not found a chassis/enclosure yet but hopefully something will come along, short of making my own. Thanks again for all the feedback Cheers Wayne
A 35-0-35Vac transformer will give you ~±50Vdc. That is good for 100W into 8ohms and about 130W into 6ohms. Two channels of 130W comes to a total of 260W. You should use a transformer with a 260VA to 520VA to hit those targets. Any 35-0-35Vac transformer from 250VA, 300VA, 400VA, 500VA will do.
A 30-0-30Vac transformer will give you ~±43Vdc. That is good for 70W into 8ohms and about 90W into 6ohms. Two channels of 90W comes to a total of 180W. You should use a transformer with a 180VA to 360VA to hit those targets. Any 30-0-30Vac transformer from 180VA, 200VA, 250VA, 300VA, 400VA will do.
A 30-0-30Vac transformer will give you ~±43Vdc. That is good for 70W into 8ohms and about 90W into 6ohms. Two channels of 90W comes to a total of 180W. You should use a transformer with a 180VA to 360VA to hit those targets. Any 30-0-30Vac transformer from 180VA, 200VA, 250VA, 300VA, 400VA will do.
I´m curious about Meerkat´s amplifier, I see a communications problem here:
Not only nobody corrected him, but he was suggested:
Quite evident for us, not so sure about a relatively green builder.
So meerkat .... what transformer did you actually buy ?
That literally means a 15+15 VAC transformer.
Not only nobody corrected him, but he was suggested:
Hope he noticed it really means 30+30VAC transformer.
Quite evident for us, not so sure about a relatively green builder.
So meerkat .... what transformer did you actually buy ?
Transformer used.
Thanks for the reply.. The transformer I actually used was not the 30-0-30. I picked up a new surplus Plitron one that is 400 vamps with a 25-0-25 which is giving me about 32.5 volts of DC. This is below the amount that I wanted but I wanted to try out the amp. I am looking for another transformer in the interim. The amp is now operating, there are no problems so far, no noise , hiss or hum. I am currently powering a pair of Heathkit AS103's ( Kit version of AR3A) and there seem to be no issues. The sound is clean and the lower bass is very tight.. am estimating that with the 32 volts the amp is only putting out about 60-75 watts not the 100, but the speakers are 4 ohms so they are drawing a bit more current. I used a Dynaco 120 chassis and posted pictures in the Gallery section of the forum. This is my first project and it turned out well. The wiring could be neater but it works.. Thanks again for the reply,... Wayne
Thanks for the reply.. The transformer I actually used was not the 30-0-30. I picked up a new surplus Plitron one that is 400 vamps with a 25-0-25 which is giving me about 32.5 volts of DC. This is below the amount that I wanted but I wanted to try out the amp. I am looking for another transformer in the interim. The amp is now operating, there are no problems so far, no noise , hiss or hum. I am currently powering a pair of Heathkit AS103's ( Kit version of AR3A) and there seem to be no issues. The sound is clean and the lower bass is very tight.. am estimating that with the 32 volts the amp is only putting out about 60-75 watts not the 100, but the speakers are 4 ohms so they are drawing a bit more current. I used a Dynaco 120 chassis and posted pictures in the Gallery section of the forum. This is my first project and it turned out well. The wiring could be neater but it works.. Thanks again for the reply,... Wayne
I use PC cases for my amplifier projects.
They are a lot cheaper than most bought in amp enclosures.
I strip out the power supply leaving the mains socket.
I use the PSU fan housing for my own fan.
I can pick up used PC cases for about £20.
Even a new one with a low wattage power supply isn't a lot more.
Hey guys this is going to be a dumb question but here I go I’m need to know what voltage to power my Mx50se not the dc power that’s all set but how much voltage does the board need to be powered with I am totally green with this I started getting all my wiring together adding my 12 V to other components figuring I only need a DC for my MX 50 SE as it turns out I noticed it also needs to be fed with power I really feel dumb does anybody know what power I’m supposed to supply that with ac or dc and with what voltage ??? Thanks guys and try not to be to mean !! Lol
What you have purchased is a pair of amplifier boards that will require what is called a dual supply, is seen if you look at the schematic of the boards. There’s an upper portion that operates on one voltage, with the lower half running on a negative power.
That means 0-40 volts +, and 0-40 volts -.
So that will be three wires total, and it is DC voltage, not what will be coming out of the transformer as it is plugged into the wall.
This means that after the transformer that there will need to be an arrangement of diodes (rectifier bridge) to rectify the ac into +/- DC, along with at least a pair of large capacitors. This is commonly known as a power supply.
I would suggest spending some time looking at popular, common amplifier schematics until you can almost draw it on your own, noting important details like safety grounding, fuses, and securely mounting things that could cause harm if allowed.
Here is an amplifier manual from a product that was offered as a kit, so a lot of what you need is actually spelled out for you. There is a schematic that shows the power supply amp that you need as well.
https://hafler.com/pdf/archive/DH-500_amp_man.pdf
Hope this can help to get you headed in the right direction.
That means 0-40 volts +, and 0-40 volts -.
So that will be three wires total, and it is DC voltage, not what will be coming out of the transformer as it is plugged into the wall.
This means that after the transformer that there will need to be an arrangement of diodes (rectifier bridge) to rectify the ac into +/- DC, along with at least a pair of large capacitors. This is commonly known as a power supply.
I would suggest spending some time looking at popular, common amplifier schematics until you can almost draw it on your own, noting important details like safety grounding, fuses, and securely mounting things that could cause harm if allowed.
Here is an amplifier manual from a product that was offered as a kit, so a lot of what you need is actually spelled out for you. There is a schematic that shows the power supply amp that you need as well.
https://hafler.com/pdf/archive/DH-500_amp_man.pdf
Hope this can help to get you headed in the right direction.
That looks great, should be a nice setup.
Just double, triple check each connection one wire at a time before you power anything up.
Also I would install some fuses starting with one on the A/C, before the transformer, and four more, one on each power wire to the two boards.
There is a very handy device made from a screw-in incandescent light bulb fixture, 60w incandescent bulb, standard plug/wire. By inserting the bulb filament in series with the A/C, you create a softer connection that will indicate if there is a problem by illuminating the bulb.
Usually the bulb surges bright for a second or two, then dims down as the capacitors are charged. If there is a problem, the bulb will become very bright immediately and stay bright, and with one hand on the plug, can be quickly de-energized. This is less of a hard start than a straight wire, is highly recommended to avoid smoked parts.
Just double, triple check each connection one wire at a time before you power anything up.
Also I would install some fuses starting with one on the A/C, before the transformer, and four more, one on each power wire to the two boards.
There is a very handy device made from a screw-in incandescent light bulb fixture, 60w incandescent bulb, standard plug/wire. By inserting the bulb filament in series with the A/C, you create a softer connection that will indicate if there is a problem by illuminating the bulb.
Usually the bulb surges bright for a second or two, then dims down as the capacitors are charged. If there is a problem, the bulb will become very bright immediately and stay bright, and with one hand on the plug, can be quickly de-energized. This is less of a hard start than a straight wire, is highly recommended to avoid smoked parts.
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