Hi
To a start, this is my first post, was a hi-fi geek in the "old" days but have never tried to build anything before.
I am trying to build my first amplifier, just lo learn and to get better at it.
Now I am getting to selecting a transformer.
And I am wondering about if I get, lets say a 300VA I have to specify how high voltage I want and thereby decide how much current there are, if the speaker needs it.
I could choose 20V and have 15A or select a 60V with 5A.
What effect would it have on some "standard" 8Ohm 90db speakers?
To a start, this is my first post, was a hi-fi geek in the "old" days but have never tried to build anything before.
I am trying to build my first amplifier, just lo learn and to get better at it.
Now I am getting to selecting a transformer.
And I am wondering about if I get, lets say a 300VA I have to specify how high voltage I want and thereby decide how much current there are, if the speaker needs it.
I could choose 20V and have 15A or select a 60V with 5A.
What effect would it have on some "standard" 8Ohm 90db speakers?
A transformer for an audio power amplifier has to be adapted to the type of amplifier (bridged/non-bridged) and the impedance of the speakers you intend to use.
The bridged amplifiers use a single supply voltage (for instance 40V), the non-bridged typically a symmetrical supply voltage (for instance +/- 40V).
The power amplifier you choose for has got a maximum operating voltage you have to respect (stay below).
For the speaker impedance you intend to use, you choose the current rating of the transformer such that at the maximum voltage the amplifier will operate, the transformer has got the current rating which two speakers, with the intended impedance, consume.
Thus, you do not buy a transformer and then decide for an amplifier, it is the other way around:
* choose your speaker impedance (and speaker maximum power rating),
* decide for the amplifier you want to build,
* from the maximum voltage the amplifier can operate at, you calculate the nominal voltage of the transformer,
* with the nominal voltage of the transformer and the speaker impedance, you calculate the current needs.
So, you better look for the type of amplifier you would like to build. We can help you deciding for a transformer afterwards.
The bridged amplifiers use a single supply voltage (for instance 40V), the non-bridged typically a symmetrical supply voltage (for instance +/- 40V).
The power amplifier you choose for has got a maximum operating voltage you have to respect (stay below).
For the speaker impedance you intend to use, you choose the current rating of the transformer such that at the maximum voltage the amplifier will operate, the transformer has got the current rating which two speakers, with the intended impedance, consume.
Thus, you do not buy a transformer and then decide for an amplifier, it is the other way around:
* choose your speaker impedance (and speaker maximum power rating),
* decide for the amplifier you want to build,
* from the maximum voltage the amplifier can operate at, you calculate the nominal voltage of the transformer,
* with the nominal voltage of the transformer and the speaker impedance, you calculate the current needs.
So, you better look for the type of amplifier you would like to build. We can help you deciding for a transformer afterwards.
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You also need to decide the type of amplifier: Class A, B or D?
How will you use it: real music with wide dynamic range at normal domestic loudness levels, or heavily compressed music at the loudest levels your neighbours will tolerate?
The answers to these two questions could vary the needed transformer VA by a significant factor.
How will you use it: real music with wide dynamic range at normal domestic loudness levels, or heavily compressed music at the loudest levels your neighbours will tolerate?
The answers to these two questions could vary the needed transformer VA by a significant factor.
You are great!
My goal is to build my own system but starting with the amplifier.
I would like it to drive any speaker I can throw at it.
The design will be a class AB dual mono with two separated transformers.
Each transformer shall be a (don't know the name) dual rail (i.e 300VA with 26 - 0 - 0 - 26 VAC) 6 amp.
The amp shall play most classic, jazz, flute, solo song, violin and the big church orgel in a volume from low background to realistic levels.
My goal is to build my own system but starting with the amplifier.
I would like it to drive any speaker I can throw at it.
The design will be a class AB dual mono with two separated transformers.
Each transformer shall be a (don't know the name) dual rail (i.e 300VA with 26 - 0 - 0 - 26 VAC) 6 amp.
The amp shall play most classic, jazz, flute, solo song, violin and the big church orgel in a volume from low background to realistic levels.
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Well, I would advise updating your profile on the forum to show where you are located. I know it's a bit old fashioned using flags but it works. Because choosing a trafo may depend on your choice of suppliers. In the USA I would shop here: Transformers - Page 1 - AnTek Products Corp
They make good stuff at very good prices.
I think you're on the right track with 300VA, you might get away with something smaller. I am happy using 180VA to 200VA.
Without going for exotic power hungry speakers you'll likely do just fine with a 50W to 100W power amp. If you want to be able to throw any kind of speaker at your amplifier then it's harder to advise as I have no experience with outlandish stuff.
I favour +/-42V for power rails for Class AB amplifies - more or less what I use in my projects at least. Allows the use of 50V capacitors for starters although I do use 63V quite often as I feel it offers some benefits. Anyhow, I think something in the range of 28Vac to 30Vac secondaries is the sweet spot.
They make good stuff at very good prices.
I think you're on the right track with 300VA, you might get away with something smaller. I am happy using 180VA to 200VA.
Without going for exotic power hungry speakers you'll likely do just fine with a 50W to 100W power amp. If you want to be able to throw any kind of speaker at your amplifier then it's harder to advise as I have no experience with outlandish stuff.
I favour +/-42V for power rails for Class AB amplifies - more or less what I use in my projects at least. Allows the use of 50V capacitors for starters although I do use 63V quite often as I feel it offers some benefits. Anyhow, I think something in the range of 28Vac to 30Vac secondaries is the sweet spot.
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choice of the transformers for a power amp, starts with the power the amp will draw from the power traffo..
then class of service, while class d and AB can get by with smaller traffo than a class A would, this is also a primary consideration..
then temperature rise, how hot are you willing to allow in your power traffo...?
armed with all these info, then you can go look at vendors' catalogues for a suitable traffo..
i design and build traffos in all of my projects, choosing is not a big deal then...
then class of service, while class d and AB can get by with smaller traffo than a class A would, this is also a primary consideration..
then temperature rise, how hot are you willing to allow in your power traffo...?
armed with all these info, then you can go look at vendors' catalogues for a suitable traffo..
i design and build traffos in all of my projects, choosing is not a big deal then...
WOW great answers! As stated at first, I do not know what a i.e. 10v 30A contra a i.e. 30V 10A would mean for a amplifier.
I am wondering what makes you choose one configuration over an other, you newer know what speaker you have in two years, you can't know your input devices and so on.
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If you are just starting out in DIY audio you should know the secret they don't tell you - it will suck you in, you will be addicted, no escape. You will learn so much over time that whatever you build first will be replaced with what you build next. May as well not worry too hard first time around and start making steps...
Thanks again to all!
TonyTecson I do not understand your last comment.
Bigun lol my girlfriend said something in that stile, she said that If I was smart, I should bye the "best" transformer, since she would bet that it would not be the last amplifier in my life and I therefor (to save money) should bye transformers, that could be moved from project to project
After all your comments, and hers
This is what I am thinking:
Buy two 600VA 60V 10A but in a 300V to 75V version and only "feed" it 240V, I have hard that it is better to select higher voltage and give it less, so it never work at maximum voltage
What are you saying?
TonyTecson I do not understand your last comment.
Bigun lol my girlfriend said something in that stile, she said that If I was smart, I should bye the "best" transformer, since she would bet that it would not be the last amplifier in my life and I therefor (to save money) should bye transformers, that could be moved from project to project
After all your comments, and hers
This is what I am thinking:
Buy two 600VA 60V 10A but in a 300V to 75V version and only "feed" it 240V, I have hard that it is better to select higher voltage and give it less, so it never work at maximum voltage
What are you saying?
26V-0/0-26V (AC) will leave you close to -40V/+40V in idle mode after rectification. Not a bad choice. -40V/+40V will allow around 80W in 8 Ohm and 160W in 4 Ohm. Two 300VA transformers will allow you to operate with 4-8 Ohm without heating problems.
Michala Petri for full volume.
There is no such thing as a universal transformer taking all future projects into account. When you get a bit used to DIY, you will understand why.
I will suggest you amplifiers based on the LM3886 chip or the TDA7293 chip for a start. On this forum, most will probably say the LM3886 sounds the best. As it is your first amplifier, I will not recommend you an amplifier made with only discrete components. With the same power supply(ies) you can make very complicated designs later. The chip amplifiers will be cheap.
For each power supply, use 10000uF to 22000uF decoupling on each rail.
NB: Standard transformers have 230V or 115V inputs, not 300V (to 75 V). Keep it simple and cheap - use standard components until you are well acquainted with DIY.
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Yes hi does!
I am properly aiming for 8 ohm's speakers with db's from 85 to 105.
But what I do not understand, is that a fabricant of amplifier can't know the speaker there amplifier have to drive and they can't know if it has to play heavy metal or Eric Clapton all day.
How do they select the transformer?
Many amplifier manufacturers design their amplifier apparatuses such that they work best with a certain speaker loading. It is not so that if the power supply is optimized for 4 Ohm speakers, you have no sound if you use 8 Ohm speakers instead. You just have much less power with 8 Ohm and the same size of transformer could have been designed to give more amplifier power had the manufacturer known it would be used with 8 Ohm instead.
Yes, why do you build an amplifier with 0.001% THD and then play "death metal" on it? (my immediate excuses to the supporters of death metal for any perceived discrimination!)
Yes, why do you build an amplifier with 0.001% THD and then play "death metal" on it? (my immediate excuses to the supporters of death metal for any perceived discrimination!)
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I feel that I am asking an impossible question or don't understand your answers but it sounds so logical and "easy" for me.
If you chose to build an amplifier that shall play into 8ohm speakers of different sorts.
It can't be enough to just say: use 300W and you are fine.
Wattage are Voltage times current.
A 5V 60A is not the same as a 60V 5A, even if they both are 300VA.
Can no one please knock into my head, what the different of higher voltage is contra higher current?
If you chose to build an amplifier that shall play into 8ohm speakers of different sorts.
It can't be enough to just say: use 300W and you are fine.
Wattage are Voltage times current.
A 5V 60A is not the same as a 60V 5A, even if they both are 300VA.
Can no one please knock into my head, what the different of higher voltage is contra higher current?
To say it like this: you bring your 230V Danish electrical shaver to the US and connect it to their 115V, but it will be of little use. The shaver impedance (motor design) is not matching the voltage.
You buy an incandescent lamp (glow-type) intended for 230V and use it in the US with 115V -> little light because the resulting current with that impedance is reduced. Then, you buy an incandescent lamp intended for 115V in the US and take it back to Denmark. With 230V you have a very bright light for a second and it is over: the impedance did not match the voltage and the resulting current became too much.
"Ohm's law" is terribly useful.
If you tell me you have a transformer with 40 Volts and 8 Amperes (320VA, nominally), I can find an optimum impedance (40/8 = 5 Ohm) where the 40 Volts result in the 8 Amperes through that optimum impedance. If I increase the impedance (say to 10 Ohm), the 40 Volts will no longer be sufficient to have 8 Amperes running through the impedance, but only 4 Amperes (with 10 Ohm). If I lower the impedance to 2 Ohm, the 40 Volts should result in 20 Amperes, but that is far above the 8 Amperes and the transformer voltage will be pulled down while the transformer overheats and burns from excessive current.
For audio, you can (typically) choose between 4, 6 or 8 Ohm impedance. Thus, you have to adapt the supply voltage and resulting current depending on the impedance and how much power you want dissipated in the load.
5V/60A would only allow little power in a 4 Ohm impedance, but 5V/60A can handle many 4 Ohm loads in parallel.
60V/5A would not be sufficient to handle even a single 4 Ohm impedance because 4 Ohm on 60V would require 15A of current.
The principle is exactly the same for audio amplifiers though the calculations are a bit more complex because you rectify the AC voltage from the transformer.
You buy an incandescent lamp (glow-type) intended for 230V and use it in the US with 115V -> little light because the resulting current with that impedance is reduced. Then, you buy an incandescent lamp intended for 115V in the US and take it back to Denmark. With 230V you have a very bright light for a second and it is over: the impedance did not match the voltage and the resulting current became too much.
"Ohm's law" is terribly useful.
If you tell me you have a transformer with 40 Volts and 8 Amperes (320VA, nominally), I can find an optimum impedance (40/8 = 5 Ohm) where the 40 Volts result in the 8 Amperes through that optimum impedance. If I increase the impedance (say to 10 Ohm), the 40 Volts will no longer be sufficient to have 8 Amperes running through the impedance, but only 4 Amperes (with 10 Ohm). If I lower the impedance to 2 Ohm, the 40 Volts should result in 20 Amperes, but that is far above the 8 Amperes and the transformer voltage will be pulled down while the transformer overheats and burns from excessive current.
For audio, you can (typically) choose between 4, 6 or 8 Ohm impedance. Thus, you have to adapt the supply voltage and resulting current depending on the impedance and how much power you want dissipated in the load.
5V/60A would only allow little power in a 4 Ohm impedance, but 5V/60A can handle many 4 Ohm loads in parallel.
60V/5A would not be sufficient to handle even a single 4 Ohm impedance because 4 Ohm on 60V would require 15A of current.
The principle is exactly the same for audio amplifiers though the calculations are a bit more complex because you rectify the AC voltage from the transformer.
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You are starting backwards
First you decide what speakers are you going to use.
Nothing too complex:
* will you drive them quietly in an appartment at night, listening to Jazz or string quartets? 15W is more than adequate.
* general purpose, just on some weekend play them loudish? 30 to 60W per channel will do in most cases.
* call the Police annoy the whole block Heavy Metal ? he he, 100/150W per channel will accomplish that
Speaker impedance comes next but is easier, most speakers are 8 ohm but quite a few are 4 ohm, so choose an amplifier which can drive 4 ohms easily.
Once you have chosen the amplifier, the circuit will *ask* for a certain power supply.
All state voltage at the schematic itself, a few even suggest a specific transformer or give its ratings in detail (either in Amperes or VA); if not assume VA 150% to 200% the RMS output and you won´t be wrong.
Practical example: suppose you choose a 100W into 8 ohm amplifier.
It will use rails around +/-45V , or 90V rail to rail, the schematic or assembly manual will clearly state that.
Then you need a 150 to 200VA transformer . (150 ton 200% RMS rating)
Now 45+45V DC mean 0.707*45V AC=32+32VAC windings (64V C.T. or end to end).
How much current?: 150/64=2.4A ; 200/64=3.12A .
So a 32+32VAC , 2.5 to 3A transformer will be fine for such amp.
Repeat the calculations for what your schematic asks for.
That´s why I said "you started backwards"
, in fact the proper path is : actual needs > amplifier choice > supply choice > calculate what transformer you need.It´s the last step, not the first one
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