Good morning to All,
the mains voltage transformers inside the amplifiers are still quite mysterious objects to me. I have often read that the quality of the transformer has a decisive impact on the performance of the amplifier. For example, the secret behind the successes of brands like Naim would be the transformers designed and built to very high quality standards.
So I have questions running through my head. But in particular one.
How important is the current output capacity of a transformer for the final sound quality? I believe very much
Let's take a 500VA unit for example. Now you can get 500 with 100V (i.e. +/-50V) and 5A ... but also with 50V (+/-25V) and 10A.
is there an optimum ratio between V and A in a transformer to be used in an audio amplifier ?
In the case above we go from a ratio of 20 to 5 .... a big difference
The lower the better ?
I do not know for sure but i suspect that the transformers used by Naim are low in voltage and high in current ? is this a recipe for good sound ?
Thanks and best regards, gino
the mains voltage transformers inside the amplifiers are still quite mysterious objects to me. I have often read that the quality of the transformer has a decisive impact on the performance of the amplifier. For example, the secret behind the successes of brands like Naim would be the transformers designed and built to very high quality standards.
So I have questions running through my head. But in particular one.
How important is the current output capacity of a transformer for the final sound quality? I believe very much
Let's take a 500VA unit for example. Now you can get 500 with 100V (i.e. +/-50V) and 5A ... but also with 50V (+/-25V) and 10A.
is there an optimum ratio between V and A in a transformer to be used in an audio amplifier ?
In the case above we go from a ratio of 20 to 5 .... a big difference
The lower the better ?
I do not know for sure but i suspect that the transformers used by Naim are low in voltage and high in current ? is this a recipe for good sound ?
Thanks and best regards, gino
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The ratio is power output in Watts, add the efficiency (50Watt output at 50% efficiency would need a 75VA supply).
The more copper in the winding combined with the way the primary and secondary windings are placed on the bobbin for E-I transformers or proximity for toroidial, the heavier current that can be transformed from the primary (mains supply) to the secondary (low voltage supply).
The more iron used means the more efficient the transformer will be at lower frequencies because the induction is higher.
The more copper in the winding combined with the way the primary and secondary windings are placed on the bobbin for E-I transformers or proximity for toroidial, the heavier current that can be transformed from the primary (mains supply) to the secondary (low voltage supply).
The more iron used means the more efficient the transformer will be at lower frequencies because the induction is higher.
i asked that question to a famous audio guru, his answer was to get the biggest that fits into your box.....
we design out traffo for psu that will pass FTC testing for a claimed power output, but then we listen to the amp using music, so herein lies the rub, music power is but a small portion of sine wave power....as much as 10 to 1.....
we design out traffo for psu that will pass FTC testing for a claimed power output, but then we listen to the amp using music, so herein lies the rub, music power is but a small portion of sine wave power....as much as 10 to 1.....
a traffo rated for 500va is for a certain temp rise and fixed losses, it does not mean you can not draw 600va out of that, you can, but duty cycle is important, for how long?, if just for seconds at a time, temp rise will not be high....
Hi thanks a lot for the very kind and valuable advice. Speaking of a stereo amp this 50W would mean 25W/channel. But i understand that power varies with load impedance. That is a another doubt for me ... i mean 25W on 8 ohm are not like 25W on 4 ohm.
VA rating instead i can usually found from the specs or on the back of the unit ... the max power consumption i mean. I always look at the back to get an idea of the potential of an amp
Thank you very much again. My main question is ... how important is the max current that a transformer can provide to the output stages ?
my guess is a lot because it can happen that a lower wattage amp sounds more powerful than a higher wattage amp especially on demanding loads.
Is it all in the current that the transformer can provide to the output devices ?
Can a 40W/channel Naim sound more powerful than a 80W/channel with a weaker transformer ? my answer is yes.
So we have to look always to transformers ... they are the first and decisive important bottleneck for power.
Then when i think that the transformer is by far the most expensive part in a power amp ... anything becomes clear. The good ones are more expensive.
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Hi thanks a lot for the very kind and helpful advice.
My feeling is that for home listening it would be better to look at low wattage amps but with powerful power supply inside.
Low wattage can use lower V rails ... so a low V and high A transformer can be used. If high SPLs are needed better to select a high efficiency speaker that could be used with low wattage amps.
I mean ... 50W on a Klipsch can provide very high SPLs.
But it is in the bass that the very differences can be heard. The higher current amp will sound stronger and better.
I listen to a quite high W pro amp on a pair of difficult Tannoy monitors. Even rising the volume the sound remained flat ... almost no bass to speak of. 😕 I am sure a lower W Naim could have sound better 😱
Some speakers seem to need more current than voltage.
I think that a +/-20V transformer can be ok for a 50W amp.
The best amps have all great transformers ... always.
And they are expensive. Like caps.
no one but your wallet with prevent you from using bigger traffos, myself is a fan of that, i like to overbuild traffos as i design my own....
A very good question. But it cannot eat what is not served by the psu.
But yes ... and i think that they put flimsy transformers and protection because they skimp also on heatsink.
I see often very little heatsink that look undersized for continuous operation at the max rated power.
Pro-amps have all fans for that reason. They are supposed to work very hard for prolonged periods.
A designer of respected pro amps once gave that rule of thumb:
- take the expected power of the amp for a given impedance (picking the impedance lower than a nominal rating).
- for a class AB amp, you need about 2/3 of that power for your transformer VA rating.
- for a class D amp, about 1/2.
Only test signals run an amp at full power for an extended period of time which is rather pointless as we amplify musical signals.
Class A amps are another problem.
Edit: the above assume you picked your power rails voltages sensibly with respect to the load.
- take the expected power of the amp for a given impedance (picking the impedance lower than a nominal rating).
- for a class AB amp, you need about 2/3 of that power for your transformer VA rating.
- for a class D amp, about 1/2.
Only test signals run an amp at full power for an extended period of time which is rather pointless as we amplify musical signals.
Class A amps are another problem.
Edit: the above assume you picked your power rails voltages sensibly with respect to the load.
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I see. I understand that it is a very fundamental part in an amplifier.
I have seen the many recent commercial amps have very nice look but they have usually weak transformers. It seems to me that they prefer to invest in the look of the units instead of investing in better parts ?
And i am talking about amps that are not exactly cheap.
An example here
DENON PMA-2500NE - Denon Singapore
310W of max consumption= transformer VA rating ... a value that can be found in many decent old integrateds at a fraction of the price ?
In a 3kUSD amp i would expect to find a 1kVA transformer ... considering how important it can be for the sound. And PS caps like Coca Cola cans ...
I like this page for the well engineered info and a description that most people would understand:
Taming the LM3886 Chip Amplifier: Power Supply Design – Neurochrome
There is no voodoo in PSU design; you can pretty much calculate what you need and is appropriate for the amp.
Of course you have the choice to account for permanent sine wave testing or count in a more realistic crest factor of music.
A totally oversized transformer just shows lack of understanding and creates problems rather than solve any. (like inrush currents being exceedingly high, so the stupid DIYer tends to use too big a fuse
)If you are worried about rail voltage sag (which can of course be a problem, especially with the more simpler amps), you have to regulate your rails anyway.
Hi thanks a lot and very interesting.
If i understand right a 100W/4 ohm class AB mono amp should have at least a 100 x 2/3= 66 VA transformer ? not that much ... i honestly thought quite more.
i am not that hot on class A 🙂 ... as i understand very good sound can be obtained with good class AB units. i like cold amps with warm sound.
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@ginetto61: yes. But that assumes your amp doesn't "waste" VA as unnecessary voltage. So a bit above 30VDC voltage rails in your case.
I found the reference back: https://www.diyaudio.com/forums/sol...spect-wattage-power-amplifier.html#post432191
I found the reference back: https://www.diyaudio.com/forums/sol...spect-wattage-power-amplifier.html#post432191
Thanks again. This formula changes completely my belief.
I am reading it with the biggest attention. Thanks again and kind regards, gino
Audio tends to run surprisingly little power on average (The usual practise for PA amps that are typically run much harder then domestic stuff) is to do the thermal design assuming 1/8th duty cycle).
Transformers have massive thermal mass and are (for the mains transformer and assuming reasonable design) basically unimportant to the audio quality of the doings because they spend most of their time disconnected! For a cap input power supply (The usual kind for a SS amp) the transformer is only meaningfully connected when the bridge rectifier is conduction, and that only happens when the secondary voltage exceeds the voltage on the caps.
They do however have that heavy metal quality to them that encourages people to over size the things (Which increases stresses on the diodes and caps as the conduction angle falls).
Class A is of course a different game.
Transformers have massive thermal mass and are (for the mains transformer and assuming reasonable design) basically unimportant to the audio quality of the doings because they spend most of their time disconnected! For a cap input power supply (The usual kind for a SS amp) the transformer is only meaningfully connected when the bridge rectifier is conduction, and that only happens when the secondary voltage exceeds the voltage on the caps.
They do however have that heavy metal quality to them that encourages people to over size the things (Which increases stresses on the diodes and caps as the conduction angle falls).
Class A is of course a different game.
I always add 50 to 100% for transformer power.
While music isnt a pure single sine wave it is made up of sine waves.
Then it depends how much the music is compressed as to how much power it needs.
Heavy compression needs more power to reproduce.
Then it gets complicated by current impulses into smoothing caps which are very short bursts taken from peak of transformer output.
While music isnt a pure single sine wave it is made up of sine waves.
Then it depends how much the music is compressed as to how much power it needs.
Heavy compression needs more power to reproduce.
Then it gets complicated by current impulses into smoothing caps which are very short bursts taken from peak of transformer output.
Home Audio is LIGHT duty so assuming 1/8 duty cycle is fine.
Now PROFESSIONAL use, such as PA, DJ or Musical Instrument use is a VERY different thing, and you need VA rating at least 150% of maximum (clean continuous/RMS) power output, all channels driven if more than one available.
Now PROFESSIONAL use, such as PA, DJ or Musical Instrument use is a VERY different thing, and you need VA rating at least 150% of maximum (clean continuous/RMS) power output, all channels driven if more than one available.
That doesn't make any sense. Nor does it apply to the laws of physics.
ANY amplifier MUST have at least the same number of watts being supplied to it as that it is producing at its output.
Maybe I am misreading your post ? A 100W Class AB amplifier would require somewhere in the region of a 160VA transformer (MONO).
The power supply needs to be low impedance so that bass transients are not lost. This of course is tied into the design of the amplifier. A high quality amplifier would benefit from a transformer with heavier secondary windings.
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No you're not misreading my post. A 100W class AB amp could quite happily work on a 66VA transformer (the voltage/current specs depend on the intended load though). Not full time for full scale test signals but quite happily at high power for music with an average crest factor of 10db.
The link given in post 12 goes to Tomchr's website and goes into the technical details.
The link given in post 12 goes to Tomchr's website and goes into the technical details.