Hi Jackinnj
Well, up to now, on power amplifiers I use x-formers whose VA is two to three times the maximum output power of the amplifier. My observation on better sound with oversized x-formers is based on listening to levels way below (I would say not more than 5-10%) the maximum output of the amplifier.
For pre amplifiers, tuners, ect. the x-formers I use are three to ten times the required power.
In all the cases (low and high power equipment) the core of the x-formers does not raise more than 20-25 d. celsius above ambient temperature.
As for the efficiency (by definition), oversized x-formers are a waste of energy (but in case you are reffering to the higher efficiency of the higher power x-former per se, I have to agree with you).
By the " " over the regulated, I believe you mean "stressed".
The fact is that I do not stress them.
Your point is valid though, and I wish that it would fit in my case.
Regards
George
Well, up to now, on power amplifiers I use x-formers whose VA is two to three times the maximum output power of the amplifier. My observation on better sound with oversized x-formers is based on listening to levels way below (I would say not more than 5-10%) the maximum output of the amplifier.
For pre amplifiers, tuners, ect. the x-formers I use are three to ten times the required power.
In all the cases (low and high power equipment) the core of the x-formers does not raise more than 20-25 d. celsius above ambient temperature.
As for the efficiency (by definition), oversized x-formers are a waste of energy (but in case you are reffering to the higher efficiency of the higher power x-former per se, I have to agree with you).
By the " " over the regulated, I believe you mean "stressed".
The fact is that I do not stress them.
Your point is valid though, and I wish that it would fit in my case.
Regards
George
Hi Jacco
My understanding is that that the power factor of a x-former changes with the drawn current. For low current it is below 1.
It increases to 1 as the drawn power reaches the rated VA of the x-former (on well designed x-formers).
Please correct me if am wrong.
Regards
George
My understanding is that that the power factor of a x-former changes with the drawn current. For low current it is below 1.
It increases to 1 as the drawn power reaches the rated VA of the x-former (on well designed x-formers).
Please correct me if am wrong.
Regards
George
Hi, Jacco,
How to calculate the diode rating needed? For example 100W to 4ohm and 500W to 4ohm, what is the diode current (and voltage) rating needed?
How to calculate the diode rating needed? For example 100W to 4ohm and 500W to 4ohm, what is the diode current (and voltage) rating needed?
George,
my mistake, using the term power factor was confusing.
The continuous power draw for the A9 is about the same percentage of the nominal VA rating of the transformer as for the A90 with a higher bias and bigger toroid.
For class A amps, 3 to 4 times the dissipation is plenty extra.
3 times the continuous output in 8 ohm for a class AB amp.
The factor 10 seems to be like a general for preamps, probably because 6VA transformers usually stink.
David,
why not ask one the audio designers overhere, i'm just an audio librarian.
If you are talking rectifying bridges, i've often seen the minimal approach used by economical audio designers on class AB amplifiers.
Twice the ac voltage of the secondaries for the voltage rating, because of having the secondaries in series across the bridge, plus the additional extra for voltage surges.
And the current of the continuous power in 4 ohms for the current rating of the bridge rectifier.
Often, the current rating is taken even a bit lower than that because it's class AB.
Rectifying diodes usually have tremendously high peak current capability because of thermal reserves.
The reason why rectifying diodes on class A amplifiers have to be much more sturdy, and you have to use rectifying bridges that can be heatsinked.
On class AB amplifiers i've used the plastic rect. blocks without any issues in the past. For example, a B80/C5000 for 30Vac secondaries of a 150 watt in 4 ohm class AB amplifier.
Oversizing diodes seems common practice as well, not sure if the square metal rect. blocks are even sold below 10 amps and 100volts.
my mistake, using the term power factor was confusing.
The continuous power draw for the A9 is about the same percentage of the nominal VA rating of the transformer as for the A90 with a higher bias and bigger toroid.
For class A amps, 3 to 4 times the dissipation is plenty extra.
3 times the continuous output in 8 ohm for a class AB amp.
The factor 10 seems to be like a general for preamps, probably because 6VA transformers usually stink.
David,
why not ask one the audio designers overhere, i'm just an audio librarian.
If you are talking rectifying bridges, i've often seen the minimal approach used by economical audio designers on class AB amplifiers.
Twice the ac voltage of the secondaries for the voltage rating, because of having the secondaries in series across the bridge, plus the additional extra for voltage surges.
And the current of the continuous power in 4 ohms for the current rating of the bridge rectifier.
Often, the current rating is taken even a bit lower than that because it's class AB.
Rectifying diodes usually have tremendously high peak current capability because of thermal reserves.
The reason why rectifying diodes on class A amplifiers have to be much more sturdy, and you have to use rectifying bridges that can be heatsinked.
On class AB amplifiers i've used the plastic rect. blocks without any issues in the past. For example, a B80/C5000 for 30Vac secondaries of a 150 watt in 4 ohm class AB amplifier.
Oversizing diodes seems common practice as well, not sure if the square metal rect. blocks are even sold below 10 amps and 100volts.
Hi,
The smoothing capacitance rule I have seen many times and adopted is 2mF to 3mF per A of peak output current.
eg. 100W into 8r gives Vpeak=40Vpk and Ipeak=5Apk.
this requires 10mF to 15mF for 8ohm.
But if this same amplifier is designed to drive 4ohm loads then the Vpeak remains the same and Ipeak doubles requiring double the smoothing capacitance i.e. 20mF to 30mF for 4ohm.
Similarly the transformer can be rated @ 1 to 2 times the maximum (total for stereo) output power and most find that 1.5times works well for good value. Small, but diminishing, improvements are available upto about 3times for an unregulated PSU.
The smoothing capacitance rule I have seen many times and adopted is 2mF to 3mF per A of peak output current.
eg. 100W into 8r gives Vpeak=40Vpk and Ipeak=5Apk.
this requires 10mF to 15mF for 8ohm.
But if this same amplifier is designed to drive 4ohm loads then the Vpeak remains the same and Ipeak doubles requiring double the smoothing capacitance i.e. 20mF to 30mF for 4ohm.
Similarly the transformer can be rated @ 1 to 2 times the maximum (total for stereo) output power and most find that 1.5times works well for good value. Small, but diminishing, improvements are available upto about 3times for an unregulated PSU.
jacco vermeulen said:
Excuse me Mr Jacco.
When you speak of "transformer efficiency" you mean "regulation factor"?
Actually I notice that from about 500 VA the regulation stays constant, at about 5% for the better brands.
Thanks and regards,
beppe
transformer regulation
The better brands will go down to the region of 3% to 4% regulation at around 1kVA.
By design (and cost) transformers can go even lower.
I have some cheap 625VA (bought new in 1980 when copper was relatively cheaper) that achieve 4% regulation.
The better brands will go down to the region of 3% to 4% regulation at around 1kVA.
By design (and cost) transformers can go even lower.
I have some cheap 625VA (bought new in 1980 when copper was relatively cheaper) that achieve 4% regulation.
Re: transformer regulation
Thank you very much Mr Andrew, very impressive figures indeed.
My present monos have ILP toroids, they look about 300VA things.
Not bad for amps rated 90W/4 ohm I believe.
I recapped them (they are 25 years old now) and went for 22.000uf per rail per channel (BHC ALS30 series caps).
Now I understand I have exaggerated a little.
Maybe 4700 were more than enough at a much lower cost.
For the umpteenth time I repeat that discover the paramount importance of the transformer in an audio amp has been a historical revelation, at least for me.
Thank you very much indeed.
My best wishes,
beppe
P.S. now if only I could find a very good and cheap line stage, I would be done for a long, long time ....
Thank you very much Mr Andrew, very impressive figures indeed.
My present monos have ILP toroids, they look about 300VA things.
Not bad for amps rated 90W/4 ohm I believe.
I recapped them (they are 25 years old now) and went for 22.000uf per rail per channel (BHC ALS30 series caps).
Now I understand I have exaggerated a little.
Maybe 4700 were more than enough at a much lower cost.
For the umpteenth time I repeat that discover the paramount importance of the transformer in an audio amp has been a historical revelation, at least for me.
Thank you very much indeed.
My best wishes,
beppe
P.S. now if only I could find a very good and cheap line stage, I would be done for a long, long time ....
Regardless of class (i.e., for a class A it would be that number for the idling current)?AndrewT said:
Re: Re: transformer regulation
In a class A amp with capacitance multiplier power supplies (kind of regulation, but designed for efficiency with ultra-low dropout that tracks the long-time constant variation of the mains), I find no difference in sound if I double the VA (actually hook up a second identical transformer in parallel with the first one), where the initial is twice the W draw of the amp.beppe61 said:
smoothing capacitance
2mF to 3mF/Apk applies to low bias ClassAB.
Nelson Pass & Krell (KSA50) goes to about 6mF/Apk to 10mF/Apk for ClassA.
I have seen others adopt similar smoothing and it's down to minimising hum at near zero output voltage but with significant ripple on the heavily loaded PSU.
not as far as I have read.Nixie said:
2mF to 3mF/Apk applies to low bias ClassAB.
Nelson Pass & Krell (KSA50) goes to about 6mF/Apk to 10mF/Apk for ClassA.
I have seen others adopt similar smoothing and it's down to minimising hum at near zero output voltage but with significant ripple on the heavily loaded PSU.
Here's the capacitance multiplier I was talking about, I think the page author is a member of diyaudio (Mr. Evil): http://mrevil.pwp.blueyonder.co.uk/amp/amp4/sub/psu2.shtml
I'm using on each rail C-L-C-mult-C, where the Cs are 35 mF each. Definitely overkill for a 100 W class A (amp draw about 300 W). Transformer is 600 VA only. Tried adding a second one in parallel and there was no difference, just very slightly higher voltage.
I'm using on each rail C-L-C-mult-C, where the Cs are 35 mF each. Definitely overkill for a 100 W class A (amp draw about 300 W). Transformer is 600 VA only. Tried adding a second one in parallel and there was no difference, just very slightly higher voltage.
Re: Re: Re: transformer regulation
Thank you Sir.
For class AB amp is the same ?
Since I knew that very good sound can be obtained from class AB amps I lost a little my interest in class A designs.
Kind regards,
beppe
Thank you Sir.
For class AB amp is the same ?
Since I knew that very good sound can be obtained from class AB amps I lost a little my interest in class A designs.
Kind regards,
beppe
Dear Mr George, thank you very much for the interesting link.
If I am not wrong an increase in capacitance does have a beneficial effect.
What is your opinion ?
Kind regards,
beppe
Hi beppe
Theory predicts it.
Steady-state measurements prove it.
Yet, soundwise results are not always positive.
Where is the fault?
Theory can not be wrong (but it may very well be incomplete, though I do not believe this is the case).
Most probably it is the “strays” of the actual implementation and the increase of the polluting electromagnetic radiation due to the increased charging currents.
(I can not help but think of the difficulty one faces driving a powerful sport bike like Ducati for the first half hour. Specs perfect, but you feel like you are riding on the back of a mule trying to throw you down. Is it the bike no good?)
Regards
George
Theory predicts it.
Steady-state measurements prove it.
Yet, soundwise results are not always positive.
Where is the fault?
Theory can not be wrong (but it may very well be incomplete, though I do not believe this is the case).
Most probably it is the “strays” of the actual implementation and the increase of the polluting electromagnetic radiation due to the increased charging currents.
(I can not help but think of the difficulty one faces driving a powerful sport bike like Ducati for the first half hour. Specs perfect, but you feel like you are riding on the back of a mule trying to throw you down. Is it the bike no good?)
Regards
George
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