I see where you are coming from.
I would expect a 100W amplifier to be able to supply 100W with overhead.
I would expect a 100W amplifier to be able to supply 100W with overhead.
I agree.
If a 66V/A transformer feeds the amplifier, it becomes a 66W amplifier no longer capable of producing 100W RMS.
If a 66V/A transformer feeds the amplifier, it becomes a 66W amplifier no longer capable of producing 100W RMS.
Thanks a lot and very interesting. This PSU design issue is very confusing to me. Let's say that i would like to upgrade a little a psu. Better to put bigger and better caps than a higher current mains voltage transformer ? i am asking because i read many times about the benefits of having a high current transformer ... it made sense to me. I understand that a more powerful transformer could put under stress the output devices and often they are not heatsinked well enough. But this i can mod also. I like a lot modding ... taking something basically sane (and with nice sound) and improve it.
There are some simple design famous for great sound ... and often their limits are in the psu and heatsinks. Too small parts used.
Hi and thanks a lot. This is what i also think. The max power that i could get from an amp is given by the transformer VA x its efficiency ?
Anyway there could be an almost trivial test to do. To put a analog voltmeter across the PSU big caps and watch the needle ... if it stays still even during loud passages then the PSU it is up to the task. If it sags the PSU (i.e. transformer plus caps) is undersized.
One more comment on low impendance secondaries.
A friend of mine has an impedance meter that he uses for his speakers projects ... we measured two same VA transformers secondaries.
One had 2-3 ohm of impedance ... the other one about 100 😱
Again ... practically same VA.
I am pretty sure the 1st one would have been a much better choice to power a power amp.
Another story ... i do not know if this applies to the discussion.
I made a dummy load with two 10ohm/100W resistors in parallel to test some amps. (My thinking is that if an amp is good at delivering current to a 5 ohm load it should stay warm and heat up a lot the dummy load ... i know ... it is trivial ... like me)
I connected a pro amp i have. (by the way ... this amp has very weak bass compared to others on the same speakers. It does not push the woofers well)
So i connected the dummy load and put on some music with the volume at 12". Well the transformer got very very hot and the output devices cold 😱😱😱
I was not able to measure the impendance on the secondaries ... but i am pretty sure that i would have found an high ohm value.
That transformer is very bad. My guess is that it must be also very cheap considering how much i paid the entire amp.
Again the very good transformers together with the big psu caps are the most expensive parts in an amp (also heatsinks by the way).
I think that before doing anything i would get an impedance meter first and check the transformers secondaries for low impedance (measured at 50-60Hz)
A transformer with high impendace (i.e. high loss) secondaries is the very worst way to start a power amp
And i am pretty sure Naim transformers have very very low impedance secondaries (big section for secondary windings ?)
Am i wrong ?
P.S. this is a very good brand for instance ... ILP Toroidal Transformers | ILP Transformers Unirange - IndustrySearch Australia
you get what you pay ... almost always
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bear in mind that a 66va power traffo can supply 100va easily...and if just for 5 minutes of FTC testing can survive the ordeal...it is never as if a 66va traffo will shut its doors when 67va is attempted....
temp rise, and losses increases as the 66va nominal rating is exceeded, but by how much exactly? you can only tell by actual testing...
weight is another good metric, a heavier traffo will output perform a lighter weight traffo of the same rating...yes, different manufacturers have their own interpretation of what a 1000va traffo is made...some will consider regulation and temp rise and so would probably weigh more and cost more, another will have cost as first consideration and so will weigh in lighter...
Thanks again. If i have learnt one thing is that quality very seldom comes cheap. It is very difficult that very good parts are cheap. 😱
While it quite possible that so so parts are expensive 🙁
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once in a while you will come across very good quality parts that did not cost much, but knowing how to look for them is the art in itself...
i am very bad at theory. So i tend to rely more on instruments. But i must have them and know how to use them properly. From now on i will check the transformers secondaries resistance for sure
Just to see for differences. Thanks again. 🙂
Thread moved to Power Supplies
No, in Hi-Fi we only argue, never experiment. (😉?)
In Concerts In The Park I have metered my amplifiers as they strained to throw Latin music all the way to the railroad tracks. Yes the B+ sagged; but also I was clipping a lot of music (party-goers do not mind).
Also: is sag bad? A little? A lot?
Several really excellent amplifiers have had quite small power supplies.
psu sag is an inevitable thing as sure as the sun rises at dawn and settles down in the evenings.....
how much of it can you tolerate? that is up to you.....
how much of it can you tolerate? that is up to you.....
of course you can, but if it were me with two identical traffos, i will just use the two as separate psu for each channel.....
the Japanese used to to that in their offerings in the 80's.....think channel separation...or dual mono in a single casing...
Smaller trafos have poorer regulation at a given *percent of full load* than bigger ones. Two 800 VA in parallel will drop more voltage than a single 1500 VA for the same DC current. With AC loading it might be a wash, but DC loading causes more of that pesky drop than AC loading does, even if you take power factor into account.
Now if it’s a question of what’s available, what fits, or what doesn’t cost a fortune, you might choose two parallel (or series, in the case of class H) over one big one. But as far as the better power supply is concerned, one big one wins.
Hi sorry i did not mean to be offensive ... 😱
As i said above i am very bad a theory ... my biggest regret. I am just very slow to understand. So i have to rely on meters ... and meters often tell the truth 😉
😱 well this was a very extreme situation ...
why ? do you doubt ? 🙂
I had an old integrated ... now destroyed. It had two Sprague about 8000uF each for both channels in the psu. At an audio fair i bought some refurbished big caps used in industrial equipment.
So i replaced them with two Mallory 40mF .... they were so big that did not fit in so i left them out of the amp chassis ...
I was shocked by the sound ... it was very different in a good way ... more like a tube amp. I remember that when i was switching the amp off it was sounding for almost one minute or so on the energy stored in the caps. Amazing. Since then i salivate when i see big caps in an amp ... the good ones are very very expensive and the used one ... a big risk i understand
What is wrong with oversizing ? (cost aside) .... of course always within a reasonable limit. My limit would be like 15-20mF per rail per channel.
i wonder how they could have sounded with a not-sagging psu 🙄
Seriously ... they were good also as bass response ? and when you say small do you refer to transformer or caps ... or both ?
Thanks a lot again.
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Over sizing the caps does not necessarily prevent sagging rails. You *need* about 20,000 uF per rail with normal speaker impedances, and anything beyond that does very little other than let it play longer after you pull the plug. The power supply will still draw down based on the current demand - and the transformer’s impedance determines that more than anything else. It may hold up at full voltage for a few more milliseconds, but not put out one watt more sustained power. Sustained sine wave capability (for a short term) power determines how loud it will play, period.
I’ve found that “the right amount of sag” is such that the DC voltage drops down to the unloaded RMS secondary voltage when the amp is driven with sine waves at 2 ohms. It’s about a 4X overload to its VA capacity, but will run long enough to make the measurement. Any idea amp that can’t run at a sine wave at 2 ohms long enough to take a power reading isn’t good enough for my use. Doesn’t have to run that way much longer, but anything that shuts down or blows up before I can read the instruments isn’t going to like being bridged into 4 ohms playing music at clipping.
I’ve found that “the right amount of sag” is such that the DC voltage drops down to the unloaded RMS secondary voltage when the amp is driven with sine waves at 2 ohms. It’s about a 4X overload to its VA capacity, but will run long enough to make the measurement. Any idea amp that can’t run at a sine wave at 2 ohms long enough to take a power reading isn’t good enough for my use. Doesn’t have to run that way much longer, but anything that shuts down or blows up before I can read the instruments isn’t going to like being bridged into 4 ohms playing music at clipping.