hi friends. i want to learn this if i use smaller transformer for amplifiers need.
exm. 500w power amp and i use 250w. what can be happen? transformer get damage or just amplifier working half power?
exm. 500w power amp and i use 250w. what can be happen? transformer get damage or just amplifier working half power?
The transformer will overheat if run continuously over its rating. The voltage will also fall under over current situations current limiting the amplifier power... by how much depends on the transformer. Transformers have huge thermal inertia and you won't damage one in a couple of minutes but long term overheating will risk the insulation breaking down.
If you fuse the transformer correctly (primary and secondary) then you can use it safely knowing that it is protected against overload.
If you fuse the transformer correctly (primary and secondary) then you can use it safely knowing that it is protected against overload.
It will be ok so long as you don't go above half power.
I use a 2 amp transformer in an amplifier test bed.
I use a 2 amp transformer in an amplifier test bed.
I would divide the question into 2 parts:
Possible output power: The output power mainly depended by the secondary voltage of the transformer. If it is same, as in the bigger transformer, the peak power can be close. Continous power will be lower, because the output of the overloaded transformer will fall.
Possible transformer failure: The transformers are very robust parts, not easy to kill them. I did some tests, when I built PA amplifiers. 750VA toroidal transformer easily handle the continous double power for 15-20 minutes, without failure. The internal temperature was close to 90 degree, but it is normal in this case. Using music, the average consumption of the amplifier is relatively low, so underrated tranformer usually survive.
Sajti
Possible output power: The output power mainly depended by the secondary voltage of the transformer. If it is same, as in the bigger transformer, the peak power can be close. Continous power will be lower, because the output of the overloaded transformer will fall.
Possible transformer failure: The transformers are very robust parts, not easy to kill them. I did some tests, when I built PA amplifiers. 750VA toroidal transformer easily handle the continous double power for 15-20 minutes, without failure. The internal temperature was close to 90 degree, but it is normal in this case. Using music, the average consumption of the amplifier is relatively low, so underrated tranformer usually survive.
Sajti
Use larger caps to reduce hum and maintain peak amplifier power.stocktrader200 said:
Use smaller caps to reduce heating in the transformer.
You choose which is most important.
OK, so this might win the daft question of the day award, but would you mind explaining the reasoning behind this? Is the effect of extended power bandwidth really that big?
Often it is overboard to put a 500W transformer in a 500W amp, unless you listen to techno pop whereby a synthesizer is playing a continuous low freq bass note for long duration and you have the volume way up and you don't care about your ears or disturbing you neighbors.
There are may designers that abdicate using a TX 2/3 the power of the amp rating.
There are may designers that abdicate using a TX 2/3 the power of the amp rating.
Actually I think this is a very interesting and important question that depends on what you expect to be demanded of the amplifier.
Let's say what you want is an amplifier with high headroom for short transients. For the most part the amp will only be delivering 1-10W continuous power, but peaks of 100-500W without clipping should be handled. You could do this using a "500W" amplifier module and an undersized (e.g. 100W-200W) rated transformer. As someone mentioned, it would be helpful to have lots of capacitance in the power supply. Such an amplifier would be a "100W amplifier with headroom". What's wrong with that?
The smaller transformer is cheaper and lighter. As the power output demand grows the conduction angle will increase and that is not such a bad thing. Still, it's going to be a "100W amplifier" only. Do not expect anything more.
Let's say what you want is an amplifier with high headroom for short transients. For the most part the amp will only be delivering 1-10W continuous power, but peaks of 100-500W without clipping should be handled. You could do this using a "500W" amplifier module and an undersized (e.g. 100W-200W) rated transformer. As someone mentioned, it would be helpful to have lots of capacitance in the power supply. Such an amplifier would be a "100W amplifier with headroom". What's wrong with that?
The smaller transformer is cheaper and lighter. As the power output demand grows the conduction angle will increase and that is not such a bad thing. Still, it's going to be a "100W amplifier" only. Do not expect anything more.
>> Use smaller caps to reduce heating in the transformer.
> ...explaining the reasoning behind this?
Cap-input rectifiers have BIG current spikes. These count more for RMS (heat) than you might expect.
However the difference is not huge. I tried 1,000uFd against 100,000uFd. Now, 1,000uFd might be typical for a $9.95 phono from 1975, while 100,000uFd is still considered pretty heroic (maybe not in this crowd). Big difference in uFd. 22%-33% difference in transformer RMS current.
I figured two ways: one 8-ohm channel driven to FULL Sine output, and one such channel sitting idle (actually hot idle: 180mA). Normal everyday use of spech/music audio amplifiers is a lot closer to "idle" than FULL. However it is customary to bench-test audio amps at FULL, at least for a moment, and under old FTC regs at part-power for an hour(?). And the kids don't hear distortion and turn-UP as soon as you leave the house. IMHO if it survives a few hours at FULL, it will live forever near idle.
> ...explaining the reasoning behind this?
Cap-input rectifiers have BIG current spikes. These count more for RMS (heat) than you might expect.
However the difference is not huge. I tried 1,000uFd against 100,000uFd. Now, 1,000uFd might be typical for a $9.95 phono from 1975, while 100,000uFd is still considered pretty heroic (maybe not in this crowd). Big difference in uFd. 22%-33% difference in transformer RMS current.
I figured two ways: one 8-ohm channel driven to FULL Sine output, and one such channel sitting idle (actually hot idle: 180mA). Normal everyday use of spech/music audio amplifiers is a lot closer to "idle" than FULL. However it is customary to bench-test audio amps at FULL, at least for a moment, and under old FTC regs at part-power for an hour(?). And the kids don't hear distortion and turn-UP as soon as you leave the house. IMHO if it survives a few hours at FULL, it will live forever near idle.
Attachments
so its not get ower heating and the coopers short inside? i am not going to use it just asking for understand it. ty for answer
designs assumed sine waves, for lack of better reference, for amps...
but once any amp is up and running, music is played, not sine waves...
so that the energy content is way lower....
if you are not doing any FTC testing on your amps, you can get away with a much smaller traffo, just be careful not to overheat it too much...
but once any amp is up and running, music is played, not sine waves...
so that the energy content is way lower....
if you are not doing any FTC testing on your amps, you can get away with a much smaller traffo, just be careful not to overheat it too much...
Almost all amplifiers sold today use transformers (or switching supplies) sized for typical music loading and no more. Take the stated current draw on the nameplate, multiply by 120 or 230, whichever is appropriate, and that is the VA rating of the transformer (to the nearest standard size). It’s always less than the amp’s “continuous” power rating, because “continuous” means a steady state sine wave - not that it may be operated like that continuously. If you did the music would be unlistenable and the speakers turned to chrarcoL. Big transformers are really great integrators - as long as the average over several minutes is within rating it is safe to run much higher intermittently. “Pro” amplifiers are no exception. The trafos and heatsinks are sized for typical loading (1/8 power with pink noise into 4 ohms). “Touring grade” amplifiers will take more, but usually no more than 2X what a cheaper amp will. At one time, amp’s intended for fire signaling and other emergency applications were required to produce full power for 8 hours. A Bogen or University 250 watter would set you back 2 grand. I haven’t even seen those on the market since the 80’s. An old PV CS-800 would almost do it - it could at 8 ohms but not 4.
Regardless of transfirmer size, how loud an amplifier will play is related to how much power the amp will put out “continuously”, as in sine wave. An amp with a 1500VA trafo might have unloaded rails of 65V, reducing to 60V when playing a sine wave just at clip. Another may have a 400VA trafo, with 95 V rails which reduce to 60V with sine wave loading. You will get the same perceived loudness when driven to obvious clipping (war volume). The higher rail amp with the smaller trafo will sound more dynamic when used “properly”.
DIYer is free to size the trafo to whatever meets his goals and cost targets (if any). I typically size my PA amp trafos for 1/3 power at 4 ohms, and 1/4 power at 2. There have been exceptions -
Regardless of transfirmer size, how loud an amplifier will play is related to how much power the amp will put out “continuously”, as in sine wave. An amp with a 1500VA trafo might have unloaded rails of 65V, reducing to 60V when playing a sine wave just at clip. Another may have a 400VA trafo, with 95 V rails which reduce to 60V with sine wave loading. You will get the same perceived loudness when driven to obvious clipping (war volume). The higher rail amp with the smaller trafo will sound more dynamic when used “properly”.
DIYer is free to size the trafo to whatever meets his goals and cost targets (if any). I typically size my PA amp trafos for 1/3 power at 4 ohms, and 1/4 power at 2. There have been exceptions -
Smaller caps mean longer and smaller charging pulse, so less heating.sgrossklass said:
No idea what you are referring to.
But 33% difference in current is 77% increase in transformer heating... Heating goes as I-squared. To me that's a huge effect as your transformer needs to be sized a lot larger, with size and cost implications. However you can also tune this trade-off by adding extra resistance in series with the windings to limit peak currents - allows larger caps without bigger transformer, but you lose voltage under continuous load, and the resistors waste power. This stuff can be simulated of course if you want to tweak everything for you particular requirements.
What I say, is if you want a transformer based amplifier, the last thing I would do is under rate the transformer. Large transformers are available in abundance in many non working amplifiers. The usual mode of failure is usually in the power supply rails due to the robustness of toroidal power supplies.
Pick up a used, non working pro audio amplifier , and you got large gauge wiring , a large transformer, and plently of heat sinking for next to nothing, that can be reused for your project. Your entire amplifier can then have an audiophile overbuilt power supply. the way I think they should be.
It is interesting to note that a few companies like zepher labs in india, and a few others have found that the usual burst limitations of SMPS amplifiers, can be cured with the use of transformer, rather than using SMPS supplies. A great solution for powering Class D in my opinion.
Pick up a used, non working pro audio amplifier , and you got large gauge wiring , a large transformer, and plently of heat sinking for next to nothing, that can be reused for your project. Your entire amplifier can then have an audiophile overbuilt power supply. the way I think they should be.
It is interesting to note that a few companies like zepher labs in india, and a few others have found that the usual burst limitations of SMPS amplifiers, can be cured with the use of transformer, rather than using SMPS supplies. A great solution for powering Class D in my opinion.
Last edited:
Use a chip amp from a car radio.
Or from a party speaker.
Simpler.
All you need is a portable amp...nobody will make out the tube amp sound quality in a march past.
Or from a party speaker.
Simpler.
All you need is a portable amp...nobody will make out the tube amp sound quality in a march past.
Peavey Valve King is a 100W 16kg/35 pound tube guitar amp monster, VERY unsuitable for any marching band use ... unless on a truck bead or trailer powered by a gasoline generator.
Quite similar, both are 100W tube heads.
NO mini transformers available or physically possible.
Please spell i-m-p-o-s-s-i-b-l-e
As Naresh suggests, get some solid state solution.
There are excellent pedal sized simulators available.