Hi @all,
I'm currently building a surround amplifier based on 5x LM3886 mono blocks and one IRS2092 based amplifier (sub woofer channel).
Which voltage to use is clear. The compromise between IRS2092 and LM3886 is 2x25VAC.
But my question is: Do I really use a toroidal transformer with 800VA? (5x100VA LM3886 + 300VA IRS2092) or do i calculate with more realistic values. I'm not able to run the amp at full load because of the neighbors.
If you could give me a hint on choosing the right power for my project I would be very grateful.
Best regards
hackspider
I'm currently building a surround amplifier based on 5x LM3886 mono blocks and one IRS2092 based amplifier (sub woofer channel).
Which voltage to use is clear. The compromise between IRS2092 and LM3886 is 2x25VAC.
But my question is: Do I really use a toroidal transformer with 800VA? (5x100VA LM3886 + 300VA IRS2092) or do i calculate with more realistic values. I'm not able to run the amp at full load because of the neighbors.
If you could give me a hint on choosing the right power for my project I would be very grateful.
Best regards
hackspider
Will all the 6 amplifiers be asked to produce maximum power at the same instant?
Will any amplifier be asked to deliver near maximum power for a continuous period?
A single amplifier will run quite well when the transformer VA is from one times to two times the maximum power output in watts.
i.e. a 3886 will operate well with a 68VA to 136VA transformer if you run it at +-40Vdc.
If you use a 25+25Vac transformer the maximum power is likely to be around 50W to 60W (certainly not 100W).
Will any amplifier be asked to deliver near maximum power for a continuous period?
A single amplifier will run quite well when the transformer VA is from one times to two times the maximum power output in watts.
i.e. a 3886 will operate well with a 68VA to 136VA transformer if you run it at +-40Vdc.
If you use a 25+25Vac transformer the maximum power is likely to be around 50W to 60W (certainly not 100W).
For about the third time this week I find myself agreeing with Andrew.
I'll only add that, if you really need all that power, you might find independent supplies (ergo multiple transformers) easier to manage and probably cheaper too.
If you can GUARANTEE that the maximum power will never exceed 625VA then you will get away with a smaller transformer. For safety and piece of mind I would go with a bigger transformer.
yes, for me it is better that you have it and not need it, than not have it and then need it....
i build my own traffos used in my own amps and i make it a point to have more headroom, hey, this is diy.....
Many years ago I suggested adding the two stereo channel maximum powers together and then add on half the remaining maximum powers of the 5.1channels to arrive at a sensible maximum power, that will be rarely if ever exceeded.
After that, apply a factor from 1times to 2times to arrive at an adequate music reproduction VA.
But this is not a normal 5.1
It's more like a 5.6 because the bass channel is six times the power of any other channel.
Is the bass speaker really 6times less sensitive than the other speakers?
After that, apply a factor from 1times to 2times to arrive at an adequate music reproduction VA.
But this is not a normal 5.1
It's more like a 5.6 because the bass channel is six times the power of any other channel.
Is the bass speaker really 6times less sensitive than the other speakers?
First of all, thanks for all the answers. I'm very glad that some experts share their experience.
@AndrewT
I doubt that the amplifier ever have to produce the maximum power. That would be round about 370W (5*50W + 1*120W) of output power in a normal sized living room. Neither peak nor continuously.
@AJT
The difference in price is less than 10 bucks but the space in the box is limited as you already figured out.
@all
My calculation for one LM3886 was based on some Kit-Manuals (BrianGT) that mentioned 220VA for a stereo amplifier. So i went with ~100VA per LM3886 channel. But that seems to be a little bit to much if the LM3886 works well from 68VA to 136VA.
So considering the bass channel AndrewT pointed out a very embarrassing mistake I made. I was going for a single channel version of the IRAUDAMP7S (120W Version). But instead of cutting the power in half also I was continuing calculating with the 240W of stereo power (+ efficiency and headroom = 300W). 150VA seems to be a more realistic value.
So the choice is between a 630VA or a 800VA transformer so lets do some math on it:
Seems even the 630VA transformer has enough headroom AND is a reasonable choice. But I wouldn't go lower than this.
Just for fun lets calculate the rule of thumb by AndrewT:
My inner voice tells me the amplifier would run with such a transformer also. But I think this leads more into a minimum calculation than to a reasonable solution.
Best regards
hackspider
@AndrewT
I doubt that the amplifier ever have to produce the maximum power. That would be round about 370W (5*50W + 1*120W) of output power in a normal sized living room. Neither peak nor continuously.
@AJT
The difference in price is less than 10 bucks but the space in the box is limited as you already figured out.
@all
My calculation for one LM3886 was based on some Kit-Manuals (BrianGT) that mentioned 220VA for a stereo amplifier. So i went with ~100VA per LM3886 channel. But that seems to be a little bit to much if the LM3886 works well from 68VA to 136VA.
So considering the bass channel AndrewT pointed out a very embarrassing mistake I made. I was going for a single channel version of the IRAUDAMP7S (120W Version). But instead of cutting the power in half also I was continuing calculating with the 240W of stereo power (+ efficiency and headroom = 300W). 150VA seems to be a more realistic value.
So the choice is between a 630VA or a 800VA transformer so lets do some math on it:
Seems even the 630VA transformer has enough headroom AND is a reasonable choice. But I wouldn't go lower than this.
Just for fun lets calculate the rule of thumb by AndrewT:
My inner voice tells me the amplifier would run with such a transformer also. But I think this leads more into a minimum calculation than to a reasonable solution.
Best regards
hackspider
I agree, I would not use a factor of 1times.
Using a factor of 1.5times gives ~300VA
and as you have shown a factor of 2times gives ~ 400VA.
A 300VA or 400VA will power all six channels.
BUT
what is the power output of the bass channel when running on the same voltage rails as the 3886 chipamps?
Using a factor of 1.5times gives ~300VA
and as you have shown a factor of 2times gives ~ 400VA.
A 300VA or 400VA will power all six channels.
BUT
what is the power output of the bass channel when running on the same voltage rails as the 3886 chipamps?
The bass channel will provide 120W output power by +-35VDC (25VAC * 1.414) with a >80% efficiency.
So I calculate with 150W * 0.8 = 120W.
Best regards
hackspider
So I calculate with 150W * 0.8 = 120W.
Best regards
hackspider
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