Hey,
I am going to build the chipamp.com lm3886 kit to drive 8ohm speakers and I am wondering a few things. I want to try and get the most out of the chip without causing issues.
I know that the 3886 should run just fine with a 25+25v transformer (+33v -33v after rectification) but will using a trasformer with 28v secondaries (+38v -38v) pose any issues to sound quality of the chip or endanger the chip (the data sheet says it should be fine but I want to make sure). This way I can get the most out of the chip with the 8ohm load.
Will the other components of the chipamp.com kit be able to handle this voltage.
The transformer that I was looking to use is this one from antek Antek - AS-3428 I realise that it also has 15+15v outputs but I will simply not connect them and cap them until I get around to finding a use for them, assuming that this does not cause a problem.
If it is not safe or smart choice I will just go for the 25+25v transformer.
Also I know that using that much voltage will create a lot of heat, With the 38v supply would a 4''x 6''x 1.25''high heatsink be enough for both chips? or should I use one heatsink of that size for each?
Thanks in advanced for any input, it all really helps!
I am going to build the chipamp.com lm3886 kit to drive 8ohm speakers and I am wondering a few things. I want to try and get the most out of the chip without causing issues.
I know that the 3886 should run just fine with a 25+25v transformer (+33v -33v after rectification) but will using a trasformer with 28v secondaries (+38v -38v) pose any issues to sound quality of the chip or endanger the chip (the data sheet says it should be fine but I want to make sure). This way I can get the most out of the chip with the 8ohm load.
Will the other components of the chipamp.com kit be able to handle this voltage.
The transformer that I was looking to use is this one from antek Antek - AS-3428 I realise that it also has 15+15v outputs but I will simply not connect them and cap them until I get around to finding a use for them, assuming that this does not cause a problem.
If it is not safe or smart choice I will just go for the 25+25v transformer.
Also I know that using that much voltage will create a lot of heat, With the 38v supply would a 4''x 6''x 1.25''high heatsink be enough for both chips? or should I use one heatsink of that size for each?
Thanks in advanced for any input, it all really helps!
The LM3886 can work till +41V to -41V DC on 8 ohm impedance speakers. However the 8 ohm speakers have a nominal impedance of 8 ohms and it can be lower sometimes thereby overloading the amplifier leading to activation of protection circuitry inside the chip which in turn leads to a lot of noise.
The ideal and safe transformer voltage for 8 ohm loads is 24-0-24V AC which gives you around 33-35V DC after rectification and filtering. VA rating of 300 to 500VA.
The ideal and safe transformer voltage for 8 ohm loads is 24-0-24V AC which gives you around 33-35V DC after rectification and filtering. VA rating of 300 to 500VA.
A 25+25Vac transformer is going to give a lot more than +-33Vdc when feeding a chipamp.
A 230:28+28Vac transformer is very likely to overvoltage a chipamp in worst case "normal" operating conditions.
Expect upto ~+-43Vdc when mains voltage is high. That exceeds the 84Vdc limit for the 3886 when signal is present.
A 230:28+28Vac transformer is very likely to overvoltage a chipamp in worst case "normal" operating conditions.
Expect upto ~+-43Vdc when mains voltage is high. That exceeds the 84Vdc limit for the 3886 when signal is present.
I ran a simulation in multisim and I was getting about 38v per rail after rectification and diode drop from a 28v ac source. I am also assuming that this would drop under amp load. I really want 35v per rail running into my amp.
Should I just go with the 25+25v transformer and take the hit on output power?
Should I just go with the 25+25v transformer and take the hit on output power?
Yes you should.
You will anyway get about 39V if in the UK (can't see where you are from here). The change in power will be insignificant but the chip will be a lot cooler.
Edit: I see you are in the States, so you can probably get away with 28V. (Our mains is still mostly higher than the 220V it's specced at. In fact the ref is 230 in UK which is close enough for Euro compliance. Yours doesn't have a problem so the transformers will be wound just for US.) So, go with what you have.
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I am just going to go with the 25v one. I forgot to account for the mains voltage running high sometimes and with an unregulated supply running close to the max that could be a killer. Also when I ran my simulation I set the transformer to be wound with a 120v primary (my local mains voltage), when in fact the transformer I am looking to buy is wound with a 115v primary. After changing that in the simulation I was getting 35v on the rails after rectification with 120v in. exactly what I was looking to get.
Thanks for all of the input!
Thanks for all of the input!
Andrew, that 84V is with signal. It's 94V no signal.
I've run one amp at +-44V with no prob (and I assume there was a decimal point xx as well or it would have shown 43). That was a 30V 300VA transformer on UK mains, A farnell standard, btw. It did not blow up, though I doubt it put the chip at ease. 39V is no problem.
I never listen to my chipamps with zero signal at the input ! Do you listen to music/audio with no signal at the input?
I prefer to work within the specifications of the equipment and/or components. I recommend to other builders to similarly operate within specifications.
You can choose to do otherwise.
I deplore any Member's recommendation to other builders to operate their equipment and/or components outwith the manufacturers' specified limits.
you have to take in account temporarily higher mains voltage , as AndrewT points out. It depends on which country and you local power net of course and is impossible to foresee.
But dont forget regulation of the transformer either.
The 28V is specified at rated VA ,and assuming 5% regulation this means the voltage is almost 30V at very light loads.
It is very possible to operate at 28VAC but not without precautions , like an overvoltage protection which blows the fuses for the powersupply when necessecary. It will take a few ms to load the cap banks so an early detection is a good idea.
But dont forget regulation of the transformer either.
The 28V is specified at rated VA ,and assuming 5% regulation this means the voltage is almost 30V at very light loads.
It is very possible to operate at 28VAC but not without precautions , like an overvoltage protection which blows the fuses for the powersupply when necessecary. It will take a few ms to load the cap banks so an early detection is a good idea.
I have another quick question and I don't want to statrt up another thread. I plan on using 25v transformer with the chipamp.com kit. My question is that if I use a 300VA transfomer with 20000-25000 microfarad of smoothing caps on each rail, will I need a soft start? Part of me wants to just to keep any chance of major inrush current to a limit as this will be running in my dorm room at school and I really don't want to blow anything. I am really interested in this soft start system Connexelectronic but I can't get the product to "add to cart" for checkout.
Pretty much any suggestions for soft starting would be great, or please talk me out of one if it really isn't needed.
http://connexelectronic.com/product_info.php/products_id/49
Pretty much any suggestions for soft starting would be great, or please talk me out of one if it really isn't needed.
http://connexelectronic.com/product_info.php/products_id/49
Maybe the grid was having a surge on the day I measured (several years ago)
And the voltage regulators did not work at the time?
Depends on what else in connected to the same circuit. A 300VA transformer alone won't need a soft start. With the right amount of other consumers in the same circuit, the transformer's inrush current may however be the straw that breaks the camel's back. You'll have to find out by the proven method of trial-&-error.
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