Hi All
Sorry for the really stupid question but......
I have just bought one of Brians LM3886 kits and I now need to get a transformer.
I live in the UK and I bought a standard LM3886 kit (2 LM's and one PSU).
What type of transformer will I need and where is the best (not really the cheapest) place to get one.
And if its not too much trouble, what wires go where ?.
Thanks in advance.
H
Sorry for the really stupid question but......
I have just bought one of Brians LM3886 kits and I now need to get a transformer.
I live in the UK and I bought a standard LM3886 kit (2 LM's and one PSU).
What type of transformer will I need and where is the best (not really the cheapest) place to get one.
And if its not too much trouble, what wires go where ?.
Thanks in advance.
H
Hi,
Maplins do some very good torroidal pretty cheap.
I have just received 2 * 120va 22 volt one for my dual mono setup.
If you want they have larger but the prices are far cheaper than anything esle in the u.k. that i have found.
For example mine cost £30 for two delivered. Maybe you want the higher rated one but in the confines of the case i bought they were a no go. I think that 22v ones are the best and they have 120va and 160va which are ideal for the dual mono setup.
For the stereo kit maybe the 330VA 2 x 24V, but this might be a little high voltage wise.
Hope that helps
Phil
Maplins do some very good torroidal pretty cheap.
I have just received 2 * 120va 22 volt one for my dual mono setup.
If you want they have larger but the prices are far cheaper than anything esle in the u.k. that i have found.
For example mine cost £30 for two delivered. Maybe you want the higher rated one but in the confines of the case i bought they were a no go. I think that 22v ones are the best and they have 120va and 160va which are ideal for the dual mono setup.
For the stereo kit maybe the 330VA 2 x 24V, but this might be a little high voltage wise.
Hope that helps
Phil
I am interested in starting a gainclone also and would like to know what is a good transformer for 8 ohms use, available in the US
I am wondering if a person can't step down the voltage a little in this case? BrianGT had said he was going to use the above mentioned tranny, and i myself have got a 2*30V (300VA) toroid. I hope this'll be okay for this application.
thanks,
Mantisory
Perhaps I got lucky but if you're not in a rush check out what's on Ebay. I bought four ILC 300VA torroidal transformers with dual 0-21v secondaries for £2.50 each a couple of weeks back. I have a set of Brian's boards/parts to go with them.
Unfortunately bathroom DIY has overtaken audio DIY but I'll get there soon!
Unfortunately bathroom DIY has overtaken audio DIY but I'll get there soon!
That is definately too much. You will have to use the regulated supply for that trafo.
It is not advisable to use a trafo close to the limit of these chips.
I am using 2x18 volts and there is plenty of power. Furthermore, the amp can safely be connected to speakers rated at 4ohms, without getting sweat'y😉 I would say 2x22 volts is about max.
Steen.
BTW You could also unwind the trafo to get the right voltage.
It is actually easier than it sounds.
Isn't Brian's offering regulated? I thought so....if not, what are the MUR860's in the power supply? Or do you mean i'd need to further regulate it.
On the national 3886 spec sheet here , it says that the max power supply voltage is 84V, which is 42 per side?
I am not sure where the problem is...
mantisory said:
30V AC * 1,4 = 42V DC - so you are practically on the edge.
Furthermore when a transformer is unloaded it gives out more voltage than indicated, so in practice you may get out more than 42Volts DC of your PSU - even when your LM3886 is connected, because it doesn't use much idle current.
If you have a voltmeter (multimeter), some loose resistors, a calculator *and* know Ohms law, you can test it for yourself -
*always* be careful messing with transformers .
No. The Mur's are rectifierdiodes! Check the datasheet again regarding railvoltage/outputpower.
I guess if you want to run a 84 volt supply, you would need a speaker with an impedance of 30ohm or something like that. Impossible.
Steen.
so...I bought this transformer thinking it would be the right one, but apparently i was wrong. Now what? Should i try a regulator circuit (based on the lm375 or something) or should i try to trade in my transformer?
The LM338 regulated supply would be great, see this:
http://users.verat.net/~pedjarogic/audio/ .
I think Digi01 made some pcb's for something similar. You could go for something like +/-32 volts on the rails. A further benefit from this approach is that the regulated supply is claimed to be the best sounding. Mayby you did the right thing after all😉
Good luck and cheer up
Steen.🙂
http://users.verat.net/~pedjarogic/audio/ .
I think Digi01 made some pcb's for something similar. You could go for something like +/-32 volts on the rails. A further benefit from this approach is that the regulated supply is claimed to be the best sounding. Mayby you did the right thing after all😉
Good luck and cheer up
Steen.🙂
if you read the lm3886 datacheet, you will find that it accepts a higher unloaded voltage then +-42v, i think it was +-48v or 46v, so you dont have to get a nother transformer.
altso when using high voltage trannies, you are limited to 8 ohm speakers that are true 8ohm, no dips down to 3 ohms or such are tolerated. maby 5 ohms are good though..
i remember doing a lot of reading when deciding on what chip to use for my first amp, practicly memoriced the datacheet..🙄
altso when using high voltage trannies, you are limited to 8 ohm speakers that are true 8ohm, no dips down to 3 ohms or such are tolerated. maby 5 ohms are good though..
i remember doing a lot of reading when deciding on what chip to use for my first amp, practicly memoriced the datacheet..🙄
demogorgon said:
You are right, that +/- 47 volts is absolutely maximum, but that is *without* signal. *With* signal it is +/- 42 volts. With this in memory and what I said before regarding a transformers overvoltage, it should work with the 2*30 volts transformer after all IF the PSU "only" produces no more than +/- 47 volts.
But IMHO one should still check the actual produced DC voltage, before one connects the chip.
Depends on the speakers. 4ohms speakers has reached the limit of these chips at +/-30 volts rails (measured after the caps in the supply). An amplifier producing 68 watts into 8 ohms is not considered very good if it can't handle a 4 ohm load.
The reproduction of music will be more authorative, if it (amp) can produce the needed current when the impedance of the speakers dips. We all know the doubling thing, saying of amps, 30 watts into 8 ohms, 60 watts into 4 ohms 120 watts into 2 ohms. This would be the perfect behaviour of an amp. It is not to be achieved with a chipamp, and certainly not with the rail voltages discussed here🙂 The sound of SpiKe_TM is horrible😉 But ofcourse,
you (Mantisory) can try it in your setup and see if it works. I wouldn't recommend connecting the amp to a 4 ohms speaker though😉
Steen.
Thanks for the comments!
i think my b&w cm4's are 8 ohms nominal, but go down to around 4 (haven't seen measurements of impedance vs. frequency)
in any case, i guess i should make sure to have some real good heatsinks!
i think my b&w cm4's are 8 ohms nominal, but go down to around 4 (haven't seen measurements of impedance vs. frequency)
in any case, i guess i should make sure to have some real good heatsinks!
Can I ask a really stupid transformer question?
When a transformer is advertised as 24 VCT does that mean that it is 12-0-12 or 24-0-24. This always confuses me.
When a transformer is advertised as 24 VCT does that mean that it is 12-0-12 or 24-0-24. This always confuses me.
B&W's are notoriously a difficult load. Nuuk has a quite nice description on regulated supplies too:
http://www.decdun.fsnet.co.uk/gainclone6.html
The site is crammed full of information on chipamps, and a lot more. Thanks NuuK😉 The regulated supply is easily made on stripboard thanks to NuuK. Mail me your adress and I will send you two LM338! Hate to be the messenger😎 😎
Steen.
http://www.decdun.fsnet.co.uk/gainclone6.html
The site is crammed full of information on chipamps, and a lot more. Thanks NuuK😉 The regulated supply is easily made on stripboard thanks to NuuK. Mail me your adress and I will send you two LM338! Hate to be the messenger😎 😎
Steen.
Trafo choice
The National Overture Design Guide spreadsheet is a very helpful tool to determine transformer ratings and component values. If you stick to the TA package, a 24-0-24 transformer can drive a 4 ohm load with authority if a suitable heatsink is chosen.
If you key in the transformer voltage, the spreadsheet will calculate exactly how many amps are required from the tranny secondaries to supply sufficient current. For instance, for a 24-0-24 transformer, you'll need 180vA per channel.
I'm running a Toroid Corp 617.242 transformer per channel , and it's a perfect match for the National spec's at 4 ohms output impedance. The amps drive B&W 705s very nicely.
Follow the link below. You can find a link to the spreadsheet in the center column, toward the bottom.
National Design Tools
The National Overture Design Guide spreadsheet is a very helpful tool to determine transformer ratings and component values. If you stick to the TA package, a 24-0-24 transformer can drive a 4 ohm load with authority if a suitable heatsink is chosen.
If you key in the transformer voltage, the spreadsheet will calculate exactly how many amps are required from the tranny secondaries to supply sufficient current. For instance, for a 24-0-24 transformer, you'll need 180vA per channel.
I'm running a Toroid Corp 617.242 transformer per channel , and it's a perfect match for the National spec's at 4 ohms output impedance. The amps drive B&W 705s very nicely.
Follow the link below. You can find a link to the spreadsheet in the center column, toward the bottom.
National Design Tools
blip said:
24 Volt, with a tap in the centre, so it's 12-0-12.
No questions are stupid. (then again...) If you were brave enough to stick your hand up and ask, it is guaranteed that there are other readers out there with the same question... 🙂
Paul
Hello all, I got quite the same problem here. I've just got a 2*24v 300va toroidal. But I use old Fisher KS-2 (don't have lot information on them, they are old) they are rated at 8ohms but mesured with multimeter it drop at +-6.70ohms. Do you think it will work (with a 3875 and the toroidal) or should I use a led to drop the power on the rail? Or somethong else?
And for your 30v toroidal, good luck for the regulated system, I will follow the thread if you are ready to start the experience 🙂
And for your 30v toroidal, good luck for the regulated system, I will follow the thread if you are ready to start the experience 🙂
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