Hi,
I have two toroidial 115V transformers while we have 230V. I want to connect the primaries in series and use for a mosfet class ab power amplifier. I wonder if there should be any problem doing that. I assume that the load is balanced on the two rails and since we have capacitors, there won't be load variations on the two transformers. What do you guys think?
I have two toroidial 115V transformers while we have 230V. I want to connect the primaries in series and use for a mosfet class ab power amplifier. I wonder if there should be any problem doing that. I assume that the load is balanced on the two rails and since we have capacitors, there won't be load variations on the two transformers. What do you guys think?
Hi Bibliophile,
thanks for your response. I usually use a single rectifier but I have no problem using two of them. Now for some details on my project:
I am going to build this amp 300 Watt MOSFET Real HI-FI Power Amplifier | EEWeb
I am going to have 2 x 27VAC transformer and would welcome a suggestion for a quality power supply.
thanks for your response. I usually use a single rectifier but I have no problem using two of them. Now for some details on my project:
I am going to build this amp 300 Watt MOSFET Real HI-FI Power Amplifier | EEWeb
I am going to have 2 x 27VAC transformer and would welcome a suggestion for a quality power supply.
Hi elic
Each of those 27 Volt windings would give you about 38 Volts DC if used individually.
If you want to combine them into a single supply, you would have to series the secondaries and use the junction as the centre tap.
To make this work, the windings have to be correctly phased or you will get nothing out. To do this, connect your primaries in series, the actual wiring is not important at this stage. Power it up and measure the voltage accross the two secondaries in series. If you get double the voltage of each secondary, all is well. If not, reversing one secondary or primary winding should fix the problem. There is no need for a series light bulb in the primary but by all means use one if it makes you feel more comfortable. If you were paralleling windings, then a light bulb is a must.
Each of those 27 Volt windings would give you about 38 Volts DC if used individually.
If you want to combine them into a single supply, you would have to series the secondaries and use the junction as the centre tap.
To make this work, the windings have to be correctly phased or you will get nothing out. To do this, connect your primaries in series, the actual wiring is not important at this stage. Power it up and measure the voltage accross the two secondaries in series. If you get double the voltage of each secondary, all is well. If not, reversing one secondary or primary winding should fix the problem. There is no need for a series light bulb in the primary but by all means use one if it makes you feel more comfortable. If you were paralleling windings, then a light bulb is a must.
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Running two 115 volt primaries in series is only safe if the secondary loads are balanced, If they are not the transformer with the greater load will attempt to take more current and therefore the voltage across it will reduce and the other transformer will see an overvoltage. Since I would assume that you would run the 27 volt secondaries in series to achieve the + and - supply rails the load cannot be assumed to be equal on each transformer if the amplifier current is not exactly symetrical.
But the question is can't I assume that in an audio amplifier the two rails are balanced since it's an AC signal. Maybe not exactly but close enough to not show any noticeable difference.
The two halves should be balanced but they may not be. More importantly you are assuming no fault condition. If one half of the amplifier fails in some way or even a supply wire falls off you are likely to end up with quite a lot of smoke. It is bad practice to operate transformers in this way even if it will mostly work.
in that case you can connect primaries in series ;
will explain later , have some things to do
ANY imbalance will become expensive when they become apparent. A few Euros saved at this point may cost hundreds of Euros in the future.
Have a look on E-Bay and at http://www.rs-online.com There are loads of 625VA transformers for about £60.
http://www.amazon.co.uk/MULTICOMP-T...TPIG/ref=sr_1_3?ie=UTF8&qid=1333966730&sr=8-3
Have a look on E-Bay and at http://www.rs-online.com There are loads of 625VA transformers for about £60.
http://www.amazon.co.uk/MULTICOMP-T...TPIG/ref=sr_1_3?ie=UTF8&qid=1333966730&sr=8-3
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Hello Guys,
Incidentally I had the same question, but for a Class A amp (FirstWatt F2J):
I found 2 very nice Avel Lindberg 337W sealed toroids second hand (and cheap!)
Primary: 2 x 115V
Secondary: 2 x 37V
Mains is 230V where I live and I was thinking of putting each primaries (totally 4 windings) in series to get 4 secondaries at 18.5 VAC (that I would parallel 2+2 to get 2 channels).
Is this any better idea in Class A than class AB ?
And also, do I somehow lose the reduced crosstalk benefit of having 2 seperate toroids by doing so ?
Thanks a lot !
Incidentally I had the same question, but for a Class A amp (FirstWatt F2J):
I found 2 very nice Avel Lindberg 337W sealed toroids second hand (and cheap!)
Primary: 2 x 115V
Secondary: 2 x 37V
Mains is 230V where I live and I was thinking of putting each primaries (totally 4 windings) in series to get 4 secondaries at 18.5 VAC (that I would parallel 2+2 to get 2 channels).
Is this any better idea in Class A than class AB ?
And also, do I somehow lose the reduced crosstalk benefit of having 2 seperate toroids by doing so ?
Thanks a lot !
Hi,
as long as you connect the secondaries of different transformers in series you should be OK. In fact, I am going to do the same but with four different 110V transformers. I will connect each two's primaries in series and connect secondaries in series (that's because I have only one secondary in each transformer).
as long as you connect the secondaries of different transformers in series you should be OK. In fact, I am going to do the same but with four different 110V transformers. I will connect each two's primaries in series and connect secondaries in series (that's because I have only one secondary in each transformer).
WOOOAAA.
Be VERY VERY careful.
If you keep everything IN PHASE then you should be OK.
Funny things do happen with transformers in series though. You would be better to sell on the different transformers and buy the correct one in the first instance.
Theoretically it seems OK. However, my experience of connecting transformers in series has always been poor results.
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