Need circuit for transformer

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I have a single rail 0-36V AC 400 watts EI transformer, interested to build a power amplifier any suggestion for reasonable sound quality circuit?

and I also have a 36.8-0-36.8V AC 230VA toroidal transformer and same would like to build a power amplifier and still looking for circuit.

Thanks for help.

I dont know about the EI core transformer I dont like them much for audio use ....

As for the toroidal, this should give about +/-40V after rectification allowing for voltage sag.

so you've got a supply capable of +/-40V @ 3A continuous

this might be suitable for some sort of preamp circuit or an amp driving a high resistance load eg. 16ohms
The 135W amp was very likely class B or lightly biased AB. No big deal.
The EI might make a nice stereo Zen with a choke input filter (instead of cap input) to hold the voltage down.
EI transformers work just fine for audio. Been used since the beginning of time for some very nice sounding circuits. They're somewhat less efficient and can cause hum if they're too close to high gain circuitry, but careful positioning can take care of that.
Have fun.

I'd have to agree with Grey but even then they have scimped quite majorly on the transformer rating. If it had been a 23-0-23 230VA transformer you could have gotten 85W into 8ohms per channel stereo using Class A/B quite happily... unfortunatly the toroidal transformer you've got is just not a great combination between current and voltage for the VA rating and the resistance of the speakers you want to use.
So any suggestion for me to use these two transformer ?

Anthony Holton Hitachi lateral mosfet amp ?

and Where can I get info on stereo Zen with a choke input filter ?

I'm poor to buy a new transformer.........

my hope with these transformer gone.........


I've recheck the transformer and found that I can get a 34V DC by adjusting the primary to 240V AC (by default is 220V AC)
so I think I would like to build Zen amp. My place here is 230V AC supply.

Is it possible ? 400 watts should be enough for stereo?
avxt ..... your calculations do not sound correct. you say 34V DC and 400W therefore i assume you are referring to the 0-36V AC 400VA EI transformer .... to get 34V from this supply using the standard bridge + caps power supply the transformer secondary voltage would need to be no higher than 32V AC also if you decrease the primary voltage in order to decrease the secondary voltage you will also decrease the VA rating of the amp ... the voltage will decrease and the current remain the same hence a lower VA. if you increase the primary voltage slightly the VA rating will remain more or less constant only this time you will have to draw less current to compensate for the heat generated by the higher voltage.
Sorry, I'm not so understand what you explain, mind to describe more details?

May be I describe again how I get 34V DC.

The primary connection of the trans is like this


At default the equipment I took out the transformer connect to 0 and 220V for the neutral and live respectively.

Then I connect 0-240V to the main wall supply which is 230V I checked with multimeter. From the secondary which connected to a bridge rectifier and without load I measure the DC is around 35V DC.

simply using a bridge rectifier doesnt get you proper DC ... you need big caps after the bridge ... say between 10,000uF and 100,000uF.

Ok i now understand how you have connected your transformer... i thought you were using an autoformer.

The way you have connected the transformer now will get you 34.5V AC which after rectification will be 37-43V DC and the transformer will probably be good for 380VA the way you have connected it...

But, you cant use it at 380VA continuous.... So, If you wanna build a Zen amp which is Class A and hence constant current draw you cant really use more than 190VA continuously (even this is pushing it) ... and if you were gonna build 2 for stereo this drops to 95VA per channel ... now i havent looked @ the Zen stats lately but i know 95VA is probably only good for a few watts @ the best.

For the 400VA EI transformer i suggest you build the Class AB JLH amp that Geoff suggested earlier in this post and and use the toroidal transformer to build a monoblock amp which would also be Class AB.
IE Transformer


Take Geoff's advice and build a the JLH Class-AB amp. It is a relatively simple amp to build and according to the sources I can find a very good Class-AB comparable to a Class-A but not quite.

I have a transformer that is only a single 20 Volt AC rail, but churns out about 10 amps. I am building the JLH Class-AB with it.

Unless you have a big listening room or terribly ineffiecent speakers, you will have plenty of horsepower and if you build the amp carefully you will have performance on par with some of the best amps on the market.

I have the full circuit for the amp on a jpeg format, that I will be happy to send to you as soon as Geoff will give me the go ahead that is a safe and complete circuit.

Class-A is great, but I already have a Class-A and if you live in the tropics as I do, you will appreciate the coolness of a Class-AB amp. You cannot believe how much heat a Class-A amp will contribute to a room. of course if you live in Canada or Siberia who cares.

Surf, Sun & Sound
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