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Iso-transformer from 2 toroids with multiple secondaries
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Author:  tizman [ 22 Aug 2017, 00:21 ]
Post subject:  Iso-transformer from 2 toroids with multiple secondaries

Hi All. A quick question. I built an amp recently that sources its 120 AC from 2 EI frame 0-35 volt power transformers with their secondaries connected. This is working fine with respect to the electrical operation and sound of the amp, but the two tranformers create a mechanical buzz that is easily audible from the listening position, and therefore annoying and distracting. I have on hand two toroid transformers that I could use instead. These transformers have multiple secondaries. They are as follows:
0-24V @ 48VA (green-red)
0-24V @ 48VA (brown-blue)
0-10V @24VA (white-grey)
9-0-9V @18VA (orange-yellow-orange)

While the connection of the EI transformers is very straightforward, the toroids have multiple secondaries. Should I connect all like colored secondaries wires together except for the yellow center tap wire on the 9 volt? Should I only use some of them? I am hoping to have as much capacity as possible for the circuit, although it will only draw about 70 milliamps.

Thanks in advance for your help with this.

Author:  steakhead [ 23 Aug 2017, 20:29 ]
Post subject:  Re: Iso-transformer from 2 toroids with multiple secondaries

perhaps it might be a good idea to embark on obtaining a suitable transformer
that would be more comfortable to the ear. this would not degrade your amplifier
performance, that's assuming the original was worth listening to

Author:  tizman [ 23 Aug 2017, 21:17 ]
Post subject:  Re: Iso-transformer from 2 toroids with multiple secondaries

The schematic for the original amp is located on the Headwize archive. It is a 6dj8 6as7 OTL headphone amp designed by Aren van Waarde. It sounds fantastic, but only if you put the amp in another room so that you can't hear the transformers buzzing. I tried temporarily connecting only the two 24 volt primaries, and they are completely silent both in the circuit and mechanically. To be honest, although I have come across some silent vintage power transformers over the past few years that I have been building, pretty much every new power transformer that I have purchased has some mechanical hum. Every single new Hammond transformer that I have purchased, for example, has mechanical hum. Some were so bad that I returned them. These two toroids do not hum at all. I have searched the web several times and not found any guidance on how to best connect two identical power transformers with multiple secondaries to create an isolation transformer.. Any advice on how to best connect them would be greatly appreciated.

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