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replacement transfomer for Stax SRD7 adapter
replacement transfomer for Stax SRD7 adapter
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Old 15th March 2011, 09:00 AM   #1
Jmmlc is offline Jmmlc  France
Join Date: Oct 2005
Default replacement transfomer for Stax SRD7 adapter


In the Stax SRD7 adapter of my electrostatic headphones, one of two transformers has one of the half secondaries cut.

On the other transformer which looks good I could measure a ratio:

1 : 70 with Center Tap

This is a somewhat suprisingly high value for me.

Does this value seems OK to you or not?

Do you know any available replacement transformer that will fit inside the adapter.

Could I use a transformer with a lower ratio? Which minimum ratio is possible?

I was thinking about the possibility of using the Sowter model 8650
Sowter Type 8650

which is of the same dimensions and could be used after changing its flanges by the actual one (I think the 8650 tranfsormer fits in the Stax flanges).


Best regards from Paris, France

Jean-Michel Le Cléac'h
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Old 4th June 2011, 03:03 PM   #2
owenhamburg is offline owenhamburg  Germany
diyAudio Member
Join Date: Oct 2009
Location: Hamburg
Dear Jean-Michel,

I am not so surprised by the ratio. Its perfectly normal ration for speakers.

Admittedly speakers often have a far higher voltage in them.

I think you might want to check the electrostatic speakers forum. Many people their are using medical grade power transformers in their speakers.

Personally I would give up on transformers, and build a dedicated and targeted amp


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Old 14th September 2013, 11:03 PM   #3
owenhamburg is offline owenhamburg  Germany
diyAudio Member
Join Date: Oct 2009
Location: Hamburg
Dear Jean-Michel,

A follow up is required now as I have learnt a lot more.

1) The referanced transformer does nto specify it maximum operated voltage so it may break down with the voltages you intend to drive it.

2) You would need to drive the transformer with 40 V to get 400 V and so we are talking a greater than 200 W amp (into 8 Ohms) driving these speakers near its voltage limits.

3) In my experiance, distortion goes up a lot as amplifiers near maximum output.

If this transformer is rated for the voltages you want, then it might be a good candidate for a dedicated high voltage low current amp.

I suggest you do what I did, and buy a second hand stax electret adaptor, and reuse these transformers in your Stax SRD7. Stax SRD-4 often go for relatively low prices on ebay as they do need soem modification to make them able to drive electrostatics, and it is quiet tricky to get the center tap of the transformer, as Stax cut this off in this model, soem times very close to the windings so it makes conisderable acuracy not to drop solder on the transformer windings.
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