1:1 vs 1:2 transformer question.

[Seon]

Hello, I'd like to transformer balance in and out an Eventide H910 and a FL201.
For the input I think I will use a Jensen JT-11P-1 that I have laying around.
On ebay I can find the original output transformers that were used in the FL201 (and I think the H910 to some extend) but those are 1:2.
I did a few research and understand that I can get twice the voltage for half the current if connected to an input with the proper impedance with this kind of transformer but I wonder if 1:2 winding are of common use in studio gears ?
What are the pros and cons ?
Also would you recommand a totally different transformer for those gears ?

 

[KrIVIUM2323]

I did a few research and understand that I can get twice the voltage for half the current if connected to an input with the proper impedance with this kind of transformer but I wonder if 1:2 winding are of common use in studio gears ?

It's not uncommon: Neve's designed gear commonly use 1:2 output transfo: focusrite ( isa 110) same with Amek 9098 ( both with a twist though).
Api classic designs use 1:2 output transfo too but with a discrete aop ( daop) 2520, not a common opamp ( there was not a lot of them in early 70's and there is caveat... see below).

What are the pros and cons ?

Pro: transformers can offer 'free' voltage gain ( noiseless), galvanic isolation.
Cons: you need a a driving stage able to source current needed to drive the primary.

Eg: Focusrite isa 430 ( 110 derivative) state +26db into 600 ohm load. It means the secondary will output +15,5v rms ( +21,84v peak) into 600r so : 21.84/600= 36,41 ma on secondary side.
On primary it'll need 145ma ( 4x more current - ratio of (prim/sec)2) and 10,94v (7,74v rms) voltage drive.
That is a lot of current for an opamp ( even a daop). This is why a discrete buffer ( which offer current gain with unity voltage gain) is used right after the driving opamp in the 430.

Other issue is distortion in low end but it's common to every transformers whatever the primary/secondary ratio.

Also would you recommand a totally different transformer for those gears ?

You'll have to study the schematic and especially the output stage capability.

 

[Seon]

It's not uncommon: Neve's designed gear commonly use 1:2 output transfo: focusrite ( isa 110) same with Amek 9098 ( both with a twist though).
Api classic designs use 1:2 output transfo too but with a discrete aop ( daop) 2520, not a common opamp ( there was not a lot of them in early 70's and there is caveat... see below).



Pro: transformers can offer 'free' voltage gain ( noiseless), galvanic isolation.
Cons: you need a a driving stage able to source current needed to drive the primary.

Eg: Focusrite isa 430 ( 110 derivative) state +26db into 600 ohm load. It means the secondary will output +15,5v rms ( +21,84v peak) into 600r so : 21.84/600= 36,41 ma on secondary side.
On primary it'll need 145ma ( 4x more current - ratio of (prim/sec)2) and 10,94v (7,74v rms) voltage drive.
That is a lot of current for an opamp ( even a daop). This is why a discrete buffer ( which offer current gain with unity voltage gain) is used right after the driving opamp in the 430.

Other issue is distortion in low end but it's common to every transformers whatever the primary/secondary ratio.



You'll have to study the schematic and especially the output stage capability.

Hello, sorry for my late response !

Thank you very much for your explanations.
May I ask you one more question please ?
In a recording or mixing situation, when such piece of gear (1:2 ratio) is switched in and out of the signal path, I guess a huge difference in volume occur. Isn't it inconvenient when for example doing an A/B comparison ?

Finally, if you happen to have any book recommendation about audio transformer, I'd love to learn more !

Thank you again.

 

[gyraf]

You are not supposed to switch it in and out of circuit really

 

[Seon]

I see.
Thank you !

 

[ruffrecords]

It's not uncommon: Neve's designed gear commonly use 1:2 output transfo: focusrite ( isa 110) same with Amek 9098 ( both with a twist though).
Api classic designs use 1:2 output transfo too but with a discrete aop ( daop) 2520, not a common opamp ( there was not a lot of them in early 70's and there is caveat... see below).



Pro: transformers can offer 'free' voltage gain ( noiseless), galvanic isolation.
Cons: you need a a driving stage able to source current needed to drive the primary.

Eg: Focusrite isa 430 ( 110 derivative) state +26db into 600 ohm load. It means the secondary will output +15,5v rms ( +21,84v peak) into 600r so : 21.84/600= 36,41 ma on secondary side.
On primary it'll need 145ma ( 4x more current - ratio of (prim/sec)2) and 10,94v (7,74v rms) voltage drive.

You only need 2X the current (ratio 1:2) but even so, 70mA is a lot of current for an op amp to output.
And for the same power you only need half the voltage and this is the reason for the 1:2 output transformer ratio because the power supply was only 24V.

Cheers

Ian