The Mad Science Challange -DIY MIC IPT

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volker

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I also have a couple of the same Vacuumschmelze cores laying around for quite some time. Also some of the russian cobalt ones that are so ubiquitous on ebay. So thanks for doing the groundwork (y). Latest one looks great, which size is that? If I remember right they go up in prize quite steeply.
You might want to crack open one of the Haufe and Pikatron toroids if you need more inspiration for winding patterns. I've never had one open, so I don't know if they are potted on the inside.
 

solkatten

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I also have a couple of the same Vacuumschmelze cores laying around for quite some time. Also some of the russian cobalt ones that are so ubiquitous on ebay. So thanks for doing the groundwork (y). Latest one looks great, which size is that? If I remember right they go up in prize quite steeply.
You might want to crack open one of the Haufe and Pikatron toroids if you need more inspiration for winding patterns. I've never had one open, so I don't know if they are potted on the inside.
[/QUOTE

Its 45*25*15 mm al:88u. Price: 16 euro
Se datasheet in post 1
 

solkatten

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3000 turns later…👍

1:8
primary inductance 10H dcr 8 Ohm

-3db 5Hz-35 KHz 200 Ohm source.

I think this is the best I can do . Its impossible to hand wind a true progressive secondary… It has to be done on a machine ☹️

Next I will wind 1:5 version. It will really improve the upper freq response… Its 1000 less turns on the secondary and the impedance ratio is almost one third …
 

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gyraf

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Aah, well done!

I'm currently working this very same route with a local talent here

5Hz at 10H indicates a driving impedance of ca. 300 Ohms - is this in the ballpark of what you're measuring it at?

If so, perhaps try measuring at 600 also, many dyna-mic's go toward here at higher frequencies - to get an idea of how interaction can be expected to play out..?



/Jakob E.
 

solkatten

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Aah, well done!

I'm currently working this very same route with a local talent here
5Hz at 10H indicates a driving impedance of ca. 300 Ohms - is this in the ballpark of what you're measuring it at?

If so, perhaps try measuring at 600 also, many dyna-mic's go toward here at higher frequencies - to get an idea of how interaction can be expected to play out..?



/Jakob E.

Thanks…

Yeas the low freq was calculated because my sound card rolls of earlier

The hi freq roll of was calculated with a 2k source in series

I hope you get sucess with the toroid IPT

Primary inductance was calculated and measured to 10H
 
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solkatten

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I will install the trafo in my 4in1 mic pre today and see how its performance in real like.

The freq response is with a 200 Ohm source

My REW doesnt work right now so I cant do any accurate THD measurment

Jakob have you tried progressive winding?
 

gyraf

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Yes, progressive winding tends to help significantly for keeping self-capacitance/potential "distance" low, making it easier on the high frequencies
 

solkatten

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Heres the 1:5 toroid.. Great succes... the -3db is 15K with a 2K source, that would be ten times higher with a 200r source, so -3db is above 100KHz...
Primary inductance is 10H so the -3db is in the 5Hz range..

Primary: 360T 0,25 mm. 10H 5ohm
Secondary 1800T 0,1 mm /55 sections. 33T/section. 250H 125ohm

My 1:8 had a slight roll off before 20K and the OPT had a slight roll off as well, in my 4in1 pre. But with a 1:5 on the input the OPT start to drop after 15K, if I want flat response to 20KHz I probably would need to implement feedback on the pp stage lower source Z or switch to Lundahl PP trafo with better freq response...

My sound card is also down 1 db at 16Khz and down 14 db at 20Khz
 

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solkatten

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Came to realize that interwinding capacitance was high in my trafos so I made a new one with a electrostatic screen between pri and sec. It was very good for the high freq response. Though its closer to 1:4 than 1:5. It had better high freq response than LL 1538. I will post the measurments tomorrow👍 Its the first time I beat my reference trafo😎
 

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solkatten

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Heres the trafos with a extreme source impedance of 20K. On top 1:4 toroid on the bottom LL1538... The Lundahl rolls off faster....
 

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solkatten

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I have wrestled with REW to make meaningful measurments, Now my soundcard is down 1 db at 20k and so is my trafo with 475 ohm source. Extrapolation made from my earlier measurments doesnt seem to hold up, so this one has the absolute best freq. response of all my trafos...
 

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Tubetec

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Had been meaning to ask , what sample rate do you have REW set to ?
Are you using asio drivers ?
If you can go with at least 96khz sample rate , I think the general concensus has been ASIO drivers are the best option also . If your soundcard doesnt have its own asio driver you can give ASIO4all a try , with that installed your soundcard will become available in preferences ,driver ,ASIO , ASIO4all in REW .
 

solkatten

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At first REW only worked with my old sound card at 48khz But now I managed to re-route the inputs and ouputs of my focusrite. Now Im measuring at 96khz. 👍 I have a Mac computer at home
 

solkatten

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Hi thanx 5v333… I have signal generator but no scope, Im thinking about buying a scope so I can measure those high freq. 👍
 
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