Hey guys ! I have been building an output transformer to the Manual written by Robert G Wolpert.
A measure for primary inductance depending on cutoff frequency , -1db loss at the lower bound frequency f1 is given by:
L = (Primary Impedance)/(pi*f1)
here using my primary value of 4KOhm and frequency of 20Hz , I get an inductance value of ... 64 Henry. Which seems like a lot and not a very realistic value to design towards.
However , another equation that works using maximum flux density (B) is ;
N = (V * 10^8)/(K * A * f1 * B * 6.45) where A is the Bobbin Area and K is the stacking factor.
here using my values of V=346 , A=3.68 , f1=20 , B=14KGauss , a much more reasonable value of 1302 turns is shown.
So my question is , do I go ahead with the 1302 Primary turns to hopefully wind up a whopping 64 Henry primary inductance ? Or should I be less ambitious and go for -3db loss at 20Hz , or even -1db loss at 40Hz or so ?
Thank you for the help guys !
A measure for primary inductance depending on cutoff frequency , -1db loss at the lower bound frequency f1 is given by:
L = (Primary Impedance)/(pi*f1)
here using my primary value of 4KOhm and frequency of 20Hz , I get an inductance value of ... 64 Henry. Which seems like a lot and not a very realistic value to design towards.
However , another equation that works using maximum flux density (B) is ;
N = (V * 10^8)/(K * A * f1 * B * 6.45) where A is the Bobbin Area and K is the stacking factor.
here using my values of V=346 , A=3.68 , f1=20 , B=14KGauss , a much more reasonable value of 1302 turns is shown.
So my question is , do I go ahead with the 1302 Primary turns to hopefully wind up a whopping 64 Henry primary inductance ? Or should I be less ambitious and go for -3db loss at 20Hz , or even -1db loss at 40Hz or so ?
Thank you for the help guys !
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Is this for a single-ended or push-pull transformer?
If you look at transformer data sheets, 64H doesn't seem so unusual for se.
For pp you often see L approaching a kH (both primary sections).
Jan
If you look at transformer data sheets, 64H doesn't seem so unusual for se.
For pp you often see L approaching a kH (both primary sections).
Jan
64H looks quite normal for push pull. An ordinary 4k SE transformer might only be 20H or so, but high-end devices may aim for something in that range.
For 4k primary impedance an inductance value of around 30 Henry is enough (4k / (2 x pi x 20)).
Unless you have a massive core you will not get 64 Henry with 1300 turns.
With the appropriate core dimension, let's say a core with around 20 square cm of Afe, for an application of a SE air-gapped transfomer with ~ 100 mA of primary DC current, you would need something between 2000 and 2500 primary turns to give you an idea.
Unless you have a massive core you will not get 64 Henry with 1300 turns.
With the appropriate core dimension, let's say a core with around 20 square cm of Afe, for an application of a SE air-gapped transfomer with ~ 100 mA of primary DC current, you would need something between 2000 and 2500 primary turns to give you an idea.
64H is for high Ri tubes (845; 211).
For PP normal values are between 100 and 250 H (both primary sections in series).
Sorry for not specifying ! Its 4 EL84's running in Push-Pull.
It's a relief to hear 64H isn't a high value. Lots of examples I see worked online come up to values closer to the 20H range.
Thank you so much!
I actually have a pretty oversized core I think ! Its around 24 square cm in the Bobbin in push-pull pulling about 150mA of current max. Thank you for the response !
I'm currently experimenting with a VDV-GIT80 which sports 900H (measured at 50Hz) over both PP primaries.
What am I missing??
Jan
What am I missing??
Jan
Apples vs. oranges.
The first equation if for the (small signal) frequency response. The second equation is for the maximum power handling' capability. They are separate and independent of each other.
Also, the inductance of an ungapped core winding is a strong function of the signal level and frequency - near saturation it may be more than an order of magnitude greater than at small signal levels.
The first equation if for the (small signal) frequency response. The second equation is for the maximum power handling' capability. They are separate and independent of each other.
Also, the inductance of an ungapped core winding is a strong function of the signal level and frequency - near saturation it may be more than an order of magnitude greater than at small signal levels.
@rehankromodoyo : is this your first transformer? The secret is to push the self resonance as high as possible, at least 2x the highest audio frequency. This means keep the self capacitance and the stray inductance low. They are contradictionary requirements. Splitting the primary and secondary into interleaving sections, like p-s-p-s-p and cleverly connecting them in series and/or parallel is the solution, but the devil is in the details. Best to copy a proven winding arrangement.
@lcsaszar yes it is ! I am vaguely following a document of someone winding the exact OT , although I am winding mine with a bit of a more hi-fi bandwidth in mind as opposed to the usual guitar amp OT of 70Hz to 14KHz or so (as I've read online). I haven't still come up with an interleaving arrangement yet but the one used by Robert G. Wolpert in his book looks very appealing (pg 48) ; he uses a 4:5 interleave for primary : secondary. It's a bit more tricky due to the multiple secondary taps as well! Thank you for the response !
The laminations I'm using are EI-114 laminations but they were bought from a pretty shady shop with no manufacturers details. Does anyone know a way I can determine an Inductance formula for this lamination ? Thickness of 0.5mm. Are there any safe approximate equations I can use without any manufacturers details?
Edit: Maybe I ought to make a new post for this doubt. They are Silicon Steel laminations , 4% I believe . I really bought this core at a time I wasn't really sure what I was doing. I doubt the shop-owner could tell me the lamination composition but I will try to ask !
Edit: Maybe I ought to make a new post for this doubt. They are Silicon Steel laminations , 4% I believe . I really bought this core at a time I wasn't really sure what I was doing. I doubt the shop-owner could tell me the lamination composition but I will try to ask !
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You can get a good set of data sheets from Tempel. By far, the most commonly manufactured thickness is 0.36mm, so double-check your measurements.
Also, I believe that you will find that inductance goes down at saturation, not up.
Also, I believe that you will find that inductance goes down at saturation, not up.
Jan, you're missing the fact that inductance of these transformers is measured with 230 VRMS at 50 Hz across the full primary.
That yields impressive specs but is not comparable with the much lower voltages of normal inductance meters used by transformer winders.
By the way, VDV-GIT80 is specified for 600H.
In my DS it says 900H.
But what I don't understand is why the inductance varies with the measurement voltage.
I would think that inductance depends on the number of turns and the core parameters.
Do the core parameters vary with signal level and frequency?
As long as you stay within the reasonable linear part of the B/H curve, which you would, no?
Jan
But what I don't understand is why the inductance varies with the measurement voltage.
I would think that inductance depends on the number of turns and the core parameters.
Do the core parameters vary with signal level and frequency?
As long as you stay within the reasonable linear part of the B/H curve, which you would, no?
Jan
Attachments
Jan,
Inductance varies very much with voltage and frequency; this is basic transformer stuff.
There is a VDV-GIT80 and a VDV=GIT80-t, different transformers (EI and toroidal core respectively).
Inductance varies very much with voltage and frequency; this is basic transformer stuff.
There is a VDV-GIT80 and a VDV=GIT80-t, different transformers (EI and toroidal core respectively).
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That is the toroid, the -t. The GIT80 is EI core.
What is causing the change in inductance with level and frequency?
Is that specific to transformers?
I mean, if I buy an inductor for a crossover filter, it better have constant inductance with level and frequency!
So what is the difference with an OPT then?
Jan
What is causing the change in inductance with level and frequency?
Is that specific to transformers?
I mean, if I buy an inductor for a crossover filter, it better have constant inductance with level and frequency!
So what is the difference with an OPT then?
Jan
The keyword is effective permeability.
For transformers with cores...yes.
Crossover filter inductors are (normally) coreless, so inductance is constant with voltage and frequency.