BV08 transformer capacitance, comparable to mic cable capacitance?

[ELS]

Yes it's a very random question.
Does anyone know the primary winding capacitance of the BV08 transformer? or around what capacitance it could be?
I'm wondering how that compares to like 15 feet of mic cable, which would be around 750pF.

 

[CJ]

Depends on which capacitance, pri to gnd. Sec to gnd. Pri to sec. Turn to turn capacitance , layer to layer capacitance etc.

Should be pretty low. Much less than 750 pf.

Layer C and turn to turn C are hard to measure so formulas are usually used .

Pri to sec and pri or sec to gnd(core) can be measured with a meter.

 

[ELS]

Depends on which capacitance, pri to gnd. Sec to gnd. Pri to sec. Turn to turn capacitance , layer to layer capacitance etc.

Should be pretty low. Much less than 750 pf.

Layer C and turn to turn C are hard to measure so formulas are usually used .

Pri to sec and pri or sec to gnd(core) can be measured with a meter.

I was interested in the primary, across the entire primary.
what would a typical value be? perhaps like 80pF?

 

[Khron]

Why exactly are you looking for that capacitance? And/or do you 100% know what you're looking for?

 

[ELS]

Why exactly are you looking for that capacitance? And/or do you 100% know what you're looking for?

I just want to have some idea of what impedance I should aim for in my tube mic design, as I don't want to use an output transformer but I don't want to have a lot of high end roll off. So I'd like to use the U47's transformer's primary capacitance to calculate the high end roll off that would create, as a guideline.

 

[Khron]

I'm no transformer expert, but i'm nearly certain the "primary capacitance" is the main cause of top-end roll-off.

Do you mean the parasitic capacitance of the windings of the transformer primary? As @CJ very pertinently pointed out, capacitances are usually specified between two elements.

https://sound-au.com/articles/audio-xfmrs.htm#s1
"A transformer's high frequency response is limited by leakage inductance. This is caused by magnetic flux that manages to 'escape' from the core, and it appears as a separate inductance in series with the primary. There are ways that are used to minimise leakage inductance, and these must be applied in any transformer that has a significant step-up or step-down ratio. 1:2 or 2:1 ratios (or less) are usually easy enough to make with acceptable leakage inductance. While measuring leakage inductance might seem to be a rather esoteric test, in reality it's actually quite simple - short circuit the secondary and measure the primary inductance."

 

[ELS]

I'm no transformer expert, but i'm nearly certain the "primary capacitance" is the main cause of top-end roll-off.

Do you mean the parasitic capacitance of the windings of the transformer primary? As @CJ very pertinently pointed out, capacitances are usually specified between two elements.

https://sound-au.com/articles/audio-xfmrs.htm#s1
"A transformer's high frequency response is limited by leakage inductance. This is caused by magnetic flux that manages to 'escape' from the core, and it appears as a separate inductance in series with the primary. There are ways that are used to minimise leakage inductance, and these must be applied in any transformer that has a significant step-up or step-down ratio. 1:2 or 2:1 ratios (or less) are usually easy enough to make with acceptable leakage inductance. While measuring leakage inductance might seem to be a rather esoteric test, in reality it's actually quite simple - short circuit the secondary and measure the primary inductance."

I've said what I am looking for for like the 3rd time now, and ya'll perfectly understood what I meant, yet you post Transformer basics 101 like I would've asked 'what was winding capacitance'...

 

[Khron]

What we might not have understood is why that particular parameter, and only that and nothing else, is responsible for the effect you mention, at least in your view.

 

[ELS]

What we might not have understood is why that particular parameter, and only that and nothing else, is responsible for the effect you mention, at least in your view.

I just want to have some idea of what impedance I should aim for in my tube mic design, as I don't want to use an output transformer but I don't want to have a lot of high end roll off. So I'd like to use the U47's transformer's primary capacitance to calculate the high end roll off that would create, as a guideline.

^
I mean if you have other parameters you can feel free to post them, it might help someone else in their mic design.

 

[Khron]

^
I mean if you have other parameters you can feel free to post them, it might help someone else in their mic design.

https://sound-au.com/articles/audio-xfmrs.htm#s1
"A transformer's high frequency response is limited by leakage inductance. This is caused by magnetic flux that manages to 'escape' from the core, and it appears as a separate inductance in series with the primary. There are ways that are used to minimise leakage inductance, and these must be applied in any transformer that has a significant step-up or step-down ratio. 1:2 or 2:1 ratios (or less) are usually easy enough to make with acceptable leakage inductance. While measuring leakage inductance might seem to be a rather esoteric test, in reality it's actually quite simple - short circuit the secondary and measure the primary inductance."

Ahem...

 

[ELS]

Ahem...

oh I didn't know the winding capacitance was ignored in amplfiier design. my bad.

 

[Khron]

Well, there's always the tiniest possibility there's a reason for that. Could it be that (most likely) the effects of leakage inductance dwarf the effects of the primary capacitance?

But fine, feel free to disregard established facts, and good luck on your endeavor then
(Not intending to sound particularly passive-aggressive, but this is one windmill i'd rather not fight any further )

 

[ELS]

Well, there's always the tiniest possibility there's a reason for that. Could it be that (most likely) the effects of leakage inductance dwarf the effects of the primary capacitance?

But fine, feel free to disregard established facts, and good luck on your endeavor then
(Not intending to sound particularly passive-aggressive, but this is one windmill i'd rather not fight any further )

Well sorry, it's just that I see far too many people on forums post replies the don't have anything to do with the question at all and when you call them out they call you an inconsiderate prick

 

[gyraf]

Classic XY-problem: The XY Problem

When designing your mic out transformer, start out by selecting a core (for mic output I'd say that size dosent matter), then based on its perm and expected driving-source-impedance calculate the needed number of pri turns to get below minimum wanted low-frequency turnover point.
Then calculate number of turns for your sec (from your wished ratio)
Now wind the transformer and measure actual response under irl conditions. if you have unneded too high high-frequency freq response, you can exchange some of that for even more turns of primary - giving you better lowend stability

It's all about finding the right compromise..

/Jakob E.

 

[gyraf]

CJ:

Layer C and turn to turn C are hard to measure so formulas are usually used

Any short-form explanation of how one might quantify this?

/Jakob E.

 

[Murdock]

I don’t think he wants to make his own transformer.
Is it possible that you’ve read about the Hiller M60 mic?
It has the output transformer outside of the mic in either a separate box or in the power supply. It could only be used with a special cable as the cable capacitance was part of the circuit and the hf loss was accounted for.

 

[Khron]

Classic XY-problem: The XY Problem

/Jakob E.

THIS.

 

[Murdock]

This is a translated excerpt of the description:

A special feature can be seen in the frequency response (Figure 5) and the output impedance. Due to the capacitance of the cable between the microphone and the preamplifier, the frequency curve drops by around 8db at 15 kHz. This drop is compensated for by suitably dimensioning the microphone capsule. At the same time, the impedance of 200 ohms at 1000 Hz drops to 60 ohms at 15,000 Hz. In practice, however, only a high-impedance termination of the capsule (downstream amplifier input 5 x Ri) comes into question. Here the curve is sufficiently straight.

The capacity of this cable must have a very specific value (1750 pF), since the cable capacity is included in the frequency response. One core of the cable and the shielding serve as heating lines for the MSC2 tube. For this reason, the loop resistance of these two lines must be within very narrow tolerances. These conditions place high demands on the cable manufacturer.

 

[Murdock]

So it seems rather complicated. Maybe use a cathode follower? As far as I understand it would make things a lot simpler when you want to avoid a transformer but want to use tubes.

 

[Lampie519]

https://gyraf.dk/schematics/Radiometer_Mic.GIF