kurganyuriy1987
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K47 capsule with EF86
- Thread starter kurganyuriy1987
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Help Support GroupDIY Audio Forum:
Thats quite similar to an EF86 based mic I built, back plate connected to polarising voltage ,capsule front direct to grid like the U47. 1gigaohm grid resistor does seem a bit high ,my guess is you'd need to very carefully select your ef86 to work with that value .U67 uses a similar value but ef86's dont live all that long in them in my experience . 40 megohms is the listed as the highest grid resistor for the ef86 I believe ,I ended up using an 80 or 120 meg resistor in mine .Worth using a ptfe tube socket in this application also if you can get it .
kurganyuriy1987
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Here you have two options of EF86 mic which fit k47 capsule
https://groupdiy.com/index.php?topic=64687.msg819492#msg819492
https://groupdiy.com/index.php?topic=62441.0
S316 use psu switch to change polarisation voltage, you can skip it - for k47 c3 isn't needed.
High impedance resistors from 100M to 470M.
For your schematic - don't need to install two plate resistors and filtering cap - there's marginal benefit from it, but the phase is much better without it.
For cathode - G7 arrangement was experimental to use feedback. Without any feedback this arrangement doesn't work good.
Choose between one cap and one resistor or just one resistor.
Output capacitor 0.5uF is enough and there's positive audible benefit from using lower value. 2.2uF is totally to high. In both cases low end level is the same. Proper cathode biasing will give proper low end level
Polarisation voltage - you need to use divider! Currently your capsule will die quickly with 160V. Max what you can use is 3M/2M (this side to ground) and add high impedance resistor + filtering cap.
Hope this help somehow
https://groupdiy.com/index.php?topic=64687.msg819492#msg819492
https://groupdiy.com/index.php?topic=62441.0
S316 use psu switch to change polarisation voltage, you can skip it - for k47 c3 isn't needed.
High impedance resistors from 100M to 470M.
For your schematic - don't need to install two plate resistors and filtering cap - there's marginal benefit from it, but the phase is much better without it.
For cathode - G7 arrangement was experimental to use feedback. Without any feedback this arrangement doesn't work good.
Choose between one cap and one resistor or just one resistor.
Output capacitor 0.5uF is enough and there's positive audible benefit from using lower value. 2.2uF is totally to high. In both cases low end level is the same. Proper cathode biasing will give proper low end level
Polarisation voltage - you need to use divider! Currently your capsule will die quickly with 160V. Max what you can use is 3M/2M (this side to ground) and add high impedance resistor + filtering cap.
Hope this help somehow
kurganyuriy1987
Member
- Joined
- Oct 10, 2012
- Messages
- 11
ln76d said:Here you have two options of EF86 mic which fit k47 capsule
https://groupdiy.com/index.php?topic=64687.msg819492#msg819492
https://groupdiy.com/index.php?topic=62441.0
S316 use psu switch to change polarisation voltage, you can skip it - for k47 c3 isn't needed.
High impedance resistors from 100M to 470M.
For your schematic - don't need to install two plate resistors and filtering cap - there's marginal benefit from it, but the phase is much better without it.
For cathode - G7 arrangement was experimental to use feedback. Without any feedback this arrangement doesn't work good.
Choose between one cap and one resistor or just one resistor.
Output capacitor 0.5uF is enough and there's positive audible benefit from using lower value. 2.2uF is totally to high. In both cases low end level is the same. Proper cathode biasing will give proper low end level
Polarisation voltage - you need to use divider! Currently your capsule will die quickly with 160V. Max what you can use is 3M/2M (this side to ground) and add high impedance resistor + filtering cap.
Hope this help somehow
Thank you a lot!
I done test layout. Circuit is working.
But I can't understand one thing..
After divider 3m3 and 1M series resistor i got 75v. But after 100M in the backplate point only 1v..
so.. do I need to use 100M ?
Your multimeter has an input impedance of 1M, or maaaaaybe 10M if you're lucky. Together with that 100M, that forms a (huge) voltage divider That's why you're measuring next-to-nothing "after" it.
PS: For whatever reason, i can't see the attachment. But if you did that 3.3meg / 1meg divider from 160v, unless my math is seriously wrong, that would only result in about 37. ???
160v x 1meg / 4.3meg (total) = 160v * 0.23 = 37.2
That's why you're measuring next-to-nothing "after" it.PS: For whatever reason, i can't see the attachment. But if you did that 3.3meg / 1meg divider from 160v, unless my math is seriously wrong, that would only result in about 37. ???
160v x 1meg / 4.3meg (total) = 160v * 0.23 = 37.2
kurganyuriy1987
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- Oct 10, 2012
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Khron said:Your multimeter has an input impedance of 1M, or maaaaaybe 10M if you're lucky. Together with that 100M, that forms a (huge) voltage divider
PS: For whatever reason, i can't see the attachment. But if you did that 3.3meg / 1meg divider from 160v, unless my math is seriously wrong, that would only result in about 37. ???
160v x 1meg / 4.3meg (total) = 160v * 0.23 = 37.2
Sorry, reload attachment
Is this correct circuit, or need change something?
Attachments
Umm..... In short, yes, changes ARE required.
First of all: https://en.wikipedia.org/wiki/Voltage_divider
(Hint: the "Vout" from the above link, goes to the backplate)
https://groupdiy.com/index.php?action=dlattach;topic=62441.0;attach=46826
Looking at the capsule side only, in your case, your R3 (the "top" resistor of the voltage divider) would be the 3.3meg, but to get about 60v at the capsule, your R6 ("bottom" resistor) would need to be around 1.2-1.3meg. Using (more) standard values, 2.7meg and 1meg would get you there. That is assuming a 160v "starting" voltage.
With 137v or so, you miiiiiiiight get away with a 1:1 resistor ratio (say, two 3.3meg ones), which would give you about 66-67V or so. A bit on the high side, but workable, i think. Maybe if you bumped up your R5 from 10k to 12-15k, that would bring the "B+" (137v) down a few volts, and with it, the capsule bias voltage as well.
First of all: https://en.wikipedia.org/wiki/Voltage_divider
(Hint: the "Vout" from the above link, goes to the backplate)
https://groupdiy.com/index.php?action=dlattach;topic=62441.0;attach=46826
Looking at the capsule side only, in your case, your R3 (the "top" resistor of the voltage divider) would be the 3.3meg, but to get about 60v at the capsule, your R6 ("bottom" resistor) would need to be around 1.2-1.3meg. Using (more) standard values, 2.7meg and 1meg would get you there. That is assuming a 160v "starting" voltage.
With 137v or so, you miiiiiiiight get away with a 1:1 resistor ratio (say, two 3.3meg ones), which would give you about 66-67V or so. A bit on the high side, but workable, i think. Maybe if you bumped up your R5 from 10k to 12-15k, that would bring the "B+" (137v) down a few volts, and with it, the capsule bias voltage as well.
kurganyuriy1987
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KrIVIUM2323
Well-known member
Hi,
Using the capacitor bypass the 'natural' feedback that occurs (sometimes called degeneration feedback) when you put a resistor in series with cathode.
The cap indeed increase gain, but raise distortion too and cathode being low impedance 'the sound' of capacitor is audible (one of the reason you sometimes see some film cap 1/100 the value of electrolitycs parraleled).
If you like the sound without cap keep it like this... or add a jumper to have both options.
A little bit of theory (easy to understand) about unbypassed and bypassed grounded cathode amplifier:
https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiopqa6kcPXAhVHwBQKHUleAn8QFggnMAA&url=http%3A%2F%2Fken-gilbert.com%2Fimages%2Fpdf%2Facpart1.pdf&usg=AOvVaw2wR3eUwBpksZ-uIGXpSdpL
Edit: if link don t work google 'Crowhurst Audio Classroom part1'
Using the capacitor bypass the 'natural' feedback that occurs (sometimes called degeneration feedback) when you put a resistor in series with cathode.
The cap indeed increase gain, but raise distortion too and cathode being low impedance 'the sound' of capacitor is audible (one of the reason you sometimes see some film cap 1/100 the value of electrolitycs parraleled).
If you like the sound without cap keep it like this... or add a jumper to have both options.
A little bit of theory (easy to understand) about unbypassed and bypassed grounded cathode amplifier:
https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiopqa6kcPXAhVHwBQKHUleAn8QFggnMAA&url=http%3A%2F%2Fken-gilbert.com%2Fimages%2Fpdf%2Facpart1.pdf&usg=AOvVaw2wR3eUwBpksZ-uIGXpSdpL
Edit: if link don t work google 'Crowhurst Audio Classroom part1'
For chinese K47 remove C1 and R2 - you will get better response.
In case of cathode cap - with EF86 you are able to get decent level without it, so try both options but without the cap you need to re-bias circuit to get similar level in comparison. Another thing to try is wiring output transformer. Especially for unbypassed cathode - negative node connection - cathode vs. ground (you can use simple switch to make comparison).
In case of cathode cap - with EF86 you are able to get decent level without it, so try both options but without the cap you need to re-bias circuit to get similar level in comparison. Another thing to try is wiring output transformer. Especially for unbypassed cathode - negative node connection - cathode vs. ground (you can use simple switch to make comparison).
KrIVIUM2323
Well-known member
Like in the 'Church' mic Piotr?
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