A Tube Mic
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Help Support GroupDIY Audio Forum:
Martin B. Kantola
Well-known member
- Joined
- Jun 24, 2005
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- 209
[quote author="mata_haze"]*I still get hum in the audio chain and I wonder:could the heater supply cause hum in the audio path?
*I have used an LM317 to stabilize it, is that alright or shall I use something else?
*how do I see how much ripple I get from the B+? my oscilloscope will fry if I stick it to the B+ directly...[/quote]
Yes, you should suspect the heater supply, but there are many other suspects too. The 317 is OK, but only if your grounding and other stuff is correct. Is your mike properly shielded? Wrap it in (grounded) tin (alu) foil to make sure. How are the grounds from the two supplies tied together? In the PSU or in the mike? Your mike output connector is awfully close to the power transformers, that might induce some hum. Does the hum stop when you turn off the mains power? (before the mike dies)
Sure, you can look for hum on both the heater and even B+ with your scope by using a high voltage cap in series.
Martin
*I have used an LM317 to stabilize it, is that alright or shall I use something else?
*how do I see how much ripple I get from the B+? my oscilloscope will fry if I stick it to the B+ directly...[/quote]
Yes, you should suspect the heater supply, but there are many other suspects too. The 317 is OK, but only if your grounding and other stuff is correct. Is your mike properly shielded? Wrap it in (grounded) tin (alu) foil to make sure. How are the grounds from the two supplies tied together? In the PSU or in the mike? Your mike output connector is awfully close to the power transformers, that might induce some hum. Does the hum stop when you turn off the mains power? (before the mike dies)
Sure, you can look for hum on both the heater and even B+ with your scope by using a high voltage cap in series.
Martin
mata_haze
Well-known member
hi I am drawing the full schematics right now, get it posted ASAP!
[quote author="Martin"]Is your mike properly shielded?
[/quote]
I guess it is.the whole case is connected to the common ground (ground of B+ and heater supply) in the microphone itself.
[quote author="Martin"]How are the grounds from the two supplies tied together? In the PSU or in the mike?[/quote]
in the microphone,I have used two separate wires from the PSU to the mic.
[quote author="Martin"]Does the hum stop when you turn off the mains power? (before the mike dies)
[/quote]
it does disappear when I switch the mains off..
it seems like the problem is narrowing..
I am now trying to measure the ripple across the heater supply: is it just matter of sticking the probe across it?
Best,
Mattia.
[quote author="Martin"]Is your mike properly shielded?
[/quote]
I guess it is.the whole case is connected to the common ground (ground of B+ and heater supply) in the microphone itself.
[quote author="Martin"]How are the grounds from the two supplies tied together? In the PSU or in the mike?[/quote]
in the microphone,I have used two separate wires from the PSU to the mic.
[quote author="Martin"]Does the hum stop when you turn off the mains power? (before the mike dies)
[/quote]
it does disappear when I switch the mains off..
it seems like the problem is narrowing..
I am now trying to measure the ripple across the heater supply: is it just matter of sticking the probe across it?
Best,
Mattia.
Martin B. Kantola
Well-known member
- Joined
- Jun 24, 2005
- Messages
- 209
[quote author="mata_haze"][quote author="Martin"]How are the grounds from the two supplies tied together? In the PSU or in the mike?[/quote]
in the microphone,I have used two separate wires from the PSU to the mic.[/quote]
So where does the audio ground get connected then? What about the PSU box and power safety ground? I see a yellow wire, but what about from the XLR connector, does it also get tied to chassis ground? How about in your preamp?
Sorry about more questions and no answers, but that's how you can zoom in on the problem.
[quote author="mata_haze"]
I am now trying to measure the ripple across the heater supply: is it just matter of sticking the probe across it?[/quote]
Why not use a multimeter set to AC?
Peace,
Martin
in the microphone,I have used two separate wires from the PSU to the mic.[/quote]
So where does the audio ground get connected then? What about the PSU box and power safety ground? I see a yellow wire, but what about from the XLR connector, does it also get tied to chassis ground? How about in your preamp?
Sorry about more questions and no answers, but that's how you can zoom in on the problem.
[quote author="mata_haze"]
I am now trying to measure the ripple across the heater supply: is it just matter of sticking the probe across it?[/quote]
Why not use a multimeter set to AC?
Peace,
Martin
mata_haze
Well-known member
GOT IT!
the microphone works perfectly and the HUM I was getting was due to the RIPPLE coming from the Power Supply.
amazing how much difference a well built PSU can make!
quick question:
the capsule polarization made by the 1.5M and 1M resistors gives me around 80V at the 1G resistor.
what is the principle behind it? does that point have to be HALF of the B+ rail in order to give correct polarization and polar diaghram?
If I use a B+ of 250V shall that be 125? or does it have to stay at 80V?
any hints would be much appreciated,
Best, Mattia
the microphone works perfectly and the HUM I was getting was due to the RIPPLE coming from the Power Supply.
amazing how much difference a well built PSU can make!
quick question:
the capsule polarization made by the 1.5M and 1M resistors gives me around 80V at the 1G resistor.
what is the principle behind it? does that point have to be HALF of the B+ rail in order to give correct polarization and polar diaghram?
If I use a B+ of 250V shall that be 125? or does it have to stay at 80V?
any hints would be much appreciated,
Best, Mattia
G
Guest
Guest
Apply less then needed to stick membrane to base, it depends on tension. The higher you apply, the better is S/N ratio.
mata_haze
Well-known member
[quote author="Wavebourn"]Apply less then needed to stick membrane to base, it depends on tension[/quote]
not sure to understand, may I ask you some figures as example?
my B+ is 250VDC..
Many thanks,
Mattia.
not sure to understand, may I ask you some figures as example?
my B+ is 250VDC..
Many thanks,
Mattia.
G
Guest
Guest
[quote author="mata_haze"][quote author="Wavebourn"]Apply less then needed to stick membrane to base, it depends on tension[/quote]
not sure to understand, may I ask you some figures as example?
my B+ is 250VDC..
[/quote]
I know.
Do you know how much you can apply to your particular capsule before it stops working because it's membrane sticks to a base?
Let me repeat: as much as possible of a voltage is desired to apply because the more you apply the higher is output, i.e. signal / noise ratio. But capsules are electrical-mechanical thingies that are very different one from other. You can buy a party from a manufacturer that specifies a max voltage, though...
not sure to understand, may I ask you some figures as example?
my B+ is 250VDC..
[/quote]
I know.
Do you know how much you can apply to your particular capsule before it stops working because it's membrane sticks to a base?
Let me repeat: as much as possible of a voltage is desired to apply because the more you apply the higher is output, i.e. signal / noise ratio. But capsules are electrical-mechanical thingies that are very different one from other. You can buy a party from a manufacturer that specifies a max voltage, though...
mata_haze
Well-known member
Great now it's crystal clear!
I am using a Peluso CK367 , I am trying to get the data sheet now.
Analag, what is your suggestion on this?
many thanks,
Mattia.
I am using a Peluso CK367 , I am trying to get the data sheet now.
Analag, what is your suggestion on this?
many thanks,
Mattia.
Most LD capsules are designed for 60V; that's usually a safe voltage. Sometimes you get away with some more, others won't like higher voltages. I once modified a Chinese mic with a DC converter that generated 75V. It worked OK, but you could tell that it didn't "like" the high voltage. The mic originally had a weird convoluted KM84-meets-Schoeps circuit which obviously drew some current and dropped P48 to something like 35V. At 75V it worked, but it became much more sensitive to pops. It was an experiment; once I go back to that mic, I'll probably drop the voltage somewhat. 60V should suffice, and S/N shouldn't be me much worse. Keep in mind that you have to double the voltage for 6dB more output. More voltage will tension the diaphragm some more, which of course alters the sound to some degree.
G
Guest
Guest
[quote author="Gus"]What Waveborne posted about wanting the max voltage is not always true.
Look at some old tube microphone schematics try the voltages you see on the schematics[/quote]
"He is wrong; look for examples that prove that he is right".
Gus, I appreciate that! :thumb:
Theoretically tension can cause distortions...
Look at some old tube microphone schematics try the voltages you see on the schematics[/quote]
"He is wrong; look for examples that prove that he is right".
Gus, I appreciate that! :thumb:
Theoretically tension can cause distortions...
G
Guest
Guest
[quote author="Martin B. Kantola"]Please switch back to Russian you two. This is not better.
[/quote]
No problems Martin;
a Russian guitarist from Canada Andrew Krylow was my guest the last Sunday:
http://www.wavebourn.com/music/akrylov/samples/aksample01.mp3
If Marik has a good will to tune my upright "balalaika" I may record him using my humble equipment. The main condition is, he has to play in front of guests: I am a hunter as opposed to a supermarket buyer; I record fresh live unique concerts instead of artists singing and playing for a wall in a studio.
[/quote]
No problems Martin;
a Russian guitarist from Canada Andrew Krylow was my guest the last Sunday:
http://www.wavebourn.com/music/akrylov/samples/aksample01.mp3
If Marik has a good will to tune my upright "balalaika" I may record him using my humble equipment. The main condition is, he has to play in front of guests: I am a hunter as opposed to a supermarket buyer; I record fresh live unique concerts instead of artists singing and playing for a wall in a studio.
Hopefully we can get this thread back on track?
Marik could you let me know what you think are the sonic diffences with different value grid resistors?
I would expect that changing it from say 250M to 1G will increase the low frequency response?
Any comments from you or anyone else would be appreciated.
Sorr
Marik could you let me know what you think are the sonic diffences with different value grid resistors?
I would expect that changing it from say 250M to 1G will increase the low frequency response?
Any comments from you or anyone else would be appreciated.
Sorr
Sonic
Well-known member
I in the microphones use the resistor face value in 100 M-tried to put and resistor 840 M, but with my caps of the big difference in sounding low frequencies have not noticed. On lamps microphones "LOMO" were used resistors value 100M , but as sound! Though, can, those and did not come across to you.
P.S. To Wavebourn and Marik. Приятно почитать по-русски на импортном сайте, но будте цивиллизованней, на русских форумах говна хватает, а вы его ещё сюда перетаскиваете, хотя Марик уже раскаялся. Давайте продолжим про микрофоны. :wink:
P.S. To Wavebourn and Marik. Приятно почитать по-русски на импортном сайте, но будте цивиллизованней, на русских форумах говна хватает, а вы его ещё сюда перетаскиваете, хотя Марик уже раскаялся. Давайте продолжим про микрофоны. :wink:
G
Guest
Guest
[quote author="Sonic"]I in the microphones use the resistor face value in 100 M-tried to put and resistor 840 M, but with my caps of the big difference in sounding low frequencies have not noticed. On lamps microphones "LOMO" were used resistors value 100M , but as sound! Though, can, those and did not come across to you.
P.S. To Wavebourn and Marik. Приятно почитать по-русски на импортном сайте, но будте цивиллизованней, на русских форумах говна хватает, а вы его ещё сюда перетаскиваете, хотя Марик уже раскаялся. Давайте продолжим про микрофоны. :wink:[/quote]
Ok; if Cgs of 2SK170 is 30 pF it means 133 Mega Ohm on 40 Hz frequency.
What is capacitance of the capsule you are speaking about?
P.S. To Wavebourn and Marik. Приятно почитать по-русски на импортном сайте, но будте цивиллизованней, на русских форумах говна хватает, а вы его ещё сюда перетаскиваете, хотя Марик уже раскаялся. Давайте продолжим про микрофоны. :wink:[/quote]
Ok; if Cgs of 2SK170 is 30 pF it means 133 Mega Ohm on 40 Hz frequency.
What is capacitance of the capsule you are speaking about?
Sonic
Well-known member
Capacity of a cap with a membrane 25мм-80-90pF;
Cap with a membrane 32мм-120-135pF.
Data are resulted approximately as especially exact device at hand is not present.
Gaugings of capacity of a cap on LOMO MKE-271 have shown 35pF, but the resistor on shutter FET KP303 by face value 560M there is used.
Cap with a membrane 32мм-120-135pF.
Data are resulted approximately as especially exact device at hand is not present.
Gaugings of capacity of a cap on LOMO MKE-271 have shown 35pF, but the resistor on shutter FET KP303 by face value 560M there is used.
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