A Tube Mic
- Thread starter analag
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mata_haze
Well-known member
[quote author="analag"]I assume it is rectified and filtered (DC) right?[/quote]
precisely, through a LM317.
thank you for the tip.I'll do that right away.
Mattia.
precisely, through a LM317.
thank you for the tip.I'll do that right away.
Mattia.
mata_haze
Well-known member
[quote author="analag"]Case closed....I think. [/quote]
almost...
the modification you suggested me did work perfectly,the noise floor dropped from 20mVpp to 10mVpp with mic on the bench and no shielding around.
I am now prototyping the board and putting it all together.
after this I'll test it again in the mic enclosure to see what happens.
we'll keep you posted with the results.
thank you for your support analag!
Cheers,
Mattia.
almost...
the modification you suggested me did work perfectly,the noise floor dropped from 20mVpp to 10mVpp with mic on the bench and no shielding around.
I am now prototyping the board and putting it all together.
after this I'll test it again in the mic enclosure to see what happens.
we'll keep you posted with the results.
thank you for your support analag!
Cheers,
Mattia.
mata_haze
Well-known member
ok first test passed.
the microphone works but there is some background noise for which I would like to have your opinion if possible.
I have added two sound files one through a Neumann M149 (ECC83 I guess) and the other is the Analag 6AU6, the noise is right at the very beginning of the file.
do you think it's due to a bad tube?
[I know my voice sounds funny though...]
Best Mattia.
Neumann
http://www.supload.com/sound_confirm.php?get=210255224.wav
Analag 6AU6
http://www.supload.com/sound_confirm.php?get=875356830.wav
the microphone works but there is some background noise for which I would like to have your opinion if possible.
I have added two sound files one through a Neumann M149 (ECC83 I guess) and the other is the Analag 6AU6, the noise is right at the very beginning of the file.
do you think it's due to a bad tube?
[I know my voice sounds funny though...]
Best Mattia.
Neumann
http://www.supload.com/sound_confirm.php?get=210255224.wav
Analag 6AU6
http://www.supload.com/sound_confirm.php?get=875356830.wav
I try to keep the grid connection off the board because with a such high resistor even the grease off your finger becomes a conductor also try a few more tubes. You might have to go through a few to find one with an acceptable noise level.
mata_haze
Well-known member
YES!
it was due to the tube of course.we managed to get some NEW ones in and now the noise level it's really low!
on the other side there is a constant hum at the output.
I am going to do a new layout of the board to see if I can keep the grid away from everything to begin with.
DO you think there could be a big difference in level between a 7:1 and a 5:1 output transformer?
Best,
Mattia.
it was due to the tube of course.we managed to get some NEW ones in and now the noise level it's really low!
on the other side there is a constant hum at the output.
I am going to do a new layout of the board to see if I can keep the grid away from everything to begin with.
DO you think there could be a big difference in level between a 7:1 and a 5:1 output transformer?
Best,
Mattia.
mata_haze
Well-known member
[quote author="analag"]If you want to use a 5:1 ratio I would suggest you use this tube I'm going to PM you about. It's my favorite of the 6A*6 variant. I'm also going to suggest a slight modification for less noise.
[/quote]
brilliant!
[/quote]
brilliant!
skipwave
Well-known member
Tube puzzles are fun. The candidates are....
6AB4
6AG5
6AJ5
6AK5
6AK6
6AM6
6AQ6
6AS6
6AW6
A couple are no good for this application for obvious reasons, but I threw them in anyway. I like the look of 6AW6.
This is a useful resource for quick checking lots of tube models:
http://www.nj7p.org/Tube4.php?index=1
6AB4
6AG5
6AJ5
6AK5
6AK6
6AM6
6AQ6
6AS6
6AW6
A couple are no good for this application for obvious reasons, but I threw them in anyway. I like the look of 6AW6.
This is a useful resource for quick checking lots of tube models:
http://www.nj7p.org/Tube4.php?index=1
synthi
Well-known member
Hmmm... 6AK5?
Is used in a couple of tube mics so I bet for this one.
Synthi
Is used in a couple of tube mics so I bet for this one.
Synthi
mata_haze
Well-known member
Hello,
couple of questions regarding noise figure on the tube mic, so I know what I should expect.
the microphone it's working (using 6AU6 for now, but updated tube soon to be used!), lot's of gain and very good overall sound.
I do have some issues which I would like to know if they can be addressed.
1) there is a persistent HUM at the output (20mVpp)
2) there is a constant buzz on the high end side
3) the polar pattern seems to not be doing much,although it does increase the hum when switched on figure of 8. I have used partition resistor to obtain the following voltages (applied at the "P" junction on the circuit).
A-> figure of 8 = B+
B-> cardioid 1 = 150V
C-> cardioid 2 = 100V
D-> cardioid 3 = 50V
E-> omnidirectional = 0 V
is this the way I should be doing it ?
any tips or suggestion will be much appreciated.
couple of questions regarding noise figure on the tube mic, so I know what I should expect.
the microphone it's working (using 6AU6 for now, but updated tube soon to be used!), lot's of gain and very good overall sound.
I do have some issues which I would like to know if they can be addressed.
1) there is a persistent HUM at the output (20mVpp)
2) there is a constant buzz on the high end side
3) the polar pattern seems to not be doing much,although it does increase the hum when switched on figure of 8. I have used partition resistor to obtain the following voltages (applied at the "P" junction on the circuit).
A-> figure of 8 = B+
B-> cardioid 1 = 150V
C-> cardioid 2 = 100V
D-> cardioid 3 = 50V
E-> omnidirectional = 0 V
is this the way I should be doing it ?
any tips or suggestion will be much appreciated.
mata_haze
Well-known member
here it is:
hopefully there is something silly I have done which makes it noisy.the two 500M resistors are connected in parallel to get a 250M value.
this is the whole mic body
and the amplifier section
any comment will be much appreciated.
hopefully there is something silly I have done which makes it noisy.the two 500M resistors are connected in parallel to get a 250M value.
this is the whole mic body
and the amplifier section
any comment will be much appreciated.
rbaker
Well-known member
[quote author="analag"][quote author="SSLtech"]I don't know about the CEK-367 -Does it not have an inbuilt HF boost?
Keith[/quote]
Look at the 500pF that's tied between the plate and cathode circuit. Rounds it off nicely.[/quote]
I have used one of those capsules in a tcm1050 (along with some other changes) It sounds great, my only complaint is that it might be a little bright.
Figuring out what to add to accomplish the same results is far beyond me. Is there anyway you might look at what I've used and tell if/what/where to do that to my mic?
here's the schematic I used and it includes what I've pulled out and changed...
http://www.ryanbakerproductions.com/micschematic.jpg
I used an ami/tab bv314 transformer..it's a bv8 core but with a t14 ratio to match the 6072.
Also if there's anything else you see that I could/should change, feel free!
Keith[/quote]
Look at the 500pF that's tied between the plate and cathode circuit. Rounds it off nicely.[/quote]
I have used one of those capsules in a tcm1050 (along with some other changes) It sounds great, my only complaint is that it might be a little bright.
Figuring out what to add to accomplish the same results is far beyond me. Is there anyway you might look at what I've used and tell if/what/where to do that to my mic?
here's the schematic I used and it includes what I've pulled out and changed...
http://www.ryanbakerproductions.com/micschematic.jpg
I used an ami/tab bv314 transformer..it's a bv8 core but with a t14 ratio to match the 6072.
Also if there's anything else you see that I could/should change, feel free!
Martin B. Kantola
Well-known member
- Joined
- Jun 24, 2005
- Messages
- 209
[quote author="mata_haze"]here it is:
hopefully there is something silly I have done which makes it noisy.... any comment will be much appreciated.[/quote]
May I suggest you draw and maybe post a full schematic of the mike, cable assembly wiring and PSU you're using? They are all equally important in a mike like this. You might notice something when you draw it, like ground loops and such...
In your pictures I noticed you are running very hi impedance wires in spiral shape down to the little PCB, might not be optimal...
Martin
hopefully there is something silly I have done which makes it noisy.... any comment will be much appreciated.[/quote]
May I suggest you draw and maybe post a full schematic of the mike, cable assembly wiring and PSU you're using? They are all equally important in a mike like this. You might notice something when you draw it, like ground loops and such...
In your pictures I noticed you are running very hi impedance wires in spiral shape down to the little PCB, might not be optimal...
Martin
mata_haze
Well-known member
[quote author="Martin"]In your pictures I noticed you are running very hi impedance wires in spiral shape down to the little PCB, might not be optimal... [/quote]
thanks for the suggestion, I'll straighted the wires up and I gained something on the noise floor.
this is the power supply I am using:
I have pretty much used what I had ready available at home.
the two trafos I am using for the B+ gives 300VDC after the bridge diodes and each >10uF 3K9< cell drops the voltage by 5 V (not much I will increase the value of the resistor as to get 200VDC at the output of the power supply).
there are poly caps across each diode on the bridges (10nF on the B+; 4n7 on the heater).
*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...
Any comments would be much appreciated.
PS thank you analag, the mic is just A-M-A-Z-I-N-G.. we are prefering it to our M149..despite the hum.
Best
Mattia.
thanks for the suggestion, I'll straighted the wires up and I gained something on the noise floor.
this is the power supply I am using:
I have pretty much used what I had ready available at home.
the two trafos I am using for the B+ gives 300VDC after the bridge diodes and each >10uF 3K9< cell drops the voltage by 5 V (not much I will increase the value of the resistor as to get 200VDC at the output of the power supply).
there are poly caps across each diode on the bridges (10nF on the B+; 4n7 on the heater).
*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...
Any comments would be much appreciated.
PS thank you analag, the mic is just A-M-A-Z-I-N-G.. we are prefering it to our M149..despite the hum.
Best
Mattia.
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