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Best 7025/12AX7 mic tube?
Old 10th November 2006
  #1
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muddbros's Avatar
 

Talking Best 7025/12AX7 mic tube?

Hello,

I have a CAD VSM-1 microphone that needs a new tube. Currently it has a Sovtek 12AX7WA. I was wondering if someone would recommend a different tube or if I should just stick with the same one.

I have been using the VSM-1 for years with mostly Manley gear (VoxBoxes, DualMonos and VariMus) as well as a Neve 1073/33609, Amek, TubeTech, etc... and it has always sounded great.

I JUST WANT TO MAKE SURE I'M GETTING THE MOST OUT OF THIS MIC W/ THESE HIGH-END PRE'S.

Any advice would be greatly appreciated!!

Thanks,

Jim
Old 11th November 2006
  #2
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Wavebourn's Avatar
 

Quote:
Originally Posted by muddbros View Post
Hello,

I have a CAD VSM-1 microphone that needs a new tube. Currently it has a Sovtek 12AX7WA. I was wondering if someone would recommend a different tube or if I should just stick with the same one.

I have been using the VSM-1 for years with mostly Manley gear (VoxBoxes, DualMonos and VariMus) as well as a Neve 1073/33609, Amek, TubeTech, etc... and it has always sounded great.

I JUST WANT TO MAKE SURE I'M GETTING THE MOST OUT OF THIS MIC W/ THESE HIGH-END PRE'S.

Any advice would be greatly appreciated!!

Thanks,

Jim

I would try all of them available. The test is simple: use a screwdriver to lightly knock on the tube to select one with the lowest microphone effect. However, if all of them have enough of emission.

You just need only one, instead of running production, so I think the brand does not matter, as well as their performances in other applications from guitar preamps to phase splitters.
Old 3rd October 2019
  #3
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Hi!
Did you finally tried tubes for your vsm1?
I just ordered a cad vsm 1.whuch tubes do you suggest (not more than 100$) which ll make it better sounding than the stock one?
Iam interested mostly for vocals,a tube which is not harsh with transients,i want to make them softer !(in the 4-9khz area)
Old 4th October 2019
  #4
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ruffrecords's Avatar
I spent a lot of time trying different versions of 12AX7 tube for my tube mic pre designs. I concluded the most consistently low noise AND low microphonics type is the Sovtex 12AX7WA so I would recommend you stick to them.

Cheers

Ian
Old 4th October 2019
  #5
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Quote:
Originally Posted by ruffrecords View Post
I spent a lot of time trying different versions of 12AX7 tube for my tube mic pre designs. I concluded the most consistently low noise AND low microphonics type is the Sovtex 12AX7WA so I would recommend you stick to them.

Cheers

Ian
Did you try telefunken Nos?what about sovtek's freq response -harshness in the upper mids compared with telefunken-mullard-brimar?
Old 4th October 2019
  #6
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ruffrecords's Avatar
Quote:
Originally Posted by Stergios T. View Post
Did you try telefunken Nos?what about sovtek's freq response -harshness in the upper mids compared with telefunken-mullard-brimar?
Yes, I managed to borrow some NOS Telefunkens. Very variable and not particularly quiet - much as you would expect for a tube over 50 years old.

The Sovteks frequency response is flat to 100KHz in my tube mic pre design. Never heard any mid range harshness. I suspect it is a myth put about by those trying to sell exotic NOS tubes.

Cheers

Ian
Old 4th October 2019
  #7
I used old Telefunken smooth plates. I've not found any 12AX7A that come close to those. I get -127.5 db EIN at +60 db of gain and .003% THD with zero negative feedback in my tube mic preamps.

Guitar amps get 12AX7A EH or Tungsol for extra gain.
Old 4th October 2019
  #8
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ruffrecords's Avatar
Quote:
Originally Posted by Jim Williams View Post
I used old Telefunken smooth plates. I've not found any 12AX7A that come close to those. I get -127.5 db EIN at +60 db of gain and .003% THD with zero negative feedback in my tube mic preamps.

Guitar amps get 12AX7A EH or Tungsol for extra gain.
Interesting. I would love to see the schematic of that, also details of how you measure EIN including what reference you measure your dBs relative to, plus the output level, load and frequency range over which you measure 0.003% THD.

As I am sure you are aware, achieving -127.5dBu (note unambiguous units) EIN is as much about the way the mic pre is constructed and powered as it is about the performance of the tube.

Looking forward to hearing all the details.

Cheers

Ian
Old 5th October 2019
  #9
The design is a bit unique as it cascades two sections with a dual ganged gain pot. Gain is actively taken off the grids, the tube bias is balanced. There are no attenuators used as those degrade the s/n ratio. The input transformer is the JT-115KE at 10/1 ratio. The second stage is -6 db gain from the first to maintain the s/n ratios. All the power rails are fully regulated and large caps are used.

It uses bulk foil and wirewound resistors plus exotic oil and paper silver foil capacitors. Internal wiring is silver cable. It was tested with my Audio Precision analyzer. THD was measured with a 22k hz bandwidth and a 100k ohm load. THD does degrade slightly at 600 ohms, no output transformer is used. The preamp is flat to 80khz, then the transformer rolls off the bandwidth. It's flat to 1/4 db at 200k hz line in.
Old 5th October 2019
  #10
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Quote:
Originally Posted by Jim Williams View Post
The design is a bit unique as it cascades two sections with a dual ganged gain pot. Gain is actively taken off the grids, the tube bias is balanced. There are no attenuators used as those degrade the s/n ratio. The input transformer is the JT-115KE at 10/1 ratio. The second stage is -6 db gain from the first to maintain the s/n ratios. All the power rails are fully regulated and large caps are used.
It would be great if you could post a schematic
Quote:

It uses bulk foil and wirewound resistors plus exotic oil and paper silver foil capacitors. Internal wiring is silver cable. It was tested with my Audio Precision analyzer. THD was measured with a 22k hz bandwidth and a 100k ohm load. THD does degrade slightly at 600 ohms, no output transformer is used. The preamp is flat to 80khz, then the transformer rolls off the bandwidth. It's flat to 1/4 db at 200k hz line in.
Distortion into 100K load at an unspecified load is not terribly meaningful in terms of normal operation.

I am still interested to hear exactly how you measured your EIN

Cheers

Ian
Old 5th October 2019
  #11
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chipss36's Avatar
 

Not sure about mics, but with blackface amps I am pretty hard headed about the brand tubes I use...lol
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Best 7025/12AX7 mic tube?-a31baac2-bfca-4bda-a79b-3ae2980e2b9d.jpg  
Old 6th October 2019
  #12
Quote:
Originally Posted by ruffrecords View Post
It would be great if you could post a schematic

Distortion into 100K load at an unspecified load is not terribly meaningful in terms of normal operation.

I am still interested to hear exactly how you measured your EIN

Cheers

Ian
+60 db of gain plus unweighted s/n measurement with the Audio Precision. It's a standard test. A weighting could make it look better but that's not an honest measurement. Buy a new AP at $15,000 and you can do all these tests too. Standard AP loads are 100k and 600 ohms. A strapping resistor can be used to present different loads.
Old 6th October 2019
  #13
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Quote:
Originally Posted by Jim Williams View Post
+60 db of gain plus unweighted s/n measurement with the Audio Precision. It's a standard test. A weighting could make it look better but that's not an honest measurement. Buy a new AP at $15,000 and you can do all these tests too. Standard AP loads are 100k and 600 ohms. A strapping resistor can be used to present different loads.
I am pleased to hear it is an unweighted measurement. However, there is still a lot of information missing about the measurement:

1. Was the source a 150 ohm resistor, a short or something else?
2. The measurement is dB is relative to what absolute level?
3. What is the measurement bandwidth?
4. Is the measurement and average, rms , quasi peak or some other type?

All these factors can make a considerable difference to the measured value.

Cheers

ian
Old 6th October 2019
  #14
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In my tests with a Summit TPA200 mic pre, I found the Sovtek tubes to be too dark (a drop in the highs). Of new tubes, I found the EH 12AX7 to sound quieter in the preamp than the low noise Sovteks, and they had a flatter response (no drop in the high end).
Old 7th October 2019
  #15
Quote:
Originally Posted by ruffrecords View Post
I am pleased to hear it is an unweighted measurement. However, there is still a lot of information missing about the measurement:

1. Was the source a 150 ohm resistor, a short or something else?
2. The measurement is dB is relative to what absolute level?
3. What is the measurement bandwidth?
4. Is the measurement and average, rms , quasi peak or some other type?

All these factors can make a considerable difference to the measured value.

Cheers

ian
A low noise 150 ohm resistor is soldered inside the case of a male XLR, it's a standard noise source test device. Everything is done dbu here, that's also a standard. As I previously mentioned I used the 22khz measurement bandwidth. Humans don't hear noise above 20khz. I will measure noise to 200k hz but that's only to catch errors. RMS measurements are computed with the AP. Check their website for more data about the Audio Precision test proceedures.

There is good reason why they are the audio test standard of the world. And no, I'm not giving out the schematic.
Old 7th October 2019
  #16
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Quote:
Originally Posted by Jim Williams View Post
The design is a bit unique as it cascades two sections with a dual ganged gain pot. Gain is actively taken off the grids, the tube bias is balanced. There are no attenuators used as those degrade the s/n ratio. The input transformer is the JT-115KE at 10/1 ratio. The second stage is -6 db gain from the first to maintain the s/n ratios. All the power rails are fully regulated and large caps are used.

It uses bulk foil and wirewound resistors plus exotic oil and paper silver foil capacitors. Internal wiring is silver cable. It was tested with my Audio Precision analyzer. THD was measured with a 22k hz bandwidth and a 100k ohm load. THD does degrade slightly at 600 ohms, no output transformer is used. The preamp is flat to 80khz, then the transformer rolls off the bandwidth. It's flat to 1/4 db at 200k hz line in.
do you think that i ll notice a significant improvement with a telefunken 12ax7 compared to the stock sovtek 12ax7wa in the cad vsm1 mic??
Old 8th October 2019
  #17
Only you can determine that.
Old 8th October 2019
  #18
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Quote:
Originally Posted by Jim Williams View Post
Only you can determine that.
Ok..to be more specific,do you think that a telefunken tube is smoother in the 3khz-9khz area?i want to record mostly vocals with the cad.Do you think that telefunken can be more gentle with vocal ''ssshheesss''' ??
Old 9th October 2019
  #19
Smooth plates have an extended top end, much more details.
Old 9th October 2019
  #20
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All you people who hear differences in tubes, how much difference? How small a difference do you think you can hear? If you think about this electronically, what parameters of the tube would cause these variations? Apart from noise, which will vary according to tube construction, you would need gross changes in tube parameters to change frequency response. And of course none of you ever do double blind testing.
Old 9th October 2019
  #21
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Karloff70's Avatar
 

Watch out guys, the blind testing police is here..
Old 9th October 2019
  #22
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Quote:
Originally Posted by Radardoug View Post
All you people who hear differences in tubes, how much difference? How small a difference do you think you can hear? If you think about this electronically, what parameters of the tube would cause these variations? Apart from noise, which will vary according to tube construction, you would need gross changes in tube parameters to change frequency response. And of course none of you ever do double blind testing.
If you can’t hear the difference between tubes Doug, I’m sorry for you. They sound different. Measure as much as you like, chalk it up to imagination if you must, but I can hear the difference. It’s easy. The differences are huge and not subtle. Ears are much more sensitive to sound qualities that your machines don’t even detect, because they weren’t designed to detect those changes. You can test this by doing double blind tests with musicians and audio engineers. The jury isn’t out, different tubes sound different. Some sound “better” ... let’s not forget that this is about art. So better means just that. Just like caps, you can measure two different caps and find they have the same capacitance, but their material greatly influence their sound.

Maybe try measuring their frequency response? Harmonic distortion? Maybe their distortion at different frequencies? It is certainly interesting from an academic perspective.
Old 10th October 2019
  #23
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So you are saying the differences are huge and not subtle? In what way? Frequency response? Distortion? I will agree, a bad tube will measure and sound different. But I am talking about good tubes.
If the differences are huge they will be measureable. A meter can tell a .1dB difference. Your ears can not.
By the way, dont be sad for me, I'm a very happy person!
Old 10th October 2019
  #24
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ruffrecords's Avatar
Quote:
Originally Posted by Jim Williams View Post
A low noise 150 ohm resistor is soldered inside the case of a male XLR, it's a standard noise source test device. Everything is done dbu here, that's also a standard. As I previously mentioned I used the 22khz measurement bandwidth. Humans don't hear noise above 20khz. I will measure noise to 200k hz but that's only to catch errors. RMS measurements are computed with the AP. Check their website for more data about the Audio Precision test proceedures.

There is good reason why they are the audio test standard of the world. And no, I'm not giving out the schematic.
Thanks for the additional info Jim. On that basis -127.5dBu EIN rms is not a bad figure for a tube mic pre. Unfortunately most of us cannot afford the $15K for an AP. However, with REW running on a PC and a decent converter I suspect you can measure withing a fraction of a dB of the AP for a tenth the price.

Cheers

Ian
Old 10th October 2019
  #25
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frans's Avatar
The original post is from 2006 - nonetheless, if there's a russian equivalent of a tube, i would have a listen. The axis of evil never stopped building tubes for their military and if you get those, have a try.
Russian 12AX7s: better than most Believe?
In germany it's easier to get them than, say, Michigan, as you run the risk of committing a crime dealing with the enemy ... or something like that. Look for a "6N2P" and make sure a good tech has a look to judge if the circuit and the tube will be happy together - as in many things, it's not a single part doing the work but a whole circuit that gets the best from each (quality) part in harmony.
Old 10th October 2019
  #26
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Quote:
Originally Posted by Radardoug View Post
So you are saying the differences are huge and not subtle? In what way? Frequency response? Distortion? I will agree, a bad tube will measure and sound different. But I am talking about good tubes.
If the differences are huge they will be measureable. A meter can tell a .1dB difference. Your ears can not.
By the way, dont be sad for me, I'm a very happy person!
It’s simple: 2 good tubes. Very different sounds, musically speaking. No instruments. No measurements. I 100% guarantee you that the human ear hears more information in sound than we have devices to measure a sounds chatacteristics in numbers. please don’t conflate the conversation to suggest that I am comparing a good tube and a bad tube.

A meter can numerically measure differences ears cannot pick up on sure, just like some cameras can see things that fall outside of our eyes light spectrum. Pictures from some cameras look different (better?), are you suggesting that there is no difference? Both pictures look good, but camera A consistently takes better looking photos.

Basically what I am saying: just because we don’t have the tools to measure a difference our ears can clearly hear, doesn’t negate that difference, nor renders it out of existence. If your ears can’t hear that difference, and you require some objective numerical measurement to “prove” it’s there, I suggest you start to develop new measuring tools.
Old 10th October 2019
  #27
Quote:
Originally Posted by ruffrecords View Post
Thanks for the additional info Jim. On that basis -127.5dBu EIN rms is not a bad figure for a tube mic pre. Unfortunately most of us cannot afford the $15K for an AP. However, with REW running on a PC and a decent converter I suspect you can measure withing a fraction of a dB of the AP for a tenth the price.
Cheers
Ian
PC based test software is dependent on the resolution of your ADC converter. The AP will measure noise in the analog domain down to -140 dbu. Most ADC's don't do well past -100 dbu.
Old 10th October 2019
  #28
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Quote:
Originally Posted by Jim Williams View Post
PC based test software is dependent on the resolution of your ADC converter. The AP will measure noise in the analog domain down to -140 dbu. Most ADC's don't do well past -100 dbu.
All test software, including AP, is dependent on the resolution of the ADC AND the number of samples taken to perform the FFT. These two together determine the resolution PER HZ of the system. Most software takes more than enough samples to allow a display that shows the noise per root Hz on the display. These are the ones where you typically see the noise bumping along on the -140dBu level. However, this is NOT the rms noise in a 20KHz bandwidth. such as you would see on an analogue meter.To get that you need to integrate the noise per root Hz over the 20KHz bandwidth and most software will do this for you too.

Bottom line is REW display bumps along on the -140dBu line just like an AP with a Scarlett 2i2 at 16 bits.

Cheers

Ian
Old 11th October 2019
  #29
A 16 bit system will not offer the analog resolution of the Audio Precision. FFT's are usually used to detect distortion products. The AP's noise vs amplitude test does an excellent job. Load the noise vs frequency sweeps and then you can see exactly where the noise resides. That is paramount for removing it as you need to understand the noise spectrum as well as the amount.
Old 11th October 2019
  #30
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Quote:
Originally Posted by enginefire View Post
It’s simple: 2 good tubes. Very different sounds, musically speaking. No instruments. No measurements. I 100% guarantee you that the human ear hears more information in sound than we have devices to measure a sounds chatacteristics in numbers. please don’t conflate the conversation to suggest that I am comparing a good tube and a bad tube.
OK, how can I take you up on that 100% guarantee? Thats a very bold statement. I've been around sound for 50 years, and done electronics all that time as well. I like the way the golden ear brigade insist that measurements dont quantify audio accurately, and so they dont bother to measure anything.

So what specific metrics as applied to an audio system can we not measure accurately enough?

The defining characteristics of an audio system are:
1/ Frequency response
2/ Noise
3/ Distortion

Which of these metrics can we not measure accurately enough?
Or have I missed one?
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