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Have you used tube preamps for recording acoustic and classical music ?
Old 2nd November 2021 | Show parent
  #121
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wildplum's Avatar
 
🎧 15 years
Quote:
Originally Posted by JMoss1 ➡️
Heterodyning or Intermodulation Distortion can occur when two or more signals are mixed through a non-linear device. LIKE YOUR EAR. Your ear is a nonlinear device where heterodyning (intermodulation distortion) does occur. Messy indeed.

Transient response is one of the performance requirements any Pro Audio vacuum tube design should have built in. A lot of it depends on the audio transformers used. There are many things I had to consider when designing this preamp. LOTS of things. Safety issues included.

Sagging power supplies are sometimes there on purpose, designed in. I thought about doing that, but decided against it. My preamp power supplies are fully regulated, even the HV B+. I use a higher than usual High voltage to get the sound I wanted. A lot of guitar amps use starved plate designs. It is a sound. I just wanted a much more robust design. My design can maintain the proper design internal voltage on the 120 Volt setting anywhere from 80 Volts to 135 Volts. I am sure it will handle higher and lower voltages than that. I just don't claim that. Same for the 240 Volt setting.

I have been recording field festivals where the power line voltages went down to 80 volts. They were then adjusted with a Variac.

I leave the studio on 24 hours at a time with no oscillation, within or outside the audio bandwidth. The proper design of a HV power supply takes that into consideration. That is all you need to have a power supply turn into a UHF oscillator. That is just good design. Also, the ability to operate for days with all the vents closed off and the room temperature at 90F is an important thing to design in. I had great mentors I could go to for advice. They kept me out of trouble. Maybe even had me over build too much, but better safe than sorry.

In some of your comments you seem to be talking about solid state preamps or HIFI systems. I am not commenting on them.

Jim Moss
the incessant hawking of the gear you sell is getting a little boring.
if you want to talk tech, great. if you want to sell your gear, buy an ad.
Old 2nd November 2021 | Show parent
  #122
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emrr's Avatar
 
24 Reviews written
🎧 15 years
I don't record much classical, but a lot of acoustic Americana/pop/traditional stuff. I do whole sessions with nothing but 1930's-1950's preamps I've restored. You put something like an MKH 30 into a 1940's triode preamp, it forces a larger slice of reality through it, and highlights the colorations, also forces the S/N in the best possible direction. I use a lot of ribbons with those sorts of preamps, only have noise concerns if there are extremely quiet passages, and thoughtful capture of wild sound combined with RX9 takes care of that easily.

If you go back to preamp circuits that are more like many tube mic circuits (low/no feedback), they make every bit the same amount of color as the mics. The last year I've done a lot of vocal sessions with a U67 into a late '30's RCA 87-A, and I'd say they add roughly equivalent amounts of color, in their own ways.

I honestly hear the most color out of the transformers in old gear more than the circuit types. Some 1960ish tube and transistor gear can sound remarkably the same, if the transformers are similar make.

I'm not in the 'back to mono' camp that records to tube Ampex machines exclusively, or am chasing entire vintage tone pictures with only antique mics and placement techniques, I make modern records. Modern mics, old mics, close mics, diffuse field ambient mics, multitrack, etc. People who think they want the sound of tape as a magic elixir still tend to think my work sounds too 'digital', even if it's entirely 1940's preamps and ribbons! That may give some idea of the color hierarchy.
Old 2nd November 2021 | Show parent
  #123
Lives for gear
 
🎧 5 years
I have enjoyed the design dialog and appreciate the contributions to the thread. Great information.

Quote:
Originally Posted by wildplum ➡️
the incessant hawking of the gear you sell is getting a little boring.
if you want to talk tech, great. if you want to sell your gear, buy an ad.
Old 2nd November 2021 | Show parent
  #124
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wildplum's Avatar
 
🎧 15 years
Quote:
Originally Posted by StevenLMorgan ➡️
I have enjoyed the design dialog and appreciate the contributions to the thread. Great information.
I agree- on the tech talk. the gear plugging is another thing.
Old 3rd November 2021 | Show parent
  #125
Gear Guru
 
1 Review written
🎧 5 years
c'mon...

there are a couple of manufacturers, small and large, who invade threads frequently and sometimes aggressively (do i need to mention names?!) and they even get applauded...

...so as long as someone (mis-)uses a thread to both share some of his/her expertise and to promote gear, i think this should be okay.



[however, i strongly advocate that manufacturers and people working for a manufacturer or distributor, radio station or cultural institution should be recognisable as such, for example by colour coding]
Old 3rd November 2021 | Show parent
  #126
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kludgeaudio's Avatar
 
Quote:
Originally Posted by JMoss1 ➡️
In some of your comments you seem to be talking about solid state preamps or HIFI systems. I am not commenting on them.
Just giving as many different examples of why listening and measuring go hand in hand, from as many different parts of the audio world as I can. They are like beans and cornbread.
--scott
Old 3rd November 2021
  #127
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emrr's Avatar
 
24 Reviews written
🎧 15 years
I’d love to know in what world cool looking gear sells studio time, I’m clearly not in it.
Old 3rd November 2021 | Show parent
  #128
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wildplum's Avatar
 
🎧 15 years
I'll tell you what, Sir. You stop pimping your merchandise in the body of a post and, instead, add a link to your website in your post signature- and I'll call it even.

Please read the Gearspace terms of service: https://gearspace.com/board/terms/
and the gearspace FAQ as it pertains to manufacturers: https://gearspace.com/board/faq.php?...l&titlesonly=0
Old 3rd November 2021 | Show parent
  #129
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Plush's Avatar
 
5 Reviews written
🎧 15 years
Quote:
Originally Posted by M50k ➡️
Classic TF understatement.

To Tony directly - did you ever aquire any of the Decca M50s that were converted to FET?
Tony is a great fellow and friend. I have learned so much from him, primarily about recording and mic philosophy.

TO WIT: I can comment on Decca fet M50 mics.

I bought some M50 Decca fet modified mics and used them for many years. They sounded fantastic. Very quiet and very dynamic. Typical M50 sound except for the tube modus sound which of course they did not have. But having used tube M50's a good bit as well, I would say that the fet versions had 80% of the real M50 sound.

I have discussed this with Tony F. and he offered that he "was sorry for me" that I had to use the fet version. I laughed and said that I agreed.

But any engineer working with orchestra, piano, and other instruments with prodigious bass is VERY fortunate to use any version of the M50 mic.

The unlimited Deutschmark investment in the design of the M50 (with semi-government research involvement), is probably not to be seen nowadays.

But I still hope that Tony will encourage RODE to release the TF50 into the wild.
Attached Thumbnails
Have you used tube preamps for recording acoustic and classical music ?-m50-hand.jpg  

Last edited by Plush; 3rd November 2021 at 05:02 PM..
Old 3rd November 2021 | Show parent
  #130
Lives for gear
 
🎧 5 years
Great info - thanks.
Old 3rd November 2021 | Show parent
  #131
Gear Maniac
 
🎧 10 years
Quote:
Originally Posted by Plush ➡️
Tony is a great fellow and friend. I have learned so much from him, primarily about recording and mic philosophy.

TO WIT: I can comment on Decca fet M50 mics.

I bought some M50 Decca fet modified mics and used them for many years. They sounded fantastic. Very quiet and very dynamic. Typical M50 sound except for the tube modus sound which of course they did not have. But having used tube M50's a good bit as well, I would say that the fet versions had 80% of the real M50 sound.

I have discussed this with Tony F. and he offered that he "was sorry for me" that I had to use the fet version. I laughed and said that I agreed.

But any engineer working with orchestra, piano, and other instruments with prodigious bass is VERY fortunate to use any version of the M50 mic.

The unlimited Deutschmark investment in the design of the M50 (with semi-government research involvement), is probably not to be seen nowadays.

But I still hope that Tony will encourage RODE to release the TF50 into the wild.
Hi.
I heard the Decca solid-state modified M50's during sessions at Kingsway Hall and wasn't wholly convinced they sounded as warm and deep. I understand why they did it all the same - annoying cables, annoying power-supplies, expensive hassle to replace the tubes. However the tube M50's are special, and manageable for an operation of the scale of yours and mine. I have no control over RODE's commercial time-lines, but I know that the TF-M50 is very special. I'll be using my samples this weekend.

I was ultra lucky getting my tube M50's when I did, when colleagues were sick of the power supplies, cables and upkeep and wanted mics they could simply plug in and run with. They did not cost me a lot at the time, but they do cost money in upkeep.
Old 3rd November 2021 | Show parent
  #132
Lives for gear
 
🎧 5 years
It's always puzzled me how M50/49s and U47s are kept alive when the tubes go - is there that much AC701 and VF14 NOS still out there?
Old 3rd November 2021 | Show parent
  #133
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ISedlacek's Avatar
 
1 Review written
🎧 15 years
Oh, my thread Well, (not sure if I mentioned it before), I tried some tube preamps in the meantime on various acoustic instruments and found that comparing to my Forssell SMP-2 preamp they all sound a bit limited, 2D, small and not very natural, simply worse ... So I am not bothered by this option any more ...

Some years ago I tried tube Schoeps bodies (very expensive). They stopped producing them long time ago. I was also happy that I have CMC6

But yes, for vocals it is good (like U47 I have here). I tried even stereo pair of U47 on acoustic instruments ... Quite bad comparing to Schoeps
Old 3rd November 2021 | Show parent
  #134
Gear Head
 
Back in 2000 when I went back to trying out tube preamps, that was my first impression, that it was like 3D. The Neotek Elan that have here has great sounding preamps. Tubes were like another world. I had done some sessions back in Nashville and was trying to match my violin sound on a track that we had not used for the album. I was going to add a second violin. So I called the engineer studio owner and asked him about it. He told me to try out a vacuum tube mic preamp because that is what he was using. So I did.

I had nothing to compare to back in 1967 when everything was tube that I used.

Jim Moss


Quote:
Originally Posted by ISedlacek ➡️
Oh, my thread Well, (not sure if I mentioned it before), I tried some tube preamps in the meantime on various acoustic instruments and found that comparing to my Forssell SMP-2 preamp they all sound a bit limited, 2D, small and not very natural, simply worse ... So I am not bothered by this option any more ...

Some years ago I tried tube Schoeps bodies (very expensive). They stopped producing them long time ago. I was also happy that I have CMC6

But yes, for vocals it is good (like U47 I have here). I tried even stereo pair of U47 on acoustic instruments ... Quite bad comparing to Schoeps
Old 3rd November 2021 | Show parent
  #135
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kludgeaudio's Avatar
 
Quote:
Originally Posted by M50k ➡️
It's always puzzled me how M50/49s and U47s are kept alive when the tubes go - is there that much AC701 and VF14 NOS still out there?
The thing is, those microphones were designed for exceptionally long tube life. Part of what makes for the coloration of the U47 is how they run the tube with low filament voltage for low emission and long lifespan, so tubes really do last a lifetime. That's a requirement in the broadcast world.

The truth is there aren't very many VF14s out there anymore, even though they were picked originally because they were plentiful and cheap on the war surplus market. For a long time people would just swap the tubes in the mikes when they suspected anything, because the tubes were cheap and easy to replace. Now they aren't so plentiful and they sure aren't so cheap.

Worst case: when the VF14 fails you put the nuvistor kit in there and the mike sounds better with the nuvistor anyway...
--scott
Old 4th November 2021 | Show parent
  #136
Gear Head
 
Isn't there any alternatives that can be used as a substute? I seem to remember when I bought my U67 that the seller included a tube that was an alternative. I always liked the U47 fet better. Someone must have a upgrade for the U47.

Jim Moss


Quote:
Originally Posted by kludgeaudio ➡️
The thing is, those microphones were designed for exceptionally long tube life. Part of what makes for the coloration of the U47 is how they run the tube with low filament voltage for low emission and long lifespan, so tubes really do last a lifetime. That's a requirement in the broadcast world.

The truth is there aren't very many VF14s out there anymore, even though they were picked originally because they were plentiful and cheap on the war surplus market. For a long time people would just swap the tubes in the mikes when they suspected anything, because the tubes were cheap and easy to replace. Now they aren't so plentiful and they sure aren't so cheap.

Worst case: when the VF14 fails you put the nuvistor kit in there and the mike sounds better with the nuvistor anyway...
--scott
Old 4th November 2021 | Show parent
  #137
Gear Head
 
Yes, 7000V/us slew rate is Very Fast. Will make a good UHF oscillator.
The question is, for audio, what is needed?

The 12AX7's don't have the current drive capability provided by other tubes of that series like the 12AU7. These tube were developed for 5 tube radios. Not quality electronics. They work great where the users are not that picky. Applications like guitar amps. I don't use them. There are better tubes.

The TI TL072 op-amp has a bandwidth roll off built in. We used them for phone company 54kHz chopper modulators back in the 1980s when some engineer decided to actually design to published specs. That caused a lot of problems with parts we were making for MCI, SP and others until we figured it out. Then we went to another company brand. That fixed everything.

This is a good link for Slew Rate with graphics. They mention tubes too.
https://mynewmicrophone.com/what-is-...t-performance/

Jim Moss


Quote:
Originally Posted by Jim Williams ➡️
The common 12AX7A has a 12v/us slew rate, similar to a TI TLO72 opamp. Driver tubes like 12BH7 are slower. 12AY7's are faster due to less stray capacitance.

Some rf tubes are very fast but not suitable for audio usage. Transistor designs here go up to 7000V/us slew rate, that is very fast.

Transistors are faster than tubes.
Old 4th November 2021 | Show parent
  #138
Gear Head
 
There are design measures that discourage oscillations. A combination of ferrite beads and capacitors work great. Even though the Honeybee mic preamp / optical limiter is a vacuum tube preamp, I use an opamp for a VU meter buffer for calibration and isolation.

Jim Moss


Quote:
Originally Posted by kludgeaudio ➡️
From intermodulation effects that you don't see. From slew limiting. From transient effects like power supplies sagging. Maybe it breaks out into oscillation after running for an hour but you never notice that on a short test. What you describe is a very good test, but not a universal test. There are a lot of tests that can measure that stuff, but you need to know to use them first.

--scott
Old 4th November 2021 | Show parent
  #139
Lives for gear
 
🎧 15 years
audio tubes

Quote:
Originally Posted by JMoss1 ➡️
The 12AX7's don't have the current drive capability provided by other tubes of that series like the 12AU7. These tube were developed for 5 tube radios. Not quality electronics. They work great where the users are not that picky.
complete nonsense.
12A*** tubes are found in time tested, highly regarded audio equipment.
manufacturers include McIntosh, Ampex, Marantz, Scott, Fisher.
5 tube radios used a variety of tubes, but not from the 12A family.
https://en.wikipedia.org/wiki/All_American_Five
Old 4th November 2021 | Show parent
  #140
Lives for gear
 
🎧 5 years
The Mercury Living Presence recordings don't exactly have a 'slow' sound. Most were recorded with Pultec MB1s as mic pres (bypassing the Ampex's mic inputs), which were 12AX7 > 12AX7 > 12AU7.
Old 4th November 2021 | Show parent
  #141
Gear Head
 
I have bags of these I collected back in my teenage years that came out of radios. My point was that with an amplification factor of 100 and only 1.2 watts in dissipation it is not the best for low distortion high gain amps. They can start to sag. They are used in lots of radios like Drakes and Swans to mention a few.

https://frank.pocnet.net/sheets/049/1/12AX7A.pdf

Complete nonsense? This is an angry crowd.


Jim Moss



Quote:
Originally Posted by cathode ➡️
complete nonsense.
12A*** tubes are found in time tested, highly regarded audio equipment.
manufacturers include McIntosh, Ampex, Marantz, Scott, Fisher.
5 tube radios used a variety of tubes, but not from the 12A family.
https://en.wikipedia.org/wiki/All_American_Five
Old 4th November 2021 | Show parent
  #142
Gear Maniac
 
🎧 10 years
Quote:
Originally Posted by M50k ➡️
It's always puzzled me how M50/49s and U47s are kept alive when the tubes go - is there that much AC701 and VF14 NOS still out there?
My solution for sourcing AC701 tubes for our M50 and KM53 mics is EBay. You have to be cautious as ever with EBay, but I have a drawer with several spares in it.

Funky Junk has done great work for us servicing our M50's, power supplies and cables - they presumably have a drawer of AC701's and VF14's too.

The original Neumann power supplies for our M50's became potentially lethal decades ago because they were never built to last 60 years bouncing from one location to another. After a couple of electric shocks we had a new rack built with six independent channels of power.

All part of the deal of keeping old tech operational.
Old 4th November 2021 | Show parent
  #143
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kludgeaudio's Avatar
 
Quote:
Originally Posted by JMoss1 ➡️
Isn't there any alternatives that can be used as a substute? I seem to remember when I bought my U67 that the seller included a tube that was an alternative. I always liked the U47 fet better. Someone must have a upgrade for the U47.

Jim Moss
Yes, but they all sound different. Because of the way that tube is set up for long life, it adds a lot of coloration. Put an EF86 or a nuvistor in there and it's a lot cleaner and people don't like that.

I agree completely that I think the FET sounds better.... and I think the nuvistor kit sounds a lot better than the original tube too... but you and I seem to be in the minority.
--scott
Old 4th November 2021 | Show parent
  #144
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by JMoss1 ➡️
I have bags of these I collected back in my teenage years that came out of radios. My point was that with an amplification factor of 100 and only 1.2 watts in dissipation it is not the best for low distortion high gain amps. They can start to sag. They are used in lots of radios like Drakes and Swans to mention a few.

https://frank.pocnet.net/sheets/049/1/12AX7A.pdf

Complete nonsense? This is an angry crowd.


Jim Moss


There is nothing wrong with 12AX7 tube if used correctly, even in a high gain circuit. Its high output impedance won’t drive any real-world load, but the spec sheet already tells you that. Combine the two triodes of a 12AX7 together in a cascading circuit can get you more than 70dB of clean, low noise and wide bandwidth gain. If you can’t design good sounding equipment using 12AX7 tubes, you need to read some more textbooks, or reverse engineer some good old great sounding gear. 12AX7 is not your problem, that is for sure.

There is absolutely nothing new about any tube equipment that we don’t yet know, in terms of circuitry, sonic merit and shortfall. There are no new wheels to be invented with tubes. For boutique low track count recording studio, If one likes the tube sound, go for it. On the other hand, tube stuff had passed its expiration date long ago for the commercial classical recording productions where 32-64 tracks are often used. Just imagine this; hauling 32 boxes of stereo mic-pres to a recording gig.
Old 4th November 2021 | Show parent
  #145
Lives for gear
 
🎧 5 years
As TF so pithily put it - 'bit of a pest'.
Old 5th November 2021 | Show parent
  #146
Gear Head
 
Now here is an old guy story.
When I went to college we studied tubes/transistors/fets side by side. That was in the early 1970s. This thread started with slew rate and noise. I find 12AX7 tube amps having pretty high THD+Noise. The best I have seen has been a preamp with 1% THD_Noise. That is great for a guitar amp, but for a modern Pro Audio preamp that is bad. My preamp is around 0.02% to 0.05% (20Hz to 20kHz) in final testing consistently.

Why would you care? Because when it comes to THD you are getting lots of problems on instruments with lots of strings. Like Guitars, Pianos... etc. So I don't use 12AX7 tubes in my designs. It maybe good for some people. Not so good for others who know better. It is like Iron core audio transformers... It just depends on your taste and what your objective is in getting sound you like.

Jim Moss


Quote:
Originally Posted by dseetoo ➡️
There is nothing wrong with 12AX7 tube if used correctly, even in a high gain circuit. Its high output impedance won’t drive any real-world load, but the spec sheet already tells you that. Combine the two triodes of a 12AX7 together in a cascading circuit can get you more than 70dB of clean, low noise and wide bandwidth gain. If you can’t design good sounding equipment using 12AX7 tubes, you need to read some more textbooks, or reverse engineer some good old great sounding gear. 12AX7 is not your problem, that is for sure.
Old 5th November 2021 | Show parent
  #147
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kludgeaudio's Avatar
 
Quote:
Originally Posted by JMoss1 ➡️
Now here is an old guy story.
When I went to college we studied tubes/transistors/fets side by side. That was in the early 1970s. This thread started with slew rate and noise. I find 12AX7 tube amps having pretty high THD+Noise. The best I have seen has been a preamp with 1% THD_Noise. That is great for a guitar amp, but for a modern Pro Audio preamp that is bad. My preamp is around 0.02% to 0.05% (20Hz to 20kHz) in final testing consistently.
Oh, I can give you way lower distortion than that.... but.... only if you're willing to increase the current through the tube and get lower gain, or if you're willing to do a cascode configuration and have more tubes in the box. Same thing as with a jfet although the 12AX7 is like a pair of jfets with really low idss. Lower gain per stage means you need more stages.

But if you want to get as much gain as possible out of a single tube stage in order to save weight, power, and cost, you're going to get more distortion. The same would be the case of a jfet, although of course the jfet is inherently smaller and cheaper.

In the solid state world, you have enormous amounts of gain, and you can use well-designed negative feedback networks to improve linearity a lot. In the tube world you don't have so much gain to throw away and that becomes a problem fast.

Most of the actual distortion in classic tube gear comes from the transformers and not the tube stages. Most of the audible coloration too. That's the real issue, and that's something they never told us in freshman circuits class.
--scott
Old 5th November 2021
  #148
Lives for gear
 
🎧 10 years
Another way to get high gain, low distortion with high standing current is to use constant current source as your load. As I said before, a single 12AX7 can get you 70dB of gain, with NFB included. Been there, done that.
Old 5th November 2021 | Show parent
  #149
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kludgeaudio's Avatar
 
Quote:
Originally Posted by dseetoo ➡️
Another way to get high gain, low distortion with high standing current is to use constant current source as your load. As I said before, a single 12AX7 can get you 70dB of gain, with NFB included. Been there, done that.
Yes, and this is different than a cascode arrangement it's true. But you're still back to two tubes for the stage then, one being the amplifier and the other being the current source. (Which is why we have dual tubes like the 12AX7s and even compactrons.)
--scott
Old 5th November 2021 | Show parent
  #150
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by kludgeaudio ➡️
Yes, and this is different than a cascode arrangement it's true. But you're still back to two tubes for the stage then, one being the amplifier and the other being the current source. (Which is why we have dual tubes like the 12AX7s and even compactrons.)
--scott

I was thinking about using twin triodes as two amplifying stages and use another active device to form current source. Need much higher B+ voltage if tubes are used to form current source. Solid-state devices work great as current source, a hint.
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