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Have you used tube preamps for recording acoustic and classical music ?
Old 4 weeks ago | Show parent
  #151
Lives for gear
 
🎧 5 years
Any thoughts on the two 12AX7 gain stages with feedback used in the Pultec MB1?
Old 4 weeks ago | Show parent
  #152
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kludgeaudio's Avatar
 
Quote:
Originally Posted by dseetoo ➡️
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.
THAT IS CHEATING!
--scott
Old 4 weeks ago | Show parent
  #153
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kludgeaudio's Avatar
 
Quote:
Originally Posted by M50k ➡️
Any thoughts on the two 12AX7 gain stages with feedback used in the Pultec MB1?
That's another attempt to split the gain among two stages so you can run them with reasonable linearity but not run into noise problems. You could make things cleaner than that, but given the output stage and the input transformer colorations, you probably wouldn't affect the sound any if you did. The input stage is pretty much blameless given the environment that it's in.

Today we can get much cleaner input transformers, we can get frame grid tubes that are quieter and more linear than 12AX7s, and even when that design was made you could get a bigger tube with more current drive than the 12AU7 for that output follower. We could add a tertiary feedback winding to that output transformer, get the transformer inside a feedback loop, and reduce that distortion too. Given all these things, the input stage is the least thing that I'd put more engineering effort into.

The Pultec was an excellent design given what was available at the time and what the demands of the market were. It was designed to be as clean as possible, but today what people like about it is the coloration. Go figure. It's a weird world.
--scott
Old 4 weeks ago
  #154
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Piedpiper's Avatar
 
1 Review written
🎧 10 years
I've often wanted a lower gain tube preamp since I'm often throwing away a lot of volume in the input attenuator of my Manley preamp since I prefer not to use too much negative feedback in the gain stage. Many sources into a condenser mic don't need more than 20 or 30 dB of gain to get them in the door.
Old 4 weeks ago | Show parent
  #155
Gear Head
 
I think I accidentally deleted my last couple of posts when I was just trying to delete the very last post.

Jim Moss


Quote:
Originally Posted by Piedpiper ➡️
I've often wanted a lower gain tube preamp since I'm often throwing away a lot of volume in the input attenuator of my Manley preamp since I prefer not to use too much negative feedback in the gain stage. Many sources into a condenser mic don't need more than 20 or 30 dB of gain to get them in the door.
Old 3 weeks ago | Show parent
  #156
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by JMoss1 ➡️
I think I accidentally deleted my last couple of posts when I was just trying to delete the very last post.

Jim Moss
Swift and decisive moderation in response to forum rule violations can have the same appearance as deletions by self....
Old 3 weeks ago | Show parent
  #157
Gear Head
 
Doesn't the moderator tell you when that happened?
I did try to delete a comment, but I don't know that it works that well.
I thought my post was right on target in addressing the person's comment.



Quote:
Originally Posted by studer58 ➡️
Swift and decisive moderation in response to forum rule violations can have the same appearance as deletions by self....
Old 3 weeks ago | Show parent
  #158
Lives for gear
 
🎧 10 years
I've seen some deletions by moderators where they've added a short explanation of the reason ( eg political content, personal abuse, promotion of commercial interest, etc), and others where posts have simply disappeared. The moderator retains the right to shape the entire thread as it evolves, including retrospective deletion without obligatory justification or announcement.
Old 3 weeks ago | Show parent
  #159
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Piedpiper's Avatar
 
1 Review written
🎧 10 years
Quote:
Originally Posted by JMoss1 ➡️
I think I accidentally deleted my last couple of posts when I was just trying to delete the very last post.

Jim Moss
I saw and appreciated it before it was deleted. It's always interesting to me to hear a designer's insights.
Old 3 weeks ago | Show parent
  #160
Gear Head
 
Thanks. You are motivated by similar things as I was. I just could not find them on the open market. I mean, some of these preamps you could overdrive them and it made no difference. The problem is that they used too much Neg Feedback. This also has a sound. To me it sounds confined and constricted. That is why I made it an option. (Side note: VOX AC amps had no Neg Feedback) The so called "Tube Sound" is often a function of overdrive. That is where your second harmonics come in and the sound gets bigger and warmer. Just depends on what you are looking for. I needed to no over drive on guitars and overdrive on lead instruments like Violins and voices. I use one over the other so there is separation.

https://www.jensen-transformers.com/...rs-Chapter.pdf

Jim Moss


Quote:
Originally Posted by Piedpiper ➡️
I saw and appreciated it before it was deleted. It's always interesting to me to hear a designer's insights.
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