Which 12AX7 for a Mic Preamp?

davidguilbault

davidguilbault

Perusing the Bargain Bins
Hi folks,

I am going to do some home recording of my songs. I will have two Presonus TubePre microphone preamps. But, I understand that the Chinese tubes that come stock in those should be replaced for better performance. I know absolutely nothing about tubes.

Which 12AX7 replacement tubes should I buy for warm vocals?

Here's the blurb about the preamp on the Presonus site:

"... the TubePre is definitely all-pro, starting with a dual-servo (no capacitors) gain stage that lets you boost the program signal to smoking hot levels without significantly increasing the background noise.

The 12AX7 vacuum-tube-based preamp includes a Gain control and a Tube Drive control that lets you decide how much signal to put through the tube. You get 48V phantom power, a 80 Hz high-pass filter, -20 dB pad, and polarity-reverse switch, just like with the big preamps. And of course, the TubePre delivers the highly prized tube warmth we all love. It even sports an analog, backlit VU meter.

The TubePre is more than a mic preamp, though. Thanks to separate instrument and mic inputs, it also serves as a dynamite direct box (DI) for guitars and basses. And it’s small enough to carry almost anywhere, although you also can rack-mount it using our optional 3UMR rack adapter."

Thanks for your help. Cheers for now. David.
 
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Quiet is primary of course so selected for that is important, 7025s are a low noise version of the 12AX7. A 7025 long plate square getter would be warm. Not sure if they come in black plate. :scratch2: I have some long gray plate Sylvania 7025s that are very nice tubes. They came in my Lafayette KT-600 preamp. :yes:
 
I've been using 12AX7LPS tubes due to the low noise floor in my phono stages, which are roughly the same level of gain and signal magnitude found in the DI/preamp stage for mics and guitars.

For another point of reference the Universal Audio LA-610s, an contemporary tube-based industry device available today, uses JJ brand tubes which have been selected according to microphonics and burn-in reliability (hint: they were getting 60% failure rates some 5 years ago when I worked there).

From my own recording experiences across the same time period, I'd not put too much worry into the choice of tube. Odds are you're not going to hear it as the noise floor in the recording room is going be a lot higher than the electronics. Spend your time and energy choosing the most appropriate mics to use first.

Cheers,

David
 
I like the RCA clear top 12ax7
Northern Electric 12ax7

Others you might want to look at:
EI ecc83
Genalex Gold Lion Ecc83
 
diamondsouled said:
Quiet is primary of course so selected for that is important, 7025s are a low noise version of the 12AX7. A 7025 long plate square getter would be warm. Not sure if they come in black plate. :scratch2: I have some long gray plate Sylvania 7025s that are very nice tubes. They came in my Lafayette KT-600 preamp. :yes:
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Hi. Thanks for the info. Since I'm a tube newbie, I don't know the distinctions between gray and black plates. Can you clue me into that? Are there sonic differences? Cheers. David.
 
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davidguilbault said:
Hi. Thanks for the info. Since I'm a tube newbie, I don't know the distinctions between gray and black plates. Can you clue me into that? Are there sonic differences? Cheers. David.
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The distinction is the color of the plates. As for the sound it's subjective but some folks say they prefer black plates. It may be more a question of vintage though and not plate coating/material. :yes:
 
I did some 12AX7 tube rolling a few weeks agon in my modded Dynaco PAS-2.
I have NOS GE's, EH's, reissue Tungsol's, reissue Mullards, NOS RCA 7025's, and NOS Sylvania 7025's.
In the end I found the Sylvanias to be the most dynamic and satisfying,
The RCA's were the Slov 7025s and were very dynamic as well, but I found them to be very fatiguing over time. Of the reissues, I like the Mullards the best.
The short grey plate GEs were my leat favorite. I found them too subdued.

Al. Wise
 
Thanks for the input folks. I bought a pair of NOS Philips JAN 12AX7WA tubes, date coded A-9/87. Per your recommendations, I may also buy a pair of the Sovtek 12AX7LPS tubes for comparison. As I am a baritone, I'm looking for something that gives warmth and presence to my low voice. Is that what people mean when they say the tone of a tube is "dark"? Cheers for now. David.
 
For tubes call Andy at Vintage tube services. I have known Andy for many years. When it comes to knowledge of tubes and what works best for your application he is the best. Not always quickest turntround time, sometimes hard to connect with but keep trying. He has thousands of vintage tubes, used and nos. He tests them for noise and a number of other things. Then grades them. Don't use email! He is old school all the way. If you want the best he is the man. He help me pick tubes for my HK cit II and Eico hf85. I will never buy from anyone else.

Vintage tube services (616) 794-1540
 
If you have the funds and the opportunity, try some original Mullards, which carry the "warm" reputation. If gain isn't an issue, try some 5751's which are identical to 12AX7's, except with only 70% of the gain....:thmbsp:
 
12AX7 Tube Rolling

Well, I tested the GrooveTube GT12AX7C and the Philips JAN12AX7WA in two different Presonus TubePre microphone preamps today.

Couldn't tell a huge difference between the two tubes. However, there was a soft hiss with both of them.

Tonight I pulled a GE 12AX7 and a Silvertone 12AX7 from a Sherwood tube amp I haven't been using. I'll try them tomorrow and see what I hear.

I'm also going to order a pair of Sovtek 12AX7LPS tubes, just for the heck of it.

I can tell this "tube rolling" is going to become as addictive as collecting turntable cartridge/stylus combinations.

Oh, well. Such is life.
 
Personally, on a mic preamp, my first choice would be Tungsram if I wanted a very even reproduction. I find Mullards(original, not "re-issue") will add warmth, and Telefunkens to be so precise that they can sometimes sound too bright. Tungsrams always, to my ears, walked the line right in between.

A word of caution about Sovtek LPS tubes: if you have a cathode follower in the circuit without an offset filament supply (I usually run mine at about 70V), they can break down easily; their limit of Vhk is about 100V, as opposed to the customary 200V that vintage tubes used to get.

Oh, and EI tubes were pretty darn good in their day (before we bombed their factory), but they command high enough prices to where you can buy some good RCA, GE, or Sylvanias for the same price.

Just my opinions, but you asked.

rooster.
 
Tungsram

rooster18 said:
Personally, on a mic preamp, my first choice would be Tungsram if I wanted a very even reproduction.
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Thanks Rooster. I hadn't heard of Tungsram. I'll keep my eyes open for them. The prices I've seen for Mullards and Telefunken are out of my budget.

I just bought a matched pair of the Sovteks (12AX7LPS) with 4 balanced triodes. We'll see how they sound.

I'm hoping that when I start recording my singing (through a Neumann KMS105 hand-held condenser mic and the PreSonus TubePre) that I don't have any noise.

So, I'll do some tube rolling and see which is the quietest of the tubes I've collected so far - GrooveTube GT12AX7C, Philips JAN 12AX7WA, Sovtek 12AX7LPS, Silvertone 12AX7 and GE 12AX7.
 
drtechno said:
also try different mic cords. they do sound different with 105's
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Oddly enough, I have very expensive Zaolla mic cables and could get no sound from the Neumann KMS 105 through them. So, I switched to some Canare cables and the mic worked. Then, when I switched back to the Zaolla's it worked, too. Something, somewhere in the chain needed to warm up, I guess.
 
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