Trying to decide on tube mic preamps

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GalenH

Well-known member
Joined
Dec 15, 2022
Messages
50
Location
Portland, Oregon
Hello,
I have been researching tube preamps, I am looking for 4 channels of tube preamps for use with a stereo pair of Pearl Elm As, (dual output mics).

I record folk music, and would use them for minimalist recording and main pairs. I am really inspired by Kavi Alexander's recordings with rectangular diaphragm condensers into the EAR 824 tube preamp into tape.

So sound wise, I am looking for a sound that is clear, open, but not harsh at all. Every time I have done listening tests, I land on tube preamps being the most pleasant to listen to.
But I am also looking for things found in tube amps made to be more linear/ "transparent" eg DW Fearn, Knif Audio, EAR, etc. Low noise, high gain, lower distortion, not purposefully creating distortion....

The mics I'm using specify 1k+ input impedance is ideal, so that would be good.

I have really liked the sound of Tube Tech pm1a when I have heard them, and ideally I would use something like 4 channels of those, because they are modular, I was also looking at the builds of Gyraf GIX 51X.

Anything else is getting to be bigger than desirable for my rather mobile purposes. But Pm1a are out of production, and I keep reading about low end rolloff in the GIX 51X, ideally I would have a flatter response.

Has anyone copied the PM1a, as it is no longer in production? They seem almost impossible to find used.

I almost bought the Sebatron VMP Quad Plus recently, but I think it may not be linear enough at higher gains, although I think it is well built, and It is still in the running.

I would be interested in getting a quote from a good builder to make something like the pm1a if possible, or something like the GIX 51X if there was a solve for the low end rolloff issue. That is for another post, right now I'm just trying to figure out what's possible.

So basically TLDR,
-looking for 4 channels of modular tube preamps.
-At least 60 db gain
-Relatively flat response.
-Linear at higher gains
-Low distortion for a tube amp
-1k+ input impedance
-Low noise (for tube)
-Maybe something like a 2 tube stage design with step up input transformer, 20db pad, lundahl, cinemag, jensen? transformers...
-2 rack unit space or less.

I am not experienced enough to build tube equipment myself, so I am just asking to see if there is a diy design out there that I could hire someone to build for me, OR if there is someone who is building something like this who I could purchase from.
Thanks in advance!
 
Budget is ideally in the realm of 2,000 (unrealistic likely) to 5,500, so that rules out 4 channels of telefunken likely, although there are other reasons I would tend to stray the other direction from the old telefunkens, is concern about components becoming unreliable and parts hard to find when they need repairing. I don't know enough about electronics to know if this concern is reasonable.
 
Budget is ideally in the realm of 2,000 (unrealistic likely) to 5,500, so that rules out 4 channels of telefunken likely, although there are other reasons I would tend to stray the other direction from the old telefunkens, is concern about components becoming unreliable and parts hard to find when they need repairing. I don't know enough about electronics to know if this concern is reasonable.
For Telefunken style preamps I would consider AMI product line without a doubt.

https://www.tab-funkenwerk.org/tab-products/microphone-preamps/
 
I would be interested in getting a quote from a good builder to make something
Having built several tube preamps, there's a lot of labor involved. Add the cost of materials. High quality transformers are the biggest ticket item. To have something of the quality of Fearn or Mercury (V76 clone) I don't see how you'll have a custom build come out much less expensive. But maybe?
If you can do the metal work for the case for the assembly, the labor is dramatically reduced. If your builder had a case and front panel drilled and ready to fit all the components, It could be soldered, assembled, tested, and ready to go in a much more reasonable time.
 
Why not a Gyraf ?
A Gyraf Audio Gyratec IX Dual Tube Microphone PreAmp will set you back $2295 (@ VintageKing.com) and you will need two of those - unless SixtyNiner meant a Gyraf DIY (and NO - it's not a kit, but Vintage schematics).

Per
 
Why not a Gyraf ?
Two things about the Gyraf that I have a question about-
I was reading in the threads about the 51x DIY version, that some people experience a significant (-3 to -10 db @ 20hz) bass rolloff, depending on the input transformer.

I don't know if people have been able to eliminate that in the 51x version? Also issues with hum?
the second thing- With the 2 ru model, 4 channels would require 4 rack units of space. Ideally I would like 4 channels to take up 2 ru or less. That narrows things down a lot.
I am definitely considering a gyraf though, with Lundahl Transformers.

Does anyone know if it might be possible to fit 4 channels in a 2 RU case without significant issues? Maybe with an external power supply? I don't know if this question is naive or not.
And does anyone know about the bass rolloff in both the 51x diy version and in the larger versions, production and DIY?
 
A Gyraf Audio Gyratec IX Dual Tube Microphone PreAmp will set you back $2295 (@ VintageKing.com) and you will need two of those - unless SixtyNiner meant a Gyraf DIY (and NO - it's not a kit, but Vintage schematics).

Per
For the quality they are it's not terrible. Definitely expensive but not Fearn expensive.
 
Are you definitely looking for a vintage design or is something more modern OK?

Cheers

Ian
I don't know if I understand enough of the differences you are specifically referring to, to say.
However I can say, something that uses parts that aren't going to disappear imminently, has low (for tube) self noise, and is built to be fairly clean, not intentionally creating distortion beyond that which is inherent in tubes and transformers is what I am looking for.
Modern designs and vintage designs could both work if they worked within those intentions.
 
Having built several tube preamps, there's a lot of labor involved. Add the cost of materials. High quality transformers are the biggest ticket item. To have something of the quality of Fearn or Mercury (V76 clone) I don't see how you'll have a custom build come out much less expensive. But maybe?
If you can do the metal work for the case for the assembly, the labor is dramatically reduced. If your builder had a case and front panel drilled and ready to fit all the components, It could be soldered, assembled, tested, and ready to go in a much more reasonable time.
I definitely wouldn't expect a fully custom build to be much less expensive, especially with economies of scale. But one thing I was wondering is if the gix 51x or similar would be something someone could build, if the questions about the low end rolloff and hum issues were answerable. More than trying to get a "deal," I am asking around to see if something compact and to these requirements is possible and what it might cost, and then go from there.
 
Having built several tube preamps, there's a lot of labor involved. Add the cost of materials. High quality transformers are the biggest ticket item. To have something of the quality of Fearn or Mercury (V76 clone) I don't see how you'll have a custom build come out much less expensive. But maybe?
If you can do the metal work for the case for the assembly, the labor is dramatically reduced. If your builder had a case and front panel drilled and ready to fit all the components, It could be soldered, assembled, tested, and ready to go in a much more reasonable time.
Oh, on the case, I imagine I could order a case from redco to specifications and then have it shipped to whoever was building?
 
There is no bass roll off in the two g9 units I put together (unless you engage the HPF, obviously) but these are not the 500 series variant which uses different transformers.

If you are not building these yourself then Jakob’s commercial units are very reasonably priced for the parts, labour and quality assurance. I think they sound very good.
 
What about Jonte Knif‘s Therapy Preamp?
I haven’t build it yet, but definitely will.
From the description it seems to tick all boxes.
Oh! That looks interesting. It seems it is designed to distort but that it runs pretty cleanly? I didn't know that Jonte was doing stuff on here, his production preamp looks incredible. I wonder what the differences are between this and his preamps that he sells are. Do you have any insight on that?
 
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