tube microphone preamps for recording 18W

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myker
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tube microphone preamps for recording 18W

Post by myker »

hey guys, i have built many a tube amp. SLO clones to 18 watts, and a bunch of hybrid stuff in between. I have also built a couple of API 312 and Neve 1272 style Preamps that i use in my project studio. I have always been a cloner, but never had what i consider to be any "real" technical knowledge, so I am asking now.
Does anyone have knowledge of building tube microphone preamps, such as the UA 610 or the Telefunken, Neumann, or Ampex stuff? Do they drive the OT the same way that a tube guitar amp does? When recording, the mic pre makes a HUGE difference on the tone of the guitar as many of you know, but what influence does this have on the design of the tube mic preamp?
Sorry if this is the wrong forum to post, but I wondered if anyone has the same questions as me, will my 18 watt be best translated to recording medium by a tube mic pre design or is it a matter of taste?
thank you,
-mike
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WesKuhnley
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Post by WesKuhnley »

Personally, I would not recommend a tube pre for any electric guitar, your Neve and API clones are better suited to the task. I find tube pres to be useful when something needs to be softened like strings, acoustic, or jazz drums. Some tube pre topologies are better suited than others to the task. I find that a fully-differential amplifier is usually cleaner and more direct sounding than a single-ended ones. The LA610 you mentioned is a very colored circuit, and I consider it a low-rent unit, at least when you consider the alternatives.

If you really stuck on needing a tube pre, check offerings from A-Designs, Hamptone, Roll Music, or LaChapelle Audio.
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myker
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Post by myker »

i own the la610, and as you were stating, it is very colored and can get really gritty sometimes adding to the sound in a pleasing way if thats what you are looking for. but sounds a little on the slow side for drum use as you said you use it for softening drums sometimes. i guess what i was looking for was tube warmth, but a little more sterile, getting out of the way of the sound of the amplifier, and having a bit more punch. wondered if any of you guys dabble in this or just use whatever mic and pre are available when you record your 18 watt clips.

mike
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justinm
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Post by justinm »

Not that I have a lot of experience designing mic-pre-amps, but I'm starting to get into this as well. In general, I'd say the output transformers are not driven exactly the same way as guitar amps. Partly because you are making a line level signal, you don't need big voltage swings to induce a lot of current on the secondary do drive a speaker. Some of the mic-pre topologies I've been looking at are strict differential designs and some are class A not unlike a guitar amp pre. Remember that the phase inverter of an 18Watt Marshall (like all long tailed pair PIs) is essentially a differential amp. I've seen a Pultec mic-pre design that drives the OT directly from a 12AX7 differential amp with the plates connected to the OT the same way you would on a power amp. In this case the tubes are not swinging as much voltage as most power amps.

Check out the Jensen transformers site- they have a bunch of sample schematics to go along with their products.

http://www.jensen-transformers.com/apps_sc.html
There are some tube schematics.
Also read the white papers by Bill Whitlock- he's been doing this for a long time and knows what he's talking about.

Justin
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myker
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Post by myker »

interesting about the pultec, i have been interested in some of the pultec stuff as well as langevin. thanks for the info on the jensen website.
-mike
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bentaro_rifferashi
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Post by bentaro_rifferashi »

you would do well to check out the prodigy pro forum:
http://www.prodigy-pro.com/forum/index.php
those guys are building all kinds of pro audio gear and its a massive knowledge base.
personally i think you will struggle to find anything better than the 2 pres you mentioned :wink:
Ben
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