Could I re-build a tube PA head into...

[Midnite Zone]

Hi everyone.  I'm wondering if I could take the preamps from a tube Pa head, and use them as stand-alone tube mic pres.  Now, I don't actually have a tube PA head yet...  So I'm not sure if it would likely have balanced or unbalanced inputs, transformer coupled, etc...  But you guys are the experts, so I'm sure someone could give me a heads-up.

Basically I want to end up with a 4-channel or 8-channel tube mic pre.  I want to run it into an old Layla Echo soundcard (eight 1/4" inputs).  I'm thinking that if I start with an old tube PA, it would save me money & time.  I'm not trying to build any specific mic pre, or get any specific sound, I'm just a working musician & long-time DIY-er trying to get a good sounding signal into my PC.

So is it possible?  I mean, couldn't a 6-channel PA head easily become a 6-channel mic pre?  .......................ken

 

[PRR]

The vast majority of tube PA had *optional* input transformers, very rarely installed.

The "preamps" were minimal: one stage, gain of 30-100, with a very high output impedance, 100K to 470K. That's all you need to drive a short wire to pot, mix-net, and then another one stage to bring you up to a Volt.

And darn few tube PA had XLR connectors.

> if I start with an old tube PA, it would save me money & time

Probably not. Even if you found a full set of input trannies, you need another stage per channel to get down from ~~200K to the <10K you need to drive external cabling and modern inputs. And you are likely to desire more gain. At tube impedances, that will mean two more stages.

And classic podium mike situations rarely beat 10mV input. The levels of modern studio mikes may overload classic transformers and first-stages.

Possible? Yes. Expedient? Maybe not.

Can you access this PDF file?

 

[Midnite Zone]

Ah...  Glad I asked before shopping around for an old head.  Thanks .....................ken

 

[shabtek]

what is your budget? how much additional time and $ do you want to invest? what are you feeding/ harsh environment requires balanced output? a PA head is has features you don't need (power amp/spkr out. and is not designed for full,flat audio bandwidth)

build a few 1-bottles they work well as hi-z instrument in and are perfect for experimentation. A simple valve topology. If I could rewind time I'd go back and reinvest my efforts in 1bottle variations. in a small recording environment balanced outputs may not really  be worth the diy effort.
edit:
I have found no 'near-readymade-budget solution' to high quality mic pres with some of the usual bells and whistles...
"color and character" can be found everywhere

 

[Midnite Zone]

Thanks for the input.  Right now my only preamps are in my Mackie 1402 mixer...  I only make home demos of my music, not serious professional recording, and my budget is always low.  I don't NEED tube mic pres, but I thought if it was easy enough, I could simply pick up an affordable PA head & get to work.  But now that my bubble has burst, I'm gonna point my budget elsewhere...  Drum heads, cymbals, cables, mics, mic stands, new power tubes...  It never ends!  I actually have four Green Pre PCBs on my desk, but I just haven't had the money for parts...

I'm never happy with how my recordings turn out, and lately the results have just been abysmal.  So I've decided to blame my gear!  Maybe better mic pres will help, or maybe not...  Hell, maybe I need better everything.  Or maybe I'm just doing something wrong...  There should really be a support group for DIY musicians ...............................ken

 

[CJ]

there is a CTA album with terry kath using a bogen pa for a preamp into a fender dual showman.

yucky track, free from guitar, possibly the worst, but i'm jus sayin...