bluebird

peerless/altec 15356 600:600?
« Reply #20 on: October 04, 2004, 07:22:21 PM »
If I wanted to make it balanced in I have some 7K:10K input transformers laying around.

I do remember you posting specs but I didn't save them.


rafafredd

peerless/altec 15356 600:600?
« Reply #21 on: October 04, 2004, 07:34:50 PM »
But if you have some shielded 600:600, try terminating this with a 1.5k-4.7k at the secondary, shunting to ground, and try as a mic preamp. Maybe it will give you exactly what you are looking for.

bluebird

peerless/altec 15356 600:600?
« Reply #22 on: October 04, 2004, 07:47:48 PM »
Alright I'll give it a try. so you think the 4.7K termination will do the trick?

I could just try a 5K pot.

I'll use the Altecs.

thanks Rafa

NewYorkDave

peerless/altec 15356 600:600?
« Reply #23 on: October 04, 2004, 08:39:47 PM »
If your mics are hot and your soundcard has a high-impedance input, why not just try a mic input transformer right into the soundcard input?

This makes more sense than padding down a hot signal just to amplify it back up again.

Don't laugh, but some of those "inline" low-Z to high-Z mic transformers can do a decent job. The ones from Shure and AT have a good rep. The AT one is very inexpensive.

rafafredd

peerless/altec 15356 600:600?
« Reply #24 on: October 04, 2004, 08:46:15 PM »
I always think... What is inside those inline mic xformers?

Is it a mumetal cased high nickel core transformer?

NewYorkDave

peerless/altec 15356 600:600?
« Reply #25 on: October 04, 2004, 08:47:49 PM »
Oh, come on.  :roll:


 :green:

rafafredd

peerless/altec 15356 600:600?
« Reply #26 on: October 04, 2004, 08:52:49 PM »
OK  :roll:  :roll:  :green:  :green:

NewYorkDave

peerless/altec 15356 600:600?
« Reply #27 on: October 04, 2004, 09:04:39 PM »
Actually, Bluebird, your 1:3 transformer might be just the thing to interface a hot mic to your soundcard input.

Suppose your soundcard has an input Z of 10K. (This is a reasonable assumption). This will reflect to your mic as 1.1K, which should be high enough to make it happy. And you get 9.5dB of gain from the transformer. A reasonably high-output mic close to a drumkit can peak out near 0dBU, so this should be plenty of signal to drive your soundcard, especially if it's capable of working with so-called "-10" consumer input sources.

There is one problem with the inline transformer I mentioned earlier. I went and did a reality check just now and found that they seem to be rated for 250:50K. This means a 1:14 turns ratio. So, that's 23dB of stepup right there, possibly too hot for your soundcard (or maybe not... it depends). However, if your soundcard input impedance is 10K, this is reflected to the mic as a miniscule 50 ohms(!). No good.

The inline jobbies do a good job, however, working into a very high-Z input such as a tube grid, such as the high-Z mic inputs on old tube tape recorders. Matter of fact, those inlines were sold originally for the very purpose of interfacing low-Z "professional" mics to such devices.

bluebird

peerless/altec 15356 600:600?
« Reply #28 on: October 04, 2004, 09:08:44 PM »
Dave its funny you should suggest that. I just tryed it last week.

I have a box that has phantom and the triads on thier highest ratio right out to the sound card.

It actually worked but the signal was not quite loud enough. I was barely hitting -6 db in the DAW.

I'm still messing around with it.

Oh my sound card is 24K input impedance balanced, and 12K unbalanced.

I havent tryed to set the inputs to -10 on the sound card. maybe that will do it.

NewYorkDave

peerless/altec 15356 600:600?
« Reply #29 on: October 04, 2004, 09:14:40 PM »
Funny, when recording digital, I try to keep my peaks around -6dBFS. I want headroom!

If you're recording at better than 16-bit, there's really no sane reason to try to mash everything up to close to full-scale, anyway. Even with 16-bit, it's arguable whether or not it's a good idea.


rafafredd

peerless/altec 15356 600:600?
« Reply #30 on: October 22, 2004, 12:46:16 PM »
Hey Bluebird, I found my langevin datasheet.

Your board specs:

gain:

40mV for +4dBm/600ohms

FR: +-0.25dB 30-15kHz

output impedance: 110 Z

recommended load impedance: 600Z

THD 0.5% 30-15kHz

Noise: 70dB below +4dBm

Power: 42v, 40mA

That´s all. I hope it´s some help.


 

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