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Using mic-to-tube preamp vs tube mic? ART tube preamp.

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Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby Elephone » Tue Jun 11, 2019 6:13 pm

Hello. I have an ART tube preamp and just wondered if this is comparible to using tube mics when used in conjunction with a mic.

The effect of the ART tube box seems quite subtle, so to for more obvious effect, should I try introducing it (pass the signal through it) several times?

What's the best use of it with a guitar amp? Can you create the some of the effects of valve amps with tube preamps?

Thanks.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby blinddrew » Tue Jun 11, 2019 9:17 pm

If your tube mic sounds like your other mic when fed through the ART then yes, otherwise no. ;)

All of which facetiousness just means that it will all depend on a whole host of factors and the simple answer is just to experiment and see if you like what you get. You might have to push the ART pretty hard to get any significant colouration on it though so starting with a low-output mic would probably help.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby Sam Spoons » Tue Jun 11, 2019 10:40 pm

Surely a high output mic will push the Art harder?
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby blinddrew » Tue Jun 11, 2019 10:44 pm

Interesting question.
My thinking was that if you have a low output mic, the pre-amp will have to do more work to raise the gain. Hence it would be imparting a greater colour to the proceedings.
But i see where you're coming from.
I will defer to someone with greater knowledge (i.e. anyone!) :)
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby Sam Spoons » Tue Jun 11, 2019 10:46 pm

:D me too.....
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby ef37a » Wed Jun 12, 2019 7:59 am

Now, I do not own a valve capacitor microphone but am not that convinced that any desirable sound quality, real or imagined, is down to the valve?

The triode (or triode strapped pentode) is used as a cathode follower so it enjoys 100% negative feedback. Even used as a voltage amplifier of say 30dB gain, at about a volt rms out even a poor sample such as the ECC83 would be producing well under 0.5% distortion and progressively less at lower outputs, i.e 0.05% at -20dBu 'ish. As a cathode follower the distortion would be even lower by a considerable margin.

Then, surely the makers of the old mics would have selected a valve type and sample FOR lowest THD? (the 83 is not a good one. The E88CC is much better)

I suspect the "quality" of valve mics is due to the back plate design, higher polarizing voltage than FETs and maybe the transformer which is virtually a necessity unlike many modern FET mics?

Anyone have an old £5k tube job I can rip the valve out of and fit a FET to check the matter?

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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby ore_terra » Wed Jun 12, 2019 8:15 am

don't have an opinion on the potential quality you'd get from the ART pushed hard. but assuming it has an output knob, is it still subtle if you crank the input and lower the output down to the desired level?
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby Arpangel » Wed Jun 12, 2019 8:24 am

Isn't the ART one of those valve devices that has one strapped across the output? It's not actually a preamp designed using valves in the preamp circuitry, like more expensive preamps, or a good valve microphone.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby CS70 » Wed Jun 12, 2019 10:07 am

Hello. I have an ART tube preamp and just wondered if this is comparible to using tube mics when used in conjunction with a mic.

Hm in general, not really. Valve mics need a transformer on the output to be able to drive the signal over reasonable cable lengths, and that changes more the sound than the tube itself with respect to mics which don't need and have the transformer (like many solid state).

Yes, if pushed into distortion the head amplifier will distort differently if the amplifying element is a tube or a solid state component, but a good design usually is made so that the amplification stays transparent over the voltage range that the capsule can produce.. there's no "gain" control on the mic (only how loud you shout :) ), so given that the designer knows the max voltage that can be generated by the condenser, he can design an amplifier which does not distort even if there's a tube in. The tube may or may not impair some little character but it really shouldn't. Transformers on the other side change the sound quite noticeably. Most of the "tube" sound is really the fact that there's a transformer.

On the other side, preamps can be easily overdriven and have a specific character when so pushed: they distort the signal big time, and some tube ones do that in a pleasant way.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby ef37a » Wed Jun 12, 2019 12:40 pm

Don't want to be "ok'ard but I even think transformers get a bad press in many cases?

From pictures I have seen the transformers in valve mics seem easily big enough for the levels involved? The amount of power a valve could dump into a traff is limited anyway, 0dBu with a 600 Ohm load would only be a mW (of course) The transformer would have to be very wee and a bit crap to distort at that voltage and 775mV is a heck of a mic signal!

Then there are transformer input pre amps (into an IC) that do not have much "attitude".

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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby CS70 » Wed Jun 12, 2019 1:24 pm

Woudln't say a bad rep, many much loved mics exist with or without transformer output?

I don't know enough, but I remember reading in SOS that transformer introduce phase shifts and can become nonlinear with higher signal level? Whatever it is, it is not by all means bad, I like my 87 or the Copperhead just as much as my 102 and Dolly.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby SimonZ » Wed Jun 12, 2019 1:29 pm

ef37a wrote:The triode (or triode strapped pentode) is used as a cathode follower so it enjoys 100% negative feedback........
Dave.

Almost exclusively plate followers Dave, and not much if any feedback used either.
Charge amplifier might be a better description.
Plenty of opportunity for non linearity.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby James Perrett » Wed Jun 12, 2019 1:51 pm

When I did a comparison between my U47fet and the valve version the sound was very close - just a slight treble lift from the valve version. It was obvious to me that the sound of the mic was very much down to the capsule rather than the electronics and it made me realise that there was no need for me to spend thousands on an old valve mic.
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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby ef37a » Wed Jun 12, 2019 1:54 pm

SimonZ wrote:
ef37a wrote:The triode (or triode strapped pentode) is used as a cathode follower so it enjoys 100% negative feedback........
Dave.

Almost exclusively plate followers Dave, and not much if any feedback used either.
Charge amplifier might be a better description.
Plenty of opportunity for non linearity.

"Plate follower" is a term I am not familiar with unless you mean a conventional common cathode stage with the valve working as a virtual earth amplifier and the capacitive capsule running constant current?
I would be interested to see a schematic?

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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby ef37a » Wed Jun 12, 2019 2:16 pm

Ok, found a few circuits and yes, the valves all seem to be connected as inverting voltage amplifiers.

However, if you take the E86 as a triode it has a mu of only 33 (and that at 250V!) and judging by the size of the anode coupling caps used, the anode impedance is not that high and so a gain of 20dB max seems likely? For typical mic signal levels, say -20dBV ish? Linearity is surely going to be good?

Next step (bloody obvious innit! DOH!) see where the mic makers 1% THD point is specc'ed?

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Re: Using mic-to-tube preamp vs tube mic? ART tube preamp.

Postby CS70 » Wed Jun 12, 2019 3:25 pm

James Perrett wrote:When I did a comparison between my U47fet and the valve version the sound was very close - just a slight treble lift from the valve version. It was obvious to me that the sound of the mic was very much down to the capsule rather than the electronics and it made me realise that there was no need for me to spend thousands on an old valve mic.

Don't they both have a transformer coupled output? Different transformers tough I'd guess.
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