It would be nice to have such a preamplifier.
So that a signal of tremendous signal to noise ratio is conditioned to sound as a finished product.
Similarly to connecting a Pleiades V0 prepreamp or a Neumann U47 prepreamp to the EMI RS61 preamplifier, (see a previous euroelectron blogspot).
The output then may be attenuated back to almost mic level to feed a portable or non portable digital recorder input, an analog to digital converter an iPhone or iPad with Garagband etc.
The anode voltage can be as low as possible to get to the enhanced sound as quickly as possible. Why should we power tubes with hundreds of volts so that signal conditioning or limiting effects start when the signal out is of a magnitude of hundreds of volts at the anode when we might just like to drive an analog to digital converter?
A high Megohm resistor from anode to grid frees electrons and make electron tube operation possible at even less than 6 volts with normal transconductance.
The Pleiades V5 with 2 EF183 triode connected electron tubes powered by 7.4V is such an example.
One more ie three stages are needed. With an attenuator after the front end stage ie the prepreamp stage. Drawing inspiration from Altec 1566A, Telefunken V72, EMI RS61 and front end Neumann U47...
How would they be coupled? Resistor at the anode? Interstage transformer? Inductor at the anode?
It may be a good idea not to use a resistor at the front end. Using an EF183 triode connected with 3.6 volts at the anode gives such a low noise behaviour that thermal noise of an anode resistor may contribute most of the noise. It has to be investigated. If you are interested please do your own experiments. All Pleiades concepts and schematics are open source.
The output stage may have an output transformer. And the front end at the input an input trasformer. Compensation for Fletcher-Munson and voice effort curves and proximity effect can be arranged by
lower inductance of the transformer or transformers.
Great transformers can be wound in the lab, at home or possibly outdoors using a Magnetec Nanoperm Nanocrystalinne ring tape wound cores which have extreme inductance index.
A small inductance interstage transformer can be made too. This can simulate tape recording and tape playback at the speed of light. Speed of light can be interpreted both as in real time and as having the full sound enhancing quality of a reel to reel tape recorder running tape at an extraordinary speed. The primary would simulate the recording head. As the inductance is low and the output impedance of the electron tube is high we would have a constant current with respect to frequency on the primary as is done on tube reel to reel recorders when driving the rec head. So the frequency responce will be rising in frequency in terms of voltage. Like a Pleiades filter. But in terms of current, ie the source of magnetic field, we would not just have nice transformer saturation on the bass frequencies only but at all the frequency spectrum. The secondary of the interstage transformer will simulate the playback head. Integration ie high cut will bring us back to flat frequency responce and at the same time rounding the spikes that had been instantaneously limited. Almost exactly like tape recording operates or disc recording RIAA reproduction, FM transmission with premphasis like in an Orban limiter and post emphasis on the radio, how Mike Oldfield produces his electric guitar sound etc. The tape on our simulation will be the tape wound ring core to which the primary and secondary are wound. No bias frequency is needed as everything is happening on the same core and the distorted current waveform will be converted to an undistorted voltage waveform at the secondary, see transformer theory (excitation current etc).
And then when we have a great signal from an as simple as possible path as possible, how do we add many such signals, one for example from each instrument or voice? Connecting many output transformers in series or in parallel? Connecting them with the use of hybrid transformers? Use constant impedance attenuators between preamp outputs and a passive console with hybrid transformers (see an older euroelectron post on adding signals)?. Or connecting many anodes together as is done on the Bouyer ST30 for example (valve or electron tube) cinema amplifiers? It should be found in practice.
Reference:
Pleiades V0 connected to EMI RS61 - euroelectron blogger
On preserving transconuctance of an electron tube at anode potential as low as 3 volt - euroelectron blogger
Operating features of the Audion - Edwin H. Armstrong
Tubes vs Transistors is there an audible difference? - Russel O. Hamm, JAES
Electric Crayons Anyone?
http://www.tangible-technology.com/tubes/altec.html
thats 2funny made my day
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