Πως να φτιάξετε έναν προ προ ενισχυτη μικροφώνου με σωλήνες ηλεκτρονίων (λυχνίες κενού), χαμηλού θορύβου που λειτουργεί με μπαταρία.
Με δίκη σας ευθύνη.
At your own risk.
Take all precautions, we must be careful even with low voltages and batteries must have a fuse in series.
The microphone is connected to the primary of an input step up transformer (e.g. 1:14) through XLR connectors.
The stepped up signal voltage from the secondary is applied to the grid of the ECC82 (12AU7) through a coupling capacitor of say 10nF (according to how much bass cut is needed). The capacitor is important as it keeps the grid free.
The other side of the secondary is connected to ground -.
The cathode of the tube (valve) is connected to ground - too.
The grid is also connected to anode through a 10MΩ (Megohms) resistor to neutralize the existing negative charge on the grid when heaters are on, and to free electrons so that they can travel to the anode (plate) at very small anode voltages.
The anode is also connected to the primary of an output transformer (e.g. 20KΩ to 600Ω). The other wire of the primary is connected to the battery through a fuse holder and its fuse.
The secondary of the output transformer is the output and can be connected through XLR output connectors to the mic input of an ordinary microphone preamplifier as you would connect the output of the internal Neumann U47 amplifier of the condencer capsule.
One side of the 12V heaters is connected to ground -. The other side is connected to the battery through the fuse or a different fuse.
The amplifier was tested with amazing results with various dynamic microphones including an AKG D190.
Although the heaters of the 12AU7 are specified at 12.6 Volts the amplifier can be connected to a battery of 12Volts but also 6Volts! including the anode and you may find that you prefer the more easy, smooth and more detailed? sound.
At lower than specified cathode temperature apparently there is less electron cloud (steam) trafic, almost none temperature secondary emission effects from other electrodes (also because of the very low anode voltage). And the tiny signal still has in its service plenty of electrons to send it amplified to the anode.
You may experiment with a rheostat for various heater voltages i.e. temperatures and you may find a sweet spot where (thermal or shot?) noise is further reduced while signal is increased with great almost like an electron microscope revealing sound.
Pins 3 of the chassis XLRs are connected to the metal chassis box, (the extra pin on the XLR chassis connectors) and you can enjoy the smooth sound and complete absence of hum and other noises the battery operation offers. The battery should preferably be inside the box too to avoid radio frequency pickup. You may wind your own Pleiades transformers using Magnetec tape wound Nanoperm toroidal cores and you can vary the primary winding turns if you need to compensate for the proximity bass effect.
You may also like to experiment with an EF183 electron tube triode connected (i.e. anode, supressor grid and screen grid connected together). You may find that it can operate even with 3 volts for both heater and anode! Additional information on the Pleiades V6 preamplifier can be found on previous euroelectron post.
Setup:
AKG D190 at 2in - Pleiades ECC82 booster preamp - Realistic disco mixer - Sennheiser HD580
Με δίκη σας ευθύνη.
At your own risk.
Take all precautions, we must be careful even with low voltages and batteries must have a fuse in series.
The microphone is connected to the primary of an input step up transformer (e.g. 1:14) through XLR connectors.
The stepped up signal voltage from the secondary is applied to the grid of the ECC82 (12AU7) through a coupling capacitor of say 10nF (according to how much bass cut is needed). The capacitor is important as it keeps the grid free.
The other side of the secondary is connected to ground -.
The cathode of the tube (valve) is connected to ground - too.
The grid is also connected to anode through a 10MΩ (Megohms) resistor to neutralize the existing negative charge on the grid when heaters are on, and to free electrons so that they can travel to the anode (plate) at very small anode voltages.
The anode is also connected to the primary of an output transformer (e.g. 20KΩ to 600Ω). The other wire of the primary is connected to the battery through a fuse holder and its fuse.
The secondary of the output transformer is the output and can be connected through XLR output connectors to the mic input of an ordinary microphone preamplifier as you would connect the output of the internal Neumann U47 amplifier of the condencer capsule.
One side of the 12V heaters is connected to ground -. The other side is connected to the battery through the fuse or a different fuse.
The amplifier was tested with amazing results with various dynamic microphones including an AKG D190.
Although the heaters of the 12AU7 are specified at 12.6 Volts the amplifier can be connected to a battery of 12Volts but also 6Volts! including the anode and you may find that you prefer the more easy, smooth and more detailed? sound.
At lower than specified cathode temperature apparently there is less electron cloud (steam) trafic, almost none temperature secondary emission effects from other electrodes (also because of the very low anode voltage). And the tiny signal still has in its service plenty of electrons to send it amplified to the anode.
You may experiment with a rheostat for various heater voltages i.e. temperatures and you may find a sweet spot where (thermal or shot?) noise is further reduced while signal is increased with great almost like an electron microscope revealing sound.
Pins 3 of the chassis XLRs are connected to the metal chassis box, (the extra pin on the XLR chassis connectors) and you can enjoy the smooth sound and complete absence of hum and other noises the battery operation offers. The battery should preferably be inside the box too to avoid radio frequency pickup. You may wind your own Pleiades transformers using Magnetec tape wound Nanoperm toroidal cores and you can vary the primary winding turns if you need to compensate for the proximity bass effect.
You may also like to experiment with an EF183 electron tube triode connected (i.e. anode, supressor grid and screen grid connected together). You may find that it can operate even with 3 volts for both heater and anode! Additional information on the Pleiades V6 preamplifier can be found on previous euroelectron post.
Setup:
AKG D190 at 2in - Pleiades ECC82 booster preamp - Realistic disco mixer - Sennheiser HD580
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