It is interesting.
By implementing the time constants (low cut usually) on the transformers themselves the transformer design and making is extremely simplified. Very few relatively turns are needed. Sooner or later a young person will be able to make a world class electron tube, JFET or bipolar transistor microphone preamplifier at home including the input and output transformers.
Only one electron tube was used. The legendary EF183 used on Pleiades V4 and V5.
As the V6 is in experimental stage, connections were in breadboard (surrounded by a metal opened box), including Neutrik XLR male and female chassis connectors.
Anode current: 100μA.
Supply voltage, Vb=5.8V
Anode voltage is very close to Vb as the output trasformer (carrying the anode current) is connected directly to anode. Very similar to single ended class A triode 300B power amplifiers. The stage of course behaves as an extremely low noise front end preamplifier.
Heater voltage Vh=3V
The low noise performance of the V6 is described earlier on euroelectron.
This time it was time to listen to the other extreme driving directly 300Ω headphones. The Sennheiser HD580 was bridged to mono with a special XLR female to headphone connector cable. So the load impedance is 150Ω.
Setup:
Sony portable CD player headphone out - Canford red high to low trasformer inside 1/4in jack - Altec green 4722 step up - coupling capacitor - EF183 triode connected with 8.2MΩ from anode to grid - Pleiades Magnetec 070 16H:140mH output transformer - Sennheiser HD580
CD used: Ray of Light - Madonna
It sounded nice!
Louder than expected.
It was easy to overload now by increasing the volume out on the CD player headphones out. The distortion was a nice electron tube distortion.
Substituting the Altec 15095 the distortion was worce as the low frequency responce was more extended due to its very high primary inductance.
It was then decided to drive a microphone input again instead of the headphones.
Setup: as above but stereo disco mixer included.
Sony CD - Canford red - Altec green - EF183 (8M2 from anode to grid) - Pleiades 070 - realistic disco mixer - HD580
CD used : audio test CD from the Ηχος magazine with tones from 20Hz to 20KHz
As now the load impedance (the disco mixer input impedance) is 5KΩ, both transformers are expected to have a worst case scenario low frequency response.
With the Altec output transformer the 3dB point was at 100Hz and 10KHz.
With the Pleiades Magnetec 070 (with relatively few turns) the 3dB points were 340Hz and 11KHz.
The high frequency cutoff made be due to the Altec or Canford input trasformer. The Canford was used as a step down trasformer to reduce the signal, as much as possible. A resistor pad should have been used.
The 350Hz cutoff was very promising and since it represents the cutoff used on the Pleiades filter to make the Sennheisr MD21 sound very natural on voice,a Sennheiser MD21 HL was decided to be connected. On previous experiments the 380Hz, 6db per octave high pass was implemented with a 82mH Pleiades filter in parallel with the microphone output.
New set up:
Sennheiser MD21 used as low impedance - Altec input trasformer - EF183 (8M2 from Plate to grid - Pleiades Magnetec 070 output trasformer - realistic disco mixer mic input - Sennheiser HD 580
The sound on make voice, speech or singing was amazing. So natural that it sounded as the microphone instead of cable was connected to and acoustic waveguide of flat frequency responce, the other side of the waveguide touching the ear.
With the Altec output trasformer the voice was bass heavy as expected and ambient low frequency rumble could be heard.
The MD21 sounded so detailed and sensitive that sounds from very far could be heard as is the case when testing condenser microphones.
Conclusion:
A flat input trasformer can be used on a Pleiades V6 one electron tube one battery pre preamplifier and a Pleiades bass compensating trasformer this time at the output of the Pleiades pre preamplifier.
Or if a Pleiades compensating input trasformer is used (82mH primary inductance in the case of MD21)...
Then the output trasformer could play the role of a second time constant to simulate a tape recording amplifier pre emphasis. Another combination may be a flat input trasformer and a high cutoff at the output trasformer. Then an integrating circuit (post emphasis) and integration stopped at the proximity effect frequency as explained on a previous euroelectron post.
This would allow the making of the output trasformer very easy as the time constant to simulate 30ips tape recording use is a high pass filter at aproximately 10KHz.
The output trasformer can now become an interstage step up transformer. Its secondary simulating playback (coupled coils without tape use). The interstage trasformer can drive another EF183 battery powered amplifying stage.
In fact a transformer is like a record head kissing a playback head on the air gap! It may be interesting to experiment with two magnetic tape heads mounted in such a way at the one touches the other to the lips thereby completing the magnetic circuit. The air gap may be useful since DC current is passing from the anode of the driving electron tube. But winding both coils on a toroidal Magnetec or other core is great too. In this way both coils are hugging each other and music passes on from the one to the other with the aid of the electrons dancing inside the magnetic circuit!
Then at instantaneous playback a low pass filter on the other electron tube stage with a 3dB point at 10KHz can be used to get back to flat frequency responce. The advantage is rounding off of any instantaneous peak limiting waveform by the high cut action (sharp edges are created by high overtones) and making tape simulation sounding as expected. Loud and big.
By implementing the time constants (low cut usually) on the transformers themselves the transformer design and making is extremely simplified. Very few relatively turns are needed. Sooner or later a young person will be able to make a world class electron tube, JFET or bipolar transistor microphone preamplifier at home including the input and output transformers.
Only one electron tube was used. The legendary EF183 used on Pleiades V4 and V5.
As the V6 is in experimental stage, connections were in breadboard (surrounded by a metal opened box), including Neutrik XLR male and female chassis connectors.
Anode current: 100μA.
Supply voltage, Vb=5.8V
Anode voltage is very close to Vb as the output trasformer (carrying the anode current) is connected directly to anode. Very similar to single ended class A triode 300B power amplifiers. The stage of course behaves as an extremely low noise front end preamplifier.
Heater voltage Vh=3V
The low noise performance of the V6 is described earlier on euroelectron.
This time it was time to listen to the other extreme driving directly 300Ω headphones. The Sennheiser HD580 was bridged to mono with a special XLR female to headphone connector cable. So the load impedance is 150Ω.
Setup:
Sony portable CD player headphone out - Canford red high to low trasformer inside 1/4in jack - Altec green 4722 step up - coupling capacitor - EF183 triode connected with 8.2MΩ from anode to grid - Pleiades Magnetec 070 16H:140mH output transformer - Sennheiser HD580
CD used: Ray of Light - Madonna
It sounded nice!
Louder than expected.
It was easy to overload now by increasing the volume out on the CD player headphones out. The distortion was a nice electron tube distortion.
Substituting the Altec 15095 the distortion was worce as the low frequency responce was more extended due to its very high primary inductance.
It was then decided to drive a microphone input again instead of the headphones.
Setup: as above but stereo disco mixer included.
Sony CD - Canford red - Altec green - EF183 (8M2 from anode to grid) - Pleiades 070 - realistic disco mixer - HD580
CD used : audio test CD from the Ηχος magazine with tones from 20Hz to 20KHz
As now the load impedance (the disco mixer input impedance) is 5KΩ, both transformers are expected to have a worst case scenario low frequency response.
With the Altec output transformer the 3dB point was at 100Hz and 10KHz.
With the Pleiades Magnetec 070 (with relatively few turns) the 3dB points were 340Hz and 11KHz.
The high frequency cutoff made be due to the Altec or Canford input trasformer. The Canford was used as a step down trasformer to reduce the signal, as much as possible. A resistor pad should have been used.
The 350Hz cutoff was very promising and since it represents the cutoff used on the Pleiades filter to make the Sennheisr MD21 sound very natural on voice,a Sennheiser MD21 HL was decided to be connected. On previous experiments the 380Hz, 6db per octave high pass was implemented with a 82mH Pleiades filter in parallel with the microphone output.
New set up:
Sennheiser MD21 used as low impedance - Altec input trasformer - EF183 (8M2 from Plate to grid - Pleiades Magnetec 070 output trasformer - realistic disco mixer mic input - Sennheiser HD 580
The sound on make voice, speech or singing was amazing. So natural that it sounded as the microphone instead of cable was connected to and acoustic waveguide of flat frequency responce, the other side of the waveguide touching the ear.
With the Altec output trasformer the voice was bass heavy as expected and ambient low frequency rumble could be heard.
The MD21 sounded so detailed and sensitive that sounds from very far could be heard as is the case when testing condenser microphones.
Conclusion:
A flat input trasformer can be used on a Pleiades V6 one electron tube one battery pre preamplifier and a Pleiades bass compensating trasformer this time at the output of the Pleiades pre preamplifier.
Or if a Pleiades compensating input trasformer is used (82mH primary inductance in the case of MD21)...
Then the output trasformer could play the role of a second time constant to simulate a tape recording amplifier pre emphasis. Another combination may be a flat input trasformer and a high cutoff at the output trasformer. Then an integrating circuit (post emphasis) and integration stopped at the proximity effect frequency as explained on a previous euroelectron post.
This would allow the making of the output trasformer very easy as the time constant to simulate 30ips tape recording use is a high pass filter at aproximately 10KHz.
The output trasformer can now become an interstage step up transformer. Its secondary simulating playback (coupled coils without tape use). The interstage trasformer can drive another EF183 battery powered amplifying stage.
In fact a transformer is like a record head kissing a playback head on the air gap! It may be interesting to experiment with two magnetic tape heads mounted in such a way at the one touches the other to the lips thereby completing the magnetic circuit. The air gap may be useful since DC current is passing from the anode of the driving electron tube. But winding both coils on a toroidal Magnetec or other core is great too. In this way both coils are hugging each other and music passes on from the one to the other with the aid of the electrons dancing inside the magnetic circuit!
Then at instantaneous playback a low pass filter on the other electron tube stage with a 3dB point at 10KHz can be used to get back to flat frequency responce. The advantage is rounding off of any instantaneous peak limiting waveform by the high cut action (sharp edges are created by high overtones) and making tape simulation sounding as expected. Loud and big.
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