It was decided to connect the output of the Pleiades V6 pre preamp to the low impedance input of the Sony TC-D5 pro. The TC-D5 mono option was switched on so that sound could be heard on both headphone drivers.
Signal path, setup
Male singing voice - microphone - Pleiades V6, 140mH transformer primary, 8MΩ from anode to grid, 22nF grid coupling capacitor - Sony TC-D5 pro on mono - Sennheiser HD580
The Pleiades V6 (in breadboard stage) electron tube pre preamplifier was powered by 3 AA rechargeable batteries. So anode voltage was roughly 3.9V. A variable wirewound series resistor to heaters was used to further reduce the cathode temperature.
When the heater voltage was 3.9V the anode current was 100μA. When the rheostat was at 9Ω the heater voltage would have been 2.5V? and anode current was measured to be 40μA.
Firstly the Sennheiser MD211 was used at 0 to 2in.
The sound was amazing. As if one was recording in the finest recording studio. All the fine detail one can imagine. Very low noise. High output. The recording level potentiometer on the Sony TC-D5 pro was at position 3 out of 10 for full modulation even with a very soft singing voice. A behaviour similar to connecting a high output world class condenser mic such as an AKG C24. When the gain was increased on the TC-D5 pro sounds from dozen of meters away could be heard with prestine detail, birds etc. There was a nice balance of ambient sound frequency spectral content with no bass of rumble exaggeration to listener's brain. It seems the 140mH primary inductance of the mic input transformer is a nice choice. In fact it almost happened by chance. It is the transformer that did not make it as the output transformer. The turns ratio of both transformers used is 1:10.
The Sennheiser MD611 M (medium impedance) was connected too. It sounded loud, somewhat less low noise, and somewhat less refined. Nevertheless it was a nice sound.
The SM58 Mexico was then connected. It sounded fine. An optimum distance was 4-5in. At less than this the sound was becoming bass heavy, and at larger than this thin, (proximity effect). When increasing gain the ambient noise only consisted of very high frequencies and hiss (proximity effect again). There was a little handling noise.
The MD 211 N sounded so refined!
Most listening tests were done with just Ia=40μA, ie the electron tube further underheated. When the EF183 triode connected electron vacuum tube is further underheated (when the anode current is less than say 70μA and more than 40μA) the sound is even more interesting. As if one gets with a microscope to even more detail. Louder too. There may be an euphonic distortion too? Or is it that at 100μA the sound is so clear that it is not natural. Also at 40μA is some of the high end and low end is possibly reduced making the voice sounding more correct, with a more flat frequency responce from singer's vocals chords to listener's brain.
Canelina the cat and the patient tortoise handshaked each other for the Pleiades V6.
References:
Pleiades V6 schematic
On preserving electron tube transconductance with only 3V at the anode - euroelectron blogspot
Flat frequency response from actor's, singer's vocal chords to listener's brain, Sound picture recording and reproducing characteristics - Loye, Morgan - Journal of the Motion Pictures Sound Engineers
No comments:
Post a Comment