Thursday, May 6, 2021

A 2 open base transistors long tailed pair microphone booster preamplifier with no capacitors , no resistors, only 2 transformers

Mic is connected at primary winding of input transformer. Secondary winding is connected to each transistor base. Emminters to minus supply ground. Collectors to to output transformer primary. Center tap to Vb+ through a fuse for protection. Secondary is lower Z balanced output. It is thought to be tried with 2 BC109C or BC549 and 1:3 input transformer and 3:1 output transformer. Will it work? How would it sound like?

Monday, May 3, 2021

Listening to the Pleiades Siemens AC151 one transistor open base front end microphone amplifier at overload level

Signal path: Shure VP64 with male singing voice or Alan parsons Sound Check 2 CD played on Sony Walkman cD Player with its line out attenuated by a 600ohm to 600ohm variable dB laboratory Solartron attenuator - Pleiades Siemens AC151 with Cb 56n when mic is used or 220nF when cD is used for -3bD at 100Hz and flat beyond 20KHz with no negative feedback, base open, Vb=9V, RL=56K, Cout+820nF - Realistic disco mixer at mic in or line in when mic was used or line in when CD was used - Sennheiser HD580 fed by disco mixer or directly by AC151 through a Canford red output transformer inside a Neutrik 1/4in jack. The AC151 prepreamplifier passes the low noise test by canselling effectively the ambient noise when mic is connected out of phase (caution to ear protection needed, see previous post). Mic sounds very clear, the WE 1:2 input transformer was also used with excellent results. The unprocessed sounds on the Alan Parsons CD, near or after overload: Sinewave nice gradual overtones at gradual overload. Voices very nice, soprano reverb out of control intermodulating. Piano nice. Acoustic guitars excellent like Torn - Natalie Imbruglia. Electric, bass guitars very nice distortion. Flute great distortion. Saxophone amazing distortion at any overload level, shows how these amps bring out the edge inside music. Percusion great like those amazing Enoch Light LPs. Cymbals sound bad at overload.Hi hat sounds amazing at overload, again detail inside music brought out. The first orchestral track sounds bad but the later one sounds very good at overload. The techno track sounds amazing. Pipe organ nice too. It seems definetly worth building this preamp inside a plastic box with 9V battery cover. Just a transistor, 2 coupling capacitors and a 56K load resistor. Current consumption at microamp level. Battery may last for ages. Solar powered too?

The more transistors are treated like electron tubes the more they behave like them

For example when comparing an open base low level amplifier transistor stage to an open grid one. The transistor becomes very low noise with a high input impedance. Even biasing with 1Mohm from Vb to base increases gain but noise becomes unacceptable high see Pleiades Siemens AC151 one transistor microphone booster front end. At open base distortion is gradual too as well as overload behaviour like an electron tube. Do transistors behave like JFETS when base is left open, unbiased?

So many decades had been wsted by looking at scopes or spectrum analysers rather than using the best instrument available in the universe which possibly is the ear brain

Forunately it is the music lovers listening and the recorders listening too that have saved electronics

I have never understood what bias to electronic amplifying devices is

At university I was told it is a voltage

Why not letting the first amplifying stage after the microphoneto be the most linear at low levels and gradualy non linear at higher level?

After all is this not what we do when we listen to Frank Sinatra on YouTube? Or what nature does with human or cat ears-brain in order to extract as much information?