Pioneer CT-777/CT-95/CT-1100 playback input replacement
A week ago i managed to change the rubber belt on a Pioneer CT-777 and, after i gave it a first run, i was simply amazed running the cd-player through the cassette deck and having it listen through it's headphones output.I started to reconsider almost every "audiophile component" statement cause i allready have a good and moded cd player(Denon dcd-1560) with higher slew rate and lower noise op-amps then most dac's dreamed having on the output and i enjoyed the music runing through some m5218 op amps with 3v of slew rate. At the same time i saw some mods on CT1100 that are believed to make this type of Pioneer better than it was as new.So I thought that first i should make a lower noise input as it's m5220 is good, but not at the same level with a Nakamichi Dragon or 1000 ZXL or even a Pioneer CT-95 input or other fet based input playback preamps. At a first glance the S/N and THD figures in Pioneers look better on paper than in Nakamichi's .If they are true than they really are clever cause they used higher noise input play back preamps than the Nakamichi did.So i though of trying to make a better input for Pioneer and see if it beats the best nakamichis because i think it allready have the potential of being the best cassette deck outhere. Replacing M5220 with AD745 is a very good hint anyway, A.N.T. pointed that many years ago, but here I used LtSpice for giving a shot to an ideea that I picked from a phono preamp used in Harman Kardon pm 645 xvi just to see how well will it work. I have one HK pm 645 vxi in a relly bad shape and i saw that the phono preamp is really interesting and inspiring. Now I applied its ideea in a tape preamp to make a faster and lower noise voltage feedback preamp.Now it's just a simulation, next days i will try building it and see if it works as expected.If not...i will let you know. My Pioneer does not have dolby s, not that i really need it having one, but i allready got 2 dolby s encoders from a Sony deck and other two are on their way so maybe the ct-777 will have a chance to work like a ct-95 one day
To be honest i think that the dolby b-c in pioneer and nakamichi is better than dolby s in sony's, better dynamics and the noise ratio is good enough with a chromium oxide based tape.It's a shame cause it looks like both Nakamichi and Pioneer gave a better use to Sony's best dolby chips than Sony did...The input preamp can be scaled for using more fet and bipolar transistors for even lower noise but i started with just two bf862 and 4 pnp bipolars.You could use any lowe noise bipolar, the ones used in simulations are just one possible choice out of many.I will actually use 2sa1038 with a noise floor at 0.2db as i have a few.The collector and emitor resistors won't probably be of any use, but i figured them to make the current probe easier to use in the sym.You wouldn't believe what i used to make a new rubber belt seen in the photo!
Last edited by dreamth; 19th July 2018 at 01:02 AM.