Posted: Sat Sep 27, 2008 8:23 pm Post subject: Jah Tubbys modified TUBE preamp
I'm proud to present what I think is the first tube modified and best Jah Tubbys preamp.
I'v also upgraded the opamps and nearly all capacitors to premium audio caps.
The opamps where simple and low cost TL072 and now are high quality opa2134.
The caps that Jah Tubbys did build in where absolutely not audio caps - industrial ones - and there was even those ugly sounding ceramic caps all over the audio path.
I did upgrade them with quality MKP,Teflon,Styroflex and 3 big paper in oil Obbligato caps.
I did a backward engeneering to get schematic and mesured all caps values - because the values were scratched off the caps by Tubbys- and then I simulated the preamp in PSPICE.
These simulation confirmed what I did hear before from different Tubbys 3 way preamp. The crossover point are very "exotic" and the values for graphic equalizer awfull.
Now the crossover is more narrow than before resulting in better low mids definition.
The value for the equalizer are now very sharp resulting in better control over the different bands.
The tubes are 6H6P with high power output capabilities to drive plenty of amps.
The tubes are on the output in an SRPP configuration.
Oh and I did ad stereo input for the two deck so now you can play those old stereo records like Twinkle Brothers Natty Dread Uptown where the voice was on the left chanel and the music on the right one. Now you can hear both!!!
I've made this upgrade for LION YOUTH SOUND SYSTEM from Geneva,Switzerland and now the sound is really awesome and they are really happy.Big%20smile
I will post some more picture later from the sound system in use.
measured all caps values - because the values were scratched off the caps by Tubbys
I did not know that this busyness was competitive enough to justify such an effort. It does not make any big difference anyway as an experienced engineer like you can measure the caps values with ease. They should consider encapsulating the whole circuit board in order to keep the components AND the pcb layout secret.
I did ad stereo input for the two deck so now you can play those old stereo records like Twinkle Brothers Natty Dread Uptown where the voice was on the left chanel and the music on the right one. Now you can hear both!!!
Do you mean the orignal amp amplifies only one channel of a stereo record?? That's incredible
Oh I did not mean to question whether your work was worth the effort. Rather I was surprised that JTS puts effort into keeping their circuit secret by scratching off the values.
I do not doubt that your work improved the sound of the unit. Many hardcore dub lovers have a spiritual approach even to electronics, so I would not be surprised If you encountered people who claim that by replacing the mediocre components and improving the exotic crossover points you actually destroy the magic of the original
How one could extend such thinking to justify listening to one channel only is beyond my imagination though..
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