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Messages - bajaman

Hi Guys
Sorry - i don't hang out on this forum very much as i must confess, i am a tube amp fanatic ;-)
The blue dots are where i removed the link wire and the green wire connects to the chassis ground.
One of life's great mysteries is why the only place i could find the schematic for a tube amplifier was on this - a solid state amplifier forum !
Anyway, sorry for the extremely late reply to this thread - i can always be found lurking on the forum or you can always email me (while i am still living)
cheers to all
Hi Diydidi
they all buzz if unmodified !
10v dc is fine ;-)
do the mods and hear what it should sound like for the first time !
Well, I just had two more of these abortions in my workshop - both with that nasty buzz/ hum ;)
I tried increasing the capacitor at the input of the 10v regulator but unfortunately the buzz was still there, although reduced slightly, SO, i decided to find out what exactly is wrong with these poorly designed amplifiers and discovered some very interesting crazy design faults.
First : The grounding scheme for these amplifiers is disgusting ! The amplifier contains three boards (well four if you include the speaker ohm selector switch board) the tube amplifier board the solid state tubescreamer, boost and input gain board, and the tone control and master volume board.
The solid state board is ground connected to the chassis by way of a m3 bolt next to the input socket. There is a badly designed attempt at star grounding the tube amplifier board, including high current output tube cathodes and regulator returns, but what is truly astonishing is that the pseudo star ground on this board does not connect direct to the chassis - instead all the noisy regulator and output tube cathodes and all the ht filter capacitor grounds are connected through a thin black ground wire to the solid state input board. What makes matters even worse is that this push on connector ground link to the chassis is not even taken from the star ground point on the board - no wonder this sucker buzzes and hums like a demon. I have never seen such a poorly designed (or not) grounding scheme in over forty years of servicing tube amps - what were Ibanez thinking when they released this amplifier on to the market ?
Okay, now the fix !
This involves breaking the ground tracks on the board in several places and adding a wire from the star ground point directly to the chassis. Cut the ground returns  from C7 and C8 and connect these directly via cable to the junction of C17 and C14 (the star ground point) - next cut the ground trace from both pin 9s of V1 and V2 and connect these directly to the star ground point. Cut the track twice to isolate the middle pin of the 10 volt regulator IC and connect this pin directly to the star ground point - make sure to connect the remaining two cut tracks with a small wire connection to maintain ground connectivity to solid state board - hope that makes sense ! Remove C18 and C19 - not needed. Remove C21 and replace with C20, BUT drill a small hole on the board and attach the ground terminal to the middle pin of the regulator. Replace C20 with a larger value capacitor - preferably 2200uf at least 25v rating. Finally break the main ground trace between C6 and C16 - this isolates the high current ground from the low current ground. Now the high current ground returns are connected through the star ground point directly to the chassis and the sensitive low ground points (including the master volume control) are connected through the ground connecting wire to the solid state board and input socket chassis connection. I also removed the black ground return wire from the pilot light led and connected this directly to the chassis - never like dirty led ground currents anywhere near the input stages - this may not be necessary but worth doing i feel.
NOW - enjoy buzz and hum free operation at last !
Sorry - this will not reduce the aforementioned hiss (yet another bad design feature)  some of Phatt's suggestions will fix this - i would suggest moving VR8 the master volume to replace R17 and connecting the wiper of the treble control VR6 directly to C10 - that should reduce the hiss and work far better  ;) - UPDATE: I did this yesterday and it made a huge difference - much lower hiss !
Thanks - extremely helpful - these amplifiers have been a curse to fix from day one - I have seen many with the same intermittent buzzing fault - almost pulled what is left of my hair trying to fix the suckers. The fault is capacitor C20, a 470uf 25v filter capacitor - I replaced this with a 2200uf 25v type - problem fixed ! Hope this helps anyone else out there :)