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Just wondering if anyone has experience with this amp (JBL/Urei 6260). I just purchased one in very nice shape and while it sounds very nice I notice the low end lacks fullness and punch..
So it doesn't sound "broken" but I'm wondering if it could be that the amp is driving very efficient speakers right now for testing that may not be a lower enough impedance load to bring out this quality... I know this doesn't make much sense so maybe there is another reason that I should explore.
Anyone have any experience with this amp?
soft recovery Schottky diodes, AND up the capacitance in the PSU to about twice the OEM uf total. And, bypass the last two PSU caps with MF PP* caps.
After that work, have the amp biassed a little more into a watt or three Class-A.
Then listen, then replace the negative-feed-back-loop caps and Rs with commercial quality teflon caps and Holco or laser trimmed Rs. Possibly, do this before recapping and re-R-ing the audio stages.
Re-listen. and then budget for replacing, any and all electrolytic signal caps with commercial quality *metallised-film poly-propylene caps. Replace all the signal Rs with decent metal-film Rs.
Re-check and re-set the DC and AC balance, in the PP output stages
IF you do this over a good space of time, all this ought to be affordable, even through a techie.
Skeptical Measurer & Audio Scrounger
Did you even look at the schematic?
I think not.
"Re-check and re-set the DC and AC balance"
There is no DC (or AC) balance control, it has a DC servo.
"replacing, any and all electrolytic signal caps "
"up the capacitance in the PSU to about twice the OEM uf total."
Why bother? The supply has 90% regulation for a 4Ω load (per channel). If you go much bigger you will have rectifier problems, especially if you go to fast types (that have poor surge current ratings).
"And, bypass the last two PSU caps with MF PP* caps."
May cause oscillation (depending on the wiring). I would replace the four pieces of 10µF bypass caps shown on the schematic, they do dry out.
Increasing C16, C18 in the bias circuit should improve the bass, try 2.2µF (or as big as will fit).
"An WCR value of 10 yields about 10 per cent ripple (pk.-pk. ) and a value of 100 has about two percent. Below 10, the
power supply will have serious problems and values of about 100 will achieve diminishing performance returns. The minimum value then, for
each of the four power supply capacitors should be about 3,000uF and
the maximum about 30,00OuF. Capacitances above this value may
cause diode bridge failure due to turn-on surges and are not
*the 6260 has four 6800µF filter cap, and four 10µF bypass caps.
Thanks Tim, I really appreciate the steer in the right direction... I'll give your suggestions a shot...
I know that amp we used to sell them in the 80's it was a studio amp. Sounded just ok back then. I'm thing that som parts are old and need refreshing. I also know their are no large storage capacitors in that amp,
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