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Hi y'all,
I have a 1997 Cambridge Soundworks SW2 that in my old and seasoned opinion was built with cheapness in mind, I've seen better.
And for the utterly rediculous price that it orginally sold for, it clearly shows greed involved. (using the Henry Kloss legacy for gain)
OK, now the original woofer was replaced ages ago, with a pretty capable 8"-100W-4ohm unit. (200W max)
The power amp, driven by a set of TL072CP's (subsonic filtering/preamp) was an STK4044V, (100W) which is history.
I decided on replacing it with a set of MJL21194/95 driven by an STK350-230 integrated driver/vas chip from an older Sony amp.
The original transformer- PS is a pretty rock stable B+55V and -55V.
Also the TL0's have their own independent +/- 15V supply. - and that part is fine.
Here's my problem...
At low levels, (background bass) the thing sounds OK. (I built the STK350-230 board similar to the Sony design with some needed changes)
When trying to increase the sub's level to higher output, the sound distorts, and sounds like a rubbing voice coil, which I confirmed is not the case.
Scoped the output on an 8 ohm dummy load, the bottom half of the wave gets a nice flat clip at higher than 3V peak-to-peak levels.
Bias is around 15mV on each side of the 0.22 ohm emitter resistors.
I do notice a small offset to the output of around -75mV.
Info on that STK Vas chip is scarce, I'd like more, to be able to see if it can suffice driving straight NPN/PNP's, instead of just Power Darlingtons like the MN2488-MP1620 as originally used with. ---and which I may be forced to use.
I'll post the schematic of the board that I built when I get one drawn up to share.
I have a 1997 Cambridge Soundworks SW2 that in my old and seasoned opinion was built with cheapness in mind, I've seen better.
And for the utterly rediculous price that it orginally sold for, it clearly shows greed involved. (using the Henry Kloss legacy for gain)
OK, now the original woofer was replaced ages ago, with a pretty capable 8"-100W-4ohm unit. (200W max)
The power amp, driven by a set of TL072CP's (subsonic filtering/preamp) was an STK4044V, (100W) which is history.
I decided on replacing it with a set of MJL21194/95 driven by an STK350-230 integrated driver/vas chip from an older Sony amp.
The original transformer- PS is a pretty rock stable B+55V and -55V.
Also the TL0's have their own independent +/- 15V supply. - and that part is fine.
Here's my problem...
At low levels, (background bass) the thing sounds OK. (I built the STK350-230 board similar to the Sony design with some needed changes)
When trying to increase the sub's level to higher output, the sound distorts, and sounds like a rubbing voice coil, which I confirmed is not the case.
Scoped the output on an 8 ohm dummy load, the bottom half of the wave gets a nice flat clip at higher than 3V peak-to-peak levels.
Bias is around 15mV on each side of the 0.22 ohm emitter resistors.
I do notice a small offset to the output of around -75mV.
Info on that STK Vas chip is scarce, I'd like more, to be able to see if it can suffice driving straight NPN/PNP's, instead of just Power Darlingtons like the MN2488-MP1620 as originally used with. ---and which I may be forced to use.
I'll post the schematic of the board that I built when I get one drawn up to share.
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