Sansui BA3000 clipping before peak power.

[Netlist]

Of course I could contact Anatech in private but for the benefit of other members I thought I’d rather start a thread on the said amplifier.
The thing plays fine up till about 70 to 100W but increase in sound pressure seems to make the amp loose control over the speakers. The resulting sound is that of a broken speakers, crackling in bass an mid when peaks are hit.
I gave it a service check, tightened the output transistor collector screws, checked all solderings, replaced a lot of caps in the secondary PSU, checked the most important voltages but I’m kind of stalled on this one.
The big supply cans look and measure good, what I’m testing right now is if the amp meets the specs with a dummy load and a 1kHz sine wave.

I can mail the service manual but your mailbox should be able to handle +/-25Mb.

/Hugo

[billdinva]

Assuming your amp checks out okay and your speakers are rated for the power with which you are trying to drive them, you may be exceeding the Xmax of the speakers. Most drivers in typical enclosures cannot deliver their rated thermal power at frequencies below Fs. Try modeling your speakers using WinISD or other program.

Another possibility is that your speakers are causing an unusual phase shift at low impedence which is triggering some current- limiting circuitry. This could also be caused by trying to drive speakers which have impedences lower than your amplifier can handle.

[Netlist]

Speakers are B&W802 series 1, IIRC rated 150W RMS.
I use them to test all sorts of amps, included PA amplifiers. Granted, some amps have better control over them than others but this one is real muddy in the peaks.
I've abused the speakers a lot and all they do is go into protection when the rated power is exceeded.

The amp meets the specs with a sine wave. With an 8 ohm load, 1kHz sine wave he clips at 43Vpp at 5.2A.
That would be 223W RMS (?). Specsheet says 170W into 8ohm.
When music is applied, I read about 12V RMS before the distortion occurs.

/Hugo