inquiry:9090db's and what not to do. preampout + amps + ON at the time of connection

greetings, ill present you with the story as i understand it and what im wondering about is what sort of damage may have occured as a result, I havnt seen the unit in person.


so hes got the 9090db powered on and running and and as he says it, was attaching an amp to the second set of preamp outs when when he heard a loud pop from his speaker and the 9090 went into protection.


he said as it sits its clicking in and out of protection and that audio is unclear.
he noted that even with the speaker selector off, he could still hear faint audio from the left side, distorted.

I had him take the driver board out, he said it seems to stay out of protection this way but driving his external amps is still muddied sound now, preamp damage? but its not clicking in and out of protection in this mode, he says, so im thinking possibly driver/output damage too? or maybe the preamp is causing the amp to behave in a way that triggers the protection..whoknows?hopefully you!


my assumption, and i havnt looked the first thing up to try to verify, is that he caused an impedance drop trying to "do it live" as they say. could this have simply blown out some resistors somewhere? the leaking audio when the speaker switch is OFF for example, to me that seems like a resistor not doing work. it does verify the left channel at least partially works on the output side tho. (off hand i dont recall the right channel being brought up, dont know what its doing)


anyway, if anyone has ever done this, or know someone who has. i'd appreciate hearing about how extensive it was, he's on the fence about doing anything at all with it so I may not get the chance to see it for myself.

Disconnect the speakers and the other amp. If it's still cutting in and out of protection, you need to check the DC Offset to see what is going on. This would also be a good time to use a dim bulb tester to help prevent further damage.

- Pete

i might get to look at it next weekend and if i do ill definitely make a post with the findings, out of curiosity tho what would dc offsets reading that were out of spec reveal to me? if it was in spec prior and now lets say it has, you know, whatever value you were picturing when you said that, what would that point to?

ive re-read through everything he has said to me about it (gotto love texting), the only mention of the right channel was in neglecting to mention it, ie, "low sound in left even with speaker selector off now" which im thinking means the right channel isnt doing anything at all, in any mode. that may be the channel he was plugging in when it went hoooey, in which case i cant help wonder if this means that channel is blown.. but, wouldnt a blown channel mean full protection mode, all the time. its clicking in and out of protection


as a precautionary measure, this might be a good time to go ahead and ask if anyone knows where i can get a good price on some outputs for this thing, just incase it has blown and needs new ones. if theres gonna be a deal breaker on him getting it repaired or not, its gonna be with these and how much they cost.

High DC offset will kick it into protection. If it's borderline speaker loading can cause it to kick in and out as the audio signal changes the load. It should be zero volts or very close to zero. If it's not in protection mode you can measure it at the speaker terminals when the volume is set to zero.

Before you start buying anything measure the DC offset. It my just need to be adjusted.

- Pete