driver noise and running in

[steve_mak]

Hi all,

I've just taken delivery of my new subs - the Peerless 830845 - and want to know if I should be concerned with them.

To run them in I've connected them to an old NAD integrated amp (3130). I have a Wavetek sig gen on the front end to supply sine waves and also have a Tek digital storage oscilloscope across the driver just to make sure the signal is OK.

When I turn up the volume greatly - close to the rails - and whiz the sig gen dial around some I can get a funny scratchy sound. The sound isn't there all through the freq range but seems to occur when I wind down from say 1kHz.

The sound is also quite intermittent and possibly doesn't occur at lower volumes (like half volume)

Have I got 2 duds ? Or is there something happening with the amp ? Some sort of overload related issue ? I can't see anything on the scope but I could perhaps do it again with the persistence turned on.

What I do know is that the old NAD is a gutless old nag ! The cone hardly moves !

TIA,
Steve

[simon5]

The cone doesn't move even at 20 Hz in free air?

If yes, your amplifier could be faulty. Maybe you're clipping it and it's outputting alot of harmonics... that you hear alot.
I doubt you got bad drivers...

[bluesmoke]

Too many variables.

First, I agree with simon5, mentioning that your drivers are (or were) probably fine.

test seperately before connecting speakers
(good speakers always come last)

1) test your signal generator... is the scratchyness coming from playing with the dial...? + what kind of output is it creating when scratching. (I prefer using a cheap CD Player, with a test tone disc, tends to be more reliable, and less chance of an unwanted output).

2) test your amp on a "beater" pair of speakers. First check with inputs grounded or input pots to zero... measure with multimeter any extreme voltage output. If OK, then try music/tones.

If all checks out, then comes the time to connect the good parts.

[steve_mak]

Thanks guys,

I'm not sure of the solution but I have a feeling it is something to do with the amp doing a soft clip thing. The noise doesn't occur at lower volumes.

Basically, I was watching the scope as I turned up the volume and was very surprised to hit the rails so quickly. All these years and I had a rather powerless amp !

Now I'm moving on to trying to measure Re.

Boy am I having problems ! But I suspect this is an issue for another thread.

Rgds all.