Hi Guys,

Not sure if this is the correct spot to post, but I'm trying to work out why I was getting an audible and visual fuzzy peak when my sub amp was putting out a reasonable level.


The amp in question is an Eclipse DA7122 amp, supposedly 500 WRMS at 4ohms and 1000WRMS at 2ohms. The sub in question is a JBL w15GTi, 3ohm nom due to parallel 6ohm coils.

I was noticing a funny sound, that I assumed was clipping at what I thought was a lower level then it should happen given I should be seeing roughly 750 WRMS into the sub. After using a CRO to diagnose, I found that with the track that I use to clearly hear this anomoly I could see the expected sine wave form up until it made the noise, where the peak would turn fuzzy, but still maintain the rough sine shape. Reducing the output back down rought it back to a clean signal again.

I backprobed the RCA output from the HU and found clean signal from the HU right up to max volume, so it's not coming down through these.

IT appears to be coming from the amp, which raised the question as to at what power output this was occuring. Tonight I connected a couple of multimeters, one to measure AC current and the other to measure AC voltage accross the speaker.

When playing tone, the 'sound' onset would occur around 40 Volts and 9.8 Amps. This suggests to me somewhere between 300-400WRMS output from the amp around when it starts to produce this fuzzy peak.

I also tried a single RCA, both left and right seperately and together and was getting exactly half the output of the amp with only one RCA connected that I was with both connected. The amps gains is set halfway between 8v and 1v input. ie 25% gain.

Internally the amp appears to be in PC, nothing to notice on the board to suggest anything is wrong with the amp, so I'm at a loss.

Should I put the amp in for repair, or can someone suggest another test that I should undertake to get an idea on the actual power figures. I don't 100% trust my figures, but they suggest I'm losing out on half the power ie 3dB + which would more then satisfy my desire for the sub to keep up with the front stage...

Thanks in advance..
Ben

The amp is rated 500wrms @ 4ohm...
This would mean it'd be capable of putting out about ~750wrms @ 3ohm, your nominal load.

Your subwoofer would also most likely be seeing impedence rise, lowering the potential output of your amplifier.

It would not surprise me if your amplifier is actually being pushed to its limits and clipping at around 400wrms if the load is rising to ~6+ ohms.

I'm with Fuz. What's your impedance level at that frequency?

Cheers Guys

V = IR, therefore 40 = 9.5 X R, resistance ® is 4.2ohms

This obviously isn't impedence as such, but arguably, providing my multimeter are reading RMS, which I'm not certain either way, 4.2 ohms and 380WRMS, which is slightly down on what I'd be expecting.

I just tested my DA6213 bridged into the sub, ie 2x250WRMS mono, 'should' put out will over 1000WRMS into the 3ohm load and the sub was clearly louder, so it might be simply the amp clipping.

I believe you mentioned about the power supply caps not being able to keep up in another thread I posted in ~thematt~ so I wasn't sure as I was expecting to see a literally clipped signal, not a fuzzy peak on the crest.