Turn on pop Rockfosgate Hafler


2012-01-16 11:26 pm
The Rockford Fosgate Hafler Pro1200 amp makes the DC pop sound on turn on, the old Hafler Pro125, or Pro230, etc amps do not have the turn on pop. What's different here?

I own all the amps above. I have two Hafler pro1200 amps that pop when you turn on the power switch. One pops louder than the other. It appears the louder popping amp keeps blowing my B&C DE10-1 compression driver. The driver has a capacitor connected in series with a 20W bulb for speaker protection. The damage though is subtle, the driver cuts out intermittently at low volume level. I put a sine wave on the driver for test and I hear it going on then intermittently off. The bad driver was replaced with a new diaphragm, I continued to turn the loud amp on/off and the issue reappeared!:eek:

The older Hafler pro125, pro230 are the same wattage and they do not pop when turned on. Is there a quick and easy way to fix amp turn on pop? Now, I disconnect the speaker first but now tired of that.

Ian Finch

Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
There are a few reasons why amps give a solid thump at start up and shut down too.
A well designed amp with parts selected for minimum DC offset can actually be very quiet but will still have some small DC transient at on/off. It can also be generated in the preamp, mixer, source, whatever - upstream. Often, repairers don't pay attention to this and any thump can become worse following their uninformed efforts.

Modern amps simply sidestep the problems by fitting speaker relays that keep speakers disconnected until a few seconds lapse and allow it to stabilize - then you get the usual "click" of most power amps. They can also have muting circuits that virtually ground the input stage for a similar effect.

Without a schematic, I can't say what you have there but if not already included, it is usually possible to retrofit a small and inexpensive relay PCB/kit, if the power supply in the amp has a suitable voltage, like 12 or 24VDC, to power it.