Recent sound deterioration shrillness, ringing

Al...thanks as usual for your insight. I always learn so much from your posts.

I have a comment and a couple of questions that I hope you can answer.

I find it hard to believe that in this day and age that a manufacturer such as Peachtree would sell a product that could potentially damage another unit. I bet there are a lot of consumers who hook up a sub using the speaker (high) level inputs.

If the amp did emit DC, wouldn't the speakers them selves be damaged? The sub he is using is a Polk Audio Micropro 4000 that has just a high level input, but no output to the speakers, (it also has a low level, but we're talking high level). I realize that the sub is powered, but wouldn't the voicecoil and/or crossover in the speakers react the same way as the sub would with DC present?

Seems to me this would be a really bad thing for Peachtree, (or any company) to produce.

Thanks, Mofi. And your questions are good ones. BTW, I myself learned about this issue with certain ICEPower class D modules (which as I indicated may or may not pertain to the Peachtree 220) just a few months ago in this thread.

A passive speaker won't care about the DC, because to a very close approximation it is present equally on the + and - terminals, and thus it will not cause any current to flow in the speaker. However a powered sub will typically connect its negative input terminal to its circuit ground, which will typically be connected to its AC safety ground through a low impedance, which in turn will be connected to the amplifier's AC safety ground through the AC wiring, which in turn may result in a near short being applied to the large DC voltage on the amp's negative output terminal. The result potentially including damage to the sub, the amp, and the listener's ears.

Also, connecting the sub's negative input terminal to a ground point on the amp, as is often done when connecting powered subs to amps having balanced or bridged outputs (i.e., amps having signals on both their + and - output terminals), would not be a solution in this case because with the sub's - input terminal being at zero volts the sub would then be subjected to the huge DC voltage on the + terminal.

My understanding is that those ICEPower modules were used by a significant number of different amplifier manufacturers. As indicated in the thread I linked to, adapters incorporating capacitors to block the DC were and perhaps still are available for connection of powered subs to those amps.

Best regards,
-- Al

Al..thank you for the link to that post and for the additional info. I was absolutely unaware of that potential problem with Class D amps!?!

Being in the high end audio business for as long as I was, I have personally seen, several times, what DC present at either the preamp or amplifier can do. All of those instances could be traced to faulty equipment. But to make gear that could cause that right out of the box is just...stupid :-)

Thanks again for your insight!!!

Thank you. I'll try to address each of your comments together.

1. I've been using the Behringer for well over a year so to whatever extent it degrades the sound, it becomes relative because the system has always sounded fine until now.
2. When I spoke with Peachtree they said the only way to hook up a sub is to use a splitter from the pre out to deliver the signal simultaneously to the powered sub and the power amp. That works but it substantially degrades overall sound to the extent that I described earlier. Also, separating the signal like that gives the EQ no control of low bass needed for auto room correction.
3. I spoke with Behringer who ok'd the use of the unbalanced aux out stereo connection for the sub. This works fine and I assume that this will accommodate auto room correction as well.

Bottom line is that it looks like this setup works but I still have this problem with degraded sound. I'll be back on it tomorrow and will report what I find.

I'm not sure about newer Icepower but older modules, including one in my Rowland 102, have this problem. It is because of usage of single supply while reversing direction of the speaker using 4 Mosfet (switches) bridge. That way, half of supply voltage appears on both speaker wires. This supply voltage can be as high as 80V in some modules. There are types of class D modules, like Hypex, that use dual supply with one speaker wire fixed at GND. Channel Island used such modules. If you have any DC voltmeter measure voltage (without the music) from one of speaker wires to chassis or GND of input connector on your sub.