To all

I recently ordered and successfully assembled a 15" Titanic MKIII subwoofer System with the new 1000w plate amp. When calibrated to the correct level (75-80db SPL) at the Dolby reference of "0" on my Outlaw 950 pre/pro, the subwoofer really rocks. However, at normal listening levels for pop/country music, the subwoofer plate amp will not go from the standby mode to the operate mode when the power switch is in the "auto on position". Also, when in the operate mode, the power light becomes bright green instead of yellow as stated in the amp manual. To achieve a calibration of 75-80db SPL, I have the amp gain set at "5" and the 950 pre/pro output at -5db. To get the amp to turn on, when in the "auto on" mode, at normal listening levels for music, I have to boost the 950 pre/pro output to +8db (the pre/pro trim range is -15 to +10db). Also, the amp turn on point seems to be dependant on the amp gain setting. For this reason, I do not believe that my amp has been adjusted to go from the standby mode to the operate mode upon receiving a 3mv input signal as stated in the product description. Do I have a malfunctioning amp? Has anyone else had a similar problem with this new PE plate amp?
Regards,
TCIII


------------------
If you are going to send someone to save the world, you better make sure they like it the way it is.

I have a PE 150W monoblock subwoofer amp and the auto detect position stopped working at some point. Instead of experimenting, I just set it to on and left it in that position. That's an interesting question you raise about it not getting the right voltage. Good luck in your investigation. I look forward to any results.

I have the PE 250w amp and it doesn't always turn on when I set the sub out on in my 1050. If I wait for something loud it will. I don't leave it the feed on from my 1050 except when watching DVDs. I turn it off for music.

Hi all,

Here is some additional information concerning my investigation of the auto turn-on problem with the PE 1000w plate amp.

Thanks for your responses. I originally set the plate amp gain a "5" and adjusted the 950 pre/pro subwoofer output to -5db to achieve a +75db SPL when the 950's volume control was set to the reference level of "0". This combination will reliably cause the plate amp to go from the standby mode to the operate mode when I run the system at home theater sound levels. However, when I listen to music at a much lower level, the plate amp will not turn on unless I raise the subwoofer output of the 950 pre/pro to around +8db with +10db being the maximum. I also did an experiment to determine the affect of the plate amp gain control on the auto-on function. I set the plate amp gain to around "3" and then readjusted the subwoofer output of the 950 pre/pro to 0db to achieve the +75db SPL at the "0" volume reference level. As usual, the plate amp would turn on at home theater volume levels, but would not turn on at music listen levels. While listening to some music, I then began to increase the plate amp gain control beyond the starting "3" position while leaving the the 950 pre/pro subwoofer output at 0db. Low and behold, the plate amp turned on at a gain control setting of between "5" and "6". This little experiment indicates that the PE 1000w plate amp auto turn-on feature is dependant not only on the level of the LFE input signal from the preamp, but also on the level of the plate amp gain setting. Because of this anomaly, I doubt that it will be possible to achieve a combination of plate amp gain and preamp LFE output that will accomodate both home theater and music level volumes and result in the plate amp turning on automatically.
At this point in time, I would not recommend buying the PE 1000w plate amp until PE resolves this auto turn-on issue. It could be that I have a malfunctioning plate amp as PE advertises that the plate amp will turn-on if it receives a signal greater than 3mv and I believe that my preamp is putting out a LFE signal greater than 3mv at normal music listening levels. After all, the PSB Sub Sonic 6 that I used to have in my system would auto turn-on at any volume level be it music or home theater.
I have emailed PE's tech support, but have yet to receive an answer and it has been longer than 24 hours.
Regards,
TCIII


------------------
If you are going to send someone to save the world, you better make sure they like it the way it is.

[This message has been edited by TCIII (edited January 06, 2004).]

I've read about similar problems with other subs, and the fix was to put a 'Y' cable into the L and R inputs on the sub. Doing that will increase the signal the sub (or sub amp in your case) 'sees'.
You'd think splitting it would have the opposite effect, but it actually does increase the signal to the sub. Worth a try, can get one cheap from RS...

Hi Dart23,

Thanks for the suggestion! I have already tried using the "Y" cable on the low level stereo inputs instead of the LFE input and unfortunately, I still experienced the same symptoms. I am pretty sure that the problem is being caused by the auto turn-on circuit receiving its input after the plate amp gain control which cause the turn-on level to be dependent on both the plate amp gain control setting and the level of the signal input on the LFE or low level stereo inputs. With this situation, I do not believe that there will ever be a combination of the plate amp gain setting and pre/pro LFE output signal that will satisfy both music and home theater listening levels and still get the auto turn-on to function correctly.
I took a look at the schematic for one of the popular 250watt plate amps that has an auto turn-on feature. The input to the auto turn-on circuit comes from the same summed right and left low level inputs that feed the gain control and other circuitry. This circuit configuration avoids having the plate amp gain control affect the auto turn-on level and makes it only dependent on the pre/pro low level input (LFE) signal.
Regards,
TCIII

------------------
If you are going to send someone to save the world, you better make sure they like it the way it is.

Dart23,

You are correct. Intuitively I for one would not think that your "Y" solution would work - at least not because it increases the signal level seen by the sub (although I note your parenthetical use of "sees".)

Not saying that it doesn't work. It's just that I'm embarrassed once again by my feeble electrical engineering skills insofar as I can't come up with a good reason why it should or shouldn't work.

I can't see it drawing more signal from the signal source. Although does the "Y" somehow change the effective impedence of the load?

I sometimes use exaggerated examples to work through a puzzle (to me) like this. Would quadruple splitting "increase the signal" even more? Would an infinite number of splits feeding an infinite number of sub inputs cause an infinite amount of signal to travel from the source through that same single connector? Since I kinda doubt that, it casts doubt in my mind that a smaller number would have any effect either.

Any electrical engineers (or others) want to take a stab at this?

As I said, I don't doubt that your fix might work. I just don't understand why.

Jeff Mackwood
(Mechanical Engineer)

Jeff,

The left and right inputs are connected to an op-amp summing circuit. The circuit adds the signals algebraically. If we use a Y cable to drive both inputs with the same signal(x)the output of the summing circuit will be 2x. Make sense? In other words, the sub doesn't see a bigger signal coming in, it sees two signals the same size but then adds them together.

tekdredger,

Makes perfect sense. I shoulda stayed awake during that 2nd year circuits and signals course!

Thanks.

Jeff

TCIII:

I too have a plate amp from Parts Express (250 w with remote control) for my subwoofer but do not have a problem like the one you’ve mentioned regardless of volume level. I’d hate to say this but you may have a defective unit. You may want to contact the tech support of the manufacturer or the retailer.

Hi Spiker,

Based on my experiments, I do not believe that the PE 1000w plate amp is defective. As I indicated in an earlier post, the popular 250w plate amps take the signal for the auto turn-on circuitry at the point where the two low level stereo input channels are summed together which, naturally, is ahead of the plate amp gain control. In the case of the PE 1000w plate amp, I found that when the plate amp gain (set at 5) and the LFE signal from the pre/pro (set at -5db) are set up to give a +75db subwoofer SPL at the Dolby reference volume level for the pre/pro, the subwoofer auto turn-on will not work when listening to normal music levels. I found that I could get the subwoofer to auto turn-on at normal music listening levels by upping the gain control level on the plate amp. This indicates to me that the signal being used to feed the auto turn-on circuit is coming from the gain control circuit. This results in the auto turn-on level being dependent not only on the LFE signal level from the pre/pro, but also on the setting of the plate amp gain control. This is not good circuit design if you want the auto turn-on circuit to only respond to the LFE signal level which is the way that the popular 250w plate amps are designed.
Regards,
TCIII

------------------
If you are going to send someone to save the world, you better make sure they like it the way it is.

Hi all,

If you were thinking about purchasing the new PE 500w plate amp, think again. I just received an email from a fellow audio enthusiast and he is having the same LFE low level turn-on problem that I have being having with the PE 1000w plate amp. Sounds like they both have the same auto turn-on circuit configuration.
Sean, at tech support for PE, told me that they will mail me a copy of the schematic of the new 1000w plate amp as soon as they get it from the manufacturer. Hopefully I can modify the auto turn-on circuit to a configuration that closely duplicates the auto turn-on circuit design of PE's popular 250w plate amp.
Regards,
TCIII


------------------
If you are going to send someone to save the world, you better make sure they like it the way it is.