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PostPosted: Fri Jan 29, 2010 9:27 am 
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You guys are talking something different now.

On a MS amp, it has a "bridged" switch. Do you know what that switch does?

All it does is run the Left RCA jack to the Right jack at the same time. If you want to run a MS amp mono, you DON'T put the switch in the bridged position. Leave it in stereo. You then connect the speaker across the outputs, and you will have a internally "summed mono" output, when you use both the right and left RCA inputs.

What the bridged switch on a MS amp is really for is say for example you want to run one MS2125 mono to your left speaker, and one MS2125 mono to your right speaker. In the bridged position, it will feed the Left RCA to both the left and right RCA jacks. You then would only need to use the one jack on each amp to fully use both outputs of the amp.

Does this make sense?

In the case of the Xenon X100.4, putting the switch in 4-channel mode means all 4-channels will require their own input signal. If you put it in 2-channel mode, the front RCA jacks are then physically connected to the rear RCA jacks. This is the same as Y-cables. However, PG amps are not capable of "stereo bridging". If you use the 2-channel input mode with a right and left RCA, there is no way to get a stereo bridged output. It will always be mono. You have to use external Y-cables to get a stereo bridged output from a PG amp.

Now, Rockford Fosgate actually did something really cool with their amps. On a RF 4-channel amp, the front is similar to most amps. One channel is live on the (+), and the other is live on the (-), but inverted 180deg so you can bridge it. Then RF took it a step further, they set up the rear in a similar way, but then went 180deg out of phase on both of the rear channels. So, on a RF amp, you can run your right and left RCA into the right and left front RCA jacks. You then put the amp in 2-channel mode so the RCAs feed all 4 channels. You then bridge across the FRONT AND REAR, not the RIGHT AND LEFT. The front and rear right will bridge to a speaker and the front and rear left will bridged to the other. You then get stereo bridging out of a 4-channel amp, with no external cables required. It really is a pretty neat trick, and something I begged PG to start doing over 5 years ago.



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PostPosted: Fri Jan 29, 2010 10:28 am 
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Just when I thought I kind of knew what I was talking about. :) That's why I love this phorum! Learn something new everyday.



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PostPosted: Fri Jan 29, 2010 11:22 am 
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Well, the most embarrassing car audio event for me dealt with this exact issue.

After working at a car audio shop for several years, and then when I was in my senior year of college, I finally learned what I have been posting here about this topic.

I put a RF Power 800a4 in my Dad's truck. I connected my o-scope to it to set the gains. First channel went fine. Second channel I connected the scope, turned the system on and the amp died. Since I worked for RF I sent it in for repair for free. Got it back, hooked it up, did the same thing and killed it. Sent it back in. This time I hooked it up in the lab at Rockford. I got all the other engineers in there with me to see what happened. Hooked it up, poof, dead for the third time.

So we all started a conference call and called the engineer at Rockford (down in Arizona) who designed the amp. He instantly told us the issue.

Not knowing exactly what bridging did or how it worked, I falsely assumed all the (+) outputs on the amp were the signal, and all the (-) outputs were ground. I was connecting the negative lead on the o-scope to the (-) on the amp channel, and the positive on the o-scope to the (+) on the amp channel. When I connected the lead to the (-) on the amp which was actually the live channel but 180 deg out of phase, I was dead shorting the amp to ground. This killed it instantly.

Looking back on it, I cannot believe how dumb I was to not know this, but really nothing was around to explain it. I knew HOW to hook up an amp bridged, but had no idea WHY it worked. If you think about it, that is the way a lot of things in life go.

To this day I don't feel all that bad though, as every other engineer I worked with did not know this either. They were just as puzzled when the amp died in front of us after connecting the o-scope to it.

Once I knew this, I could build on it and realize every amp channel needs a signal to have an output. And, that a 2-channel amp is just two mono amps in one chassis, like a 4-channel is just 4 amps in one chassis. For the most part up to this point amps were just a magic box of smoke and mirrors to me. I did not know what went on inside them. I can even remember way back to before I worked at Soundbuggy when my friend and I went in there asking how we could connect two stereo amps to a single mono load. They told us it could not be done, and for the most part they are right. You cannot bridge 4 channels into a single load.

I have since learned there are special amps which can parallel their channels, and you can use transformers to connect an unlimited number of channels into a single load. But both of these options are not that common.



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Got "schooled" by member shawn k on May 10th, 2011...
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Don't even know what Ohm's law is...
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PostPosted: Wed Apr 21, 2010 12:03 am 

Joined: Mon Apr 19, 2010 5:47 am
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Howzit gents....i'm new on the forum
Got my hand on a Pg Xenon 200.4, i know there was a batch that had that cold solder issue... I wanted to know is there any way of me knowing if the one i bought was one from the bad batch.......like by use of the serial number or markings on the box or amp etc....

Thanx


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PostPosted: Sat Jun 12, 2010 7:33 am 

Joined: Sat Jan 03, 2009 7:23 am
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Location: Syracuse, NY
Good Info Thanks !


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 Post subject: Xenon FAQ
PostPosted: Sat Oct 20, 2012 11:32 am 
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dwnrodeo wrote:
Just when I thought I kind of knew what I was talking about. :) That's why I love this phorum! Learn something new everyday.

Hmmm, I've been hooking amps up Bridged the same way forever. I currently am running two ti500.4's for my comps front channels to one amp and rears to the other. Left channel to front left input and right Channel to rear right. (Stereo) speakers bridged.
If I'm understanding Eric right, you are saying this is not actually working properly and that I should put y adapters in and have a signal going to all four channels. ie. pic 2.


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 Post subject: Re: Xenon FAQ
PostPosted: Fri Mar 14, 2014 10:18 am 
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Sorry to dig this one up from the dead, I was wondering if anyone has a proven method for polishing out scratches on Xenon amps? I have a 1200.1 with a few black marks on it, would a very fine sandpaper work, or maybe even steel wool on the aluminum? Thanks very much.



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 Post subject: Re: Xenon FAQ
PostPosted: Mon Mar 28, 2016 9:55 am 

Joined: Fri Apr 06, 2012 11:49 am
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Disclaimer: I use a Xenon 100.4 (bridged with both inputs receiving signal via y-cables) into 8 ohm loads. I also use a Xenon 1200.1 into a single 4 ohm load.

Facts to correct:

The stereo amps (x100.4, 200.4) initially power up with high fan mode then the fan settles down. The mono amps (x600.1, x1200.1) do NOT do this. Per Aleks (main aftermarket PG repair tech, RIP), the mono amps ONLY turn on their fans when a certain temperature in the amp is reached. This 100% matches what I see with my two Xenon amps respective behavior.

8 ohm mode on the stereo amps do NOT "halve" the power. They actually put out a bit higher wattage at 8 ohms believe it or not. I've measured this conclusively.

The x100.4 is VERY underrated. NOTE: I may have a "special" circumstance as the x100.4 I have was modified by Aleks with undisclosed changes. At any rate, with the gains completely turned down (i.e 8 volts setting) and feeding it a 6 volt signal from my DSP, I have measured approximately (using a 0 db 50hz sine wave) 300 watts (31-33 VAC per channel). That is insane. In other words, a "200 X 2 amp" (bridged) is actually putting out 300 X 2 (probably a bit higher as I saw some slight shift in testing) at 8 ohms! I searched high and low for such an amp at 8 ohms....very few to be found.

The SNR on the Xenon stereo amps are a bit inflated. They are NOT that great. I have the x100.4 feeding two high efficiency JBL 2118H midbass drivers (97db/1 watt) and you can hear audible hiss. NOTE: If you use the amp on "regular" efficiency car audio speakers...this is not an issue, but be warned the output section is a bit dirty in relation to filtering/SNR. So be it.

The mono amps take 2-3 seconds longer to power on than the stereo amps. Why? Who knows, but it consistently happens with the exact same remote turn-on signal being feed to both the stereo and mono amp simultaneously.

You can unplug the single blue led "indicator" led inside the amp if you chose. Personally I wish it had a "light on/off" switch on the outside of the case as it would be nice to temporarily enable to check for health, then turn it off. A bit "Bling!" to have it on all the time.

The mono amps take WAY more input voltage to reach full output potential. Once again, I am feeding 6 volts of input voltage to both amps. The x100.4 required no gain adjustments to reach full power. The mono 1200.1 required about 1/3 gain adjustment (verified via meter) to reach 1200 watt-ish. Likely due to different topology designs (AB vs D).

The mono amps are stupidly efficient (I have read report of >90%). I can attest to this. I have an OEM 170 amp alternator in my truck. With a 50hz sine wave I am seeing a voltage drop of approximately .4-.5 at 1200 rpm. That's awesome. Try that with an "old school" class AB 1200 watt amp. You'll wind up with a second alternator (or very high amp single alternator and all that fun that entails) to support the same power output. The Xenon mono amps are a No-Brainer. Just that simple. If you are running old school AB sub amps you are doing yourself a disservice.

Last but not least, the Xenon amps are very large physically. Besides the aforementioned SNR issue, fitment of these amps in smaller vehicles may be an issue. Otherwise, I 100% recommend them.


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 Post subject: Re: Xenon FAQ
PostPosted: Mon Mar 28, 2016 11:28 am 

Joined: Sun May 06, 2012 8:01 am
Posts: 1652
I call BS on the 8ohm stereo load producing more wattage than the 4ohm stereo load....just not possible with the same rail voltage it would be breaking ohm's law. But do recall my friend Cecil telling me a secrete on how to fool them and get more power out of them, don't recall if it was the Xenon or Tantrum 1200.1.


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 Post subject: Re: Xenon FAQ
PostPosted: Tue Mar 29, 2016 9:07 am 

Joined: Fri Apr 06, 2012 11:49 am
Posts: 38
You are referring to the circuit that "hides" the ohm load from a Xenon amp at startup so that it defaults to 4 ohm mode (if you will).

I am not (nor would I recommend for very obvious reasons) that. Not to mention that "trick" is only on the mono Xenon amps.

Short of me putting the amp on an amp dyno/publishing a video....see here for more evidence of the 8 ohm output:

https://web.archive.org/web/20090827211 ... _413.shtml

As you can see, I'm not the only one that has reported this admittedly odd behavior.

FYI: Notice the measured craptastic SNR. I 100% agree with that report as I have audible noise floor through my high efficiency midbass drivers that the 100.4 is powering. Truly stupid.


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 Post subject: Re: Xenon FAQ
PostPosted: Tue Mar 29, 2016 1:30 pm 

Joined: Sun May 06, 2012 8:01 am
Posts: 1652
So am assuming the 8 ohm load you are referring to is the bridge rating? If so than that is the same as stereo 4 ohm (internally the amplifier sees a 8 ohm load, twice *Front & Rear*). I thought you meant at 8 ohm stereo the amplifier would produce more output than 4 ohm stereo.

116 watts x 4 into 4 ohms is the same as 234 watts x 2 into 8 ohms
112 watts x 4 into 2 ohms is the same as 225 watts x 2 into 4 ohms

At 8 ohms stereo the amplifier would produce 50ish x 4, this is were I was saying it is impossible for the amplifier to produce more power at 8 than 4. Sorry for the misunderstanding, I agree that is a very crappy SNR.


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 Post subject: Re: Xenon FAQ
PostPosted: Wed Mar 30, 2016 7:19 pm 

Joined: Fri Apr 06, 2012 11:49 am
Posts: 38
No offense taken at all. I figured you misread the part about me using the x100.4 in bridge 8 ohm mode (the midbass drivers I use are from the proaudio world and are indeed 8 ohms...hence the need for so much power at an 8 ohm rating that I was searching for).

I find on the whole PG was just a tad dishonest in a LOT of their ratings back in the day. Go take a gander at some of the "Old School Stereo" amp dyno tests with PG gear. The ratings that PG used were mainly based on 1Khz uncertified (i.e right to clipping). Most of the amps barely even hit their power rating during that mode of testing as well. I do know that "back in the day", with the competition scene being hot lots of cheater amps, inflated marketing #s, and widely varying test standards were rife in the industry.

Don't get me wrong, I dig the old amps as much as the next "old" guy (ha). However, honestly I am quite annoyed that what is claimed to be the "best" of the old school PG amps (i.e. Xenon) are far from accurate ratings. The POWER is spot on (and then some), but the sound quality ratings are abysmal in reality. Wish I had tested/known this before I spent 2 months on an amp rack cover for the Xenons......


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 Post subject: Re: Xenon FAQ
PostPosted: Sun Apr 15, 2018 7:46 am 

Joined: Sun Apr 15, 2018 6:51 am
Posts: 1
Hello I just received a xenon 200.4 in great condition looks new a few wet spots but just need to clean and resolider I plan too
Upgrade this amplifier internals starting with the main rail caps they will be external to the amplfier as there no room in the amp
It has SMS 50v 1000uf 6 of them I plan to add nichicon maybe 2 6800uf or 10000uf and change all capacitor in the audio path
To nichicon fine gold the rectifiers are double 16 amp I'm thinking this need maybe two 20 amp rectifiers has this failed on any of these amplfier before should I upgrade the rectifiers as well any info would be great and helpful :D


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