Fan replacement for QSC PLX series power amps?

[joegold]

I bought a QSC PLX1104 power amp today.
I've got a 30 day money back return policy from the store and I'm not sure yet if I'm keeping it.

It sound pretty good I think...but....
It's not quite as loud as I expected (although it's pretty loud), so I might go for the PLX1804 instead.
But the main thing is that the fan is sort of noisey.
I may have the power amp mounted inside the double rack space in my Pearce speaker cabinet, and in some settings the fan noise could be a problem.
It bugs me enough just practicing in my work room.

I've already swapped out the fan inside my Ultra for a quieter fan.
Anybody know if this can be done with these QSC PLX Series amps too?
Probably pissin' in the wind here, but I thought I'd ask anyway.

 

[dpeterson]

my crown power amp fan was too noisy as well, so installed a switch with a resistor that cuts the voltage going to the fan in half. I use this when at home, at a gig i could turn the fan back up. you can barely hear it now. it doesnt need to blazing that fast a bedroom volumes. i wish i would have taken some pix but i found the general info on a home theater board somewhere. I used one of those big ceramic resistors.

 

[strato62]

Mmmmm
Thinking about power .... Do you know that the PLX1104 being 310W/ch in 8 ohms and 500W/ch in 4 ohms and that the PLX1804 is 550W/ch in 8 ohms and 800W/ch in 4 ohms the PLX1804 will only be 2,48dB louder in 8 ohms and even less in 4 ohms (2,04dB) ?

According to manual the fan increase speed when it delivers more power, so i wouldn't put a switched resistor in series with the fan and run the risk of forgetting to flip the switch and get the amp to overheat.

If the fan noise really bother you, then take a look here:
Step-by-Step QSC (JBL) Pro amplifier Quiet Fan Upgrade :http://www3.sympatico.ca/bonaz/JBL/Quiet-fan-upgrade/Quiet-Fan.htm

If it is the same fan in your PLX1104 then the model proposed in that thread is 10dB quieter than the original one.
Here's the datasheet : http://www.eminebea.com/content/pdf/TMP00123/I/fba08a.pdf

Hope that helps,
Claude

 

[strato62]

cough cough ...

The proposed replacement fan also displace less air than the original one 24 cfm vs 39,6 cfm for the original fan, so it may not be as good as it originally seemed ...better check with with the manufacturer for minimum cfm requirement to ensure proper cooling of the output stage.

Claude

 

[kurzweiler]

wow... the fan of PLX1104 is noisy? :shock: I do not agree. In my case I use this same poweramp with two 2x12 at 8 ohm. per side, with the qsc's master volume at twelve o'clock and the noise of fan is non-existent.

Only I understand your problem if you use the master volume at 0'001 :|

 

[strato62]

I'm a PLX1104 user also and love the amp, light, powerful, musical and all.... lol
and i agree with you Kurzweiler ...

I found the thread on fan replacement when i bought the amp and was told it could be noisy, but found this was not the case after all.

 

[joegold]

wow... the fan of PLX1104 is noisy? :shock: I do not agree. In my case I use this same poweramp with two 2x12 at 8 ohm. per side, with the qsc's master volume at twelve o'clock and the noise of fan is non-existent.

Only I understand your problem if you use the master volume at 0'001 :|

It doesn't really matter to me if you understand my problem or not but I'll try to explain it to you, again, anyway.

1. I may have the power amp mounted in the double rack space that exists in my Pearce 1X12 cabinet.
2. I play a lot of straight ahead jazz at quiet levels.
3. When in a studio, playing quietly, and mic'ing that cab, the fan noise is loud enough to be a problem.
4. When playing in a quiet intimate jazz club setting the fan noise could be a problem in-between tunes.
5. When playing at home the fan noise is a problem now.

And when I was at the store I also compared the fan noise of another PLX Series amp and it was the same or worse than the one in my PLX1104, so I didn't simply get a bad fan.

It's likely that you play different music than me, regularly at louder voulumes than me, in different venue-types than me. Certainly when playing loud the fan noise isn't a problem. Certainly when playing in a noisey environment it's not a problem either. It's a problem when not playing loud in a quiet environment.

OK?

 

[joegold]

cough cough ...

The proposed replacement fan also displace less air than the original one 24 cfm vs 39,6 cfm for the original fan, so it may not be as good as it originally seemed ...better check with with the manufacturer for minimum cfm requirement to ensure proper cooling of the output stage.

Claude

Thanks strato62.
I'll look into all that if I decide to keep the QSC.

I think I'm going to be checking out an ART SLA2 again today and do some A/B'ing.
I was hoping to get a power amp that had enough juice to also drive a pair of passive FRFR cabinets occasionally. The SLA2 might not cut it for that, but it's got a quieter fan as I recall.

 

[dpeterson]

Mmmmm

According to manual the fan increase speed when it delivers more power, so i wouldn't put a switched resistor in series with the fan and run the risk of forgetting to flip the switch and get the amp to overheat.

dont forget to flip the switch ... there is another alternative, a heat controlled switch that switches on at a certain temp. my fix works perfectly, and cost about $3 in parts.

 

[kurzweiler]

wow... the fan of PLX1104 is noisy? :shock: I do not agree. In my case I use this same poweramp with two 2x12 at 8 ohm. per side, with the qsc's master volume at twelve o'clock and the noise of fan is non-existent.

Only I understand your problem if you use the master volume at 0'001 :|

It doesn't really matter to me if you understand my problem or not but I'll try to explain it to you, again, anyway.

1. I may have the power amp mounted in the double rack space that exists in my Pearce 1X12 cabinet.
2. I play a lot of straight ahead jazz at quiet levels.
3. When in a studio, playing quietly, and mic'ing that cab, the fan noise is loud enough to be a problem.
4. When playing in a quiet intimate jazz club setting the fan noise could be a problem in-between tunes.
5. When playing at home the fan noise is a problem now.

And when I was at the store I also compared the fan noise of another PLX Series amp and it was the same or worse than the one in my PLX1104, so I didn't simply get a bad fan.

It's likely that you play different music than me, regularly at louder voulumes than me, in different venue-types than me. Certainly when playing loud the fan noise isn't a problem. Certainly when playing in a noisey environment it's not a problem either. It's a problem when not playing loud in a quiet environment.

OK?

OK, OK, sorry... do not get angry

Simply it surprises me that someone who uses a poweramp with 1100 wats, complains with an almost imperceptible noise, IMO :roll:

 

[joegold]

wow... the fan of PLX1104 is noisy? :shock: I do not agree. In my case I use this same poweramp with two 2x12 at 8 ohm. per side, with the qsc's master volume at twelve o'clock and the noise of fan is non-existent.

Only I understand your problem if you use the master volume at 0'001 :|

It doesn't really matter to me if you understand my problem or not but I'll try to explain it to you, again, anyway.

1. I may have the power amp mounted in the double rack space that exists in my Pearce 1X12 cabinet.
2. I play a lot of straight ahead jazz at quiet levels.
3. When in a studio, playing quietly, and mic'ing that cab, the fan noise is loud enough to be a problem.
4. When playing in a quiet intimate jazz club setting the fan noise could be a problem in-between tunes.
5. When playing at home the fan noise is a problem now.

And when I was at the store I also compared the fan noise of another PLX Series amp and it was the same or worse than the one in my PLX1104, so I didn't simply get a bad fan.

It's likely that you play different music than me, regularly at louder voulumes than me, in different venue-types than me. Certainly when playing loud the fan noise isn't a problem. Certainly when playing in a noisey environment it's not a problem either. It's a problem when not playing loud in a quiet environment.

OK?

OK, OK, sorry... do not get angry

Simply it surprises me that someone who uses a poweramp with 1100 wats, complains with an almost imperceptible noise, IMO :roll:

I'm not angry.
I just don't find your posts all that helpful.
Sorry.

And it's a funny thing about modern jazz guitar.
Sometimes we play with a really clean dark sound, ala Pat Martino, at relatively loud volumes.
It's surprising how much power is required to get headroom like that.
Hint: A single Fender Twin doesn't have enough clean power for what I'm talking about. A Twin will breakup when playing block chords with a loud drummer.

This is why I have little faith in the Atomic FRFR offering with it's piddly 50 watts for my needs.

Yet sometimes we play real quiet, like in a little restaurant where you can hear a pin drop in between tunes.

 

[joegold]

Meanwhile...
I've got a rented ART SLA2 over here right now.
It's fan is *way* quieter than the QSC's fan.
I think I like its sound a bit more too. It's a bit beefier on the bottom and a little more glassy on the top.

Although it doesn't fit well inside the rack space of my Pearce speaker cabinet, and I don't welcome the extra weight in my rack (it's about 20lbs vs the QSC's 13lbs.), I think I'm going to buy it and return the QSC.

I was really hoping to like the QSC.
Form factor is just about right and I got a great deal on it.
Oh well.

 

[strato62]

Joegold,

If a Fender Twin has sometime not enough clean headroom, you'll likely need a very powerful ss power amp to do the job.

Remember that to get twice the sound pressure of a given power amp you'll need 10 times the power .... so if you want twice the pressure level of say your PLX1104 you'll need something like a 3000W ss power amp !!! or get more speaker drivers for better efficiency, doubling your speakers with another set of say EV12L will get you 3 dB more efficiency, you'll be still far from doubling your clean headroom bout you are getting closer. You could of course get another PLX1104 and another 2x12 loaded with EV12L .... if cost is not an object ...

Hope that helps,

Claude

 

[joegold]

Joegold,

If a Fender Twin has sometime not enough clean headroom, you'll likely need a very powerful ss power amp to do the job.

Remember that to get twice the sound pressure of a given power amp you'll need 10 times the power .... so if you want twice the pressure level of say your PLX1104 you'll need something like a 3000W ss power amp !!! or get more speaker drivers for better efficiency, doubling your speakers with another set of say EV12L will get you 3 dB more efficiency, you'll be still far from doubling your clean headroom bout you are getting closer. You could of course get another PLX1104 and another 2x12 loaded with EV12L .... if cost is not an object ...

Hope that helps,

Claude

The problem is not volume.
It's headroom.
A Twin can get freakishly loud, but it will be breaking up.
200 watts of solid state power into a single efficient speaker is plenty.
200 watts per side is more than I'll ever need, but stereo is cool.

 

[joegold]

Meanwhile...
I've got a rented ART SLA2 over here right now.
It's fan is *way* quieter than the QSC's fan.
I think I like its sound a bit more too. It's a bit beefier on the bottom and a little more glassy on the top.

Although it doesn't fit well inside the rack space of my Pearce speaker cabinet, and I don't welcome the extra weight in my rack (it's about 20lbs vs the QSC's 13lbs.), I think I'm going to buy it and return the QSC.

I was really hoping to like the QSC.
Form factor is just about right and I got a great deal on it.
Oh well.

So now I'm thinking about the SLA1.
It's depth is only about 9.5" which would very nicely into the rack space of my Pearce cabinet.
But since the Pearce cab is designed for a single piece of double space rack gear it doesn't have bolt holes for a single rack piece or 2 single rack pieces. So I'll have to drill a few holes and fill them with wing nuts.

For gigs where I'm in mono I'll just bridge the SLA1.
For stereo gigs, 100 watts a side should be fine for me.
If I want to drive FRFR cabs I'll either rent or buy another SLA1 and use the two of them bridged.

At least that's what I'm thinking now.

I just got back from returning the QSC.
I was very disappointed, not only in the fan noise, but in the audio quality too.
No bottom end, and the top end was sort of unnaturally subdued.
Plus, I opened it up, and the built quality, especially the way the fan is mounted, is suspect to me.

 

[<MACHINE>]

I was very disappointed, not only in the fan noise, but in the audio quality too.
No bottom end, and the top end was sort of unnaturally subdued.
Plus, I opened it up, and the built quality, especially the way the fan is mounted, is suspect to me.

^^^BOLD^^^ is my edit for clarification.


Maybe you got a bad unit?

I've had the PLX-1104 for a few weeks now and have a/b'd it extensively w/my Carvin DCM-1000...no difference what-so-ever. The Carvin is pretty flat as far as I know?

I've previously a/b'd the Carvin against a VHT 2-50-2, Mesa 2:90 and a Peavey 60/60...in ALL cases tweaking the Axe produced the same results...I could get all of them to sound identical. These in addition were a/b'd against real tube pre/power setups...same results.

I dunno...a power amp like the PLX IME has shown to be flat enough to let the Axe do the work, as it should, without any additional coloration. So possibly a bad unit? Or (please don't take this the wrong way) maybe your tweaking abilities aren't up to your own standards :?:

 

[joegold]

I was very disappointed, not only in the fan noise, but in the audio quality too.
No bottom end, and the top end was sort of unnaturally subdued.
Plus, I opened it up, and the built quality, especially the way the fan is mounted, is suspect to me.

^^^BOLD^^^ is my edit for clarification.


Maybe you got a bad unit?

I've had the PLX-1104 for a few weeks now and have a/b'd it extensively w/my Carvin DCM-1000...no difference what-so-ever. The Carvin is pretty flat as far as I know?

I've previously a/b'd the Carvin against a VHT 2-50-2, Mesa 2:90 and a Peavey 60/60...in ALL cases tweaking the Axe produced the same results...I could get all of them to sound identical. These in addition were a/b'd against real tube pre/power setups...same results.

I dunno...a power amp like the PLX IME has shown to be flat enough to let the Axe do the work, as it should, without any additional coloration. So possibly a bad unit? Or (please don't take this the wrong way) maybe your tweaking abilities aren't up to your own standards :?:

It's possible that it was a bad unit, but the sales guy didn't think it likely.
As far as the fan noise is concerned, there was another PLX series amp in his rack and it's fan was just as noisey.

I don't see the ART SLA1 or SLA2 on your list.
Maybe the ART stuff just sounds better?