Help Me Decide on a Power Amp For My F-1X

[davekoch]

I need advice. I'm getting an F-1X preamp. Now I need a power amp. Lord Valve has good deals on new QSC PLX power amps, so I'll probably buy it there. Anyone have a used PLX 1602 or 2402 for sale?
 
The PLX 1602 bridged would push 1100 watts into my Eden 4x10T (500-watt cab). But in stereo, the PLX 1602 would push only 300 watts into the 4x10T. Is 300 watts too little for the 4x10 500-watt cab? For the Eden 2x10T 250-watt cab (which I don't use all that often anymore), 300 watts is fine, right?  
 
If I went with the PLX 2402, it has 425 watts a side at 8 ohms, but 1500 watts bridged. Should I be hesitant about pushing 425 watts into a 250-watt cab, and/or pushing 1500 watts bridged into a 500-watt cab?  
 
PLX 1602  
bridged at 8 ohms - 1100 watts  
stereo per side at 8 ohms - 300 watts  
 
PLX 2402  
bridged at 8 ohms - 1500 watts  
stereo per side at 8 ohms - 425 watts  
 
My (older, white background/red logo) Eden cabs are both 8 ohms:  
4x10T 500-watt  
2x10T 250-watt  
 
The 2402 is $170 more than the 1602. I don't want to buy too much power, or not enough.  
 
Guys, I need some advice here,  
 
Thanks soooooo much,  
Dave
 
(Message edited by davekoch on October 26, 2004)

[David Houck]

I would suggest you go with the 2402.
 
The PLX has output controls for each channel.  So you can run one channel full into the 500 watt cab; and on the other channel, back of a click or two for the 250 watt cab.  I would not think you would want to run either amp bridged into those cabs.
 
Also, by going with the 2402, you give yourself more options for the future.

[shakeyeraz]

What Dave recommends makes sense. I have almost the exact set up with the 1602 and 2 4X10 Eden cabs, each 8-ohms. One is a 410T, the other is an XLT. I now have an Aguilar 659 preamp but previously had an F-1X.
 
When I played in a classic rock band I used both cabs and the 1602 bridged was plenty of power to get over the top of the guitars - they were loud - so no worries on the power there. Now that I'm doing the blues/jazz band I rarely use both cabs together - I don't need the volume but I still run the QSC in bridge mode driving an 8-ohm load. The sound is clean from the low B on up and the QSC runs cool and quiet.
 
One thing I did learn about the QSCs is the configuration for bridge mode works better with most preamps when the parallel channel switches are set to 'off' - i.e. not parallel. You'll see this when you get yours. Parallel mode 'on' bridges the two channels and, more importanly, changes the impedance that the preamp sees which can change the sound. I didn't know this when I had my F-1X so I don't know the impact there but with my Aguilar it definately makes a difference in the sound.
 
Check out talkbass for more QSC info. Bob from QSC hangs out there and responds to inquiries - he is extraordinarily helpful and a great guy to talk with.
 
BTW - I purchased my 1602 pre-owned for $400
 
k

[davekoch]

Am I interpreting these posts correctly?  
 
davehouck recommends the 2402 running in stereo mode (with 425 watts per side), right? I should avoid bridge mode in any configuration with my cabs. This would underpower the 4x10 - 500 watt cab and overpower the 2x10 - 250 watt cab, right?  
 
shakeyeraz recommends the 1602 running in bridge mode (delivering 1100 watts into the 4x10), right? This would overpower the 4x10 - 500 watt cab (1100 watts into), right? I wouldn't use the 2x10 in bridge mode. In stereo mode, the 1602 would deliver 300 watts into the 4x10 and 300 watts into the 2x10.
 
How about underpowering vs. overpowering (reasonably, of course) speakers. I mostly use the 4x10 alone. Only a few gigs a year require using both the 4x10 and 2x10 together. (Maybe I should just sell the 2x10 - this would make the power amp decision a lot simpler, huh?)
 
Dave

[shakeyeraz]

I was just sharing my configuration - if I could have gotten the 2402 at the time I was looking I would have purchased that one but the 1602 was a good deal and it turns out that I'm happy with it.
 
In general underpowering is not good - too much stress on the amp and leads to premature failures. Not to mention distortion and other signal mangling. Having more power than you need generally gives you transparancy (sp?) with the power amp which is what I prefer. This is why bridge mode, though it looks like an 1100 watt monster, really provides ample power for either of my cabs with sufficient headroom. I run the volume at 1 o'clock which is just over half-way - it's probably not a linear scale but gives you an idea of how I'm using the amp's power. IT always runs nice and cool.
 
Remember too, everything in the signal path is important - use heavy gauge speaker cables and high quality interconnects between preamp and amp.
 
Bottom line is always that you need to try it to confirm that this is what you're looking for sound-wise.

[davekoch]

Hi shakeyeraz,  
 
Thanks so much for all the information. I hope I didn't misrepresent your views; if I did it wasn't intentional.  
 
Eighty percent of the time I use just the 4x10. So in your opinion, would delivering 1100 watts into a 500 watt cab be OK?  
 
What are the power ratings on each of your cabs?  
 
One more thing. Does bridge mode sound different than stereo mode? If so, can you describe the difference?
 
Parallel mode 'on' bridges the two channels and, more importanly, changes the impedance that the preamp sees which can change the sound.  
 
Thanks again.
 
(Message edited by davekoch on October 26, 2004)

[David Houck]

I do not have a great understanding of electronics; and what I do learn, I do not retain in memory.  There have been some very detailed discussions of this subject before in our group; and a good search should find them.
 
Kevin says he has his gain control set at 1:00.  With the gain control set at max, the PLX amps are increasing the input voltage 40 times, or 32db's.  At 1:00, Kevin's amp is increasing the input voltage 24db.  So, no, Kevin is not sending 1100 watts to his 4x10 unless he is seriously overdriving the input stage of the amp.  Of course, if he were to decide to turn the gain control to full and slap the stings hard with the palm of his hand, then he could cause some damage.

[David Houck]

Here's a previous discussion on the subject:
http://club.alembic.com/Images/449/7204.html

[shakeyeraz]

I haven't tried stereo mode with the Aguilar so I can't comment on the impact of the impedance in that mode. If it did (does - I'll try this at some pont), I would certainly keep it in bridge mode.
 
Daveh sums up the QSC/PLX operation perfectly - just to reiterate and IMHO, getting more power than you need is better than underpowering.

[davekoch]

1. Using the PLX1602 bridged with only the 4x10T (500W), would 1100W be too much power for the 4x10 cabinet? One guy at QSC mentioned that 500W RMS has about 1000W peak capacity. So, to prevent smoking the cab with 1100W, could I just not turn up the power amp as high?
 
2. Can the power amp be modified to reduce the power output?
 
Other thoughts?
 
(Message edited by davekoch on October 29, 2004)

[gare]

I think something that should be considered is how amps are rated. How many different ratings are there ?
Rms, peak, peak to peak, etc. The true output gets lost . If you say take an SVT tube head rated at 300 watts, what equivalent power would you need to match it in a solid state amp ?  Whats actually a true power rating ?  
Ever stand in front of a cranked up 100 watt Marshall stack ? (I understand the frequency differences), but its LOUD.    
I think the manufacturers advertising has become a numbers game.
And,like Shakeyeraz says, you're better off running more power than you need,you can run the preamp at a lower setting eliminating some noise and distortion for a cleaner sound.

[davekoch]

My main question that remains is:
 
Using the QSC PLX1602 bridged with only the 4x10T, would 1100W be too much power for this 4x10 500W cabinet?  
 
We could talk Specs all day, but in the end, it's how does it sound? As long as no clipping occurs, no damage done to the speakers, right? Actually I couldn't talk Specs all day, , I don't know enough about them. Sorta obvious, huh?
 
(Message edited by davekoch on October 29, 2004)

[davekoch]

Thanks to all of you who shared their thoughts, experience, and advice. I decided on and ordered the PLX 1602. I'm excited!!
 
Can anyone recommend a particular type, brand, or specs (gauge, plugs, etc.) for the cable(s) used to connect the F-1X to the power amp? Shorter the better (for 1/4 unbalanced), right? Anyone using, if possible, the balanced out? Recommendations? Thoughts?
 
Dave

[davekoch]

TOTAL BUMMER.
 
I received my new PLX 1602 and practically new (3-years old, but yes it's used) F1-X. The system doesn't work. With and without (plugging directly into PLX) the F1-X, the volume is VERY weak. It's about half as loud as my 35-watt Peavey Minx - I couldn't gig with this combo.  
 
Lord Valve (who sold me the PLX 1602) says it's a F1-X issue. He says going directly into the power amp will not be loud at all because there's no preamp to boost the signal strong enough so the PLX can utilize it's 1100 watts. Is this true? My bass has an onboard J-Retro preamp and with all Treble/Mids/Bass turned all the way up, it barely makes a difference.  
 
The F1-X seller says the F1-X worked perfectly before he shipped it.  
 
Should this gear work right out of the box?  
 
Does the F1-X and/or PLX 1602 need to tweaked to work with one another?  
 
My gear: Modulus Jazz with an onboard J-Retro preamp - produces a very hot signal!! Eden 4x10/2x10 cabs. I've verfied the cords all work.
 
Suggestions?  
 
HELP................?
 
I'm totally frustrated!!

[godoze]

Uh, the F1-x is a preamp is it not ? that answer makes no sense to me...