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Ampeg PF500/350, part 4
- Thread starter Chef
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ryanfenderbass said:
IMO
PF-500 has problems delivering 500 Watts into a 4ohm load. Takes more beef from the amp to push lows so it hits the poweramp harder and the limiter either can't handle it, is a poor design, or designed by Ampeg that way. Possibly all of the above.
Back off lows, problem goes away. I still feel that there's some kind of design in the circuit, or a component failure that causes the cutout when the amp drives a 4ohm load.
I've owned a few class D amps GB and Markbass and NEVER had an issue with cutting out.
I'm not buying Ampegs answer to cut back gain and bass. I think that's an excuse for a problem with the amp. It's almost like Ampeg is saying just keep turning things down till it stops cutting out.
Honestly an amp should be able to work properly anywhere within it's gain and tone structure without having to compensate settings to keep the amp working. Sure these are low pricepoint amps but they ought to work right.
I wish Ampeg would tell us exactly why this is happening. Maybe they don't know?
- Feb 16, 2008
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- John K Custom Basses
if what Ryan says is true (and i believe him), then his particular 4 ohm load is too low for the output of the amp at certain low frequencies and it's protection circuit is being activated, and as Freddels said it's not all that 4 ohm stable.
my GK 1001RBII would cut out momentarily if i really pushed it hard into one of my 4 ohm cabs, while on most all of my others it doesn't cut out at all.
my GK 1001RBII would cut out momentarily if i really pushed it hard into one of my 4 ohm cabs, while on most all of my others it doesn't cut out at all.
Based on my readings in this four-part thread, you have simply discovered that you have the most common failure:
8-ohm load = AOK
4-ohm load = potential clipping / cut-out issue
I don't recall your rig specifics (if I ever read it...).
- What two cabs do you have?
- Are they both rated at 8-ohms?
In my son's experience, it was not the number of cabs but the impedance of individual cabs. With one PF115 (8-ohm), no problem. With one SVT 810 (4-ohm), he had the problem with the old head. He has had no problems with the new head whatsoever, using either cab.
Nobody's lying. But a watt is not a watt is not a watt when it comes to driving my speaker cabs. Most of us old timers remember how bad SS amps were when they first came out -- thin and anemic, but with high wattage ratings. We always said that 100 watts tube amps were way more "powerful" than 100 watt SS amps -- MEANING, that we got more usable volume (often much more)from a tube amp than from a similarly rated transistor amp. We also got better tone from the tube amps -- balls, to be crude. Thanks to GK and others ,as SS technology improved (ex FET) that gap narrowed and the focus was on tone differences. But the first tube amps sucked in tone and volume with puzzlingly high wattage ratings.
Now with Class D we're talking about overbuying power so we can run the amps at lower levels so they won't clip/overheat/cut-out. Ampeg CS says buy the 1000 watt SVT 7 Pro over the 500 watt PF, then run it at lower settings. So, buy a 1000 watt amp so that you can use it to get 300-500 usable watts of output? Nobody's lying about output wattage, when we measure it on paper. But if I need a 1000 watt class D amp to sub for my 300 watt SVT in terms of usable power to drive my cabs then we need to standardize terminology and metrics. If I can't use those last 700 watts the amp shouldn't be rated at 1000. At the very least, as Jimmy says we need to take this into account.
Just got of the phone with Ampeg L2 tech support. 30 minute convo that included me demoing the issue with various gain/comp/eq settings over the phone. We more or less confirmed that the PF-500 cannot handle duel cabs at higher volumes without a TON of compression or killing the lows. So, my/our amps aren't faulty, they never were, they just can't hack it at 4 ohms. Meaning, my P with flats just has way to much booty for the power ceiling of my poor little PF-500 :scowl:
As for the resolution. The (totally awesome) tech who helped me is talking to his supervisors about "how they can help me out" given the misleading notion that the PF-500 can power a full stack at 4 ohms. They should be giving me a call any time now. I don't know whether I'm nervous or excited
I ran my rig predominantly at 4 ohms for the first 10 months - someitmes, at 8 ohms, with my smaller cab - but 85-90% of the time - the avatar 410 4 ohm cab - with no issue. NEVER had an issue until it just wouldn't power up. It pushed a lot of lows no prob, but I didn't run the lows THAT hard - didn't need to.
Seriously - it was solid - like no ones buisness!
I will say - after the repair - running it into the PF210 cab - it crapped out a bunch of times - and THAT was an 8 ohm cab. My first thought was I was over powering it - then the second was that I had a bad speaker cable. Settings were actually below what i would normally run, and switched cables - also instrument cables, AND basses. Still the cut out continued.
Changed over to the 4 ohm cab - it seemed to run ok - but when I took it to the gig next night - it cut out at early volume level (you know how it seems to go up through the night) and after 3-4 times or so - I jacked vloume up a little, and bass too and rolled back highs......and it would not reporduce the cut out the rest of the night - GO FIGURE.
Thats my story - seems to defy the norm -
I can't wait to hear what the fix is, or if it is dismissed - and the MIB guys come out with dark glasses and flashy thingees.
Seriously - it was solid - like no ones buisness!
I will say - after the repair - running it into the PF210 cab - it crapped out a bunch of times - and THAT was an 8 ohm cab. My first thought was I was over powering it - then the second was that I had a bad speaker cable. Settings were actually below what i would normally run, and switched cables - also instrument cables, AND basses. Still the cut out continued.
Changed over to the 4 ohm cab - it seemed to run ok - but when I took it to the gig next night - it cut out at early volume level (you know how it seems to go up through the night) and after 3-4 times or so - I jacked vloume up a little, and bass too and rolled back highs......and it would not reporduce the cut out the rest of the night - GO FIGURE.
Thats my story - seems to defy the norm -
I can't wait to hear what the fix is, or if it is dismissed - and the MIB guys come out with dark glasses and flashy thingees.
Ditto for me, except that at nearly 11 months mine is still going strong. I use a 4 ohm B25B, 4 ohm SWR big bertha, 4 ohm SVT-8x10, or occasionally my PF-210/B15N stack for a 4 ohm load. I think I've used the single PF-210 cab or other single 8 ohm cabs for maybe a handful of rehearsals, but I'd say 95-99% of the usage of this amp (which has been minimum 8 hours/week since last June) has been at 4 ohms for me. Always with passive basses, the majority of the time running through my pedal board. I always use the compressor and keep the gain above noon.
I guess the next question is, when running two cabs for 4 ohms, are people daisy chaining or running both the 1/4" and speakon? Wasn't there some problem with the Micro-VR that occurred with higher frequency when people were using both outputs vs daisy chaining? Again, another head I had no problem with aside from it's lack of power. Maybe I'm just lucky, thus far?
Very interesting
Now I'm really confused. Why rate them at 500 watts @ 4 ohms if they can't reliably deliver the goods. I could possibly see having issues if you're cabs are listed as 4 ohms but in actuality are less, but that safety factor should already be built into the head. Maybe it is and that's why they are cutting out.As for the resolution. The (totally awesome) tech who helped me is talking to his supervisors about "how they can help me out" given the misleading notion that the PF-500 can power a full stack at 4 ohms. They should be giving me a call any time now. I don't know whether I'm nervous or excited
Patiently awaiting Ampeg's response on this issue. I'm hoping that it's not "sorry but that's the way the amp is designed". If so I see a lot of calls to Ampeg asking for resolution due to being misled.
Keep Low
Well honestly, it still works like that with amps, even tube amps. If you want to run them clean, you have to have a decent amount of headroom for it, and if you want to be ear-splitting and still clean, many folks need way more power than even the mighty SVT can give you...it doesn't work miracles, either. But when people buy traditional solid state, to this day they still buy more wattage than they'd need in a tube amp because it doesn't clip as gracefully. The only difference is that as you go from tube to lead sled SS to micro, it seems to me that the gap between clipping that sounds clean and good and clipping that doesn't becomes narrower. But for staying clean and getting as loud as you can, you always want some headroom.
I don't know all the facts and I don't know why some perform better than others and why some have problems and the rest don't...I just play the stuff. But as we see more about micro design get explained to us amateur gear nerds, we're going to find out some things about it we're going to have to deal with, just like any other topology. I think there's also a lot yet to be discovered about it that isn't known yet and it's got a ways to go before fully realized. There are many who have been perfectly happy with the performance of their PF amps mixed in with those who have had issues, and my PF350 has been fine so far even when pushed hard, so I don't know. I do agree that everyone should have amps that don't cut out, though. It's not a lot comparatively speaking when buying gear but it's good money, and you should demand no less.
What does it mean? To me, it means you are running out of power (headroom). Of course, as usual, I could be wrong.
Not to inject a happy note here, but I pushed my PF500 balls to the wall at an outdoor gig this last weekend (2 Avatar 2x10s. 8ohms each) and it kicked ass! Just saying, it works for me.
Perhaps the Ampeg PF cabs are a little off on the ohms and a pair of them will result in a slightly less than 4ohm load which is causing the problem.
Maybe everyone that has had problems can sound off with which cabs they were running at the time.
Maybe everyone that has had problems can sound off with which cabs they were running at the time.
Hahaha, I get that. But the thing is, I (ideologically speaking) shouldn't be running out of headroom. Just as another member previously said, these amps aren't fairly rated to be running at 500W. But that's another argument.
Well I theoretically should be a millionaire banging hot models every day and I'm not.
Yeah, I'm a bit worried now. Just planning on buying a second pf210 to get the full 500w, but now I'm not sure what to do
If we keep quoting the newest previous post, we can have a complete list, all-in-one. (I have added my son's cab below the entry from kobass.)
Copy and paste this list and add your own to the bottom:
GK Neo 212-2 (4 ohm)
SVT 810 (4 ohm)
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