Ouch! 
What's going on here? These guys somehow pushing these amps too hard some how? Just wondering whazzup.
What's going on here? These guys somehow pushing these amps too hard some how? Just wondering whazzup.
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Ampeg PF500/PF350 - part 3, I think
- Thread starter BassyBill
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I don't get the idea that the amp only cuts out if you push it too hard. Pro amps don't do that. Someone gets a PF500 as the backline amp at a gig, they aren't going to have the manual and they aren't going to have time to play the thing in and consider it's limits.
I knock on Wood... until now, I've had no Cut outs, or other Issues. Tonight I'll do the first Club Gig with the PF500 and 1 8Ohm Cab....
Duke21 said:
A good question.
I've always set any effect I use at unity with my clean signal (or at least with what my ears tell me is unity). That way I can set ANY amp for my clean tone and nothing weird happens when I turn on an effect. Everything is at the same volume for the soundguy that way, too.
Sidenote: That philosophy stems from playing with a guitarist early in my bass playing career who didn't know his gear and/or match his settings, so volume was all over the place. We'd be playing and he'd change effects, maybe his sound would disappear completely or maybe he'd be loud as hell, it was a crapshoot. His poor amp! Lol)
If you're asking about using an effect as a boost (which would of course affect the gain at the amp), someone else might have a better answer...? I'd be interested to hear anyone else's input about that too. I suspect you'd want to set the gain knob the same way as mentioned, just with your louder overdriven signal, and then leave it there for your backed off clean signal.
5sg.
At the moment I am using a pair of TC BC212s with my PF500 and they do not do the amp any favours IME, they begin to fart and sound muddy too early and dont seem to allow the amp to give much in the way of clean tone in a 3 piece band rock/rock n roll covers band set up, cant wait two weeks for my Barefaced Super Twelve to arrive 
I was with the band last night and I still would prefer a low/mid and hi/mid EQ instead of the mid and 5 way switch , the switch seems pretty ineffective to me when compared to another mid control, just my preference for what its worth
I was with the band last night and I still would prefer a low/mid and hi/mid EQ instead of the mid and 5 way switch , the switch seems pretty ineffective to me when compared to another mid control, just my preference for what its worth
I've had a PF-350 head since June 2011, and no issues.
It seems to me that the folks with PF-500 heads that are having trouble, are all using 4-ohm cab setups. Even though the cab(s) are a nominal 4 ohm, the actual DC resistance of those setups can be in the 2 to 3 ohm range. For example, a single Eminence Basslite S2012 has a DC resistance of 5.1 ohms (8 ohm nominal). Two S2012 in parallel works out to 2.55 ohms (4 ohm nominal).
That is an overload for a 4ohm head, and the head will try to protect itself, or fail trying.
It seems to me that the folks with PF-500 heads that are having trouble, are all using 4-ohm cab setups. Even though the cab(s) are a nominal 4 ohm, the actual DC resistance of those setups can be in the 2 to 3 ohm range. For example, a single Eminence Basslite S2012 has a DC resistance of 5.1 ohms (8 ohm nominal). Two S2012 in parallel works out to 2.55 ohms (4 ohm nominal).
That is an overload for a 4ohm head, and the head will try to protect itself, or fail trying.
I guess that makes sense. Never thought of it really, except to do the easy math of 2x8 ohm typically gives a 4 ohm combination.
Surely the PF 500s are designed to run two of their PF cabs (either 115 or 210) which are designated as 8 ohm individually... I couldn't imagine Ampeg NOT designing them that way.
I'm 'educated guessing' that the 15" speaker in the Ampeg PF115 cab is an Eminence Delta 15LFA variant, with a DC resistance of 6.1ohm. Two in parallel would be 3.05 ohm DC resistance. Perhaps the head is OK into a 3 ohm minimum, but starts having issues below 3ohms... especially at higher volumes and low notes.
Makes sense, but if you use an Ampeg head with two Ampeg cabs it's rated to drive and it fails surely Ampeg hasn't done their job.
It would be nice to find this out before buying one and then two 115s or 210s. This might lean someone towards a single larger cab. But then that negates all the advantages the PF line was supposed to have in the first place...
Ampeg ought to answer these sorts of questions.
The head doesn't output DC so the nominal DC resistance can't really be connected to an issue here. Impedance does fluctuate over frequency range, but people have been having issues with a variety of different cabs, not just the PF cabs, so I don't think we can really point to impedance swing as the problem. The issue seems to be with the gain structure of the amp and amps getting too hot while being pushed to hard and going into limit/failure territory. I've pushed mine pretty darn hard and have yet to have an issue, so to me, it just seems like a component problem. Something in the amps is failing at a higher rate (or lower tolerance) than it should be. It would make sense at that point for ampeg to not have issued a circuit revision but to just replace the amps that have failed and move on.
Ive had my PF-500 and PF-210 since Thursday and played with 3 guitars and a loud drummer last night in the basement for rehersal. Also tried plugging into the 1970s 2x12 Traynor stack and both had amazing vintage warmth and kicking punch without the boominess. Had the volume up to aboiut 2pm with pretty high gain and no cutting issues,,, it wanted more but the whole house was shaking. It could take it im sure. I really enjoy the compressor on it as its the first one Ive used.
Class D amps generally convert AC power into a positive DC voltage supply, and a negative DC voltage power supply. Those straight DC voltages are then switched on and off at high frequencies (10 to 50 times greater than the audio frequencies), through a low pass filter, to the speaker(s) DC resistance load to create the audio. The value of the speaker's DC resistance is quite important to the process.
b-b-b-bass said:
As far as i understand it, dc voltage is blocked by a capacitor, or by interference in a full bridge amplifier.
Some info here
Link Removed
It doesn't even need a blocking cap: "The Class D amplifier has a low output offset, eliminating the need for a DC blocking capacitor. "
I had my first cut out issue last night at a gig. I've had the amp for 6 months and it's the first time it's happen. One difference was I pluged the pf 500 into the headliners bass cab ( a Boogie 1 15). I never checked if it was 4 or 8 0hms. To make sure we are all talking about the same problem, the amp would cut out for a millisecond when I would hit an open E. Reading through all the comments I'm wondering if part of the problem is I'm using SPB3 quarter pounders on my precision (high output passive), maybe I should engage the -15db pad like it was an active bass. Is anybody having problems with regular passive pick ups ?
John D said:
In a full bridge amp, but not a half bridge. My point was that dc signal is not passed to the speakers.
[Invalid or Expired Link Removed].
I'm not an expert on this stuff so I'm hoping one of our usual technical experts will chime in soon, but I've always heard t that dc being passed to the speakers would lead to very quick failure.
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