Thanks for all the info gents. While I'm not new to gear I'm no tech when it comes to the electrical side of things. This was very helpful.
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4ohm amp into a 2.667 ohm load. Safe?
- Thread starter jimmyjames77
- Start date
- Apr 24, 2004
- 1,359
- 53
- Disclosures
- Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification
Impedance varies WIDELY with frequency. A dynamic speaker's impedance at low frequencies is much, much lower than at high frequencies. Electrostatic speakers are the opposite situation and require more power at high frequencies than low. This is much harder on most amps, believe it or not. Gain Bandwidth becomes a big issue then and there are lots of bass amps that "ain't got much of that". I think the typical nominal rating it supposed to be at 1kHz. But I'm not sure how accurate those specs really are. A lot of times they aren't measured, but just interpolated based on the provided specs of the drivers and crossovers.
By the way, the highest note on a 24 fret 6 string bass is 0.5kHz.
You'd probably be fine, to be honest, if you just added additional cooling when you were really making the amp work hard. But if you blow it up you'll have no recourse. It really depends on the amp itself and how well designed the output stage is. If it's a consumer level type thing like a GK or whatever, I wouldn't do it because the chances are the ratings are a little "stretched" already. If it's a Crown I'd be more willing to chance it. Their amps are very conservatively rated and always have been.
Bear in mind that if the amp is stereo and bridgeable, some amps allow for series or parallel bridging. Series bridging will let you drive higher impedance loads to full power where parallel provides more current to lower impedance loads. It's the way the old, cheap Crown power base amp could drive loads from 2 ohms all the way to 16 with ease.
For what it's worth, if you want to run the speakers in parallel so you can pull more power out of the amp, you may find you'll get better results running you speakers in series (12 Ohms) and forgetting about the power rating. Chances are the actual volume level won't be much different. It'll change the sound some, but I can't say whether in a good or bad way. You'll have the benefit of moving more air which is the main advantage to more speakers vs. less. It's certainly the safer way to go.
By the way, the highest note on a 24 fret 6 string bass is 0.5kHz.
You'd probably be fine, to be honest, if you just added additional cooling when you were really making the amp work hard. But if you blow it up you'll have no recourse. It really depends on the amp itself and how well designed the output stage is. If it's a consumer level type thing like a GK or whatever, I wouldn't do it because the chances are the ratings are a little "stretched" already. If it's a Crown I'd be more willing to chance it. Their amps are very conservatively rated and always have been.
Bear in mind that if the amp is stereo and bridgeable, some amps allow for series or parallel bridging. Series bridging will let you drive higher impedance loads to full power where parallel provides more current to lower impedance loads. It's the way the old, cheap Crown power base amp could drive loads from 2 ohms all the way to 16 with ease.
For what it's worth, if you want to run the speakers in parallel so you can pull more power out of the amp, you may find you'll get better results running you speakers in series (12 Ohms) and forgetting about the power rating. Chances are the actual volume level won't be much different. It'll change the sound some, but I can't say whether in a good or bad way. You'll have the benefit of moving more air which is the main advantage to more speakers vs. less. It's certainly the safer way to go.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Did that get mentioned at the top of the thread? It certainly should have been.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Tube power sections with transformers are a different ball-game altogether. Often specific tube heads' manufacturers say you can use one tap or the other with nominal loads that aren't specifically 4 ohms or 8 ohms.
That's what I love about the net. Ten years ago the kind of info I/we can find insanely quickly was spread out over the entire world. Now it's at the finger tips.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
I played the Classic 400 but I just don't recall if it was reg'd for 2.67. But there's several vet players of that head around here and our illustrious Peavey guy BbbyBold who could tell you if it was in the THREAD TITLE.
Tubes - that opens up a whole new area. Not sure on the PV but my SVT would do that load easily, but it would go to 2 ohms.
I would assume that the PV could do that load but tube life would probably suffer somewhat. Usually my experience is that tube heads are a bit more forgiving regarding loads but that depends on how much overkill is in the transformers. If I remember right those amps don't have any type of protection / monitoring on the output tubes like the SVT's and big Fender's do (which is either a good or bad thing depending).
On a tube amp, I'd try it and just keep a constant eye on the tubes and transformers to make sure they aren't getting overly hot. Plus I'd keep a spare fuse handy. Which is something every player should do anyway and if you gig a tube head, a FULL set of replacement tubes should be in your bag, gig case, or whatever at all times. Yeah, costly I know but that's the price for big tube sound. A spare set has saved me a few times back when my back would still let me lug around 80 to 90 lb heads
We need a tech who has experience with these heads to chime in. One guy who comes to mind and would probably know for sure is ENZO over at the music electronics forum. He's worked on a lot of PV's.
Keep Low
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Well, besides BbbyBold of Peavey, I think James Hart probably could answer as regards Classic400 specifics.
well for crying out loud! why did i write that ohms faq?
tube amps can be (emphasis on CAN) tolerant of impedance mismatches of 100% to an extent. With a tube amp, you'll run into more trouble using it at an impedance HIGHER than selected. With a slight mismatch, you're safer running the 4 ohm tube amp @ 2.67 than say at 8 ohms.
BUT you really should contact peavey and/or knowledgable members here about this specific amp
That was my understanding from when I spoke to my tech about the tube amps.
I did finally get to speak to Peavey about it and he did confirm that it IS OK to run her at 2.667 when set at 4 ohms on the amp. PV has always been SO helpful about any questions I've ever had. They're great.
I did finally get to speak to Peavey about it and he did confirm that it IS OK to run her at 2.667 when set at 4 ohms on the amp. PV has always been SO helpful about any questions I've ever had. They're great.
Sorry, couldn't resist the pile-on. A Classic 400, huh? Way to go, dude. Could have saved us a lot of heartache if you hadn't left that minor detail out.
Generally speaking, no.
Fender Bassman 400 heads were rated at 4-ohm minimum, however, Fender added a disclaimer in the Bassman 400H manual that running the amp at a 2-ohm load was safe and would not void the manufacturer's warranty.
Check with the manufacturer.
Fender Bassman 400 heads were rated at 4-ohm minimum, however, Fender added a disclaimer in the Bassman 400H manual that running the amp at a 2-ohm load was safe and would not void the manufacturer's warranty.
Check with the manufacturer.
- Apr 24, 2004
- 1,359
- 53
- Disclosures
- Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification
On an unrelated topic. I didn't see a reference to 0.5 Ohms in the Sticky SO:
I hooked my amp up today to all my cabs daisy chained together just to try it out. I played it at low volume and it sounded OK. So I thought it should be OK right?
I then turned the master up to 1.5 and smoke came pouring out of the side of my amp.
Do you think it is OK? Maybe just the fan was smoking? I really want my amp to be OK. I don't know what I will do to myself if it is broken. I already have cut myself.
Somebody please tell me it will be OK... PLEASE?
EDIT: Thank You.... for the PMs. I think everything is OK now. I'm going into the backyard and port some cabs now...
I hooked my amp up today to all my cabs daisy chained together just to try it out. I played it at low volume and it sounded OK. So I thought it should be OK right?
I then turned the master up to 1.5 and smoke came pouring out of the side of my amp.
Do you think it is OK? Maybe just the fan was smoking? I really want my amp to be OK. I don't know what I will do to myself if it is broken. I already have cut myself.
Somebody please tell me it will be OK... PLEASE?
EDIT: Thank You.... for the PMs. I think everything is OK now. I'm going into the backyard and port some cabs now...
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Don't worry. You yourself with no previous knowledge can FIX IT in minutes - THANKS TO TEH MIGHTY AND AWESOME POW-ARE OF TEH INTERNUT!
Sure you have enough ammunition? Here's some more for those premium "PA cabs".
