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How can I get my amp down to 2 ohms?

#21
Scotty53 said:
I would agree with everyone who has given the option of a separate power amp. You will still get the GK tone because almost all of it is coming from the preamp. I know all power amps have some effect on the tone but you should be fine with any solid state power amp. Running the effects send from your GK head is the best way to get a direct preamp signal to a power amp. Think effects send= preamp out and effects return=power amp in.
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This is good advice, the DI out using the Post switch will keep the boost control in the signal chain though.
 
#24
David1234 said:
:ninja:

It's okay to drive your car into a telegraph pole too. The air bags will protect you. If you start to die horribly, slow down.:crying:
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Nope - it's more like the collision avoidance systems they're putting into high end cars. You won't crash into a pole in the first place. The amp protects itself. Short circuit, over-current protection is in every modern amp that calls itself pro-level gear.
 
#25
Like the guys in California with the Ferrari Enzo and the power pole. It musta been the collision avoidance system that ripped the car in half so the inebriated driver and the occupant-owner could walk away from the 160+ MPH crash. Ah what the heck the car was getting repoed anyway, right?

I love technology.

BOB
 
#27
seamonkey said:
The car metaphor doesn't work out. Overcurrent protection is not any kind of crash.
The amp turns itself off when pushed too hard. It turns itself back on after a while. It's usually a thermal trip, so it comes back when it cools down.
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This is not how overcurrent protection works in a modern class AB/G/H amp. This applies to almost all modern, conventional amps.

Overcurrent protection monitors the current through the positive & negative output stage, and when this current exceeds the threshold, the VI limiting circuit limits the current drive to the output stage, effectively clipping the output.

The problem with designing a 100% reliable limiting circuit is that there are many variables that come into play, and the threshold shifts by as much as 400% depending on things like output stage temperature, frequency, cabinet resistance and reactance, duty cycle, VI limiting hold-off, heatsink inerta, output transistor variences, device matching, emitter resistance, VI limiter type (1, 2, or 3 slope, delays, frequency weighting) etc.

To design for absolutely worst case adds considerable cost, size, weight and complexity to a product to protect against something that is generally unlikely to occur in most amps, certaily those operated within the recommended guidelines like say 4 ohm minimum load.

If you play an amp below it's rated minimum load long enough, youmight reach it's thermal limits but the action of the VI limiter along with a reactive load creates a pretty nasty sounding action anong with possibly overloading the protective backswing (or kickback) diodes while exposing the amp to these possible repetative inductive spikes as the VI limiter limits drive voltage sensed by a phase shifted current.

So basicly, it's a poor idea to assume that any amp is 100% protected from all faluts all of the time. Like a collision avoidance system or air bags, it's there as a backup to an unavoidable or accidental condition with hopes that it does the best it can. Air bags, BTW, are far from foolproof. Plenty of folks are seriously injured by air bags that deploy but are not fully effective.
 
#28
seamonkey said:
Nope - it's more like the collision avoidance systems they're putting into high end cars. You won't crash into a pole in the first place. The amp protects itself. Short circuit, over-current protection is in every modern amp that calls itself pro-level gear.
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That's an awfully broad brush you're painting with, my friend. I'll assume that "Pro-level gear" includes high end tube amps? I have yet to see a tube amplifier that has overcurrent/short circuit protection circuitry. Most of the amps that do have protection circuits are solid state, and the protection circuits won't always detect a fault in time to avoid catastrophic failure.
Just my experience as a seasoned bench tech, and EE. YMMV!
 
#31
georgestrings said:
Generally speaking, purposely ignoring a manufacturer's minimum impedence ratings is not a smart idea - do so at your own peril...


- georgestrings
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I think for the most part the OP has had his question answered, get (2) 8 ohm cabs or an additional power source.

Otherwise this has become a joke. For anyone to suggest using the protection circuit in place of following the manufacturers guidelines.:rollno:
 
#32
Yeah now thinking about it, the car analogy is poor. It's more like you and your bandmates all sitting around a campfire drinking a case of beer and then for kicks tossing one at a time Thirty-Ought-Six rounds into the fire. Great way to spend a Wednesday night BTW... Its almost as exciting as playing chicken, standing on the railroad tracks awaiting the 4:05 AM fast freight to come through... last guy to jump off the tracks er... wins.

Use your amp the way the manual says to use it, it will work good and last a long time. Abuse it and you'll be selling the carcas on eBay to some poor guy who will get stuck with it.

BOB
 
#33
If you can help it don't want to run your amp at 2 ohm's, i would pull the speaker or speaker's and talk to dave at avatar about some 8 ohm speaker's and sell your 4 ohm speaker or speaker's and get 8 ohm,that is the way i would go..good luck
 
#34
bobcruz said:
Could you explain that, Paul? I've only used my serial box with single driver cabinets so I didn't encounter this issue, but I'd like to know what would happen if I used cabs with crossovers in them. Thanks for any enlightenment.
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Single driver or multi driver cabinets are fine. It's when you have crossover components that you have to be more careful. In series the signal to each cabinet has to pass through the crossover of the other with sometimes unpredictable results.

Paul
 
#37
just because you daisy chain a few cabinets together, does not mean you have a series connection because the jacks in your cab and head will be wired in parallel. So connecting your 2 cabs together will still give you a parallel connection to the head resulting in a lower impedance. 2 8 ohm cabs give you 4 ohms, 2 4 ohm cabs give you 2 ohms, etc.

I thought that for a long time too, but after I started building and repairing cabs, I learned.
 
#38
He might mean run the two 4 ohms in series to create an 8 ohm load, and then hook that up to the 8 ohm cab in parallel for 4 ohms. That's safe but kind of silly and requires some knowledge of how to wire stuff in series :)
 
#39
BassmanPaul said:
Single driver or multi driver cabinets are fine. It's when you have crossover components that you have to be more careful. In series the signal to each cabinet has to pass through the crossover of the other with sometimes unpredictable results.

Paul
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Correct.
 

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