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Yet another ohm question

Ron Now

Ron Now

Sep 3, 2003
3,312
756
41
Chicago, IL
www.bongripper.com
Disclosures
Endorsing Artist: Fuzzrocious Pedals
#1
I swear this will be my last one for awhile. I seriously did seach for some info on this but I couldn't get the exact info I was looking for

Is it bad to hook a 4 ohm load up to an 8 ohm head? That is all, thank you for your time (and sorry if this is already been discussed).
 
#2
Ron Now said:
Is it bad to hook a 4 ohm load up to an 8 ohm head? That is all, thank you for your time (and sorry if this is already been discussed).
Click to expand...

It depends on whether the amp has a Tube output stage, or Solid State.

Tube amps get seriously stressed if they're forced to work into an impedance that is much higher than it should be, so putting an 8 Ohm speaker on the 4 Ohm output tap would not be a good idea. Going the opposite way is usually less of a problem (i.e. putting a 4 Ohm speaker on an 8 Ohm tap), but ideally you should avoid this too, as you would still be running the output tubes under far less than optimal conditions.

In general, Solid State amps don't give hoot if there's an infinite impedance on the ouput terminals (i.e. no speaker attached!)*, but can be killed off very quickly by running into a lower impedance than their rated minimum, so puting a 4 Ohm speaker onto an amp with a recommended minimum of 8 Ohms is A BIG NO-NO.

(* I say "in general", because a recent enquiry to Ashdown's tech department produced some bewildering advice that their solid state amps should never be run without a speaker!)
 
#3
I say "in general", because a recent enquiry to Ashdown's tech department produced some bewildering advice that their solid state amps should never be run without a speaker
Click to expand...
They may have stabilizing capacitors and/or inductors on the output that might offer a low impedance in the abscence of a load.
 
#6
bassybill said:
More info needed really - 4 ohm speaker is clear enough, but what do you mean by an 8 ohm head? What data have you got about the head in question and what model is it?
Click to expand...


The head would be one of those Gallien Krueger backline amps the 250 (125w at 8ohms) and I've got a 8 ohm 15" and an 8 ohm 4x10 I'd like to hook up to one (being a 4 ohm load)

*note this is not being used as a bass amp, but rather a rather big guitar setup that has both guitar and bass amplifiers running to produce a full sonic range from high to really low sub bass ranges*
 
#8
True, true, lower load then the SS head is rated for will put a lot of strain on the amp, it is like this basically:

Your amp is a guice generator output 8 Ohm is a tap size that is matched with 8 Ohm bucket it will fill the bucket and have enough guice flow. If you open the tap too much for a bigger 4 Ohm bucket, your amp needs to work twice as hard to keep up the flow. It might make it but likely it may cook.

Actually you can run tube output with mismatched load quite a bit safer then SS, I have done it in the course of many experiments.
 

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