Thunderfunk Amps

[hb3]

They're awesome, right?  
 
Here's another question. Concerning resistance. The Thunderfunk is 4 ohms. I'm currently using two 4X10 Bag End cabs at 8 ohms each. As I recall, running both cabs would be ok, but what would be the effect of running the 4 ohm amp into a single 8 ohm cabinet?
 
(Message edited by hb3 on June 13, 2007)

[dfung60]

Running one cabinet would be no problem.  Tube amps need to be set up to match the speaker impedance but solid state amps are fine with higher impedance.  The result will be lower power output however.  
 
What you need to be careful about with both tube and solid state amps is when the speaker impedance is lower than what it's rated for.  You'll get more power for a while, but run the risk of the amp running outside of it's ability to cool itself and self-destructing.  
 
What's happening here is that the lower the impedance, the more electrical current the amp can flow, and power output is proportional to the current.  This is a bit of an oversimplifcation for AC signals like audio, but is basically true.
 
David Fung

[hb3]

Thanks!  
 
What you need to be careful about with both tube and solid state amps is when the speaker impedance is lower than what it's rated for.  
 
You mean, lower than what the amp is rated for? Like, hypothetically, an 8 ohm amp into a 4 ohm cabinet?

[dnburgess]

hb - you shouldn't run a Thunderfunk amp with a 2 ohm load - i.e. two 4 ohm speakers is a no no.
 
Any impedence of 4 ohms or higher is fine.

[hb3]

They're 8 ohm speakers, so I guess I'm good. I'll probably try one.

[elwoodblue]

thanks to Marcky...I've used this a few time with great ease and success...
 
impedance calc

[elwoodblue]

...that's 'times'  
 
(...darn de-esser)

[dfung60]

With regard to minimum load impedance - you should ask the manufacturer what their recommendation is and honor that.  Depending on how they designed their amplifier and cooling, it may be 2 ohms or 4 ohms.  I doubt that you'll see anybody recommend a load less than 2 ohms.  Too much current flow and you'll let the magic smoke out, but all three of your wishes will be that your amp work again.
 
This is actually a very important consideration for people who run a stereo amp in bridge mode.  When you configure for bridge mode, you're setting one amplifier up to handle the positive side of your signal and the other to handle the negative side (a gross oversimplication, but effectively true).  This will give you a mono amp with greater output power, but the minimum acceptable output impedance is now twice what it was for each of the original stereo amps.  So, if you had a stereo power amp that had a minimum load impedance of 2 ohms you'd be fine with a 4 ohm cabinet connected to each channel and can run full bore all day until the police come over and tell you to turn down.  If you switch that same amp to bridge mode and connected up just one cabinet, you'd be running at the minimum load and possibly in danger of overheating.  If you were in bridge mode and connected up both cabinets in parallel, the sum load impedance will be 2 ohms and you'll may be looking at cooked output transistors before long.
 
David Fung

[hb3]

Well, here's what David Funk wrote to me about this:  
 
With an 8 ohm cab attached the amp puts out 300-watts. It's easy on the amp. With 4 ohms it puts out 550-watts. At 2.66 ohms it puts out 600-watts but is under strain.

[elwoodblue]

thanks David,
 I may someday need to run my stewart 2.1 bridged...I don't think I would of considered that immediately.
 (the thing is Loud in stereo!)