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Wiring/Ohms, please explain

P

Pandafist

May 6, 2008
512
8
Portland, OR
#1
Here's tis...

I'm running a 2/4 Ohm SVT CL (I leave it set to 4) through several different cabs and I was recently made aware that I might, unknowingly, be damaging my equipment due to mismatched Ohm ratings.
My room-mate says I can change the wiring in, for instance, my 500w/8 ohm Ampeg 410HE cab to make it a four Ohm. Something to do with parallel vs. series wiring.

Can anyone explain this without talking over my head like my room-mate so enjoys?

And also, I like to add cabs for different situations. I always start with the 410, sometimes adding an Ampeg 115 or a modified Sunn 215B depending on the job.
Does Ohm rating change when you use the parallel speakers out vs. when you chain the cabs. If so, how? What should I do here?
I'd like to keep using my cabs without damaging anything. I'm not unfamiliar with soldering so a simple wiring change would be a best case scenario.
Advice would really help me out here.
thanks
 
#2
Pandafist said:
My room-mate says I can change the wiring in, for instance, my 500w/8 ohm Ampeg 410HE cab to make it a four Ohm. Something to do with parallel vs. series wiring.
Click to expand...

4 drivers in a cabinet rated 8 ohms could be either: 8 ohm drivers wired in series pairs (16 ohms per pair) that are wired in parallel for 8 ohms, OR 32 ohm drivers wired all in parallel for a total of 8ohms - which is highly unusual.

To get a 4 ohm cab out of what you have, you would need either: 4 ohm drivers wired in series pairs (8 ohms per pair) that are wired in parallel for 4 ohms, or 16 ohm drivers that are all wired in parallel. Your room-mate is wrong.

Using both outputs or daisy chaining cabs both result in parallel impedance of both cabinets.
 
#3
Pandafist said:
I'm running a 2/4 Ohm SVT CL (I leave it set to 4) through several different cabs and I was recently made aware that I might, unknowingly, be damaging my equipment due to mismatched Ohm ratings.
My room-mate says I can change the wiring in, for instance, my 500w/8 ohm Ampeg 410HE cab to make it a four Ohm. Something to do with parallel vs. series wiring.
Click to expand...

Your roommate is wrong. +1 to the previous post

And also, I like to add cabs for different situations. I always start with the 410, sometimes adding an Ampeg 115 or a modified Sunn 215B depending on the job.
Does Ohm rating change when you use the parallel speakers out vs. when you chain the cabs.
Click to expand...

No. Unless you have a fairly rare amp that has its speaker outputs in series, either jacks or chaining through cabs is a parallel connection.

I'd like to keep using my cabs without damaging anything.
Click to expand...

Stop using the amp with just the Ampeg 4x10. Higher than rated loads are dangerous for tube amps and when you use only the 8 ohm 4x10, you are risking serious damage to your amp.
 
#4
OK, but...
I STILL don't know the difference between parallel wiring vs. series.
And how does wiring change your Ohm rating?

I'm sorry, but, you knowing the answer doesn't mean I understand your response. Laymans terms would be appreciated in this instance.
I need some specific instructions or a simplified explanation so I can instruct myself on how to re-wire this biznatch.
Thanks duders
 
#9
Psycho Bass Guy said:
Your roommate is wrong. +1 to the previous post



No. Unless you have a fairly rare amp that has its speaker outputs in series, either jacks or chaining through cabs is a parallel connection.



Stop using the amp with just the Ampeg 4x10. Higher than rated loads are dangerous for tube amps and when you use only the 8 ohm 4x10, you are risking serious damage to your amp.
Click to expand...

How is using multiple 8 ohm cabs safer than just one?
Does using two 8ohm cabs effectively make 4ohm resistance?
Oh god, this is just SO confusing to me!!!

After all these years, I'm still not sure I even understand what Ohm ratings mean or how I might be damaging my head by not matching them.
 
#10
Pandafist said:
OK, but...
I STILL don't know the difference between parallel wiring vs. series.
And how does wiring change your Ohm rating?
Click to expand...

Assuming the values on both cabinets/speakers are the same*, two in parallel are always half of one of them, ie, two 8 ohm cabinets = a 4 ohm load, two 4 ohm cabinets = 2 ohm load.

Series*, you add them together.

Different values combined gets trickier, involving taking the inverse of each, adding them together, and dividing into 1.

There is an Ohms FAQ, although I can understand you not wanting to wade through all of the posts there
http://www.talkbass.com/forum/showthread.php?t=144244
 
#11
Pandafist, try this water system analogy -

Voltage is like water pressure. Current is like gallons per minute of flow. Resistance is like (the inverse of) the size of the opening in the pipe.

For a given water pressure (voltage), a larger opening in the pipe (smaller resistance) lets more water flow (current).

As you decrease the load resistance (increase the hole size) there will be a voltage drop at the source (water pressure decreases) and the current flow through the hole (load) will increase. Your amplifier can be damaged by excessive current demand (too low a resistance) or excessive voltage (too high a resistance). There is an optimum load for its design.
 
#12
Ok, so from this point forward I will NEVER use just the 8 ohm 410 by itself (at least with my 4 ohm SVT CL).
However, let's say I'm using the 8 ohm in conjunction with an auxiliary 4 ohm. Should I then switch to the 2 ohm setting on my head? Or would 4 still be safe?
Or what if I used three cabs together? It's unlikely, but I'm just trying to understand.
If two were 8 ohms, and one 4, that means a 2 ohms setting, correct?
What if they were all 8 ohms?

AND>>>

how do I tell if I've already damaged my head if there is no noticeable change in it's performance? Does that mean it's still OK at this point or is there a possibility the damage is already done and I just don't know it yet?
 
#13
Pandafist said:
However, let's say I'm using the 8 ohm in conjunction with an auxiliary 4 ohm. Should I then switch to the 2 ohm setting on my head? Or would 4 still be safe?
Or what if I used three cabs together? It's unlikely, but I'm just trying to understand.
If two were 8 ohms, and one 4, that means a 2 ohms setting, correct?
Click to expand...

Either should be OK. Setting it for 4 ohms with a 2.67 ohm load (one 8 ohm and one 4 ohm cab) is safer, but a 2 ohm setting isn't instant death.

What if they were all 8 ohms?
Click to expand...

Two 8 ohm cabs are 4 ohms.

how do I tell if I've already damaged my head if there is no noticeable change in it's performance? Does that mean it's still OK at this point or is there a possibility the damage is already done and I just don't know it yet?
Click to expand...

It is possible that you have done damage that is not yet detectable. Arcs in your output transformer that may not have burned through their insulation completely may one day short and fail under heavy use. Tube damage would be immediate and obvious. Chances are that you haven't done damage, especially if you didn't play loud, but there are no guarantees. FYI, the SVT CL's manual and most answers from Ampeg support you'll get concerning this topic are wrong.
 
#15
now, what's the formula again for calculating different ohm ratings together?

more specifically. I currently have two 8 ohm cabs, and one 4 ohm.
Am i correct when i assume i should choose the 4 ohm setting when using any two together, but switching to the 2 ohm setting in the rare instance that I might want to use all three together?

thanks for all of your help here.
Any other analogies people might have concerning this subject would be appreciated. The water analogy really helped but there is still some grey area for me. CAUSE I'M APPARENTLY ********. JK... sort of. At least it feels like I am when I use this forum.
 

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