Ohmage question

[MacDaddy]

The pic is my cab.

Supposing I had 500w amp (minimum 4ohm load) which had 2, 8ohm speakon outputs.

Could I connect both amp outputs to both cab inputs to get the 'full' 500w, or would something nasty happen?

 

[MichaelDean]

I'm pretty sure you'd see some magic smoke. It'd be worth saying what your amp is or posting a picture of the speaker out connectors in case it says something you've missed or someone here knows more though. 

[Merton]

Magic smoke all the way.

You only need one cable from the amp to the cab, the cab will present its 4 ohm load and the amp will be happy.

[MacDaddy]

24 minutes ago, Merton said:

Magic smoke all the way.

You only need one cable from the amp to the cab, the cab will present its 4 ohm load and the amp will be happy.

 

But will the amp be giving the 'full' 500w? Or less watts at 8ohm?

[MacDaddy]

32 minutes ago, MichaelDean said:

I'm pretty sure you'd see some magic smoke. It'd be worth saying what your amp is or posting a picture of the speaker out connectors in case it says something you've missed or someone here knows more though. 

 

Not my amp. Yet...

[BassmanPaul]

There is no such word as ohmage unless it has an H in front of it!

 

The correct word is Impedance.

 

Never connect both outputs on an amplifier to the same speaker cabinet. Many amplifiers use two output modules that run in Bridge mode to produce more power than the single channel can provide. In Bridge, each channel is driven by. the same signal BUT with opposite polarity. Connecting them together will destroy both output modules. 

[MacDaddy]

1 minute ago, BassmanPaul said:

There is no such word as ohmage unless it has an H in front of it!

 

The correct word is Impedance.

 

Never connect both outputs on an amplifier to the same speaker cabinet. Many amplifiers use two output modules that run in Bridge mode to produce more power than the single channel can provide. In Bridge, each channel is driven by. the same signal BUT with opposite polarity. Connecting them together will destroy both output modules. 

 

Usage is the final arbiter, you'll all be saying it tomorrow! 😉

[BassmanPaul]

1 minute ago, MacDaddy said:

 

Usage is the final arbiter, you'll all be saying it tomorrow! 😉

I think not!

 

Your cabinet seems to have had a driver change.  Were the B&C drivers modelled to make sure that your cabinet was an appropriate  fit for them?

[warwickhunt]

Those Tech Soundsystems cabs are great cabs, just hope the new drivers were matched to the physical dimension of the box/cab.  

 

[warwickhunt]

1 minute ago, BassmanPaul said:

I think not!

 

Your cabinet seems to have had a driver change.  Were the B&C drivers modelled to make sure that your cabinet was an appropriate  fit for them?

 

SNAP

[MacDaddy]

Just now, BassmanPaul said:

I think not!

 

Your cabinet seems to have had a driver change.  Were the B&C drivers modelled to make sure that your cabinet was an appropriate  fit for them?

 

It was done by @Cosmicrain of this parish, so I assume so.

[Downunderwonder]

Most of the time it wouldn't make a blind bit of difference, but some amps would go poof. Best not to mess with the golden rule of one amp connection to one cab.

 

You'll get all the watts you're going to get with the one cable.

[Downunderwonder]

59 minutes ago, MacDaddy said:

 

But will the amp be giving the 'full' 500w? Or less watts at 8ohm?

The amp gives voltage. Power depends on how much load is on it. If it was a tube amp that would be different.

 

In this case the cab is 4 ohms according to the sticky tape note. You might trust it is still what it says it is 15 years later, or investigate further.

[tauzero]

When you say 2 x 8 ohm outputs, do you mean two speaker outputs each with a minimum 4 ohm load but with a minimum 4 ohm load overall, or do you mean two outputs each of which have a minimum 8 ohm load? If the former, you'll get the full whack from one output driving a 4 ohm cab, unless it's an Ashdown Superfly with two separate 250W power amp modules. If the latter, you'll simply blow it up if you connect the cab to the amp, regardless of how many cables you use.

[Downunderwonder]

8 hours ago, tauzero said:

unless it's an Ashdown Superfly with two separate 250W power amp modules. If the latter, you'll simply blow it up if you connect the cab to the amp, regardless of how many cables you use.

..or some other equally rare dual channel amp which escaped mention in the OP.

 

Rewiring of the cab to full stereo could overcome the possible unlikely issue.

 

Over to OP to clarify.

[Downunderwonder]

For completeness, most 500w amps are mono class D, either having a single output speakon jack or a parallel pair, rated for 4 or sometimes 2.6 ohms, sometimes switchable between 4 and 2.6.

 

Sometimes class D amps consist of an internally bridged pair of output stages and a pair of output speakons at whatever rating. A single cable is all that is needed to run one cab with full available power.

 

[MacDaddy]

9 hours ago, tauzero said:

When you say 2 x 8 ohm outputs, do you mean two speaker outputs each with a minimum 4 ohm load but with a minimum 4 ohm load overall, or do you mean two outputs each of which have a minimum 8 ohm load? If the former, you'll get the full whack from one output driving a 4 ohm cab, unless it's an Ashdown Superfly with two separate 250W power amp modules. If the latter, you'll simply blow it up if you connect the cab to the amp, regardless of how many cables you use.

 

18 minutes ago, Downunderwonder said:

..or some other equally rare dual channel amp which escaped mention in the OP.

 

Rewiring of the cab to full stereo could overcome the possible unlikely issue.

 

Over to OP to clarify.

 

It's an amp in the for sale thread. An Ashdown. If I can get the full whack from one cable I'll buy it, but I didn't want to influence anyone else buying just because it possibly doesn't do what I want.

[warwickhunt]

That's an odd plate/labeling.  Most, if not every amp I've ever owned (quite a few) that can operate at a min 4 ohm load has had 2 outputs BUT you could connect a single 4 ohm cab to either.  Saying that, the pic you show does seem to indicate that you can only get 4 ohm when connecting 2 separate 8 ohm cabs.  Very odd way to do things.

[BassBunny]

41 minutes ago, MacDaddy said:

 

 

It's an amp in the for sale thread. An Ashdown. If I can get the full whack from one cable I'll buy it, but I didn't want to influence anyone else buying just because it possibly doesn't do what I want.

So it's an Ashdown MiBass 550. Class D output section and those 2 output speakons should be connected together in parallel. A quick call to Ashdown will confirm. If so ONE cable to your 4ohm cab is all that is required.

Regarding the speaker swap, Mike Walsh used to be the UK distributor for TechAmp, when he had the Bass Merchant. He went on to launch Zoot speaker cabs, the best I've ever owned, and then Purple Chili. He knows his stuff.

Edited October 5, 2022 by BassBunny

[Downunderwonder]

40 minutes ago, MacDaddy said:

 

 

It's an amp in the for sale thread. An Ashdown. If I can get the full whack from one cable I'll buy it, but I didn't want to influence anyone else buying just because it possibly doesn't do what I want.

This is standard for a mono amp with parallel outputs. Two 8 ohm cabs = 4 ohms. One 4 ohm cab = ohms.

[stevie]

12 hours ago, BassmanPaul said:

There is no such word as ohmage unless it has an H in front of it!

 

Hohmage?🤥

[MacDaddy]

1 hour ago, Downunderwonder said:

This is standard for a mono amp with parallel outputs. Two 8 ohm cabs = 4 ohms. One 4 ohm cab = ohms.

 

Sorry, One 4 ohm cab = how many ohms?

[nikon F]

2 hours ago, MacDaddy said:

 

Sorry, One 4 ohm cab = how many ohms?

two 8 ohm cabs wired parallel = 4

one 4 ohm cab = 4

 

[Downunderwonder]

6 hours ago, MacDaddy said:

 

Sorry, One 4 ohm cab = how many ohms?

The ohms limit.

[tauzero]

5 hours ago, Downunderwonder said:

The ohms limit.

 

Ohm on the range.