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impedance matching box

#21
As an experiment you could try digging out a mains transformer with a primary tapped for both 110V and 220V. There's a bunch in most electrical garbage heaps.

Try using it as an autotransformer to match impedances. Might work, and if so you'll have saved yourself a bunch of cash. (Make sure you're comfortably within the power rating, of course).

edit: actually, on reflection you may be better off using the secondary side because of the higher current handling ... same principle applies. watch the voltage on the primary though!
 
#22
It was in bassplayer a few years back. I misspoke when I said it added more power. I meant not running below an amps ohm threshold

Your power out was plugged into the box and then the cabs plugged into the box.

It allowed you to safely add cabs that had different impedance with out going below your amps level of ohms.
 
#24
+1
That car audio site is probably one of the most useful sites around.


It's totally amazing how high quality and powerful an amp you can get these days. It's like the capacity, reliability, and performance of hard drives keeps going up and up. A little lightweight amp blows the big heavy old amps off the stage.
 
#25
lowfunk99 said:
It was in bassplayer a few years back. I misspoke when I said it added more power. I meant not running below an amps ohm threshold

Your power out was plugged into the box and then the cabs plugged into the box.

It allowed you to safely add cabs that had different impedance with out going below your amps level of ohms.
Click to expand...

It was discussed on Talkbass a number of times, years ago. <Something-or-other> Mate, I think? IIRC it just used (or uses) series wiring when that's the only option that works. There's never been any free lunch and there still isn't.

Edit: found it, using my scary-ninja Google powers: [Invalid or Expired Link Removed].
 
#27
brendanbassist said:
I'm not disagreeing that the change in output will be significant (I don't really know about that), but it doesn't seem to violate any laws of physics as far as I can tell.
Click to expand...
The most obvious one is conservation of energy. You can't put 100 watts into one side of a transformer and get 200 watts out of the other. A transformer will allow voltage to be increased, with a corresponding decrease in current, or for current to be increased, with a corresponding decrease in voltage. Power remains a constant, save for that lost as heat in the transformer windings.
 
#28
By lowering the impedance seen by the amplifier, the
transformer allows more current (hence, more power) to
transfer out of the amplifier and, ultimately, to the speaker.
There is no magically created power. It all comes from the amp.
Isaac Newton can rest assured that none of the laws of physics
are broken.
 
#30
billfitzmaurice said:
The most obvious one is conservation of energy. You can't put 100 watts into one side of a transformer and get 200 watts out of the other. A transformer will allow voltage to be increased, with a corresponding decrease in current, or for current to be increased, with a corresponding decrease in voltage. Power remains a constant, save for that lost as heat in the transformer windings.
Click to expand...

So say I have a Carvin DCM1000, and an 8ohm cab.

The DCM1000 is -
700W @ 8 ohm
1000W@ 4 ohm

Driving the cab directly, I've got a maximum power to the cab of 700W.

Throw a 1:2 impedance matching transformer in between the amp and the cab. The amp now sees a 4ohm load and puts out 1000W into the transformer.

Coming out the other side of the transformer will be 1000W*transformer efficiency.

As long as the transformer is >70% efficient, the cab will be receiving more power... and no violations of the laws of physics required.
 
#31
billfitzmaurice said:
The most obvious one is conservation of energy. You can't put 100 watts into one side of a transformer and get 200 watts out of the other. A transformer will allow voltage to be increased, with a corresponding decrease in current, or for current to be increased, with a corresponding decrease in voltage. Power remains a constant, save for that lost as heat in the transformer windings.
Click to expand...

Perhaps you missed part of my post:


brendanbassist said:
...the transformer steps up that voltage but decreases current, keeping power the same at both ends of the transformer. ...
Click to expand...

Or this post:


brendanbassist said:
...the transformer would bump up the voltage to the load, and pull more power from the amp to do this. The amp sees a 4 ohm load, and thus outputs more current (and more power) than if the 8 ohm load were connected directly. (The transformer does not increase the power magically, it just forces the amp to supply more current, which is fine if the amp is still seeing a load above its minimum impedance.) ...
Click to expand...
:D
 
#32
aborgman said:
So say I have a Carvin DCM1000, and an 8ohm cab.

The DCM1000 is -
700W @ 8 ohm
1000W@ 4 ohm

Driving the cab directly, I've got a maximum power to the cab of 700W.

Throw a 1:2 impedance matching transformer in between the amp and the cab. The amp now sees a 4ohm load and puts out 1000W into the transformer.

Coming out the other side of the transformer will be 1000W*transformer efficiency.

As long as the transformer is >70% efficient, the cab will be receiving more power... and no violations of the laws of physics required.
Click to expand...


Your cab can't handle the 700watts let alone the 1000. I'll leave if for the real experts to describe but common sense tells me it's just another "magic box" that some folks will be hooked into paying good money for and then somehow try to trick their brain into justifying their purchase. It violates common sense, which sometimes is at least as strong as physics.
 
#33
will33 said:
Your cab can't handle the 700watts let alone the 1000.
Click to expand...

Actually, my fEarful can handle pretty close to 700W.

will33 said:
I'll leave if for the real experts to describe but common sense tells me it's just another "magic box" that some folks will be hooked into paying good money for and then somehow try to trick their brain into justifying their purchase. It violates common sense, which sometimes is at least as strong as physics.
Click to expand...

Note - I'm not saying one of these things is a good idea.

At best (assuming your cab can handle the increased wattage) you're talking maybe a couple dB. Basically nothing. Probably won't even be able to hear a difference.

I was just pointing out that it works. From a physics perspective - it does exactly what it claims to do, within bounds of transformer efficiency. Heck - it's the reason tube amps have multiple taps for different loads.
 
#35
dincz said:
No magic at all. It's an impedance matching transformer and they've been around almost as long as electricity. It does exactly the same thing as the output transformer in a tube amp.
Click to expand...

Agreed with a but! The problem lies with the power of modern day amplifiers. it's no good trying to match impedances with a transformer that cannot handle the power being put out by the amplifier.

You could actually use a regular tube output transformer just using the secondary windings. You would have to insulate all the primary connections for safety. Again the transformer will only be able to handle up to its rated power level. Hammond's biggest is rated 280W though you could probably be safe up to about 400W. That's almost nothing as regards power and costs somewhere around $200.
 

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