Speaker Ohms vs output transformer

Speaker Ohms vs output transformer

Postby claytushaywood » Fri Feb 03, 2012 12:32 pm

So i've heard a theory from a legendary tone guru about having a single speaker per pair of power tubes. And I got to thinking that i've always dug single 12" amps and it would be nice making my amp so much lighter!

I've read its "okay" to run old fender amps with say a 4ohm output transformer with speakers of higher rating, but lower is usually not safe. I want to run a fender with a 4ohm tap with an 8ohm speaker (the speaker will probably actually meeasure in the 6ohm range. would this be a problem?

my main concern besides amp health is that this is a common "mod" for people that want to get less headroom out of there amp. it apparently makes the amp run harder and pushes the speaker harder of course (spoken in terms of having 2 8ohm speakers in paralell and disconnecting one speaker) But I also know that my 4ohm fender amp was built with an additional "ext speaker out" that allows you to connect another speaker cab in paralell. I'm assuming the engineers realized that you woulld have 4 ohms and probably connect another 4 ohm cab in paralell, giving you 2ohms. so is the amp made to run better under 4ohms (as two "8ohm speakers" that actually measure 6ohms would give you 3 ohms in paralell).

Simply put what would be the affect of running a 4 ohm fender silverface pro reverb with a single 6.2ohm speaker? bad for amp? less headroom? sweeter sound (ive heard this opinion before as well)?

Thanks guys! Sorry this is a newb question, i know
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Re: Speaker Ohms vs output transformer

Postby FretfulDave » Fri Feb 03, 2012 1:58 pm

claytushaywood wrote:So i've heard a theory from a legendary tone guru about having a single speaker per pair of power tubes. And I got to thinking that i've always dug single 12" amps and it would be nice making my amp so much lighter!

I've read its "okay" to run old fender amps with say a 4ohm output transformer with speakers of higher rating, but lower is usually not safe. I want to run a fender with a 4ohm tap with an 8ohm speaker (the speaker will probably actually meeasure in the 6ohm range. would this be a problem? ...


I was looking for information sort of along the same lines but more with respect to the new Fender Super Champ XD head and running a 4 ohm speaker cab, what the transformer does and such. I came across this reference written by Mr. Hartley Peavey about transformers and impedance, tube and solid state. A bit long but seems to explain what the issues are for transformers and speaker impedance. If I read it right, it would appear to be how well the amp is made and how good the transformer is... however this doesn't answer your question directly.

Anyway, it's interesting stuff.

http://peavey.com/support/technotes/har ... pter_7.pdf

Good luck and good reading.

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Re: Speaker Ohms vs output transformer

Postby bstormwind » Tue Feb 07, 2012 7:17 pm

I understand that a mismatch within a factor of two or so is fine for fender amps, especially when matching an amp with higher ohm speaker(s). I have read from somewhere, believe it was a recent issue of premier guitar mag that it acts like an attenuator -to run a 4ohm amp like twin or pro reverb for example with a singLe 12 inch 8 ohm speaker. Seemed like a perfect thing for me to try as i found 2 e120's loud for the venues I play and too heavy to justify schlepping around. Well i really been digging the tone usingn1 e120 and has seemed perfectly fine for my amps. Currently have 1 e120 in my pro reverb (40 watt amp) removed the other stock speaker and now have a more portable great sounding rig. Loving it so far. And plenty of clean head room and maybe a little more hair when i push the amp with my blaster equipped strat compared to when i used a proper 4 ohm load. A nice option to save a liitle weight but not sacrifice tone. just my experience fwiw.
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Re: Speaker Ohms vs output transformer

Postby claytushaywood » Fri Feb 10, 2012 1:42 pm

bstormwind wrote:I understand that a mismatch within a factor of two or so is fine for fender amps, especially when matching an amp with higher ohm speaker(s). I have read from somewhere, believe it was a recent issue of premier guitar mag that it acts like an attenuator -to run a 4ohm amp like twin or pro reverb for example with a singLe 12 inch 8 ohm speaker. Seemed like a perfect thing for me to try as i found 2 e120's loud for the venues I play and too heavy to justify schlepping around. Well i really been digging the tone usingn1 e120 and has seemed perfectly fine for my amps. Currently have 1 e120 in my pro reverb (40 watt amp) removed the other stock speaker and now have a more portable great sounding rig. Loving it so far. And plenty of clean head room and maybe a little more hair when i push the amp with my blaster equipped strat compared to when i used a proper 4 ohm load. A nice option to save a liitle weight but not sacrifice tone. just my experience fwiw.


Cool! This is exactly what I was thinking! Except now I am supposed to pick up two k120s... maybe I can sell one! we have really similar setups by the way! I'm using a strat with a blaster (in a box at the moment) into a pro reverb
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Re: Speaker Ohms vs output transformer

Postby gr8fullfred » Fri Feb 10, 2012 1:54 pm

Hint:

If you need to sell a K-120, this board just might be the place to do that!
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