Once again --- Speaker load question

[Lazarus1140]

I am planning an amp head that will have secondaries for 4 and 8 Ohm speaker loads. I am planning to use a 1-12 cabinet for practicing at home, and when the need to move more air presents itself I will use a 2-10 extension cabinet. I love that within both the Traditional and Vintage series, the Avatar 1-12, and 2-10 cabinets are dimensionally identical!

I have several questions. First, I am assuming based upon what I've read on the net that I should try to use the largest (8 Ohm) speaker input as it uses the whole OT secondary winding. Obvioulsy it does, but whether the benefit is real or internet folklore I can't be sure.

Based on the 1-12 being my primary cabinet I would definitely use an 8 Ohm speaker there.

The simplest approach for adding the second cabinet would be to use two 16 Ohm speakers in the 2-10 cab, wired in parallel, and then wire the speaker out jack on the 1-12 cabinet so that thet two cabs together present a 4 Ohm load to the head and then use the 4 Ohm tap on the amp.

But, (ass)uming that using the full secondary OT coil would be somehow more beneficial (which again, I don't know) is there an optimal way to select speaker impedances and wire the 2-10 cab so that combined with the 1-12 I could still use the full 8 Ohm winding?

I can see how to combine the three speakers to achieve 12 Ohms, but what good is that?

 

[SlyFoxx]

Re: Once again --- Speaker load question

I don't see how you could. But (ass)uming when you add the second cab you are also going to be turning the amp up more as well...you'll probably get more tonal benefit just because you're driving the amp harder.

Or you could make two 4 ohm cabs and get the benefit of the 8 ohm tap when you need to move more air. (ass)uming you'd want the better sound for performance. Trouble is you have to hook them up in series which is a pain.

 

[glassman]

Re: Once again --- Speaker load question

First, I am assuming based upon what I've read on the net that I should try to use the largest (8 Ohm) speaker input as it uses the whole OT secondary winding. Obvioulsy it does, but whether the benefit is real or internet folklore I can't be sure.

It really is a myth...but like most myths, it started out as fact and got twisted into something it wasn't.

Electrically, the unused portion of the secondary is not there...if you hook your NFB loop to the unused tap, the few uA that it pulls has literally no effect. You can thank my 20+ years in quality/applications engineering in the magnet wire industry for that little bit of info!

My assumption is that the whole myth of the unused portion of the secondary having a tonal effect probably comes from the use of what's called an air-gap in single ended amplifiers...actually it's also used in generators too...the idea is to control core saturation. It basically creates several sub-coils within a coil, each at a different impedance. The problem is, and where the theory loses its basis is that an air gap is placed in the primary primary...it would have no effect on the secondary.

I'd set up your cabs as two 8 ohm cabs. That'll give you the flexibility of either sound or both when you need it.

The only drawback I see to your plan is that there aren't nearly as many 10" selections out there as there are 12".

 

[zzmoore]

Re: Once again --- Speaker load question

Have Heyboer wind you a 1 Meg OT. Just think of all those windings you will be using.....
The OT is just a reflected impedance between the speaker and the tubes. Do not worry about which tap you are into, let other guys do that.
Just use whichever works easily for the cab(s) you have.
Best

 

[Lazarus1140]

Re: Once again --- Speaker load question

Will do. I have much to learn. Thanks to all!