mo' better bass: any substitute for watts?

Saki70, I don't like the word 'synergy' as it suggests that we are going to balance one defect against another, and I think that in the case that we are talking about, the word is 'compatible' and the answer is 'yes'.

Loop and global feedback are the same thing. Zonal is usually the same as 'local' and may or may not be loop feedback, it could also be degenerative feedback. They are all forms of negative feedback, and there is a lot of verbal shorthand around, so you have to be careful.

I think what is important if you use feedback is that a) the amplifier must be fast and low distortion to begin with and b) the feedback be low enough that the odd-ordered harmonic enhancement is kept out-of-band. That really does not allow for very much feedback in practice.

The ZERO is the only autoformer I know of (we used to make a similar product called the Z-Music autoformer years ago). The concept is all about problem solving- this or that amp can't drive a speaker load that low so here's a solution to that problem. Given that that is the case, they work very well indeed. But if you had a 16 ohm speaker to start with that would be better :)

Yes , compatible may be a better term to use .

Not necessarily using the autoformer for problem solving ...

"The fact of the matter is no transistor amplifier sounds right on 4 ohms, nor does any tube amp. If you want to really see what either one is really capable of, you need a higher impedance -16 ohms is nice- to do that."

but trying to achieve maximum potential within a present 4 or 8 ohm setup , inexspensivly..."Its all about money". Could we hear an improvement with this usage ? And how would a 16ohm speaker operate on an amp that has 4 & 8 ohm speaker taps ?

We all have read where a higher db. rated speaker is an easier load to drive for lower powered amps such as SET's .
Where does the decibel rating figure into the rest of this discussion ? For instance would the higher resistance of a 16ohm speaker be able to counter the detriment of an 85db. rating ?

One heck of an informative thread here !

Thank you .

Atmasphere,

Thanks so much for taking the time to share your insights in this discussion.

My question is how can I tell by listening to a system whether use of negative feedback is having a noticeable negative effect on what I hear short of an a/b regression test between two comparable amp designs, one with and one without?

Also, as with most technology solutions, aren't some negative feedback implementations done better than others? Are there any that do it right to the extent that the negative effects are minimal or non existent?

Saki70, FWIW Steve McCormick, who has been making solid state amps for years, reports that his amps sound better driving a 4 ohm load though the ZERO, such that the amp is loaded at 16 ohms. His amps easily double power- they have no problem driving 4 ohms. I interviewed several solid state amp manufacturers at CES this year, and independently of each other they all concurred that while their amps easily **drive** 4 ohms, that due to effects withing the transistors themselves (which are exacerbated by more current) the amps **sound** better on 16. So much better, that using a set of ZEROs to do that is effective.

Transformers are inductors and so they ring if improperly loaded. Putting a 16 ohm speaker on an 8 ohm tap will mean that the transformer is going to add some distortion due to ringing, but the tubes otherwise will see a higher impedance load. Quite often, although they will make slightly less power, the distortion will go down too.

Mapman, you bring up a good point- feedback as a design issue can be tricky to sort out. Its the sort of thing that a designer or DIY person might tinker with and compare. There are so many variables that go into an amplifier/preamplifier design that it would be hard to ascribe something you hear in such a product to any one thing. You do have to work with the designs a bit in order to begin to sort out the sonic artifacts that different design considerations bring.

However we do already know that negative loop feedback contributes to odd-ordered harmonics in the regions that the ear uses as loudness cues. The contribution is slight- 100ths of a percent- but human ears are very sensitive to that sort of thing. We perceive this as 'brightness' or 'hardness'.Conversely, even ordered harmonics can be several orders of magnitude higher and our ears don't seem to mind.

I feel we are getting OT. If you wish to continue in this direction, let's start another thread :)

Atmasphere ;
Yes we are off topic but there is sooo much info here I would hate to break it up into two threads !!!

If you would address the db rating issue , that I asked about , I would consider this discussion closed .

I would also consider this thread one of the best primers here for the budding hobbiest ! You have dispelled some myths and misinformation for me and probably others as well . I would like to think of this thread as a "one-stop-shopping" area for those who want to learn how to do it right thus saving a lot of time , aggravation and money !
Sort of "System Building 101" !

I was planning on sending others to this thread when they had questions that were addressed here .

So , please can I coax just a little more out of you here ?

Thank you .