mo' better bass: any substitute for watts?

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 .

Saki70, with regards to efficiency vs impedance, to me they seem to carry about the same weight. However if the speaker is really low efficiency, you are going to have power issues driving it (BTW 'really low' is 87db or less). Given that that is the case, you are facing compromise- with tubes, 16 ohms would be favored, with transistors I might be tempted with 4, just because of the power issue.

I am a fan of higher efficiency. Good Quality tube power is expensive and I have yet to hear a transistor amp that is better, although being who I am you have to expect that from me :) I **have** heard some excellent transistor amps though (that I liked as much or more that many tube amps), however none of them were what I would call high power. So it seems that the high efficiency/high impedance rule is a good one to follow (so long as those qualities do not interfere with resolution or bandwidth).

Note: Sensitivity and Efficiency are two different ratings. Sensitivity is 2.83V @ 1 meter, Efficiency is 1 watt @ 1 meter. 2.83V into 8 ohms works out to 1 watt, but into 4 ohms its 2 watts. So a 4 ohm speaker can have the same Sensitivity as an 8 ohm speaker but actually be 3db less Efficient.

OUTSTANDING !!!

Thank you so much for your time and expertise !