The A-B challenge: update
We have today been asked by a prospective volunteer if we would redesign the test, deleting the A-B switch (introduced in post #6, purpose explained #28, construction and parts list in post #44) and permit him to listen for ten minutes or so to a track, change the amplifier and listen again.
Since this entire thread, and the over 35,000 internet viewings on sites that have reported this thread, is focused on the instantaneous nature of the relay-operated A-B switch, we have declined and asked the poster for his permission to post his approach here. If we receive permission, we will post it and our response. In our view, that suggestion is a wholesale re-write of the terms we laid out so clearly at the beginning. We remain significantly flexible about the precise details of the procedure, have a completely open mind to any equipment/brands/models the participant may wish to bring providing that they are of broadly comparable technical performance (i.e. are checked here that they measure well into a real-world speaker load) but the A-B relay switch is an absolute must-use.
The whole purpose of this thread, as explained in the above posts is to illustrate that under (blind, level matched) instantaneous A-B listening comparison the listener may arrive at a different opinion about the two items under comparison compared with his sighted, non-level matched opinion. There are frequent postings here on HUG asking the question 'what amp should I upgrade to'. As I have stated before, a reliable answer - the best answer I'd say - is to factor in styling, cosmetics, features, after-care, brand image and the like as primary purchase motivators, and give the vague 'sound quality' the correct weight in the purchase decision. A good dealer, working with a brand from the inside, should very well know about their after care support and be able to advise on this. As I said in post #6:
I am certain that there are many alternative, equally valid, comparative tests that can be conducted on any manufactured engineering-based product such as audio equipment. Some would use measurement equipment solely, some listening solely: it's not for us to claim exclusivity over test methodology. What we are saying, and I repeat this for the very last time is this from post #28:
Amplifiers should be selected not for "sound quality" (whatever that is) but for facilities, design integrity, durability, after care and likelihood of being able to source service parts in 5 or 10 years. Also, if you're really serious, a quick peek at the financial standing of the brand might tell you if they are likely to have the financial resources to weather the economic downturn of the next few years which is effecting the whole consumer electronics sector. Some of the most likely surviving (UK) brands rarely advertise, rarely exhibit, have relatively old-fashioned designs, use standard parts, have been around for a generation and are rock solid businesses. They deserve to be respected and supported because they will be there to look after you in 10+ years.
Comparisons which remove the instantaneous relay switch-over arrangement may or may not be valid - we cannot comment on that - but they are a different sort of test to the one we propose, and have proposed from the start. They are not what this thread is about. The absolute minimum elements for our test are the use of precision instrumentation to be certain about the loudness of A and B at the ear and the instantaneous way of selecting A or B. Other tests, approaching the matter from alternative directions would not mandate these elements. But we do. They are absolutely non-negotiable.
1) We definitely, 100% do believe that people (including me) can, do and will hear differences between amplifiers randomly put in front of us, hooked up, switched on and turned up!
2) We have observed that for psychoacoustic reasons that we do not understand or pretend to understand, when those very same amps are level matched (with test equipment) and then connected to a good quality relay change-over driving one pair of speaker, that when the change-over is operated entirely at random, those big initial differences heard in 1) diminish to little or nothing. So much so that it's actually not possible (in many instances) to hear any discontinuity or change in the music at all, except the minute gap as the relays flick over - perhaps one thousandth of a second. Even that may not be audible. Surprising, yes it is to me as well. This is, I agree, counter-intuitive.
As at today, we have not received one proposal to run the comparison as we defined with the switch-over box. There is one week remaining.
Alan A. Shaw
Harbeth Audio UK