Tube Amp for Martin Logan Speakers

Clipping is always the devil to avoid when chosing an amp for speakers. Effects of clipping start as subtle and increase to major. Whatever the speakers, be sure to chose an amp that is well beyond being up to the task. Most speaker vendors quote minimum or recommended amp power rating that are suitable to get decent results for most, but not suited to get the best results possible, which is what audiophiles seek. Result is many underpowered systems out there over the years and that is valid fuel for the argument towards speakers that present an easy load.

High efficiency/easy load speakers are a viable solution to the problem, but no the only one, especially these days. Amp technology has progressed and offers major improvement in efficiency these days as well. Monster heavy and big power amps ala traditional Krell, etc. are no longer the only robust option. Class D amps are lightweight, small, efficient and offer more power for the $ than ever.

SO do not disregard modern innovations in amplifier technology when assessing options. THere are more good and affordable ones out there than ever, especially when TCO is considered.

Also, use of powered subs to offload the heavy work in the bass is another very practical tool to choose. WHen powered subs are used (most use Class D amps to very good effect here) a lot of the issues with matching speakers to amps that exist otherwise tend to go away in that the main amp is asked to do much less to drive the speakers optimally than otherwise.

Also when playing vinyl, always make sure rumble and subsonic noise in herent in many phono setups is managed properly and under control. Otherwise, most of the amps headroom will be used to produce noise. High efficiency/easy load speakers might be a band aid in this case, but not the solution.

Well stated Mapman! :)

I think the EPDR link I provided supports Ralph's comments that low impedance speakers may have an even lower EPDR rating than what is nominally reported or measured. Even more important is that speakers presenting low EPDR factors significantly contract an amp's so-called SOA.

I am not saying that 4 ohm speakers are not good performers. Just that a nominal 4 ohm load in the bass region may really squeeze the amp and possibly result in a referral to the SPCA. At a minimum, a less than optimal amp/speaker match may, as the article explains, result in distortion. So, I happen to think Ralph's comments make sense for the reasons set forth in the attached article.

Bruce

P.S. The SPCA is the Society for the Prevention of Cruelty to Amplifers.

BTW, as I read it; George didn't call you stupid, he called one of your suggestions stupid, and that was after you called him a "troll", which was after he posted a link where he recommend your product. This line of posting is somewhat out of character for you.

Hi Unsound, yes it is, and one should consider that I do refrain from that sort of thing as much as I can. Recommending the ZERO is something I have done a lot, and not just for our amps and I will continue to do so despite George's remonstrations. This is for no other reason than the ZERO really does work.

One other thing- to clarify, I am not stating that 4 ohm speakers are bad speakers. I am stating that any amplifier driving them will sound harsher and less detailed as opposed to the same amplifier driving the same speaker that was 8 ohms, were all other matters to be equal. Put another way, a simple method of making a speaker seem more transparent and easier to listen to is to make it be higher impedance.

This might be all about how important it is to an audiophile to have increased transparency/detail, coupled with a smoother presentation. I like those things myself.

Something I have not mentioned yet is the effect of the speaker cable on 4 ohm speakers- but it should be obvious that they are far more critical for a 4 ohm speaker than the cables are for 8 or 16 ohms. Damping factor of amplifiers is normally stated with respect to an 8 ohm load; that number is initially cut in half with a 4 ohm speaker. Add to that the seemingly low DC resistance of the speaker cable and the damping factor of the amplifier is reduced considerably more that one might intuit. RCA published a nomograph that showed this relationship several decades ago.

YEs, but realize that tube amps in general will distort even more than SS amps into 4 ohms, so if 4 ohms is part of teh puzzle, the answer is clear.

Any good amp, SS or otherwise can drive an easy load easier.

SO you have to look at all the pieces of each puzzle together in the right way , not take one piece from one puzzle and try to insert it into the the other and then blame it for not working.

Likewise, there is always good, better and best in any case/scenario. Its important to understand impedance and phase related issues in order to assemble the right pieces. Then you can assess system/puzzle A versus B however one likes, but better to look at the overall results than the relative deficiencies or strengths of any one element of design.

03-27-14: Atmasphere: do so despite George's remonstrations

Are you kidding, far from pleading with you Ralph.

I agree that an Autoformer is a great (pseudo) bandaid fix for whatever amp that cannot drive a speaker that is not a good match, because of it's inability to deliver current/wattage or is working out of it's SOA (safe operating area) A FAR BETTER FIX IS TO CHANGE THE AMP/S OR SPEAKERS!

You state that even a good solid state amp will measure less distortion on it's output from using a Zero Autoformer into a 4ohm load compared to 8ohm.

Yes I agree that with the Autoformer even a good solid state amp will measure slightly less distortion at it's output terminals at 4ohms (this is not to say it's out of it's SOA)
But it's what happens after the Autoformer (things like phase shifts, damping factor etc) that is far more detrimental to the sound than the slight increase in distortion before it without the Autoformer.

EG: What one would basically do to a good amp say like a Pass Labs, Krell, Gryphone or similar amp by sticking an Autoformer on it, is to turn it into the solid state series MacIntosh's that also use a type of Autoformer on their outputs, but without the benifits of using them within the amps feedback loop, to keep the (damping factor, phase shifts, etc) in check.

Cheers George