Input requested

I saw your thread yesterday, but was a little reluctant to respond, with what I thought the problem might be.I then saw "Joeabrams" reply, and said Joe nailed it. When I checked again this morning, and saw "Sean's" reply, I said there is the frosting on the cake, and it looks like an easy, inexpensive fix...Your reply of already having the Zobels in place, then brought me back to my slightly out of the box thinking.

So here goes... I viewed your system, and I noticed a smallish room 10x14 with a wall mounted shelf.

Could it be, when you turn up the volumn, that enough energy from the room's primary resonate frequency point is exciting the wall, and shaking your wall mount shelf, which would shake the the preamp, and it's tubes. Heck, if you can yell into a tube directly, and have the sound of your voiced reproduced at the speakers, then why couldn't a vibrating wall induce some distortion into the tubed preamp, and have it appear as breakup at the speaker during loud passages.

Can you temporarily replace the tube preamp with a solid state unit, or move your tube pre from the wall mount temporarily. Another thought would be to try some sort of tube damping device.

A/gon member Jax2 (Marco) complained of a very similar problem awhile back, but I fail to reply then, again do to my reluctance, and lack of experience with tube equipment.

I told you it was slightly out of the BOX thinking.

Good Luck, Dave

Nelson Pass' designs are no more sensitive to high capacitance cables than other wide-bandwidth solid state amplifiers.
Painting with a broad brush, solid state amps whose high frequency response extends well beyond 20k can become unstable when used with a high capacitance speaker cable. My comment regarding the Forte' 4 was meant to get that point across to a user who might be having that exact problem.

Generally speaking: if you have a solid state amp that does not have a transformerized output, it's not a good idea to use high capacitance cable -- most times these cables can be recognized by their shape; either very flat or very skinny. Also, any cable whose marketing literature says that "inductance must be avoided" is highly suspect. Inductive cables are fine for solid state but not for tube amps. High capacitance cables are fine for tube amps, but not for solid state.

Following up....

After switching out the Goertz MI2 biwire with the AudioTruth Midnight (four solid copper stands per, biwired), here are my initial conclusions:

a) my breakup problem has been attenuated somewhat with the AudioTruth, though not entirely.

b) the Goretz is a flatter sounding cable when contrasted against the AudioTruth which is rounder and fuller.

c) the Goertz has less air when contrasted against the AudioTruth. For example, cymbals are tight and light with the Goertz whereas the AudioTruth offers a splashier and airier sound.

My working hypothesis going forward is I need more power to address the breakup problem and I need to work with a different speaker cable to get the sound I am looking for. On the speaker cable, I like the Goertz's focus and crispness, and quite honestly, am not obsessed that my cymbals don't splash and air and tweak my right nipple :-) So I need to find a better design than the AudioTruth to deliver the focus of the Goertz without the associated flatness.

I also feel compelled to wonder aloud the objective issues which lead to these subjective differences. First, there is no doubting the Goertz's superior ability to deliver the signal it is fed to the load. It is a measurable fact. But why doesn't that deliver a superior experienced sound? I wonder if the Goertz's objective measurements are on an actual load or a resistive load, for as the inducive impedance increases at the higher frequencies, the capacitive impedance goes down; thus, the Goertz itself would offer a more attractive path for the signal than the speaker, which would result in some loss of high frequency signal to the speaker. Sean, I would be curious to hear your response to this hypothesis.

As for tube microphonics, Dave, you may be right. I am new to tubes and have much to learn.

Thanks to all who have offered input. Joe especially.

Best,

Joe: Most SS amplifier designs aren't as wide-bandwidth as most of the Threshold / Forte' designs. On top of that, these designs are also different than many other designs in terms of negative feedback and how it is applied. As such, not all SS amps are created equal and / or will respond in like fashion to a high capacitance cable. Please bare in mind that i'm NOT being critical of these designs / products as i'm a great fan of them. I'm simply pointing out that they have the potential to develop problems if certain areas of operation / system building are not properly dealt with.

As i've mentioned before, my beliefs are that system performance has to do with proper impedance matching. The only way to properly match the interface between the output of an SS amplifier and most common speakers would be to use a high capacitance / low inductance speaker cable.

As to your comments about high capacitance cables being "very flat or very skinny", i would beg to differ. Several high capacitance / low inductance designs make use of a large bundle of wires arranged in some type of a round and / or thickly braided array. On top of that, there are other cables that are quite high in inductance / low in capacitance that are "very flat or very skinny". As such, your generalization as to how to recognize a "high capacitance" speaker cable could be quite misleading.

As a side note, Nelson Pass himself wrote a rather lengthy and detailed article about the amplifier / speaker cable interface after running into various "high capacitance / low inductance" fiasco's with his earlier Threshold designs. In this article, he specifically states that both he and Matt Polk individually arrived at much the same conclusion at the same time. That is, the installation of a Zobel Network at the speaker terminals pretty much solves all of the problems associated with high capacitance / low inductance speaker cables.

In this regards, my findings and statements simply confirm what Nelson published 20+ years ago. While i'd like to say that great minds think alike, it would be far more honest of me to say that much of what i know was derived from "audio greats" ( such as Mr Pass and a few others ) that i highly respect and admire. Most everything that i post here or on any other audio forum has already been said before by others that are FAR more knowledgable / experienced than myself. I simply try to pass on the knowledge / experience that the experts have passed on to us and i've personally accumulated over the years.

Mprime: If the MI-2's are linear in power transfer, primarily due to very low inductance, and maintain a consistent series resistance to beyond 100 KHz, which is better than ANY other cable on the market, how could it be detrimental to the treble response that you are encountering?

With that in mind, isn't it possible that what you are encountering IS NOT that the Goertz is "detrimental" to treble "shimmer & air", but that the other cable IS introducing its' own "sonic artifacts" into the system because it isn't as linear??? If we study the facts, this is not a case of "the piano has been drinking" while the pianist is sober.

What i'm getting at here is the output of the amp is identical to what the Goertz feeds into the speaker at the other end i.e. a mirror image. If you look at figures 5, 6 & 7 here, you'll see EXACTLY the same input / output curves from 100 Hz up to TWO MEGAHERTZ ( this is WAY beyond the audible range ) using the Goertz MI-2's. This is with or without the use of an impedance matching ( Zobel ) Network!!! The Zobel, as used in figures 6 & 7, simply flattens out the response above 2 MHz and helps to stabilize certain amplifier designs. It does not in ANY way alter the linearity of the cable anywhere near the audible range.

Now compare the same tests using "less technologically advanced" speaker cabling. As you can see in Figures 8 & 9, the signal at the far end of the speaker cable doesn't come anywhere close to what the output of the amp tried to load into it. This is with or without the impedance compensation ( Zobel ) network. While the amp is making it out to well beyond 100 KHz, the signal at the far end of the speaker cables is starting to nose-dive at 20 KHz.

In effect, the higher inductance of the speaker cable introduces high frequency roll-off. This will in turn introduce poorer transient response, increased phase shifts, smearing and distortions within the audible upper treble region. The end result is LESS natural sound and an increase in high frequency Td ( Time delay ). Since we know that this isn't anywhere near being "accurate" ( what goes in = what comes out ), choosing to use a cable that introduces specific distortions and / or sonic colourations would strictly be a matter of personal preference.

As i've said before, don't blame the Goertz for showing you what you've got. While you might not like the sound of your system with the Goertz in it, the Goertz is doing nothing less than revealing the true nature of your system. No band-aids, no side effects, just wide-bandwidth linear power transfer. The end result is an increase in system transparency.

If used properly, this can be an effective tool and part of a system foundation that allows one to pinpoint just what the flaws are and where the deficiencies are originating from. After all, if we purposely distort the signal between the amplifier / speaker interface, how can we ever hope to hear any sonic improvements upstream? Since we can't, wouldn't it be more logical to stick with what we can verify / know works the best possible and then try to "guess" / experiment with other things that are more system / component dependent ( like interconnects ) ??? Sean
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Sean writes: "If the MI-2's are linear in power transfer, primarily due to very low inductance, and maintain a consistent series resistance to beyond 100 KHz, which is better than ANY other cable on the market, how could it be detrimental to the treble response that you are encountering?"

Because the measurements you cite come from a purely resistive load; when one considers the complex load of the speaker in series with the cables (which is exactly what the amp sees in an actual application), one can use their understanding of how such circuits work and form working hypothesis.

Sean writes: "In effect, the higher inductance of the speaker cable introduces high frequency roll-off. This will in turn introduce poorer transient response, increased phase shifts, smearing and distortions within the audible upper treble region."

Once again, I agree with a purely resistive load! (btw, it is exactly this argument and supporting data you put forward which led to my purchase) But it is nothing more than introductory electronics to understand that capacitance across a complex load will shunt the higher frequency components through it - especially if the series load is inductive (which a speaker is). So, again, the working hypothesis remains....

Of course, your hypothesis would be: within the audible frequency range, there is no attenuation of the signal into the *complex* load. Therefore, what I am hearing is *greater* control of the tweeter which is giving my ears what the signal actualy is (thus, the "air" that I hear is nothing more than sloppy control of the driver).

Now we're exploring which hypothesis explains observed and which is the better explaination is now open to objective inquiry. If you, or anyone else in the forum, have done such measurements, then that would prove invaluable in my understanding of this confusing topic.

As an aside, I am hardly trying to provoke or challenge you, Sean. There are enough flamefests which take place without a relative newbee adding to fray. Instead, I'm trying to understand and have framed the discussion in the most constructive way I know how.

Best,

Lee

a.k.a.