Input requested

I think I can help you with the break-up problem. Before you change anything else, try putting the Goertz spkr cable aside and substituting -- not permanently; just for the purpose of this experiment -- some generic zip cord or $1/ft Monster or Radio Shack/Home Depot Monster clone. You may find that the problem is gone.

As VP of Threshold Corp during the "golden years" of the Forte' 1A and Model 4, I can tell you that THAT amp does not get along with highly capacitive cable.

If the experiment turns out as predicted -- please let the Forum know either way -- and if you do decide to switch speaker cables, there are many types that have more compatible specs: Cardas, MIT, Kimber, AudioQuest (I'm not familiar with the new models that need batteries), Monster, and TARA Labs, among them.

Best of luck!
Joe Abrams

Mprime: If you are running Goertz speaker cables without the Zobel networks, you ARE going to damage your amp ( if you already haven't ). This is especially true with Threshold / Forte' amps. Having said that, the Forte's with Goertz MI-2's are a fantastic combo IF using the Zobel's. I've run various Forte' amps into Goertz MI-2's or MI-3's into speakers that are 82 dB's and 2 ohms at high volumes for sustained periods of time with no problems. According to what Joe said above, i've put my own gear "at risk" doing this for several years, so i know that it can be done and done with NO fear whatsoever.

Other than that, I've run the flat Goertz speaker cables with every amplifier i've ever had and never had any problems. That is, so long as the Zobel networks were properly installed. Given that some amps have built in Zobel's or "high frequency protection", using external Zobel's may be redundant. If in doubt, ask the manufacturer of the amp. If the amp doesn't specifically mention having high frequency protection in it, USE THE ZOBEL's !!!

As some of you might have read, Kal Rubinson ran into high frequency oscillation with a recent Adcom amp that he reviewed. Kal uses Goertz MI-2's in his system. Had Kal used the Zobel's to begin with, he would have never had ANY problems. He stated that once he was able to figure out what was going on and installed the Zobel's, the problem was cured.

As most of you know, i have stressed time and time again that the Zobel's should NOT be considered "optional" for most installations. I have mentioned this to Goertz, but they seem to have their head buried in the sand on the subject.

As to Mprime's specific situation, my thoughts are that you are probably running out of peak power / dynamic headroom. If you like the sound that you're achieving but want more dynamic punch, pick up a Forte' 6/6A and bi-amp. This is basically the same amp as the 4 / 4A, but run in AB mode and rated at 200 / 350 wpc. Using this to drive the woofers with the 4/4A running the top end will give you the sweet airiness that you're used to with greater "dynamic wallop" and headroom for louder passages. Sean
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* Due to their design, Kimber "8" series ( TC / VS / PR ) cables are also high in nominal capacitance per foot. While not nearly as high in capacitance / low in nominal impedance as the Goertz, it is possible that they too may cause high frequency instability in certain designs. The use of a properly designed Zobel will not hurt the performance of a system and can actually increase stability in areas with high levels of RFI. In fact, there are companies marketing Zobel networks as "speaker filters" at very high prices ( for what you get ). Don't be afraid to use a Zobel and / or speaker cables that are designed to achieve maximum bandwidth with a low nominal impedance. Using anything else will compromise the results to one degree or another. Sean
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First, thanks for the replys Joe and Sean (especially since I could have been damaging my equipment!). It turns out I had the Zobel's factory installed, so if Sean's correct, then I should not have damaged my amp. Still, I took the Goertz out for the time being and returned to my AudioTruth Midnight speaker cables. I am too tired to listen critically, but I will say the sound is fuller though less controlled on the softer passages (when contrasted against the Goertz). Too late to play loud and assess the more dynamic passages.

I'll give them both a good listen tomorrow and get back on the results. It will be interesting if the issue is a power or cable one, rather than the limitations of the 805 - a myraid of concerns flow either way :-(

Best,

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.

Mprime: i did not take your response as being "hostile" or "challenging" and i hope that you didn't perceive mine in that fashion either. I was simply trying to ask questions to get you thinking about the big picture and provide a point of reference via the links and explanations given.

As far as your comments go about the electrical characteristics of the cable combining with the electrical characteristics of the speaker to form an even more complex load to the amp, i agree. I have stated many times that cables act as an impedance transformer between mating components.

Having said that, the factors involved here are massively variable from combo to combo due to the lengths of cables / actual speakers used. As such, it would be hard to come up with "generic" equations that are representative of all possible combinations in terms of potential high frequency inter-action levels.

On top of that, given the typical length of speaker cable involved in most "audiophile" type installations ( relatively short ), the amount of capacitance involved with the flat Goertz isn't cumulative enough to really play havoc in the manner that you suggest. Now if one were to use a very long quantity of their MI-3's ( their heaviest gauge / highest capacitance model ), i could see some potential problems possibly arising from this. The "but" here is that much of how influential this was on the system would have to do with what type of load the loudspeaker itself produced at or slightly above the audible treble region.

As a side note, are you leaving your Forte' powered up 24/7 or turning on as needed? These amps sound SO much better after being powered up continuously that it's not funny. My findings are that 48 - 72 hours after initial turn-on, what you hear is what you get. Obviously, the main concern here is heat dissipation and power consumption. Given that this is a Class A amp, it will run quite warm and dissipate a lot of heat. As such, it's not a good amp to have encased in an enclosed rack or even an open rack with a shelf directly above it. If your rack is open to the sides and you can provide appr 6" - 8" of open space above the amp, you should be okay. Even at that distance, the shelf right above the amp will still get noticeably warm.

Based on my personal experience with these cables i had never gotten the "liquid" midrange response or "soft, delicate & airy" highs from any cabling that i had tried until i switched over to the flat Goertz cabling several years ago. Until that time, treble response was always "splashier" with less definition, more smearing and suffered from reduced harmonic structure. I had attributed much of this to reduced skin effect ( even Audioholics comments that Goertz cabling are one of the few that can actually make this claim ), a lower nominal impedance resulting in improved loading conditions and the fact that there is one consistent length signal path for the entire frequency range to travel ( solid vs stranded ). Either way, my results with using this same exact cable cable and same brand of amp is VERY different than what you are describing.

To add further confusion to the issue, i've been "upgrading" my Father's system over the last few years for him. After replacing his tubed preamp with an SS preamp of another brand ( FAR superior sonics in every aspect ), replacing his two channel amp with a five channel model of another brand ( FAR superior bass control and smoother treble ), installing a hand built DAC using audiophile grade parts ( FAR superior sonics in every respect, especially liquidity and spatial characteristics ), trying over a half dozen different digital cables, etc... my Father was the most enthused with his system after we replaced his Audioquest speaker cabling with Goertz MI-2's. His own words were "I think that those cables made a bigger difference than all of the other changes combined". While i don't agree with that, i told him "the Goertz cables finally let all of the cumulative upgrades further up in the signal chain shine through". In effect, it was kind of like adding icing to what was a potentially very tasty cake.

Even though all of the components were the same, the difference in "musicality", presentation and "texture" were extremely and vividly different when the AQ and Goertz cables were in the system. I ended up taking this a step further after we gutted and modified his speakers, which took things another step forward. I'm now working on his AC system, which should provide further gains in terms of increased liquidity, reduced grain and glare, improved dynamics and an overall lower noise floor.

There is one factor here that i've not really thought about. That is, the Zobel networks. I've never used the factory supplied Zobel's. I've always built my own using higher grade parts. While i don't know how much this would alter what you are hearing ( it really shouldn't ), i know that Jon Risch at AA is pretty adamant about using the best parts possible for a Zobel. While i would not recommend removing the Zobel's from your cables with this specific amp, you might want to think about replacing the existing Zobel's with some hand-built pieces. I don't know whether or not this will solve your problems or take you a step forward, but other than looking elsewhere in your system for potential solutions, that's about all i can suggest. The bottom line though is that you have to run what you like and think works best. Nobody will ever fault you for that. Sean
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zobels and rc networks are clearly audible. better parts result in better sound. and oh my goodness when you cryo them.
second, lee hasn't said so yet but he was experiencing a tank circuit and that was the source of his hf resonance. the use of 2 filters in a circuit results in a hf resonating circuit or tank circuit. make sure that your amp is not terminated with a zobel when you are using an external one or the same thing will happen to you. phone the amp manufacturer to be sure.
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