Amp required for cornerhorns

[Don Richard]

Great article which I'll show to some of my inveterate push-pull amp designer buddies with whom I constantly argue the virtues of single ended designs. I certainly agree with the statement, "As a result of its single-ended nature, the harmonic content of air is primarily 2nd order, and most of the distortion of a single tone is second harmonic. Air's distortion characteristic is monotonic, which is to say its distortion products decrease smoothly as the acoustic level decreases." Makes a great case for near field listening using a SET!

So what SET amplifier is Pass making these days? Is he currently making any tube amp? What I saw were solid state designs, mostly FET based, both single ended and PP. Did I miss something?

[tube fanatic]

Great article which I'll show to some of my inveterate push-pull amp designer buddies with whom I constantly argue the virtues of single ended designs. I certainly agree with the statement, "As a result of its single-ended nature, the harmonic content of air is primarily 2nd order, and most of the distortion of a single tone is second harmonic. Air's distortion characteristic is monotonic, which is to say its distortion products decrease smoothly as the acoustic level decreases." Makes a great case for near field listening using a SET!

So what SET amplifier is Pass making these days? Is he currently making any tube amp? What I saw were solid state designs, mostly FET based, both single ended and PP. Did I miss something?

Yes- i.e. design preference. Pass prefers/likes solid state. I prefer
tubes to solid state. Why does Craig build tube amps and not solid
state amps? I don't see the relevance of your statement Don.

[Chris A]

Quote

So what SET amplifier is Pass making these days? Is he currently making any tube amp? What I saw were solid state designs, mostly FET based, both single ended and PP. Did I miss something?

 

Nelson Pass wrote that he is doing FET amps because the marketplace for tube amps is crowded, and he wanted to do something different than the crowd.

 

I judge that Pass has created some designs that are superior to tube amps using the performance measures that I regard as most important, but I've only heard one of his designs. I would like to audition an F5, but they're not available now, and are out of production. Note that Pass builds the brand-named "First Watt" amps and other devices from a separate company from Pass Labs, and uses his son and one of his son's friends as company employees.

Pass has also recently introduced two new Static Induction Transistor (SIT) amps that have unique properties for use driving lower-efficiency single-driver speakers (Fostex, et al.). These are extremely interesting amplifier designs that are very simple in terms of part count, but unfortunately they have a higher noise floor and output impedance than I could tolerate with my compression drivers. But they have much increased power output with respect to his First Watt MOSFET and JFET amp designs. Pass is basically selling these new amps at part cost + labor ($5K and $10K selling prices, respectively) in order to stimulate production quantities of these special devices for commercial audio use.

 

Chris

[Don Richard]

Yes- i.e. design preference. Pass prefers/likes solid state. I prefer tubes to solid state. Why does Craig build tube amps and not solid state amps? I don't see the relevance of your statement Don.

When I looked at his websites I did a partial reading of his articles (there are a couple of dozen or so and I didn't read them all) and what I saw was much discussion of single-ended designs and why he thought SS, particularly FETs, had advantages over SETs in that type amp. He also has designs for Class A PP amps, all solid state as far as I can tell, and I was asking about any new tube designs he might have come up with.

So, since you asked, why does Craig build PP tube amps and not SET tube amps?

[rigma]

All I can say is that I have been listening to Khorns since 1965 and now Jubilees and have been through many tube and SS amps. For the past 5 years I have been using 300B SET that I built using premium components and it is by far the best I have heard, even at loud levels.

Cask the draw backs you describe are not happening with my system. I don't have an explanation as to why your experience was so different than mine. By the way I have had zero maintenance problems in 5 years, not even a tube.

rigma

[Chris A]

Quote

By the way I have had zero maintenance problems in 5 years, not even a tube.

One of my 300B tubes died one month after I installed these mono-blocks. May be the issue is the designer/manufacturer. This is hard to believe, however, that they were that bad. Another issue: the amps had about 2.5 dB gain differential right out of the box. I find that hard to believe, too. This is crazy.

 

By the way Marion, what is the output impedance of your 300B mono-blocks? I assume that you're using them with your now-famous Jub passive crossovers to drive your fronts.

 

Chris

[rigma]

By the way I have had zero maintenance problems in 5 years, not even a tube.

One of my 300B tubes died one month after I installed these monoblocks. May be the issue is the designer/manufacturer. This is hard to believe, however, that they were that bad. Another issue: the amps had about 2.5 dB gain differential right out of the box. I find that hard to believe, too. This is crazy.

By the way Marion, what is the output impedance of your 300B monoblocks? I assume that you're using them with your now-famous Jub passive crossovers to drive your fronts.

Chris

Yes, I use them to drive the front Jubilees through the custom passives. Sorry, I don't remember what the exact output impedance is but a quick calculation shows 1.58 ohm with the 4 ohm tap. They have Magnaquest FS-030 output trannies.

rigma

[Chris A]

So, since you asked, why does Craig build PP tube amps and not SET tube amps?

I think that he has answered that question on the forums, quite clearly. I was a bit surprised by the clarity of his response:

http://forums.klipsch.com/forums/p/158381/1674209.aspx#1674209

Chris

[mikebse2a3]

First note: NOT ALL AMPLIFIERS of any type are created equal so lets get that said again and out of the way..!!!!

IMHO Compression is not a factor for a well designed SET tube amp when well designed and properly implemented in a system.

IMHO the reason why music will often sound better when using a well designed SET tube amp (using common sense pairing of amp wattage/speaker efficiency/max spl desired in room for a given installation) is what they excel in and that is the perception of Clarity, Dynamics, Imaging and Soundstage. Music will have a better perception of rhythm/timing verses lesser amplifiers because of their smearing of details.

Note: In my experience there is a strong correlation between these perceptions as logic would predict because often what improves one will be perceived as an improvement in the other areas.

Well designed SET tube amplifiers do not suffer from the veils of smearing and edgyness (SSssssss....anyone) of many SS and Tube amplifiers.

I want to make it clear I'm not against SS amps or other tube type amplifiers just because I'm pointing out the perceivable benefits of the SET tube amplifiers I've experienced. Again I'm actually very open minded as my system's componet choices should be ample evidence of.

Chris just to be clear I'm impressed with the Pass F3 design so much so that I've had parts to build a clone for nearly 2 years (just haven't had the free time due to other projects and life itself but soon I hope to start the build []).

For the record the best SS amplifier I've yet experienced on a Khorn to date was a Pass design Alpha 30. I spent some time comparing this amplifier directly with some McIntosh (MC-30, MC-240, MC-275) and I would be extremely happy with any of these amps in my system.

miketn

[tube fanatic]

So, since you asked, why does Craig build PP tube amps and not SET tube amps?

I think that he has answered that question on the forums, quite clearly. I was a bit surprised by the clarity of his response:

http://forums.klipsch.com/forums/p/158381/1674209.aspx#1674209

Chris

I thought that this topic was over! Craig's statement is a reflection of his design philosophy and is no more or less correct than anyone elses. Every amp designer has his/her group of followers who consider the sound of their equipment to be absolute perfection. Craig has his, I have mine, Deckert has one, Pass has one, and so on.

In case those following this topic didn't click on a link I had provided previously (http://www.tubelab.com/BudgetOPT.htm), here's an excerpt from it:

Electra-Print:


These are the reference transformer, I have found nothing better for this
amp.
Best sound is achieved at 50 mA with 300B's. Distortion measures 2.3% at 4.5
watts
(mostly 2nd harmonic), frequency response is 14Hz to 28.7KHz, and visible
clipping
appears just over 5 watts. Specs measured at 1watt: Frequency response 3.6Hz
to 29.1KHz,
distortion 0.91%. This transformer is only rated for 10 watts, but it is 5
times the size of the others.
No visible saturation effects were seen at 5 watts and any frequency above
20Hz. The sound is excellent,
this is the amp that I use daily.

This is a frequency response
plot of the amplifier operating at 1 watt with 300B tubes through the
Electra-Print transformers. Response is ruler flat across the audio band,
except for about 1 db of loss at 20 KHz.

Distortion at 1 watt. Mostly
second harmonic, but the third and fourth are clearly visible.

Remember that this was obtained using a 300B triode. The distortion figures are wonderful, and the frequency response is similarly wonderful (don't compare this to a SS amp though- apples and oranges.) Even at 4.5 watts out, 2.3% distortion is just fine and well within the accepted design parameters for vintage amps. The 0.91% at 1 watt isn't even worth discussing, and for those using high efficiency speakers, that much power per channel is often far more than is needed for the desired listening level. It should be obvious from this (at least it is to me and my fellow SET enthusiasts) that the magical SET sound is caused by something which we are not measuring. In the shop we used to do all kinds of level matched listening comparisons with different amp configurations (SET, SEP, P-P, SS, Loftin-White to name only a few) in an effort to try to figure out just what was going on sonically and to quantify it with objective measurements. All it did was take us in circles as each configuration had its sonic virtues and negatives. Using a particular amp design to resolve a sonic issue which is disturbing is in my opinion no different from using the tone controls of a vintage amp or receiver to accomplish the same thing. Any modification to the frequency response is a departure from what is in the recording (I say this with all respect for your philosophy Chris.) Heck, even using very high capacitance interconnects will affect the frequency response and sound with some equipment. This issue was debated long before I got involved in audio in 1960 and is likely to continue well into the future. We're not going to solve it!

So, my advice to anyone who has been following this topic is to buy what you find pleasing to listen to. If your friend doesn't like the sound of your system, tell him/her to go home and listen to what they like! You may not enjoy the sound of their system either.......................

[Chris A]

I want to make it clear I'm not against SS amps or other tube type amplifiers just because I'm pointing out the perceivable benefits of the SET tube amplifiers I've experienced. Again I'm actually very open minded as my system's component choices should be ample evidence of.

I know this, Mike. I do respect your opinions. The experience with the Bottleheads was incredibly bad, however. Even if there are good SETs out there, my experience with these class of amplifiers will always be remembered and that experience transferred to any other SET. One thing that bothers me about that experience is that I read several accounts of how good the those particular 300B SETs were as starter amps. I now find it hard to trust any of those "if it sounds good, it is good" folks since these folks are clearly listening to extremely non-linear setups (speakers, amps, preamps, etc.), and they listen, most probably, to very bad recordings all the time. This is fairly difficult to fathom but understand a lot of folks here also prefer LPs to digital disks.

All this also tells me something: that I don't listen to the type of recordings/material that the these folks listen to (and that's okay), but that they only listen to those type of recordings, which I do have a little issue with. Further, they apparently don't care that they are continuing to put patch after patch on their setups, not correcting the root problems but actually changing the reproduction of them so that it "...sounds good to them...". Should I go on? I'm an engineer - and this isn't an engineering approach. This is the antithesis of hi-fi, I'm afraid. And I believe it is the basis of the strong disagreements that we see on all the forums once we get to these taboo subjects. I believe that we ought to talk about the root issues, not just the symptoms.

Chris just to be clear I'm impressed with the Pass F3 design so much so that I've had parts to build a clone for nearly 2 years (just haven't had the free time due to other projects and life itself but soon I hope to start the build ).

Mike, I've broached the subject of the First Watt F3 and F5 FET amps in other threads, but the "tube lobby" here apparently isn't listening--these are the folks spending kilobucks on their tube amps and are listening to $500 used Klipsch Heritage (...which doesn't make much sense to me, and I've mentioned that fact before). I think that they ought to hear Jubs first, yada, yada, yada. Those large resources spent on tubes would be much better spent on much better speakers, first... (IMHO).

I couldn't imagine a better amp driving my TADs on the K-402s than the First Watt F3, but me saying this apparently has no influence with the folks that believe that you've got to have tubes - how many of these folks have heard the F3s?

I attribute this to strong decision bias that doesn't want to hear that story, much like the folks that don't want to hear how much better that K-402 two-way Jubs are (especially with TAD 4002s instead of the K-69-A compression drivers) than any other Klipsch Heritage speakers, and active bi-amping or tri-amping is over passive crossovers in general. With the F3, I get all the good things that a SET would provide (IMHO), and virtually none of the bad that is asociated with SETs. And at a price point that is comparable to low to midrange priced SET monoblocks (often cheaper). My amazement is that this is not big news to the to the tube crowd - because they obviously don't want to hear it,

In fact, they go out of their way to make sure that any newcomers asking for opinions on tube-type amplifiers think that the First Watt amps are "solid state amps" which is a bit of a misnomer--wouldn't you agree?

Chris []

[Marvel]

I now find it hard to trust any of those "if it sounds good, it is good" folks since these folks are clearly listening to extremely non-linear setups (speakers, amps, preamps, etc.), and they listen, most probably, to very bad recordings all the time. This is fairly difficult to fathom but understand a lot of folks here also prefer LPs to digital disks.

All this also tells me something: that I don't listen to the type of recordings/material that the these folks listen to (and that's okay), but that they only listen to those type of recordings, which I do have a little issue with. Further, they apparently don't care that they are continuing to put patch after patch on their setups, not correcting the root problems but actually changing the reproduction of them so that it "...sounds good to them...". Should I go on? I'm an engineer - and this isn't an engineering approach. This is the antithesis of hi-fi, I'm afraid. And I believe it is the basis of the strong disagreements that we see on all the forums once we get to these taboo subjects. I believe that we ought to talk about the root issues, not just the symptoms.

You are dissin' everyone in general who likes SET amps, which I find a bit crazy. My system has been a bit haphazard, but it sounds incredible to those who have heard it. They aren't just being nice... [] I admit that my Moondogs probably would knock the socks off of the Bottlehead amps. They have huge iron for the outputs, which only helps.

I don't have the money or the time to tweak my system, and it sounds great. The only problem I've had, and only within the past month, was a noisy 6DJ8 tube in my preamp. That's the first thing I've had to change in the past 5 years. Wish you lived closer so you could come for a listen.

I mostly listen to CDs, and the good ones sound good, the bad... I just don't listen to as much.

Cheap CD palyer, JM Merlin Preamp, cheap interconnects, Welborne Labs 2A3 amps w/Magnequest OPTs, EH 2A3 output tubes and zip cord to the LaScalas. I'm pretty low rent.

Bruce

[mike stehr]

Single-Ended Class A tube amplifiers

are not very powerful, and their measurements are nothing to write home about,

but there is no denying that they have strong musical appeal to a sizable segment

of the audiophile population.

[fenderbender]

IMO. The middle of the chain is a moot point as long as it cleanly, colorlessly, "amplifies"

money and great pains should be spent on the front end and source material.... Because that's where you can get the most benefit. I will agree that three way big box speakers such as the khorn ( which I had for three years) are a fussy beast and more sensitive to the flavor of amp.... I went through a few amps before settling.

I actually have Sonics Animas in my main rig fronted by Townshend rock seven/rega/ Lyra TT. With good recordings I can use a $500 int and it sounds amazing. ( granted using a Cayin one phono pre). When I use my all tube system there is a difference but not that much..... I'm getting the most bang out if the front end.

just a thought. BTW. If you have never heard sonics animas get over to my house...,, the will knock your socks off!!!!

[Chris A]

You are dissin' everyone in general who likes SET amps, which I find a bit crazy.

Perhaps it appears that way, but I feel that there may be SETs out there that minimize the negative performance issues mentioned above and that probably sound as good as or perhaps better as the F3s. You are probably going to find that those amps may be extremely expensive relatively speaking, however, and their performance will be constantly changing by small degrees, but measurably as the tubes burn-in and subsequently age, and those amps will have extremely long warm-up times measured in hours, not minutes as in the case of the FET amps. These are performance issues that I consider in my assessment of one amp design vs. another.

I hesitated from writing about this subject for a long, long time, believe it or not, but I felt that it approximates what I do in fact think. I was able to reveal some of my thoughts because I'm not trying build or sell SETs or F3s, and I can afford to be a bit more open about my concerns, reservations, and rationale that I use in forming these opinions. I guess I could be polite and just not express what I really think. Is that the right policy? Sometimes it is, but in this case, I've revealed what I think in the hope of creating better understanding of my arguments. I've been told that I have been obscure in my writings on this subject and others that are closely related. I'm trying to be clearer for those folks that have trouble recognizing more subtle commentary that I have tried to use over time.

This isn't an ad hominem argument, in fact, I was specifically trying to avoid that (as I hope that you will also). I'm merely digging own into the details of a problem that has bothered me for a few years while reading here. If that sounds like an attack, I will apologize since that wasn't my intent at all. I actually trust more than I did that you can hear these arguments and not be personally offended by them.

But note that the specific issues I brought up were the ones that I intended to talk about, not an argument that approximates "Fords vs. Chevys". or SETs vs. JFET amps. I think that as you dig down into the arguments I presented, the issue is more about the quality of execution more than binary choices, and the relative costs of achieving the same quality using different approaches. This includes the taking into account the minimum input impedance at your speaker's passive crossover network input ports, and the input impedance of your SET amp vis-a-vis the output impedance of your preamp.

I'm still reading where folks are complaining about "too much bass" or "too little bass", etc. while using SETs and perhaps some other types of tube amps. This raises a red flag in my eyes. Amps are first supposed to be linear devices in terms of at least FR - if they are not, then something is very wrong. This isn't an instance of "relativism" IMHO, it is the basis of engineering linear systems for audio reproduction. Even the F3 will have problems driving speakers with input impedance that drops below ~8 Ohms, such as the stock Klipsch Heritage series. I believe that I've made my voice clear on this: the passive crossover networks in these speakers are designed to achieve stability over time, insensitivity to manufacturing differences of drivers and cabinets, and low manufacturing costs, but not necessarily the best optimization for listening performance. I prefer active bi-amping or tri-amping to avoid many issues found with passives, including low input impedance issues that interact with tube-type amplifiers with high output impedance.

Chris

[tube fanatic]

Perhaps it appears that way, but I feel that there may be SETs out there that minimize the negative performance issues mentioned above and that probably sound as good as or perhaps better as the F3s. You are probably going to find that those amps may be extremely expensive relatively speaking, however, and their performance will be constantly changing by small degrees, but measurably as the tubes burn-in and subsequently age, and those amps will have extremely long warm-up times measured in hours, not minutes as in the case of the FET amps. These are performance issues that I consider in my assessment of one amp design vs. another.

Just to put in a few more cents worth of my thoughts Chris. Your comment above about SETs which minimize negative performance issues being extremely expensive is absolutely wrong. It should be obvious that it doesn't cost a huge amount at all to build triode amps using excellent quality output transformers. What's wrong with an almost totally flat audio band frequency response, with low distortion, as George demonstrated in the example I cited previously? The cost of duplicating such an amp is in the hundreds, certainly not extremely expensive by audiophile standards. Sure, the performance may change incrementally as the tubes age, but is that going to be audible in most cases? Definitely not! And why do you think that extremely long warm up times are needed? It takes all of 1-2 minutes for tubes to come up to operating temperature and stabilize. I have spent a large portion of my life servicing tube type radios and TVs as well as tube type audio equipment, and have never encountered the need for hours long warm up for circuits to stabilize and perform as desired. Can you explain the basis of your assertion about this? I'm not trying to be ornery (although my wife says that such behavior is natural for me!!!), but would like to know the basis of your thinking. Regards-- Maynard

[Chris A]

First, thanks for replying to my "a bit crazy" thoughts and engaging in dialogue. I have seen many instances where neither path was chosen by readers of the thread.

And why do you think that extremely long warm up times are needed? It takes all of 1-2 minutes for tubes to come up to operating temperature and stabilize.

http://www.head-fi.org/t/373957/the-tube-amp-warm-up-time-thread

What's wrong with an almost totally flat audio band frequency response, with low distortion, as George demonstrated in the example I cited previously?

http://www.deltamedia.com/resource/impedance.html

The point is that it's not just amplifier performance into a resistive load that matters. Speakers typically behave like complex impedance devices electrically (...and acoustically): they have dips and peaks in their input impedance curves vs. frequency--sometimes these are dramatic changes such as in the Khorn's input impedance curve, shown above. This causes issues when amps with higher than 0.3 Ohm output impedance are used to drive them - FR issues among other things. If you use an amplifier with higher output impedance than this with a Khorn, it means that you will have to EQ your Khorns to achieve the same FR as using an amplifier driving them with 0.03 or less output impedance.

http://en.wikipedia.org/wiki/Tube_sound

I understand that you believe what you've said, above. I also believe what I've stated above. We can agree to disagree: it's okay with me. My gig is system design and accurate sound reproduction, not really tube electronics apologetics, and certainly never polemics.

Chris

[tube fanatic]

ml

The point is that it's not just amplifier performance into a resistive load that matters. Speakers typically behave like complex impedance devices electrically (...and acoustically): they have dips and peaks in their input impedance curves vs. frequency--sometimes these are dramatic changes such as in the Khorn's input impedance curve, shown above. This causes issues when amps with higher than 0.3 Ohm output impedance are used to drive them - FR issues among other things. If you use an amplifier with higher output impedance than this with a Khorn, it means that you will have to EQ your Khorns to achieve the same FR as using an amplifier driving them with 0.03 or less output impedance.

Totally agree about the varying speaker impedance issues (wish I had access to some Audio Precision equipment)! However, with speakers that dip to say 3.2+ ohms, the amp can be kept very "happy" by using its 4 ohm tap. The dip of a few tenths of an ohm isn't going to cause anything objectionable at the frequencies at which it occurs, assuming that its output impedance isn't nuts (again, I've never encountered output impedances of 15-30 ohms as you indicated in a previous post.) The higher speaker impedances at other frequencies will then, to a certain point, actually lower the amp's distortion somewhat. Granted, this must be considered in view of the somewhat reduced output power which goes along with it. Anyway, this discussion is fun. Hopefully, those following along will come away with some sense of what this insanity (and being an audiophile tweaker definitely fits the profile imho- this statement is not directed at you Chris; I'm as guilty of the syndrome in my own way!) is about and be able to draw their conclusions from more of a scientific viewpoint. Be glad to continue babbling if that's the prevailing consensus. A nice day to all--- Maynard

[Chris A]

Sorry, I don't remember what the exact output impedance is but a quick calculation shows 1.58 ohm with the 4 ohm tap.

This is the issue...even on the "4 Ohm" tap, SETs, with typically low forward loop gain that precludes use of negative feedback to lower its output impedance, have too high output impedance in order to not affect speaker FR (EDIT) for speakers that have their lowest input impedance less than about 10x of the output impedance of the amplifier. For rigma, this apparently isn't an issue (see below).

Even the F3 affects Khorn output at 1 Ohm output impedance, if we are to take fender bender at his word (...which I do...). The input impedance complex plane plots correspond one-to-one with his symptomatic complaints about the F3 paired to Khorns. One easy fix is to simply EQ these two regions down, but that doesn't completely erase the issues of low input impedance speakers being driven by high output impedance amplifiers.

In rigma's case, the TADs that he uses are essentially a minimum of 11 Ohms, rising to ~27 Ohms maximum in the operating band. I do not know the combined input impedance characteristics of his passive networks + the Jubs, however: my guess is that the combined curve is probably more than 8 Ohms minimum up and down the audible frequency band (nominally 20 Hz-17KHz for us more mature folks).

Chris

[rigma]

Sorry, I don't remember what the exact output impedance is but a quick calculation shows 1.58 ohm with the 4 ohm tap.

This is the issue...even on the "4 Ohm" tap, SETs, with typically low forward loop gain that precludes use of negative feedback to lower its output impedance, have too high output impedance in order to not affect speaker FR.

Even the F3 affects Khorn output at 1 Ohm output impedance, if we are to take fender bender at his word (...which I do...). The input impedance complex plane plots correspond one-to-one with his symptomatic complaints about the F3 paired to Khorns. One easy fix is to simply EQ these two regions down, but that doesn't completely erase the issues of low input impedance speakers being driven by high output impedance amplifiers.

In rigma's case, the TADs that he uses are essentially a minimum of 11 Ohms, rising to ~27 Ohms maximum in the operating band. I do not know the combined input impedance characteristics of his passive networks + the Jubs, however: my guess is that the combined curve is probably more than 8 Ohms minimum up and down the audible frequency band (nominally 20 Hz-17KHz for us more mature folks).

Chris

My passives also have LF & HF Zobels.