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La Scala II and Tubes


deadlift

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If you ask me having a power amp that asks 6v to reach full output power is wimping out and passing the buck in order to boast low noise specs.

 

I do get it, when you need the VAS stage of a power amp to to swing 140v peak to peak to drive the finals it can send some "engineers" running. FIrst order of defense is good filtration in the power supply and second is front end stages that have good power supply ripple rejection. I personally like active loads like a constant current source, you can reach near full mu of a valve along with getting excellent linearity and power supply ripple rejection. A good one can present a near infinite load (which would look horizontal for those who are into drawing load lines) and not drop much DC across unlike a high value resistive load.

 

I have heard many good DHT amps that were dead quiet on horn speakes that reached full output power with a normal input source; e.g. 1vrms. 

 

What Manley did was not considered good engineering in my book.

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2 hours ago, alzinski said:

If you ask me having a power amp that asks 6v to reach full output power is wimping out and passing the buck in order to boast low noise specs.

 

I do get it, when you need the VAS stage of a power amp to to swing 140v peak to peak to drive the finals it can send some "engineers" running. FIrst order of defense is good filtration in the power supply and second is front end stages that have good power supply ripple rejection. I personally like active loads like a constant current source, you can reach near full mu of a valve along with getting excellent linearity and power supply ripple rejection. A good one can present a near infinite load (which would look horizontal for those who are into drawing load lines) and not drop much DC across unlike a high value resistive load.

 

I have heard many good DHT amps that were dead quiet on horn speakes that reached full output power with a normal input source; e.g. 1vrms. 

 

What Manley did was not considered good engineering in my book.

Of course Albert raised some excellent points here.  However, I don't agree with the premise.  The issue of required amplifier sensitivity is something I often discussed with some fellow NYC area amp designers back in the 60s, and we all concluded that it did not need to be overly high.  We need to consider the design goal of the Horn Monos which was to provide extremely quiet operation when used with very high sensitivity/efficiency speakers which only require power levels in the milliwatt range (LSs being an excellent example) to create huge output levels.  These amps have a voltage gain of around 9 db if I recall correctly and boast a s/n ratio of close to 120 db!!!  That is a terrific combination in my book.  So, for the chosen design goals, I think it is a perfectly executed product.  

 

Even Rozenblit addressed this issue in a paper (it is short and will give a much better understanding of this discussion for those who are somewhat less technically inclined):

 

http://www.transcendentsound.com/Amp_Gain.html

 

That said, I now have to challenge Albert to a duel to settle the matter in an appropriate way.  Since we both are old farts it should be quite humorous.............

 

 

Maynard  

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Bruce Rozenblit also designs preamplifiers and a phono stage with virtually zero residual noise artifacts.  I think you observed much the same with respect to the Grounded Grid, Maynard.  I built his first published preamp from scratch via his article and accompnying schematic in Glass Audio in '93, I think it was (?).  Somwhere around that time anyway.  Also very good, but both the GG (of which I have built several) and the 300B masterpiece (yes, Al, I know am kidding myself again) are in a different league.

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I had to look at the manufacturer web page to see what we were discussing exactly, I had a good laugh.

 

 

 

So 6 volts in gets you 25 watts out, that's a gain of 2.4. A typical source of 1v doesn't even get you to 1 watt of power with that amp. Why make a 25 watt amp to only get 1 watt of power? Seems like a waste to me. IF you want to be able to reach the amps full potential power then you must get some gain from somewhere because most sources do not put out 6v. It's really not that impressive at all considering what it is.

 

To be more transparent with their specs, they should do a noise floor measurement with an unbalanced preamplifier hooked up to the input, that way there you will see the real world noise including ground loops, I am sure it will be substantially higher.

 

 

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I just found Atkinson's measurements of these amps (say what you will about the reviewers, I've always found him to be very honest in regard to measurements):

 

https://www.stereophile.com/content/quicksilver-audio-horn-mono-monoblock-power-amplifier-measurements

 

Getting back to my earlier comment about my discussions in the 60s, we all felt at that time that an input sensitivity of around 2.5-3V would be just fine and, if it was somewhat higher, it wasn't considered a big deal.  Remember, we're talking about power amps which would only be used with a preamp.  Integrated amps are another matter entirely.  Besides, what's the point of having a power amp with an input sensitivity of, say, 0.1V?  To me that's way off the chart.

 

Maynard

 

 

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What are the advantage, or disadvantaged, of moving your connection between 4/8/16ohm taps on your amplifiers output... Specifically into LSii's?

What is the audible change by moving to different taps...

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There is no easy and short answer to your question.  In general, tube output stages are designed to operate into a specific load impedance which is provided by the prmary of the output xfmr.  Unfortunately, the primary impedance varies depending on the load across the secondary.  These variations in primary impedance are partly responsible for changes in the amplifier's distortion.   As William pointed out, speakers present a widely varying load.  Some circuit arrangements, like SETs, are fairly immune to impedance variations.  If you select the output xfmr tap which is closest to the minimum impedance (I think the LSs are 3.9 ohms but that needs to be verified), distortion will actually decrease with any impedance rise.  This is good!  Pentodes are much more impedance sensitive which is why negative feedback is needed to keep distortion low.  A pentode, with a properly implemented fb circuit, can be as forgiving of impedance variations as a triode.  There are many more variables at play here, however, such as distortion varying with output level from the amp.  That can be a separate discussion at some other time.

 

 

Maynard

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As an aside I would just like to add that friends, family and myself who listen to my system find the sound thoroughly enjoyable regardless of which set of poorly engineered amps I may have hooked up at the moment. In the end - it's the music that matters and if it floats your boat - then all is well.

 

 

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We had discussed in another thread here that, according to a couple of its more illustrious contributors, nothing but distortion, excessive noise, and other deleterious by-products are associated with active line stages vs the dead silent background and accuracy (what's that?) of a simple passive, in-line attenuator.  Has that opinion changed now that we have a case with the amp under consideration and its uncommonly high input sensitivity?  First it was 'good design' and now it's not, and a preamp will be needed in order to achieve satisfactory performance?  I'm confused and somewhat bothered by the equipment bashing from others.  It seems to me that as adults we can join in a forum like this to discuss ideas and concepts, including circuit design, without having to resort to school-yard-like (sorry, I've been a public school teacher for almost 30 years -- I know) bashing of the equipment of our fellow forum members.

 

I joined this forum in 2002 under a different handle, and at that time it was fraught with insults, degradation, personal attacks.  I was up to something like 15,000 posts (not something about which I'm necessarily proud, and didn't wear like some sort of laurel wreath) when I decided to drift away and spend my time instead with my family and my own amp and preamp building projects.   We can offer ideas and opinions about all topics, but, as a contributing forum member, I want to present the possibility that all of those things can be accomplished in an atmosphere of mutual respect and appreciation, even if we may personally not agree with the ideas and, in particular, the equipment choices of another forum member.  We all spend serious money on this hobby, and it can be decidedly disheartening for someone to have his or her amp, preamp, or speakers simply flung into the pile of mis-fit audio equipment by someone else, irrespective of that person's technical understanding and prowess.

 

deadlift:  Thanks for your astute reminder.  It IS about the music, and if you, I, or anyone else is enjoying and happy with the choices we have made as far as our music-making machinery, what others may (rather unkindly, in my view) say to the contrary - and in the words of the founding father of this great company, is, quite simply, BS.

 

 

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32 minutes ago, erik2A3 said:

We had discussed in another thread here that, according to a couple of its more illustrious contributors, nothing but distortion, excessive noise, and other deleterious by-products are associated with active line stages vs the dead silent background and accuracy (what's that?) of a simple passive, in-line attenuator.  Has that opinion changed now that we have a case with the amp under consideration and its uncommonly high input sensitivity?  First it was 'good design' and now it's not, and a preamp will be needed in order to achieve satisfactory performance?  I'm confused and somewhat bothered by the equipment bashing from others.  It seems to me that as adults we can join in a forum like this to discuss ideas and concepts, including circuit design, without having to resort to school-yard-like (sorry, I've been a public school teacher for almost 30 years -- I know) bashing of the equipment of our fellow forum members.

 

I joined this forum in 2002 under a different handle, and at that time it was fraught with insults, degradation, personal attacks.  I was up to something like 15,000 posts (not something about which I'm necessarily proud, and didn't wear like some sort of laurel wreath) when I decided to drift away and spend my time instead with my family and my own amp and preamp building projects.   We can offer ideas and opinions about all topics, but, as a contributing forum member, I want to present the possibility that all of those things can be accomplished in an atmosphere of mutual respect and appreciation, even if we may personally not agree with the ideas and, in particular, the equipment choices of another forum member.  We all spend serious money on this hobby, and it can be decidedly disheartening for someone to have his or her amp, preamp, or speakers simply flung into the pile of mis-fit audio equipment by someone else, irrespective of that person's technical understanding and prowess.

 

deadlift:  Thanks for your astute reminder.  It IS about the music, and if you, I, or anyone else is enjoying and happy with the choices we have made as far as our music-making machinery, what others may (rather unkindly, in my view) say to the contrary - and in the words of the founding father of this great company, is, quite simply, BS.

 

 

 

 

Typical school teacher these days, everyone is a delicate flower, a unique snowflake, everyone gets a sticker and a pass grade for trying. Do you need a safe space because you didn't hear what you wanted to hear?  ;)

 

 

I never said active line stages are NOTHING BUT distortion and noise, my point was that they can only add more noise and distortion than a simple resistive divider, this is fact and sorry if it offended you. I am not against active line stages at all, I never once said they sounded "bad". In some cases where you have a very low ouput impedance source and very high input impedance amp, and you run very short interconnects a passive volume control can work just fine and be very transparent.  In some cases it won't work and you will need an active buffer or even something with some gain. The definition of high fidelity gets lost in these discussions, the device with the least coloration and which is the most authentic to the original material is the most hifi, whether you like it or not doesn't matter. If you have been reading, I myself use a SET amplifier and I don't for one second say it's high fidelity, I don't claim it has zero distortion, but I do like the sound. I never once said the amps being discussed in this thread sounded bad either. Just like the other Scott 299D thread the complaints were aimed more at the marketing aspect which in the audio business is most of the time a joke. My only complaint about the amps in question here is the marketing. My point was that they are intended to be used with an active preamp that has gain. The noise measurment they give for their Horn amplifier isn't impressive given the gain of the device and once you plug a preamplifier into it the noise floor will increase. It's my opnion that it's misleading,  that's i!. If you have the horn amplifier by quicksilver hooked up to an efficient horn speaker and preamp,  I suggest turning the volume up without any music being played through it and put your ear up to the speaker, I bet you will hear a little noise increase as you increase the volume. Again this doesn't make the amplifier a "bad" amplifier, it doesn't mean it will sound "bad", it doesn't really mean anything except the fact the marketing in my opinion is a joke. Some people don't understand specs and how gizmos work, they may even believe that using this amp no matter what preamp they use will have a 120db noise floor, but it's dependant on preamp being used, especially since they run unbalanced inputs.

 

A critique on the amp itself would be something like this. Since the amp is intended to be used with an active preamp, it would be much more advantagous to use an input transformer to galvanically isolate it and break ground loops, this also has the benefit of being able to accept balanced inputs which will be quieter due to common mode rejection, and it can accept unbalanced sources, this also gives you the benefit of using all differential circuitry. But good transformers are expensive and they can impart their own distortion and limit bandwidth so everything is a tradeoff.

 

If you post about your equipment on the internet you will have to accept all sorts of critics not just the good ones. I am not bashing the amp, I bet it sounds fantastic and I hope the owner is very happy with it. But this is a discussion about the product and as long as things are kept factual I don't see a problem with the truth.

 

 

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On 7/11/2017 at 8:30 AM, tube fanatic said:

Most noise in tube amps originates in the gain stages which precede the output stage.  Mike's approach in using a very low input sensitivity is a wonderful way to deal with the noise issue when the amp is to be used with very high sensitivity/efficiency speakers.  And, the measured performance of these amps is truly outstanding and far better than the majority of tube amps out there (including my own).

 

Maynard

 

 

Oh gosh Maynard disagrees with me what a surprise... on a clear day is the sky blue?

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I would also like to add something else I have learned from a long involvement in this hobby:  While I would say my technical experience and understanding is fairly reasonable, what a number of very serious listeners (many of whom were and are professional jazz or classical musicians) have taught me is that technical ability and familiarity DO NOT, by a rather long margin, necessarily equate with one's understanding of - and ability to listen to (as in one's hearing acuity) - music.  While I can rattle off technical prose about load-lines (ugh), power supply design, CCS loads, cathode followers, interstage coupling, etc., etc., etc., ad nauseam, that, again, DOES NOT mean I automatically know more about the listening to and appreciation of music than someone who does not.  That attitude makes me cringe, quite frankly.  Some of the most astute -- just amazingly talented -- listeners I have known were women or gentleman that had very little, if any, understanding of how their equipment worked, and even less about how to go about repairing or fixing them if problems were encountered - and really didn't care.  The brand of coupling capacitors used (in that type of interstage coupling), transformers (or not = OTL), brand of resistors and or inductors, hollow or solid state, and so forth, was/were not nearly as important as the components and principals of music, and of course the music itself as a whole.  I am not saying the two mind sets can't co-exist, but rather that one is not necessarily the qualifier or prerequisite for the other.

 

I am in great debt to the many non-technical but highly capable listeners and music lovers who have taught me something more about the music I like -- which tends these days to consist mostly of jazz and classical (with a bit of King Crimson, Genesis, Yes, Perfect Circle, Audio Slave, and so forth thrown into the mix ;) )

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Looking up, it seems that storm clouds might be slowly edging into this thread -- I have seen it too many times here -- and so I'm off for some shelter and to listen to music and enjoy a couple of more days with our awesome niece and nephew visiting from Texas!

 

 

 

 

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I am first and foremost a musician, I have been playing and studying music for 40+ years. I have gone through extensive music theory and ear training. I am extremely emotional and passionate about music, I am music and I would die without it.

 

Let's not confuse technical matters with emotional matters. I like what I like, you like what you like, I tend to think we probably like the same things. BUT people take it very personal when discussing technical matters, I don't know why.

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4 minutes ago, alzinski said:

I would die without it.

Never disclose a fatal weakness.

5 minutes ago, alzinski said:

BUT people take it very personal when discussing technical matters, I don't know why.

Because they are technicians.  Even economists get emotional about economics.

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Perhaps it's best if we all do what we love, I'm going to put Diana Krall Live in Paris on the turntable and sit back and enjoy, nothing like a live performance coming through the La  Scala II's.

 

Peace

 

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