Let’s simplify negative feedback = taking something ( the AC audio signal aka music ) that has ALREADY happened, flip it around out of phase ( that’s the negative part ) and feed it back into the input where something new and unequal is happening ( unless you think sine ways are music )… then apply some critical thinking….
I feel like Pavlov’s dog waiting for the bell to ring…
(like expecting every impulse transient will have a ringing exponential decay like a Cadillac with no shock absorbers going down the road.)
A better approach these days might be to estimate what the error is going be a priori and just apply that as (or along-with) the input. So more of a feed-forward approach, or pre-emphasis in control theory I think?
Then there is no feedback, and the input is driven towards a lower error. But that sort of begs a fully digital system IME.
i have not been keeping with amp design, other than the Bruno work, which Ralph mentioned. So maybe a lot of stuff is happening I am unaware of?
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Benchmark moved the game a head with their current technology that's in the AHB2.
My bet is if you plugged your tube pre into this and kept the rest of your system as is you'd be more than pleased with the results! And if not, you can return. Worth a shot!
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What this means is its possible to build a solid state amp that is every bit as smooth in the mids and highs as the best tube amps and leave nothing on the table in terms of detail, sound stage and the like, in such a way that vintage amps simply cannot compete (not that they sound bad, just they don’t sound as good). This is one of those things that is easy to hear and easy to measure.
If you are convinced that best amps can be measured, you most likely hit a goldmine of technical wisdom, although the term "smooth" might be not universal enough to define it. However, in my opinion, that is not even possible, especially because amps do not make sound on their own: the sound you hear exists in a relation to all component in the signal path. Insisting on individual component’s quality, as promised by manufacturers marketing materials, rather than emphasizing the signal path synergy is not the optimal formula to enjoy audio but, of course, it can be easily the most expensive one...
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My old Phase Linear 400B amp is almost 50 yo. I doubt that I could tell the difference between it and my newer amps in a blind AB test. Maybe others could, but as others here have said, amps haven't changed much over the years. Transistors and resisters are quieter and capacitors have improved greatly but does that end up with a better sound?
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And then, of course, there exists the prospect of overthinking things until.....
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I second @lancelock with the vintage theater amplifiers. I have the little brother of the 1570B, the Ampex 6516 monitor amplifier, that was used to master the soundtracks of movies. Of course, it needed heavy bringing up to date to be used as a stereo amplifier, but all that is largely cosmetic as we are talking about adding modern connectors, and also about taking out the first gain stage (as the input was tape level.)
Mine had seen extra heavy duty in a movie theatre for decades, so a nice tune-up was already in demand. Not because of the heavy use (which it can easily take, as it was designed to be operated 10h a day, every day, for decades), but simply because of the age.
Compared to the 1950s we have drastically better capacitor technology, and a LOT can be done to optimize the internal wiring.
Few other mods done, which are modifications and not just "oil change": power tubes running in triode mode, separate filament transformer, the C input supply changed to CLC input, feedback loop drastically reduced (and then fully removed).
For those measurement savvy, I measured it with the minimal feedback (less than 1dB), at full power output (20W) the low extension was -1dB at 10Hz. I have not re-measured after taking ou the NFB completely, but I can report that the sound is way more dynamic, live, and bass much more 3D and grabbing than with it.
Now, back to the sound quality....
It's simply astonishing. It is as emotional, pure and human as the best examples of SET amplifiers are. They have produced the MOST LIFELIKE violin reproduction I ever heard from a stereo. Well, they clock the only instance a violin felt real from recording, in any system ever. (That is was not "close" or "almost", but the real deal.) That says a lot, as even most ultra high end systems reproduce violins in cat major or flat mouse E sharp, or plastic being shredded by sharp steel A keys...
So, it's a rare form from any amplifier of any age to do the most basic form of justice to violins. The venerable Ampex excels at it. Yet, not just that... I can listen to Karyyn - Jaina or Billie Eilish When I was older, and feel as if I'm transported to another reality... these songs contain high levels of subsonic information, and these babies can deliver it like nothing I ever heard. (Well, that might show my narrow-experence with HE systems boasting sub-20Hz provess... to tell the truth, we, audiophiles never listen to such material in our audio get togethers, so who knows really.)
So yes, I think "vintage" amplifiers are well and truly deserving of our attention, whether you are an UBER-fidelity fan (for life-like violin reproduction), or a hard-core rave party addict who wants to feel the marrow moving inside his bones (wants more than just a kick-in-the-chest...)
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Apologies if I duplicate other’s comments.
I think the simplest designs with solid components, whatever their strengths or weaknesses, have longevity, whatever your judgements are of their fundamental architecture or their particular performance. More complicated ones compete with successors’ evolutionary tweaks.
The other issue is that everything ages. There can be a multitude of performance changes that result from that, more or less amenable to intelligent maintenance.
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OP, what exactly would be the problem if it WERE a hotrod job? If you use "upgrade parts" [a relative term, I acknowledge], maybe you end up w/a BETTER sound that what it was originally...I say this because I am using an OLD Sansui integrated, slightly hotrodded [by someone else], driving some old Pioneers that are majorly hotrodded [by me]. WAY better sound; I sit and shake my head in wonder every time I listen to it.
But go w/whatever you like, obviously ~ just saying that ruling out upgrading something [like caps] might be your sonic loss>>>>>
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I happen to have lots of vintage equipment and 10 integrated SS amps and 4 tube amps.I don't buy anything new.I like to find vintage equipment. I can't afford the new stuff.
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My equipment is 15 to 66 years old.
Most of my guests think it sounds spectacular.
theaudioatticvinylsundays.com
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theaudioatticvinylsundays.com
Thanks for the link to your site it seems very interesting...
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The 1912 DeForest single ended triode is an example of a classic that has been resurrected. One manufacturer described the change to class B as making compromises to improve efficiency and other tricks to enhance measurement of distortion already below what can be heard. This was done for marketing purposes. A TAS review of a McIntosh amplifier described it as sounding like a single ended triode amplifier. Don't automatically newer will always be more desirable than classic vintage gear. "The best" will not be the same for everybody's preferred sound.
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The key of the audio system is to release the emotion while you are listenning If you feel it and you love it,you definitely do not need change as you are not in audio business.
You need change if you feel boring, you feel fatigue ,you can not listen for long time,then it is demonstrate that you need do some change.
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that's a good question. when you say "Can an amp be 'timeless' and compete with today's amps". you have to then ask what is it for? What is its purpose or function? If its to amplify a signal to drive a transducer then yes Any amp that functions as intended can compete with any other amplifying device. Now you need to be specific and set up parameters to compare the two amps and decide upon listening decide which meets your expectations and which doesn't This is not including instances where a load may be 2 ohms impedance and for whatever design considerations are employed the amp is not stable to drive the load and thus your not able to judge the amp simply because its not functioning. Hi-Fi is an art and subject to any and all considerations of ugliness or beauty.
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VTL 250 mono blocks , I own for 20years , heavy yes , upkeep can be a pain , but can always be fixed , by a descent tech. I purchased them used for 3000 Used ,New today out of reach , I guess when I bias them , I appreciate them even more.
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Transient response never goes out of style
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My primary amp is a pair of Altec 1569A theater amps. WARNING-Using these unmodified in the home is dangerous as the 700 volt operating current puts out not insignificant amounts of radiation. My amps were gutted but for the case and transformers. They run at about 425 volts and the transformers are always barely warm to the touch. Six tubes replace the four and the two input tubes are 6GU7s with NOS RCA 6SN7s cathode follower. No one uses my 6BG6 output tubes. The amps are fully voltage regulated including the bias (very stable). It has four levels of adjustable feedback starting about 6db which I prefer. The internals have oil filled caps and there are 2 huge 3X7 electrolytic storage caps on top. They kill my EAR 890 amp. My second system has the best Dynaco 70 ever with tremendous bass control and dynamics. Again, moded to the central tap on the transformers with voltage regulated design including the tube bias and superior large electrolytic storage caps. Mr. Record says it’s the only good Dynaco 70.
I do not understand the "negative feedback" posts without describing what type of negative feedback. There is global negative feedback (my EAR 890 has none) and internal negative feedback which should be employed or else risk distortion. I think current VAC amps have 7 db of negative feedback and internal feedback. Another friend has a personally repaired RM9 ultralinear amp that sounds very nice. It’s in the design that counts, not the "modern" and "new parts design" that makes a great amp. True, my amps are radically different than most. Audio Research makes crude/primative versions of voltage regulated amps today which is inferior in the design in my amps sophisticated voltage regulation.
Please correct me if you think amps should have both zero global and zero internal negative feedback.
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@fleschler
Please correct me if you think amps should have both zero global and zero internal negative feedback
As wth nearly all things concerning audio it just depends. NFB will decrease the amplifier output impedance and increase damping factor. For some speakers this will be beneficial. There are speakers designed with the intention of being driven by zero or very low NFB amplifiers. It will definitely depend on specific amp-speaker characteristics and appropriate matching compatibility.
BTW I bet you modified amplifiers sound fantastic!
Charles
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There are certainly areas where significant improvements have been made over time. Anything in the digital realm, streaming, music storage etc.
Way back when I purchased (on sale) a Krell KST100 amplifier. It anchored many changes (upgrades attempted and upgrades achieved) upstream. After twenty plus years, some issues became apparent and I was faced with the dilemma of purchasing a new amp or servicing my Krell.
Looking at the market place, reading reviews and posts on websites (this one mainly) I called Krell. Had a brief discussion with a tech there who went over the ins and outs of bringing my KST to spec and resolving any problems they found.
The current marketplace for amplifiers that would deliver the the same or better attributes of the Krell would require quite a bit of money. At least what I paid for the Krell and quite a bit more than the cost of “refurbishing” it.
Luckily, especially given the original packaging was long gone, Krell is located less than an hour’s drive from me. I drove the amp up to Connecticut, the tech met me outside with a wheeled cart! The amp weighs around 45 pounds with sharp heat dissipation fins.
For around $1500 and a few weeks I had a like “new” 100 watt (measures 130) clean across the spectrum, the amp handles just about any speakers well, superb bass control (good slam factor).
The service at Krell is superb. The techs are enthusiastic helpful and a pleasure to deal with. I got good reasonable advice.
I think the main advances in power amplifiers these days are size related with class D. Integration with pre amps and/or all sort of one box combinations. Was the Krell the last word in amplification? No. Even when new Krell made “bigger better” amps. The KST was actually their “dip” into the more “affordable” domaine…we are talking some $2750 back twenty five years ago! In today’s money?
In the end, considering price, the real question is personal. I am not sure moving over makes much sense. Moving up yes. So if you have a piece of gear you are happy with change for change’s sake doesn’t make sense to me especially in Audio.
The most important factor in a good audio system are the synergies among amplifier, speakers and room.
Finally.
We audiophiles tend to get buried in the technology weeds. The key numbers/measurements for amplifiers are those that indicate how they will drive your speakers.(power, current, impedance etc etc etc).
The technology or design philosophy that achieves those numbers is at best secondary at worst a red herring. And really what counts is how it all sounds to you.
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In the end, considering price, the real question is personal. I am not sure moving over makes much sense. Moving up yes. So if you have a piece of gear you are happy with change for change’s sake doesn’t make sense to me especially in Audio.
The most important factor in a good audio system are the synergies among amplifier, speakers and room.
Finally.
We audiophiles tend to get buried in the technology weeds. The key numbers/measurements for amplifiers are those that indicate how they will drive your speakers.(power, current, impedance etc etc etc).
The technology or design philosophy that achieves those numbers is at best secondary at worst a red herring. And really what counts is how it all sounds to you.
Wise post.... Thanks....
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If you are convinced that best amps can be measured, you most likely hit a goldmine of technical wisdom, although the term "smooth" might be not universal enough to define it. However, in my opinion, that is not even possible, especially because amps do not make sound on their own: the sound you hear exists in a relation to all component in the signal path.
I define 'smooth' as a lack of audible higher ordered harmonic distortion as per my prior posts to this thread. The idea that amplifiers do not make a sound of their own is false; we've been hearing these 'sounds' for the last 6 decades. Some amps are smooth and might be a bit soft in the bass, others do bass alright but are harsh in the highs. That this is so is well-known and not controversial.
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I was reading through this thread and decided to post here what I had posted not too long ago on the SoundLab Owners Forum:
Audio Research VT-150SE mono amplifiers (1994) vs. Audio Research Reference 150SE stereo amplifier (2016).
"I recently purchased a Audio Research Reference 150SE stereo amplifier that uses eight (four per channel) of the (relatively new designed) KT-150 power tubes (150W pc) and the input tubes are four 6H30s. All of the tubes are new and matched from Audio Research. Power supply energy storage: 1040 joules total for both of the channels.
The SL A3PX full-range electrostatic speakers sound excellent when driven by it using the 8 ohm taps.
Surprisingly or not, it is not “better” (whatever that means) than the two 1994 Audio Research VT-150SE mono amplifiers I’ve been using for the past twenty-five years on SoundLab speakers. I've been comparing them directly.
The VT-150SEs are rated at 130W pc and they use eight (four per channel/amplifier) of the 6550 power tubes (GE), eight 12BH7 drivers (four per amplifier) and four (two per amplifier) 6922 input tubes. It also uses tubes (two 6550s and a 12AX7) in the power supply regulation. Power supply energy storage: 420 joules for each channel/amplifier.
When comparing the VT-150SEs on SoundLab A3PX full-range ELS, the Reference 150SE tonal balance is slightly leaner (taut) upper bass and slightly more forward upper mid-range, using the 8 ohm taps on the amplifiers. Speakers are set flat (0) with treble at 12 o’clock position.
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@fthompson251
where are located? Don’t just send them to any old shop, research a lot!
we drove many hours to Rockford,IL TO A PLACE CALLED : https://soundsclassic.com
i refuse to ship my gear, I will drive my,amps to the headquarters if needed.
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@williambf , your result would imply a difference in output resistance between the two models. Have you tried using different taps to see how you prefer the sound? I gleamed this from Stereophile, not sure they are your exact amplifiers.
This is 2012, may be similar.
As expected, the Ref150's output impedance varied according to the transformer tap selected. The 16 ohm tap measured 1.4 ohms at low and middle frequencies, rising to 1.9 ohms at the top of the audioband. The figures for the 8 ohm tap were 1 and 1.4 ohms; for the 4 ohm tap, they were 0.55 and 0.87 ohm
This appears to be a 1994 review:
The VT-150's output impedance was nearly 1 ohm (0.99 ohms) at any audio frequency measured at the 16 ohm tap. This value decreased to 0.56 ohms at the 8 ohm tap, and 0.3 ohms at the 4 ohm tap.
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I’ve tried the three options and 8 is the one (and only one) with both amps on the Soundlabs, also what Soundlabs states.
Both amps sound excellent dynamically with a subtle tonal balance difference. 6550 vs KT150 and 1995 vs 2017 or so.
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@arcticdeth They are going directly back to Kevin Hayes at VAC in Sarasota FL. Where they were built.
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