So, from the previous thread about high-end class D the Purifi module was brought up. I decided to get a cheap example from VTV, a simple stereo unit with a single Purifi module and matching Hypex SMPS. Standard input buffer. I got it in yesterday. First impression wasn't what I was expecting: weak, congested dynamics is what stood out to me. I expected greater expression through my ProAc D30Rs. The other problems such as poor soundstage, thin / boring character, etc, I marked up to needing burn-in before evaluating. So it's been 24 hours, I would still expect to get at least the high control / damping of high end class D and dynamic power, but it's just not present.
Could it be an impedance mismatch? Other manufacturers selling the Purifi with their custom input buffers are reporting 47k Ohms. VTV doesn't say in the manual or on the site. I checked the Purifi data sheet which reports...2.2k Ohms on SE???? That can't be right?? That's absurdly low! Am I reading the right spec? My preamp has an output impedance of 230 Ohms. Can someone confirm that the stock Purifi has this ultra-low input impedance?
It must be getting close to the release of the your new Class-D to respond like that with such verve and virgor with doubling of wattage v halving of impedance loading.
Take it up with the likes of D’Agostino, Curl, ect ect manufacturers of the greatest amps that are recognized as being able to drive speakers with loadings that make Class-D’s run for the hills, they will tell you the same thing.
As much as I like my NC500 monoblocks on my easy to drive secondary speakers, they can’t compete in an A/B against my friends Gryphon Antillion on his Wilson Alexia MkII’s, and the Gryphon is less than half the wattage of the NC500’s
Show us just one that’s not, and can almost double it’s rms measured
wattage from 4ohm to 2ohm. The true indication of not current limiting,
like many good A/B bjt amp.
George, seriously, you would do yourself well to educate yourself on how amps work, at a basic level.
Your metric seems to be "at full power". That is actually causing you to have confusion; its a misleading and lousy metric. What is important is that the amp behave as a voltage source, and by that I mean that it will make constant voltage regardless of the load impedance, at music power levels. If you exceed the power the amp makes into whatever impedance, it will clip (overload). I'm stating stuff that should be obvious but because you trot this trope so often, I have to assume that everything I'm telling you here is new for you.
With any amplifier the designer is faced with limitations; often verses cost. For example, our module has GaN output devices that are rated at 35 amps. This means that we should not exceed 17 amps in the field if we want the output section to survive; employing 50% margins is a good idea with any kind of semiconductor!
In addition the heatsink has to be effective, and yes you do need them for GaNFETs if you plan to run the amp at higher power levels, and especially if that involves lower impedances. So far all traditional solid state amps all have this factor in common too.
Finally you have to look at how much you want to spend on the power supply. Given you know the limitations of the output devices there's an argument for setting the power supply current to a certain maximum so that current will not be exceeded.
So really what this comes down to is what I've been harping to you all along: the current capacity of the output section, its heatsinks and the current available to support the output power of the amp are the variables and these are no different than traditional solid state.
What **is** different is that the output impedance of any class D amp employing GaNFETs is several times lower than any traditional solid state amp. That is why they can act as a voltage source to a much lower impedance than traditional amplifiers. So your metric of 2 ohms is not harder to attain than it is for traditional solid state should the designer feel its important.
If you like or need volume, that "pathetic" 20W amp sound quite anemic. So it doubles to 1 ohm. If I have inefficient mainly 8 ohm speakers it will still be anemic. There is no magic in a 160W into 1 ohm amp that halves in power all the way to 8 ohms.
You shot yourself in the foot with this really idiotic argument. I expect most people are shaking their heads reading it.
You only need the current you need. It does not matter if an amp doubles its current/power down to 2 ohms. All that matters is that it have enough current at 2 ohms to drive a 2 ohm speaker to the volume required. The IceEdge 1200 module puts out 700 watts into 8 ohms, 1200 into 4 ohms and I measured 1000 watts into 2 ohms......so what? Michael Fremer used this amp module on his 2 ohm Wilson Alexx speaker and said it was great in the bass. Of course, if he had a larger room and played way louder then maybe 1000 watts would not be enough......I mean, how many speakers are 2 ohm......not many. Let’s see......Alexx speaker is 91db sensitivity.....and say you are 10 feet back....so that would be around 82db with one watt......10 watts gives 92db and 100 watts gives 102db.....and 1000 watts gives 112db.......I doubt many listen this loud. This is why 500 watts into 2 ohms is plenty for most people and most speakers (most speakers don’t go near 2 ohms).
The Merrill class D amps all double their power down to 2 ohms.....all of them. Most class D amps don’t do this because it costs more money for larger supplies and it is generally not needed. Did you know that the big Parasound Jc1+ amp does not double all the way down to 2 ohms? Stereophile measured 500 watts into 8, 830 into 4 and 1200 into 2 ohms. I guess they should make an even bigger amp to satisfy those that need number doubling.......$16K and no power doubling.....too bad. The 60 thousand dollar Gryphon amp doubles to 2 ohm....but it only does 700 watts at 2 ohms.....so my $2K IceEdge amp I sold last year will probably play louder than the $60K Gryphon.......doubling does not matter.....only the power you need matters.
Class D amps are only current limited by the designer
Show us just one that’s not, and can almost double it’s rms measured wattage from 4ohm to 2ohm. The true indication of not current limiting, like many good A/B bjt amp.
The Purifi module does 400 watts into 4 ohm...and over 500 watts into 2 ohms (25amps)
This is pathetic to show off it’s current ability, some NAD’s can do that current, it’s actually limiting, should read closer to 800w into 2ohms if it were good at current into low impedances.
A 175w- 8ohm Gryphon will do 350w - 4ohm 700w - 2ohm 1600w - 1ohm 9000w - 1/4ohm NOW this IS an amp that does current without limiting.
02-21-2021 7:17pmWhat
you are hearing is what class d amps do they produce high wattage with
low current to save money on energy and expense of manufacture to make
more money for the manufacturer and they will not have the required
current to dive the proac speakers you have they like a good high
current ab type amplifier i am glad you did not spend much money on the
class d amp you dodged the bullet with that decision.
More making things up. I really don't consider 25 amps that limited. That's 1250 watts into 2 ohms. Class D amps primarily have thermal limits because real world music is not 1000W continuous, ever. That's a magazine test.
Class D amps are only current limited by the designer. You can make a super high current class D amp (you just need higher voltage rails and larger fast power supplies and maybe a couple more output transistors.....and great output coil). Class D idles at practically zero current....because its output stage is switching at high speed......does not need to be "on" all the time. What you hear in any class D amp is the designers knowledge...nothing more, nothing less. Tons of high end speakers use class D amps for the bass. The big Von Schweikerts for example.....no loss of dynamics there. There are tons of things in any amp that effect the dynamics.....one bad part and dynamics are history......and this is true for high-current class AB types as well. This is why all class A/B amps sound different.....in the bass/dynamics and otherwise. I do various things in my mods to the VTV Purifi amp that allow for better bass and dynamics and speed. There is no end to tweaking.....no end to knowledge. The Purifi module does 400 watts into 4 ohm...and over 500 watts into 2 ohms (25 amps).......this is enough for most speakers but getting it all out of the module in the most tweaky, dynamic and great sounding way is an art.
What you are hearing is what class d amps do they produce high wattage with low current to save money on energy and expense of manufacture to make more money for the manufacturer and they will not have the required current to dive the proac speakers you have they like a good high current ab type amplifier i am glad you did not spend much money on the class d amp you dodged the bullet with that decision.
This is what it says, "Furthermore,the NC500 OEM is an unbuffered amplifier leaving the implementation of an input buffer up to the manufacturer. The NC500 is practically devoid of any sonic signature so this external buffer is a good way of tuning in a “house sound”."
It does not say any of the other things you are implying, and there is no truth that this is true. We have noted the performance THD+D and IMD is impacted by the output impedance of the buffer when we did testing .... you know on actual test equipment.
As Hypex say, "The NC500 poweramp module is devoid of any sonic signature" this is "without the buffer". And it will give the best "sonic transparency/dynamics" if doable, as I do without any compromises, just better sound and a purer signal path from input to output. No additional "house sounding" opamp buffers with colourations/distortions in the signal path.
Take that as I would as colouration distortions, countering what they
say earlier in the same sentence as "The NC500 is practically devoid of
any sonic signature ”
Actually the two comments sound entirely in agreement with each other.
There are no such things as "copper resistors"....generally speaking. Both Nord and VTV use metal film resistors. Maybe you think the 3 polystyrene capacitors on the Nord board are "copper resistors"? You are once again mistaken. I wish people were more focused on what they write. Every word has power and meaning. Did you read above what the guy posted about the VTV board versus the Nord Rev D board? He said the VTV board sounded better. I tend to trust what people say when they do listening tests. When they just talk about something and even some of their info is wrong.....well, not a reliable source to believe.
Ok I looked at my Nords and my phone pics. I deleted the pic of the boards after I returned them..
Now I remember the whole deal. I bought 2 buffer boards and 2 Wiess opamps. They arrived but it took 4 opamps to do 2 boards. It was worded weird. I looked the boards over, and he (whoever built the boards), didn't use copper foil resistors and the work on the boards was not as nice. Plane and simple.
I didn't get to listen to the Weiss, as I recall. I was ticked that I need two more. 950.00 for a pair.. 700.00 for the Nords..
The boards side by side, LOL yea, about that... VW vs Porsche. The boards I looked over.. Even Rev C had copper foil resistors vs Weiss with cheapos.
They can take the 2590s I was mistaken, I was ticked the it took 4 Wiess Op Amps and he sent me 1/2 what I needed. Didn't make any sense.
The guy couldn't read my mind.. Go figure.. My mistake..:-)
They were sent back. Customer service was great though.. No problems at all.. Good guy to deal with..
I'll stick with Nord.. only problem it's in England.. Turns out it's not an issue so far, 5 years now with class ds Hypex NC500, no issues.. Sure like them better than the ICE products.. I have Wyred4sound, too mercy.. Where is the tone control..
Here is a comment from someone who bought the VTV buffer boards and installed them in his NC500 amp.....this is from the VTV website:
"I purchased a pair of the VTV input buffer boards for my NC500 amps using the Sparkos SS2590 opamps and WOW. I must add that I have been using the Nord RevD buffers and before that the Bellissimo Audio buffers. I had tried the SS3602 and preferred the SS2590 in each case. After installing the VTV buffers in low output configuration I was blown away. The amp was more cohesive with smoother overall performance and finer details also better bass."
The Nord board is not better made and the VTV board has the exact same options as the Nord and VTV sells more op amp options. You can use any of the the op amps that Nord sells and more. There are no copper foil resistors on the VTV board......what the heck is a "copper foil resistor"? He uses standard metal film resistors that were tested by Andrew Sparks as having the lowest noise.
The one thing I did dig out of the thread is, I need to pick up a pair of Nord built Purifi 1ET400A, with Nord buffers and Sparco 2590. He'll give me a deal.
I own 9 of his NC500. I bought 5 from him. 3 pairs of MBs and one X3 NC500 with trigger and 3 x PS (no sharing). ALL use 1200/700 PS. All but 2 have rev. d boards (rev c). Let's say we have a rapport. My 3X was the first to roll off the line with rev d boards and multi Mono rail within a single enclosures, withOUT shared (or compromised) PS 1200/700. Serious piece of gear..
Now to modify the fuse circuit. It needs to be inline and remove the onboard 15 and add a 20 amp iec copper/silver non fuse female.
These are great sounding units with small planars MUCH better than any of the earlier 400/500/700. I really didn't like that sound as ALL.
The buffer made all the difference in the world for me.. BUT then I like tone control, Mcintosh and VMPS speakers. I'm one of "those guys".
To top it all off, kenjit, kicked me off his forum, I'm heart broken.. (took a while to work). Ok I all better now.. I'll quit yipin', I mean typing. :-)
The VTV input buffer board is pretty much the same as Nord’s. However, VTV offers more op amp options and the amps cost less
<<<<<<<<<<<<<<<<<<<<<,>>>>>>>>>>>>>>>>>>>>>>>>>
Actually I did a visual side by side. The Nord is a much better made board, by no small margin either, NO copper foil resistors, and SLOPPY, solder joints. Second the Nord Rev. D has the greater options. You can not use the Sparco 2590s, or other pro op amp options.
Either buffer can use the smaller op amps, SI, or Sparco, a few of the Class A op amps..
The Wiess op amp is HUGE and has a proprietary mount, that only it can use. The cost of that buffer and opamp is the most expensive you can buy. The funny part the guy that sells the VTV boards admits the Nord with 2590s sound better and cost LESS. 1/3 less. 274.xx (Euro) 323.xx usd
He took back the VTV board, I got from him. I thought the option for Wiess was for TWO. It is for one board 442.xx usd. Over 100.00 usd difference AND the guy that makes the VTV likes the Sparco better, ASK HIM... I think both use Sparco Voltage regulators. Nord does..
The VTV input buffer board is pretty much the same as Nord's. However, VTV offers more op amp options and the amps cost less and have a 30 day money back in the US...............and you can buy their version of the Purifi evaluator amp for less than $1000 delivered.
All Purifi 1ET400A are modular, PSU, AMP, and buffer. Making them easily upgradable in future developments of our Input Buffer. They are also easy and open to maintain.
The REV D Buffer board uses modern versions of an old Op-Amp used primarily in Studio mastering and mixing equipment. Their development was focused solely on Audio performance and has been bought up to SOTA design and performance. Rev D will also accept the previous 8 pin Sparkos and Sonic Imagery Op Amps. Details of Op Amps Click
Did you test to see if they actually do that in this application?
Yes, that why I said it.
I would think that due to the low impedances involved the interconnect issues wouldn’t be an issue.
And to have the MSB buffer at the Hypex input or 1mt away with quality interconnect, is no difference at all and you know that. But what is worse, is having one buffer in series with another buffer. When if one "can" if loud enough do the job perfectly and yield even better sonic results.
You have probably already seen this, but again for the masses, from the Hypex NC500 data sheet.
Audio input The INH/INC inputs form a differential pair. Note that the input impedance is fairly low meaning that, minimalist discrete circuits or valve input stages won’t work. All op amps commonly used in audio can handle them though
Input Conditioning / Buffering Unlike in many other Hypex products, no input buffer is present as manufacturers of audiophile equipment tend to bypass it anyway and design their own. The NC500 is practically devoid of any sonic signature so this external buffer is a good way of tuning in a “house sound”.
"good way of tuning in a “house sound”" Take that as I would as colouration distortions, countering what they say earlier in the same sentence as "The NC500 is practically devoid of any sonic signature ” And this is what you hear by not! having an extra buffer in series that’s not needed.
No they are the output buffers in the rear of the MSB discrete R2R dac,
which can swing 7.5v and do it with ease into 2kohm, with no temp rise
or voltage drop or heat sink needed into the raw NC500 module
Did you test to see if they actually do that in this application? There are a lot of variables here, not the least of which is how surprising 1 watt of power actually is and how distortion can affect your perception of sound pressure, to say the least.
The issue is performance, and without a proper low impedance buffer, at
the input, not 6 feet of cable, with capacitance and inductance, the
performance suffers in my testing (with actual test equipment).
I don't doubt he did it, just pointing out that it is not an optimum implementation.
As you might know our MP-1 is a tube preamp but can drive this through 30 feet of balanced cable with no worries- but that is our module, not a Hypex or the like to which I have no exposure. I would think that due to the low impedances involved the interconnect issues wouldn't be an issue. But there is a lot to unpack here; IMO the whole thing can be taken with a grain of salt without more information.
The issue is performance, and without a proper low impedance buffer, at the input, not 6 feet of cable, with capacitance and inductance, the performance suffers in my testing (with actual test equipment).
I don't doubt he did it, just pointing out that it is not an optimum implementation.
Data sheet: Each output drives a 150Ω load to ±7.5V with ±15V supplies
The amplifiers are stable with any capacitive load
making them useful in buffer or cable driving applications.
No they are the output buffers in the rear of the MSB discrete R2R dac, which can swing 7.5v and do it with ease into 2kohm, with no temp rise or voltage drop or heat sink needed into the raw NC500 module
And the proof is how it sounds, far better than having "any additional buffers" at the input of the NC500 module/s.
And everything is direct coupled with no DC offset from dac outputs right through to speakers. ("small very fast settling" switch on low level bump from the dac) so amps go on last how it should be anyway.
As far as I know the only company not using a dedicated buffer for the input of the Purifi module is Mivera....they made a streamer last year that used just one gain stage between the DAC chip (1 volt out per phase AKM DAC chip) and the Purifi module. Normally the DAC has a gain stage and so does the Purifi.....by removing one gain stage and having it all in one box you get some serious transparency. Most Purifi amp users will want a built in gain/buffer stage. You will not know if your high gain preamp/DAC can drive the 2.2K input impedance very well, unless you listen. The only way to listen is to buy the VTV amp with the Purifi input board that has the jumper on it so you can use the built in OPA1612 op amp or run it without. However, if you like it with the 1612 buffer (read Sarajen’s review in 6 moons......he liked the buffer over his preamps direct).....then you have no choice for better op amps. The VTV amp with the Purifi buffer cannot be changed to the VTV version with the discrete buffer board.....they won’t fit....its a smaller chassis.
Here is an interesting factoid. The IceEdge amp I made last year had 47K input impedance when I was first modding it. I raised the input impedance to 150K and it sounded noticeably better. I am using 150k on my mods to the VTV Purifi amps. My source was a discrete output stage with a 50 ohm output impedance......The cable in between was low capacitance and two feet long.
So, if you have 500 ohms output impedance and you are driving 2.2K.....then maybe you should try lowering that 500 ohm resistor to say 10 ohms......I could sound much better. You do not need a 500 ohm resistor in series with anything unless it needs it for stability (which might indicate a bad design). Most high end solid state preamps have an output impedance around 100 ohm........The Gryphon Pandora is 7 ohm.
although you wouldn't be able to drive it to full power
I can't speak to the Hypex but based on the idea that its input is about 2K (and thus similar to our module in that regard) I would not be surprised that George did this.
No need to, I'm still only at 3/4 volume on the MSB for ear spitting level, I think I'd blow the 90db speakers before the amp. And so it doesn't matter if I can reach full level or not on the NC500's, think of it as a safe guard against blowing them up.
So it is possible that George was telling the truth, but that would mean that he had a pretty gutzy preamp on hand. Most preamps I can think of wouldn't drive a load like that
@unsound Thanks. There's still a bit of missing information, but you might be able to 4-5 volts out of one of those DACs (balanced), which would certainly be enough to make our module play although you wouldn't be able to drive it to full power. I can't speak to the Hypex but based on the idea that its input is about 2K (and thus similar to our module in that regard) I would not be surprised that George did this.
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.
In order to make the comparitor work properly (no offsets, no oscillation) with all the comparitors we tried we did wind up with an input impedance of about 2K. Through a lot of our prototype process, we simply drove this with our MP-1 (or MP-3) preamp, which has no problem at all driving a load like this. Of course, it was obvious that the circuit needed more gain and an easier load to work with most preamps. But it worked fine since we were not including the input buffer in the feedback loop anyway. FWIW our MP-1 can drive 32 ohm headphones- its got a miniature tube power amp (with direct-coupled output) as its line stage.
So it is possible that George was telling the truth, but that would mean that he had a pretty gutzy preamp on hand. Most preamps I can think of wouldn't drive a load like that, so I do think his comments should be held in abeyance until he can explain how he did it.
Since you really don't need much gain from the input buffer, almost any opamp that can drive 600 ohms (and most can these days) can do the job since your gain only need be a value of 2 or 3. So it would not surprise me in the slightest that the kind of opamp used has an inaudible effect. A proper buffer will have more than just one opamp of course, especially if you are executing a balanced input. But they would not need much gain so the feedback on the opamp would be very high! IME its when you are asking more than about 20dB of gain that you start hearing differences between opamps.
I am thinking more about how much better my EVS1200 + Oppo 105 with PS mods and Audio Alchemy DDP-1 + PS 5 could sound off grid. Some days the sound is magical, other less so, probably fluctuations in the grid and/or varying humidity. 2 weeks ago low temp and humidity, this past week mid to upper 80s and high humidity resulting in sticky skin
The amp is plugged into 20amp dedicated line, the other two into a CorePower 1800. What do you suggest?
and here: https://forum.audiogon.com/posts/1422053 where you help with his even at that time ignorant knowledge of Class-D (which has not improved in 4+ years I see.
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.
Once again, you have no idea! The
input impedance of the NC500 Hypex is 2k across the band, and can be
driven by any buffer from a source that has 50ohm or less output
impedance and the voltage gain needed to give you the max level that you
need listen to. Once again, you have no idea!!
I'll try to get my friend who heard it yesterday to post on it.
Well I have listened to enough audio equipment for 5 lifetimes, do I win a prize? I actually know how to design an amplifier too. People who actually know something about high performance analog design (and Class D), can reference the data sheet here on the HYPEX website. Now consider the transient performance with the source 2 meters away in a high speed feedback loop for Class-D.
George asked me to comment here. Happy to do so as I have no bias either way. But having bought, sold, reviewed & listened to enough audio for 3 lifetimes, I do have an opinion. I had the pleasure of hearing George’s Hypex NC500 mono’s driven direct (no Buffer) on his secondary system yesterday. Driven from the MSB Discrete R2R dac, it would have to be the cleanest and most dynamic Class D reproduction I’ve heard to date. And I’ve probably heard 30+ different Class D Systems over the years. Extremely low, coherent & powerful bass that remained tuneful at all times. Musical structure & impact maintained across all frequencies. For Class D and in fact any amplifier technology, the sound was superb by any measure.
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.
Once again, you have no idea! The input impedance of the NC500 Hypex is 2k across the band, and can be driven by any buffer from a source that has 50ohm or less output impedance and the voltage gain needed to give you the max level that you need listen to. Once again, you have no idea!!
I'll try to get my friend who heard it yesterday to post on it.
The VTV amps use switching supplies and idle at something like 30 watts. If you have reasonable efficiency in your speakers you will not even use 100 watts on peaks. However, all transformers sound different from each other and most isolation transformers sound like transformers.....slightly slow......even 3000 watt Topaz isolation transformers can mess with the sound in certain ways. Every thing messes with the sound. Right now I am running my super modded VTV right out of the wall (power cord hardwired into the wall....yup, no joke). I want to get a 2000 watt low distortion pure sign wave inverter to run the amp. I am currently using a 400 watt inverter on my digital front end....giving super sound......really nice to get off the grid!
Linear power supplies on amplifiers draw current in large peaks, much higher than the average power current draw. A 500W isolation transformer will act like an inductor with a current limiter. It may be better, it may be worse.
In a few more days the Weiss opamps will be at 200 hours and ready for evaluation. Also I have the amp running through a 500 watt balanced isolation transformer along with the DAC and pre; I wonder if there could be any current starvation going here.
Example, i had not listened to the stereophile first test disc in 10 years. However, my system 10 ears later was more revealing than that older system except for the fact that the original system used super highly modified original Quad electrostats.(modified by me....the most extensively modded Quads that i have ever heard of). When I played the disc 10 years later it did not sound right at all....the orchestra, the air, the bell ringing in the backround, the guy singing in Hebrew.....just not right. So, I removed the midrange from its box and put it on top of the speaker and propped it up with a paper back book underneath (no baffle) and changed the xover on the woofer so it now went to 300hz as i knew the midrange driver on an open baffle would not do anything below 300hz. After listening......most all of the difference from what I had remembered 10 years before came alive. Still not quite as good as the old super modified Quad....but now very close....the reverb was going on for ever......before it was all blunted with the midrange in the box.
Yes, indeed you can remember what something sounded like 10 years before. Anyone can do this.....with an open mind and open heart.
I can remember how something sounded 10 years ago.....really!
Righhhhttttttt
Most people can't pick their own speakers out of a line up once they are gain matched and frequency compensated, and often not even with frequency compensation.
You may remember a general impression, but from a comparative basis 10 years ago, sorry, that is just not true. You believing that does not make it right.
Toole showed in the Harmon tests how flaky most audio reviewers are. Looking at the rooms many of them used, different speakers, etc. the odds of them effectively pulling the characteristics of a single unit out are slim (to none).
In
my past experience with the Nord Hypex NC500 monoblocks using the
Sparkos and Sonic Imagery opamps, the differences were pretty obvious.
Best is no buffer at all, direct in, as I’ve done. (you don’t need a buffer driving another buffer) If
the output buffer in your source (pre or dac) is less than <50ohm
output impedance and has high enough voltage output gain to give the
volume you need, you’ll have better sound than any additional buffer
(regardless of how good) that’s in the signal path
Cheers George
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source. The input of the unbuffered amp is essentially in the feedback path. Not having a local buffer is a recipe for doing it wrong. This is the difference between people who actually know what they are doing and those who do not. People who do not make statements like this above.
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