I thought it was time we had a pro- Class D thread. There's plenty of threads about comparisons, or detractors of Class D.
That's fine, you don't have to like Class D amps, and if you don't please go participate on one of those threads.
For those of us who are very happy and excited about having musical, capable amps that we can afford to keep on 24/7 and don't require large spaces to put them in, this thread is for you.
I don’t "blame" preamps for changes in frequency response. I say high
output impedance causes frequency response changes which vary based on
the load. This is an irrefutable fact based on simple serial circuit
analysis. Anyone with a basic understanding of AC circuit analysis would
conclude the same.
And I showed the math for why that is not so: the first half of your quote here is false, the second half being based on the first is thus also false.
**Do the math**.
Its the coupling cap at the output, not the output impedance that governs the frequency response.
Example: I've seen ARC preamps with 20uf output coupling caps. If you put them on a 10K load, they will be as flat as they are on a 100K load in the audio passband. Yet the very same preamp according to ARC should not be asked to drive anything less than 30K.
Your claim to which I was objecting was that the higher output impedance of tube preamps leads to frequency response errors and the simple fact is this is not so- it depends more on the timing constant that may or may not be present at the output of the preamp in question. I showed the math. If you wish to refute this, then show the math.
I was taking a look at the NAD C390DD integrated. I like the concept of being able to change out the boards as upgrades become available. Anyone have experience with the sound quality of that model?
As we can see, if one is to point at a tube preamp and blame it for a change in frequency response,
I don’t "blame" preamps for changes in frequency response. I say high output impedance causes frequency response changes which vary based on the load. This is an irrefutable fact based on simple serial circuit analysis. Anyone with a basic understanding of AC circuit analysis would conclude the same.
It is also irrefutable that in general, tube preamps have higher output impedance than solid state. That is different than saying preamp X sucks, which is what you seem to have read.
the factor is not the output impedance (which is often only stated at 1KHz), its the coupling cap at the output. That is a bit different from ’output impedance’ and that is why I placed the correction.
A - I never limited myself to 1 kHz B - It makes no sense to talk about changes in frequency response if i was talking about a single point C - The coupling cap is a major if not THE major contributor to output impedance. However it is not the only issue. I never said it was. The factors that go into any devices output impedance is more complicated, but includes the coupling cap if any.
There is no logical way to make both of these statements true at the same time:
Tube preamps don't have a problem with output impedance
The problem with tube preamps is the impedance of the coupling cap
Since the first includes the second, you can't have both of these be true at the same time. Best,
The biggest issue with input/output impedance is the change in frequency response....(followed by supporting discussion with links to external sources)
You replied:
This is mostly misleading or outright false.
Now your latest posts seem to be supporting my argument. I’m not sure you even read what I wrote before you claimed it was a lie or misleading, but you launch into discussions about how Atmasphere preamps are different (which while informative does not make your case that I was wrong).
So I challenge your "statement of fact" as having anything which directly refutes my statement with evidence.
A statement of fact is not an attack. You are taking this personally.
Here’s the work:
What, exactly, are you claiming is a result of the choice of coupling cap? Distortion or output impedance?
Here’s a formula for calculating cutoff frequency: F=1,000,000/CxRx 2Pi
Normally you see this formula with a 1 instead of a million; I used the latter so that f is in Hz (-3db point), R is in ohms and C is in uF.
The coupling cap at the output of a preamp, in concert with the input impedance of the amplifier used determines the cutoff frequency.
example: a solid state preamp has a 10uf output coupling cap. The input impedance of the amp is 10K.
1.59Hz=1,000,000/10K x 10uf x 2Pi
We can see from this example that if a tube preamp has a 10uf coupling cap that it too will have a cutoff of 1.59Hz into the same amp.
This means there will be no appreciable phase shift at 20Hz so bass impact will be unimpaired, since the cutoff is 1/10th the lowest frequency to be played. A cutoff at 20Hz will mean that phase shift exists up to about 200Hz. The phase shift will cause the system to sound lean.
Many tube preamps **do** have such large coupling caps unless the designer has not done their homework (or has figured out that the larger the coupling cap, the more coloration it imposes, and so has elected to limit the capacitor size so as to get greater transparency). As a manufacturer you can’t forecast to what amps the preamp will be paired.
The size of the coupling cap will not affect the output impedance unless one is able to graph the impedance curve; if rising at lower frequencies the culprit will be the output coupling cap and otherwise not the output impedance of the preamp.
Now how much **distortion** the preamp makes can be affected quite a lot by the load that it drives. That is likely the more powerful argument for being careful about what preamp drives what power amp. Tube preamps often have very low distortion; in most cases its a good idea to have them drive a higher impedance so as to take advantage of that fact. Our preamps again are an exception- they regard 10K as an effortless load.
Please note:
This supports, not undermines, my statement.
yes, this is evidence of how this was simply a statement of fact and not an attack.
The biggest issue with input/output impedance is the change in frequency response...
I was very specific in what I was talking about. I did not say "the biggest issue with tube preamp sound quality." I said the issue with "input/output impedance."
As we can see, if one is to point at a tube preamp and blame it for a change in frequency response, the factor is not the output impedance (which is often only stated at 1KHz), its the coupling cap at the output. That is a bit different from ’output impedance’ and that is why I placed the correction.
The biggest issue with input/output impedance is the change in frequency response...
I was very specific in what I was talking about. I did not say "the biggest issue with tube preamp sound quality." I said the issue with "input/output impedance."
If you see another issue with input/output impedance to be more important, please show your work.
My prior post was a correction and not an attack. I was merely pointing out where the problems were and stated why, basic engineering principles included. More are below.
You called my statement:
mostly misleading or outright false.
That’s not a correction. If you had said "I feel distortion is a bigger issue" then it’s a matter of opinion as to which is more audible. If you want to say I wrote falsely or in a way to mislead back it up.
You then state:
This has more to do with the choice of coupling capacitor at the output of the preamp than it does the output impedance!
What, exactly, are you claiming is a result of the choice of coupling cap? Distortion or output impedance?
The general rule of thumb is a 10:1 impedance difference between the two; as long as you hit that margin with the amp you have in mind its likely no worries.
I'm sure you make fine products, but would you then please explain the
variance in all the tube preamps in the Stereophile section if not due
to output impedance issues?
My prior post was a correction and not an attack. I was merely pointing out where the problems were and stated why, basic engineering principles included. More are below.
We won't allow Stereophile to review our products (we don't agree with their editorial policy which seems to be tied to their advertising and I know this from direct experience) which is one example of why if you limit yourself to their pages, you won't get the full picture.
This has more to do with the choice of coupling capacitor at the output of the preamp than it does the output impedance!
Please note that this phenomena has to do with solid state just as much as tubes.
Of course, the ultimate indicator is a graph of the output impedance vs. frequency. If you see it rising as it approaches 20Hz, this **might** indicate a loss of bass impact depending on the input impedance of the amp. The general rule of thumb is a 10:1 impedance difference between the two; as long as you hit that margin with the amp you have in mind its likely no worries.
The output impedance curve of our balanced preamps looks the same as their frequency response curves; we cut them off at 1Hz. So regardless of the load its driving, the preamp will have flat response from 1Hz to over 200KHz. Ours are not the only tube preamps with direct-coupled outputs that have ever been made- as a result you can't just assume that if it has tubes that it will have troubles making bass into a solid state amp with a 10K input impedance or the like. Generalities are often misleading that way.
Perhaps you feel your preamps are less susceptible than most, which I could believe. I did not make my statements absolute. If you’d like to submit FR charts at different loads like Stereophile has and at different volume settings this would prove your preamps outstanding exemplars.
I have to say that for you to call my statement in its entirety misleading or false when anyone can pull up page after page of examples in Stereophile measurements of tube preamps showing variance in their frequency response based on difference in the impedance they are driving is pretty gutsy.
Anyone can also compare solid state preamps to this and see that in general they perform better by this measure.
So I hope that maybe you misread the generalities and nuances I was making and re-think your reply or produce engineering principles and data which makes all the other data and the basic electric principle of impedance in series and voltage division a quack science.
The biggest issue with input/output impedance is the change in frequency
response. This is especially bad with tube pres as they usually have a
high output impedance. Driving a low impedance input amp can affect the
overall response and deviate from ideal. With purist tube pre's even the
volume control setting can affect things because they lack additional
buffer stages that would prevent this.
This is mostly misleading or outright false.
Output impedance **might** affect frequency response (in some cases, certainly not if the output is direct-coupled) but also affects distortion.
Tube preamps do not necessarily have high output impedance. That depends a lot on the design of the circuit! If it employs feedback, its output impedance will be fairly low and driving a 10K impedance should be no worries- check with the manufacturer (our preamps don't employ feedback and 600 ohms or less is no worries)! In a purist tube preamp, the volume control won't affect things (other than volume) despite there being no buffer; its all about how well the design is executed!
As an example, we make two tube preamps that have balanced outputs (and were the first in the high end audio world with such) and the load that they can drive makes no difference- the frequency response is flat, owing to a direct-coupled output. They also support driving 600 ohms as they were intended to support the old school balanced standard. Yet because they lack loop negative feedback, their output impedance is relatively high (compared to most solid state preamps), yet their distortion is very low driving any amplifier made with a balanced input. I've used our MP-1 to drive loudspeakers directly; how many solid state preamps can do that?
Whew. Thanks Todd, Erik and Al. That is a lot to digest but I think I understand it a bit more now. This does a lot to explain the basis for such terms "system synergy" and "system compatibility".
And now, back to our regularly scheduled topic of Class D amps are Dandy!
In the situation Autre described in his post dated 4-29-2017 it is very unlikely that impedance compatibility issues were present. The Rogue Sphinx has a very high input impedance (more than 100K according to Stereophile's measurements). And although I don't know what the input impedance of the
Peachtree Nova 125 SE
is, it is most likely much higher than the output impedance of the solid state Onix CD player which was driving it.
Impedance incompatibilities between line-level source components, such as CD players, and integrated amplifiers such as those, or between preamps and power amps, are likeliest to arise when a tube-based output stage is driving a solid state input stage.
Regarding the 10x rule of thumb guideline which Todd alluded to, I would state it as follows:
The input impedance of the amp (or other component that is receiving a line-level input signal) should be at least 10 times the output impedance of the preamp or line-level source component that is driving it, at the frequency within the audible range for which that output
impedance is highest. Which in the case of preamps or source components having capacitively
coupled outputs (such as the majority of tube preamps) will usually be
at 20 Hz. And the output impedance at that frequency will often be far
higher than the specified output impedance (which is usually based on a
mid-range frequency such as 1 kHz), because the impedance of a capacitor rises as frequency decreases.
That doesn’t mean that there
will necessarily be a problem if the guideline is not met. It depends on
how the output impedance **varies** as a function of frequency. What it
means is that there **won’t** be an impedance compatibility problem if
the guideline **is** met.
If Stereophile has reviewed the preamp or source component, the measurements section of the review will usually indicate the output impedance at 20 Hz as well as at other frequencies. But if only a nominal impedance can be determined, such as a manufacturer's specification that is presumably at a mid-range frequency, to be safe I would suggest a ratio of 50x or preferably even 75x.
One of the spec’s commonly sited is S/N (signal to noise) or related THD+n (Total Harmonic Distortion + noise). The problem with Signal to Noise is that it is often cited at full power, and not at a more reasonable amount, like 1 watt.
So, a 1000 watt amplifier can claim 10 dB more S/N than say a 100 Watt amplifier that sounds exactly as noisy. The full power S/N ratio becomes useless for comparing amps and how quiet they are. What I wish reviewers and manufacturers did more consistently is rate the S/N at 1 watt or 10 watts. Something small so we can compare what we’ll actually hear.
Distortion is also something that tends to go down as power goes up until the limit of the amp is reached. This is why these figures can be misleading. This is something stereophile does a little better, in showing graphs of THD vs. power output. Now we can at least look at charts to compare noise and distortion as more usable power outputs.
The other thing, I think that the amplifier community is having a hard time keeping it’s prices up to make boutique manufacturing possible. This makes it necessary to have big differentiation. For instance, having a 1,400 watt amplifier is cool and all, but in my living room, at my listening levels does it mean my sound is better than my 250 W amps?
I don’t really know all the answers to these questions at all. I’m just sharing where I start to scratch my head. :)
The biggest issue with input/output impedance is the change in frequency response. This is especially bad with tube pres as they usually have a high output impedance. Driving a low impedance input amp can affect the overall response and deviate from ideal. With purist tube pre's even the volume control setting can affect things because they lack additional buffer stages that would prevent this.
Good ways to see this is to look through the Stereophile archives and look at tube preamps. In the measurements section you will see the frequency response driving different simulated amps. Here is a link:
@autre I won't pretend to be smarter than I am.. I don't understand why it matters either, but preamps have a characteristic output impedance and amps have a characteristic input impedance. If memory serves me right, the amp input imp should be 10x higher (or more) than the preamp output imp. Having them too close can apparently cause the system to sound off or cause an increase in noise.
Anyone with more detailed knowledge, PLEASE addend or add!
I'm playing catch-up on the posts but thanks for the recommendation on the Wtred gear Scott. That STI has been on my short list as well, most likely the v1 since the used prices sre mire in my budget. I just haven't been lucky enough to snag one on the forum yet....
Todd, thanks for the reply. Please pardon my ignorance but I'm not sure what you mean by different input impedance. I'm still a bit of a rookie at the terms and what they mean towards the resultant sound.
If I may throw in my thoughts on the sound quality of class D amps, I can sum it up in 3 words: I'm a fan!
Class D skeptic. I was once, the latest from Merrill Audio, is excellent The Thor mono blocks at $4800 are very musical and best in class under $7k IMO.
@samac, yes all class D amps that have been in my system took over 1K hours to break-in and stabilize. But this has also been my experience with class A/B amps, with CD players, with two tube-based line stages, and with the Rowland Aeris DAC..
On the other hand, I have not tried in my system every amp on the market today, so I will not categorically state that all amps require over 1000 hours to break in...
I love the idea of a class D website, but to what purpose? Reviewing, comparing, contrasting? Or all of that plus sales?
It sounds like fun, but also like a lot of work.. though getting a steady stream of amps to review could lessen the pain.
I’m curious now about the sound of lower power vs higher power amps at low volume. I may have to try a little Dayton audio class D one evening, though it may be meaningless to compare a $60 amp to a $1000 amp and expect any sort of meaningful conclusions.
You know, I was just thinking of something. It would be really fun to marry a Nelson Pass First watt Class A amp to Class D voltage rails via transformers.
I'm glad you mentioned break-in hours again. I'm at 300 hours with my amp and it continues to settle in and get better.
Do you feel the lengthy break-in associated with class-D runs across the board? As I mentioned above I am running an amp that does not use the more common modules. So wondering if you believe it will also "season" and settle in past the 1000 hour mark. Honestly wouldn't surprise me if it does. Anything I've purchased fromDACs to speaker to amps have taken months to fully bed-in.
That's quite a coincidence...I just ordered a pair of Bel Canto's REF600M's to try them out. The ATI 544NC amp is equipped with dual NC-500 modules in bridge mode per channel, so plenty of power (900W in 4 ohms load) to drive any speaker out there.
I didn't want to end my quest for a 'perfect' Class D amp without auditioning the REF600's.
PS: I did find @georgehifi comment about REF600's little discouraging.
I'm so very happy with all of the participation on this thread, I'm also learning a lot, since I don't get to go to shows and dealers and listen as much as I would like to.
Would it be worthwhile to put together a web site JUST for class D amplifiers? It might give me the chance to listen to a lot more gear as a regular review feature, and break the mega-linear-amp stronghold.
Yes, George, Bel Canto Ref 600Ms are very good. I am right now listening to absolutely splendid sound of Mozart Symphony #40 with them driving Focal Alto Utopia Be speakers, sourced from Esoteric K-01 through an ARC LS 25 Mk II pre.
Thanks, Erik, great info. I had no idea it might mimic or be similar to other designs.
It’s my first adventure with class-D so I have no idea if it’s better or even as good as Hypex, B&O or Pascal. I do know I like everything about it so far. It’s the easiest amp to listen to since my octal pre/845 SET combo. Refined and smooth with no listening fatigue at all.
I hope you do check out NuPrime. Would love to get your thoughts on how they fare against some of the competition out there.
I looked at the NuPrime pages VERY briefly. NuPrime’s tech sounds a lot like the Yamaha EEEngine. Small class A amplifier sandwiched between Class D voltage rails.
Again, kind of goes back to Carver’s Magnetic Field amp and NAD’s switching rails technology.
Sure gets grate reviews. I would love to give them a serious listen to see what the benefits really are.
I mean, it’s quite different from Hypex/Pascal/B&O but I have no idea if it’s much better.
The challenge with this kind of hybrid approach is again, you rely on feedback to tell you everything about what you should do from instant to instant. With the voltage rails swinging at the same time the Class A amp is swinging it is like shooting an arrow from a moving boat.
Lots of great info and feedback on the "big boys" in class D (B&O, Hypex, Pascal).
I've been using the NuPrime IDA-16, which uses proprietary modules and I'm really liking what I'm hearing. So much so that I'm pretty sure it's staying (45 day trial period).
Anyway, anybody else using class-D amps from manufactures "rolling" their own modules?
I have three Crown ITech 5000HD stereo amps (6 x 1250 watts) with incorporated active dsp crossover controlling 2 JBL M2 Master Reference Monitors and a JBL Sub18 (2500 watts bridged amp). These are called class I by Crown and are a variation of class D. Dynamic range, transient response, and headroom, are well beyond the traditional average "audiophile" system. These characteristics are, in fact, staggering when compared to my conventional Classe/B&W 801N system. No doubt, this is due in part to the extreme high wattage and active crossover of the Crown amplifiers, something not easily obtained with conventional amps. I don't sense any particular harshness with the Crowns, and, in fact, the system sounds pretty sweet, but I do constantly wonder if upper frequency refinement would improve if the Crowns were other than class I. The totally outrageous slam and bass response of the JBL/Crown system, however, is quite fun.
Jtsnead, I have been following the evolution of the Nord since the inception of them,Rollable op amps,very cool.Colin North has quite a following on audio shark forum.
The Bhk preamp looks like a good fit for me and there is several used up for sale.Thanks for the info.
Madavid,
You may want to try a warmer sounding solid state or tube preamp with your d-Sonics. Let us know the details of your current system and what kind of musical presentation or flavor that you are looking for.
I do very much so Eric , maybe it’s you that needs an bi-aural Exostosis operation.
As I said before the only one of new breed of Class-D’s that I had any time for, was the latest BelCanto 600 monoblocks to which BC from what I understood by the presenter has done their own switching noise filtering, from what is standard from NCore.
But they had to be driving a benign 6ohm load, of a top line Raven tweeter’ed two way bookshelf, to get me to like them, on the other speakers they too didn’t sound very good.
When I was trying to the latest class D experiment, Nord was on my short list. I ended up going with D-Sonic because the latest Pascal modules are supposed have technology that lowers switching noise to levels lower than previously possible and they receive universally positive reviews (so do the nCores as a matter of fact).
Another factor, I hear claims that the NC1200 is subjectively greatly superior to the lower end modules, and if that's the case it would be like robbing from myself to go with less. Unfortunately, NC1200 products are in the 10k+ range...
But here's the thing, the D-Sonics crushed my soundstage and seemed to lend themselves to listener fatigue. Do they need class A preamping or a tube stage?
Anyone looking at trying the NC500 boards should look at Nord, Kenny I am using a BHK pre with the Nord mono's and it is awesome https://www.nordacoustics.co.uk/
lalitk, I haven't used my s-500 dragon very much,I have week old speakers so I'm using my 600m's because I know their sound and they have plenty of hrs on them.
I think you would be happier with a pair of dragons with your 800 d2's.I'm not that familiar with the Ati amps,they look very good though.I think they need more pwr then one s-500 can provide.
I'm personally looking at the Ps audio 700's mono's and maybe the Bhk preamp.I will let the dust settle and see what more user impressions have to say.
Kenny, I tried this amp recently with my B&W 800D2’s. While it sounded wonderfully adequate in low end and detailed in mid’s /high’s, it didn’t quite push the 800’s the way my current amp does from ATI 544NC. In addition to being detailed, the 544NC drives the low end with such brute force that I have not felt the need to use my JL sub.
I would have been more than content with S500 if I owned the B&W 802’s. When I spoke to Ryan Tew of RDA, he recommended using a pair of S500 in bridge mode to drive my 800D2’s.
Got one more amp on my list of audition before I happily settle with my choice of class D amp. Getting closer to sit back and enjoy the music :-)
I don't have to be nice to people who are being nasty, so I'm not being nice to you anymore. You are the most transparent hater in the long list of transparent haters, and I know haters.
You previously stated you know almost nothing about Class D but now you claim to be an expert and want to bashing all the contributions of almost everyone else in
this thread. I take offense at you coming in here and deliberately
starting trouble. I trust the contributors. I value their input, and
clearly you want to ignore all of us or call us poor judges of music and
sound, which I find a personal insult to me and everyone here.
I have two questions for you:
1 - What is your income source? Are you in the audio industry or do you own a store or sell audio equipment online?
2 - Why don't you just come out, make peace with whatever point you want to make and leave us alone. You have put a tremendous amount of emotional energy contributing nothing but hatred and bashing a technology. What happened? Did a class D amp fall out of the sky and kill your dog as a child?
Sorry, but there has NOT been significant strides in class D since then -- has there? If some of the legendary names in amp design aren't good enough, what would be?
I don't think that you quite get it,
There hasn't yet been a perfect amp designed or probably will never be that satisfys everyone's ears in the Sonics that each of us individually desire.
I can fully assure you that I will always have great respect for these legendary names in amp design.
I will comment on Nelson's Amps, Over the years I have owned many of his designs starting with the 400a and several other Thresholds,Pass Aleph 30 and Aleph 2 mono's, x-150,Xa-30.8 and then building the F5 from him graciously giving to the Diy community,The last owned and recently sold was the J2.I fully enjoyed every one of them,But the class D amps that I have now Satisfy my ears with the least shortcomings of any Amp I have ever owned in my 30 yrs in this hobby.
Comparing class a amps to class d amps is like comparing apples to oranges,which one is better is always going to be highly subjective.
At the end of the day, It's all about the music and getting closer to it.
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