Discussion of Class D Amps Application & Experiences

For thirty plus years I have been a class A or A/B user.  Have used tubes and SS in various system iterations along the way.  I was curious about class D amps and wanted to reduce the extreme space heater for summer listening so after my normal research decided on a Wyred 4 Sound STI-500 integrated to see what it could do.  After letting it run for two weeks 24/7 in my office I brought it to the living room system.  Pleasantly surprised by what I was hearing.  EJ has done a great job with his execution and design. I heard zero nasties that people claim about D amp sound.  With several different speakers here that range from benign loads to difficult loads the STI-500 did exceedingly well with all of them.  W4S has the grip of some older class A amps I’ve used, clarity and spaciousness was upper class, upper register was surprisingly smooth with excellent detail.  Can honestly say that I had no intention of loving this W4S but in fact I do love it’s performance as well as the lower monthly electricity consumption.  

I would suggest researching W4S STI-1000 as an alternate option.  It is essentially his STP pre and ST-1000 in one box.  Well done and well reviewed, less real estate and one less interconnection.  

I would not switch just to switch unless there is something specific about Class D that appeals to you?

I’ve been running Bel Canto ref1000m Class D amps now for a number of years and still could not be happier. I did this because I wanted to throw the kitchen sink in terms of drive ability at my speakers which are known to benefit from that. I wanted something capable and good sounding that was also not too big, heavy and hard to deal with. Budget was limited but these fall into your price category at least the original retail price, though I acquired used for a discount in order to give it a try.

Still couldn’t be happier. If Class D did not work out I probably would have investigated building a smaller system around tubes but feel no need to explore those waters since. I’ve added other lesser Class D amps in other systems since. It’s the only way I go now. I do use a Audio Research sp16 tube pre-amp with my ref1000m Class D amps and think that is a very good way to go if one does not mind having to deal with maintaining a handful of tubes from time to time and the specific amp used has higher input impedance 60Kohm or higher for use with a tube pre-amp. No tubes in my 3 other setups built around Class D and those are all similarly good as well within their significantly lower drive limits (and cost).

I use Class D Audio CDA 254 amps in my HT side of things. With a nice tube line stage (Modwright SWL 9.0 Line Stage), with excellent results. They were kits, and the amp for my main channels has an upgraded power supply with two modules bridged to mono, @ 500 Wpc into 8 ohms.


My other two amps are SET 300B and SET 845. For very little money, you can have Class D to try out. Truth is, they sound great, even though they are relatively inexpensive.

Have fun with it. Easy to build, or you can buy fully assembled. Surprising how good they sound but, like most things in audio, you can pay a whole lot more, and get a little bit more.

Regards,
Dan 

My other Class D amps  (in addition to afore-mentioned Bel Canto ref1000m monoblocks in my main setup)  are: 

• Bel Canto c5i digital integrated amp in family room second system
• Fosi Audio BT10 that does very well driving a pair of old Boston Acoustics A40 in a small 2-channel A/V system
• 4 Class D amps built into Vanatoo Transparent One Encore powered speakers in my wife's sunroom

Years back I was at a NYC audio show and I gasped as I saw Jeff Joseph was running his Pulsars with BC Ref500Ms.  Given my prejudices at the time I was prepared to hear dry, brittle, lifeless sound but instead was treated to what I thought was one of the best sounds at the show, and my perception of Class D amps changed instantly.  I wouldn’t hesitate to try used Ref500Ms with something like a Linear Tube Audio ZOTL or Sachs SP14 preamp as I think that’d make for a glorious combination.  And if the amps don’t work out you can sell with little/no loss given BC is fairly liquid on the used market.  Definitely worth a try I’d say.  I’d make sure to have some good power conditioning for any Class D amps though.  Best of luck. 

I use power conditioning with all my gear but not the amps. No need. They are dead quiet with delicate detail. Not an issue with a good Class D design these days I find.
The ref1000ms do draw a lot of current at power up so there is that to consider though I leave mine on most of the time.

Yes I have heard the Joseph Audio Pulsars at a show with BC Class D amps as I recall. KEF ls50s I run off them in one room reminds me of those though I use a powered sub also with the little KEFs.

The most neutral Class D amplifier at the moment would be one that uses Purifi Amp modules at least they are the best measuring after that the Ncore modules. As far as neutral amp with detail I haven't seen one that betters the Benchmark AHB2 With SINAD of 113@5Watts 4 Ohm but that's class AB.

I certainly appreciate the replies thus far. I use a BPT 2.5 Signature power conditioner and figured I would try the amp(s) both through that and direct.

For a Purifi amp look at March Audio P451 mono blocks.

https://www.marchaudio.net.au/p451

Here's a little more fuel for the fire. Lots of class D units use ICE technology. Is gallium nitride a game changer such as the AGD Production amps?

Is gallium nitride a game changer

No- but it **is** a game improver :)

They allow for faster switching times, but in practice they work even better if you take advantage of their ability to turn on and off so much faster- this helps to minimize dead time constraints. Dead time is a constant regardless of switching frequency; therefore there is a quickly diminishing return if you simply use them to switch at a higher speed!

So, based on your response would you say this a 10% improvement? 20%? Worth looking at vs. ICE technology over the long term?

OP, be forewarned that class D illicits IMO the strongest views from proponents and opponents of nearly any topic in audio (maybe cables are exception but maybe not - it’s close). There doesn’t seem to be a lot of middle ground - just read the long "Class D is just dandy" thread, and you’ll see.

That said, I am kinda in the middle, I guess. My best amp is a class D (Audio Research DSI200), and I really, really like it. It’s about 10 years old and doesn’t use the preconfigured modules that most modern class D tends to - ARC designed it from scratch, although it didn’t persist or get revved to a new generation.

The more inexpensive class D’s that I’ve owned (Bluesouund Powernode 2) or auditioned (Bel Canto low end integrated cs5i?), I haven’t been as impressed with, as compared to other non-class-D at the pricepoints. Just my opinion.

@falconquest
As a manufacturer of class-D and hybrid class-D amplifiers I suggest that auditioning is important. Buy only what sounds good to you. Many brands use the same OEM boards and power supplies. Some just stuff them in a fancy box and others add tweaks. Some sound very similar and other have their own flavor. Some companies design their own. I suggest looking into all brands within your budget. Some of the expensive units use the same boards as some of the lower priced units. There seems to be a greater emphasis on eye candy than innovation these days.

Typically the shortcomings of class-D amplifiers come from inferior power supplies and a mediocre input stage, not from being class-D. This holds true for many SS amplifiers too.

The input section design can affect the sound quite a bit. For example our hybrid class-D amplifiers and our SS class-D amplifiers share the same power supply and output/power stages. The hybrid has a discrete tube input stage including its own power supply and the SS class-D is all SS. They have similar sound in some ways but are different overall.

Power supplies are very important in all equipment. We use very robust and independent (still in the same box) power supplies that are well shielded. The entire front half of our amplifiers is PS. I suggest not getting caught up in switching PS vs linear PS. They each have their strengths, as long as they are designed properly.

@kren0006 I appreciate the heads up about this topic which is why I requested to not get involved in class warfare! ;-) I would just like to hear about the experience people have had with moving to class D from A, A/B. I did read through the thread you mentioned.....or part of it. I gave up when I no longer found useful information.
@arion Thank you for your insight as well as others who have contributed. The more the merrier so long as it remains informative and civil.

I have had amplifiers from Class D Audio, D-Sonic, Mivera, and Peachtree.  The Mivera was most disappointing.  Total lack of detail and depth.  I popped the top and discovered that there was nothing in the box but the IceEdge board and the on-board power supply.  The D-sonic M3-1200S is an exceptionally fine amp, a real bargain on the price/performance scale.  Like most everything in this addiction, er hobby, it is totally subjective, but the D-Sonic amp is wonderful to my ears, and will drive any complex load without complaint.  The Class D Audio 470C also is a very good performer with very good sound.  Both amps have absolutely no background noise.  There are a lot of excellent, and not so excellent brands out there, but the search is both fun, and enjoyable.  I really don't care about an amp's design topology, class A, AB, or D.  All I go by is how it sounds to my ears.  Good luck in your pursuit.     

I am in high anticipation of receiving LSA Voyager GaN amp 100wpc $2500 (sold through Emerald Physics)



In the mean time I love my Ric Shultz EVS 1200, which is a 600wpc dual mono IceEdge 1200AS2 class D modules plus lots of Rics pixie dust < $2500

I see the class D crowd is alive and well, GOOD. I’ve have Ice units
Wyred 4 Sound SX1000 and Rs, Powerful but really lack the luster of the Hypex units. Though when coupled with a lively valve preamp it does help a lot.

The stock Hypex boards came with options that Ice boards didn’t have at the time without mods.

Hypex NC500/1200 and NC2k have buffer boards that come from the factory with standard op amps and voltage regulators,
Nord and VTV, BOTH offer bufferboard upgrades on their unit.
It is night and day with discrete class a op amps and discrete voltage regulators. The upgrades are 175-425.00 depending on the op amps you choose per monoblock unit.
It also gives you the option to customise your units with op amps rolls.
Sparco, Sonic Imagery, VTV, and a few more. Usually 150-350 for a pair of tricked out, op amps. If you already have the socketed boards

I had both with and without, the board upgrades. All of my units now have
the rev. C or D from Nord. The revision D from Nord or VTV (VTV have a gain select option) have dual sockets
(2 different footprints) for more versatility.

I only look at who made the boards, who made the case (do you like the design and case options, trigger, XLR and RCA, binding post) and do they have optional bufferboard. If they don’t, it’s simple, don’t buy them.

I opened 4-6 of the better known brands, all have either soldered in a different (not always better) opamp or bought buffer boards from, (LOL)
Nord or VTV.  Normally at 2 to 3 times the price, TO YOU..

A Hypex MB should be from 850.00-1500.00 depending on wattage, option on the bufferboards, and case options.

A shinny case alone can cost you 2000.00 more, and get a whole lot
LESS under the hood so to speak.

The boards are the same...Make sure you get the largest PS options too, it’s only a few buck and a few of the big names squeeze there, LOOK make sure..

Your budget will get you a long way into a great system, with valves included. A pre with valves or a combo of both. Tube front end sure sweetens the mix for sure. I love um’ ZERO floor noise.

Enjoy

So, based on your response would you say this a 10% improvement? 20%?

Hard to say in that regard! If properly engineered, its probably not that big a deal, as MOSFETs have gotten faster in the last few years since the GaNFETs were introduced. @arion  makes extremely good points in his post; this reflects my own experience. Some class D amps are extremely boring, some are bass shy (usually older units) and others sound extremely musical (mostly newer units).

Some class D amps are extremely boring, some are bass shy (usually older units) and others sound extremely musical (mostly newer units).

Of course the same could be said about any amp design type in general.

That’s why it’s best to not generalize. No two amps of any particular type are created equal. They all run the gamut.

Point is Class D CAN compete. That’s all.

Also I agree newer in general is better than older as is the case always with any newer and still more evolving technology. Also cost is NOT necessarily the best determining factor as usual. Even my tiny $75 Fosi Class D amp (about the size of a pack of cigarettes) with its tiny Texas Instruments Class D chip competes very well with anything else I have heard ever up for up to a few hundred dollars and will beat most vintage amps that sold for 2-5X more 40 years ago in a package 1/10th the size and the Bluetooth even works well enough for most if not the most critical 2-channel applications.

That’s how technology and progress works!

Can you believe we still use the same primitive disk-groove-based-like-riding-a-roller-coaster approach for records and playing them that was first invented well over 100 years ago? What’s up with that?

Try singing or playing a violin while riding a roller coaster sometime.

" That’s why it’s best to not generalize. No two amps of any particular type are created equal. They all run the gamut."

This is why I would like to hear from those who made the leap from class A, A/B to D to get their impressions about not only the sound but what sounds better or worse after the transition. Did they find equal or better performance for less money or were there trade-offs? I was also thinking along the lines of a tube pre but it seems hard to find one that offers a remote and no quirky aspects. (I researched the Conrad Johnson 17LS but didn't like the idea of the "click" volume control.) But I don't want to make this about pre-amps.....yet.

I wouldn't worry to much about the op amp the stock TI LM 4562 will measure right there with any discrete sparkos or sonic imagery. The newer iterations of Class D show better bench numbers but when you start getting into harmonic distortion numbers <-100 you're not going to be able to tell any difference anyway. Adding tubes to Class D amps seems self defeating to me you're adding distortion to an amp made for neutrality. The best at giving great detail without fatigue I have heard are amps with Purifi but Hypex is very close I haven't heard  ICE amps so they could be better though the few  measurements  I have seen on them aren't as good.

I had the ARC sp16 prior to the Class D amp and have had that combo for ~10 years now and still content. Next pre-amp will probably be SS. Maybe a Benchmark pre/DAC device is what I am thinking currently. 

Arc sp16 has a nice basic function remote.

djones511,651 posts04-23-2020 10:08amI wouldn't worry to much about the op amp the stock TI LM 4562 will measure right there with any discrete sparkos or sonic imagery.

I don't know your background, I don't know you. I hope you read
this.

This is from my ears to this forum, I'm very familiar, with the LM4562 NEC, E.I. T.I, op amps. played with them all, rolled them all.  ALL the discretes, I sampled, the SO was much better, even the Burson with the high failure rate due to poor regulator choice and potting problems.  

I worked with Andrew at Sparco labs to resolve some issues with the early Nord buffer boards, and the op amp SM sockets for my Mac
gear, and a few others.

From sparco webb site:

"Our discrete voltage regulators have at least 15 times lower output noise, 52dB (about 300X) better rejection of any noise coming into them, and 4X better load regulation than any other 3 terminal IC regulator that one can find to compare them against."

The regulators are the key to the Class A op amps, without this type of regulator, you can't take FULL advantage of the great discretes available,
or their sonic superiority.

Yamaha, Marantz, B&W, Channel Islands Audio, Meridian, Kharma, MM Audio, and Exodus, and about a dozen more use, Hypex NC modules

The difference in SQ between who does, and who doesn't, is very easy to hear and enjoy.

The comment on "A tube front end" is purely subjective, and you have the right to be WRONG, just as I do. I know how it sounds because I've done Mac, CJ, VTL, Marantz, and two handbuilt line preamps. ALL sounded wonderful, and pure sonic nuggets, with options...

If OPs ears are good, he'll notice the differences and certainly change them if he like. With the op amp/tube roll option, you have a lot of sonic latitude.   

Without those options, what other options do you have, PCs and ICs
No thanks...

Seems to be something djones51 hasn't tried, or, has has he?

WHY would you limit the OP options when it's obvious you, haven't hear the most popular class D boards available, ICE. I use them for bass duty. They are as good as any Hypex without op amp upgrades. For some, that's exactly what they like.. WHY? It's ALL they own. Second some ICE modules have a built in PS, that lets you expand. You can 1 or 2 amp modules depending on the model, at a very low cost. Great option.

SMPS1200 hypex power supply were powering most of 1ET400 amp modules, I listened too. Again not even close to a NCs with buffer board. Apples Oranges...Maybe djones51 listened to something else, DUNO, wasn't real clear.

Second I will only comment on what I've heard. What I've really sat down with. Not a day at a show, or a listening room. normally weeks at least. I read then I listen, and listen and.........

Happy hunting..

Regards

I had a pair of Nord NC500 rev D monoblocks for about 8 months before I decided to sell them and go back to class AB. I used them with Golden Ear Triton 2+ speakers, Bryston BDP-2 streamer, Schitt Yggdrasil DAC. Preamps were Schitt Freya and Parasound JC-2. I tried a variety of cables although nothing too exotic (all under $1K per cable or pair). 

These amps replaced a Krell FPB-300 which died and I couldn't justify the cost of getting it fixed. 

I used both the Sparkos and Sonic Imagery Op Amps. I found the Sparkos to be a little more to my liking - presentation was a bit more relaxed and top end was a bit smoother. 

What I liked: Very efficient. Lightweight and easy to move around. Good dynamics and clarity with very quiet background. Decent but not exceptional sound stage. 

The reason I replaced them: they lacked the excitement I was used to with the Krell. They just sounded boring to me. The imaging was also not as deep and wide as with the Krell. Granted, the Krell was a much more expensive amp in its day, but I was hoping Class D efficiency and more modern design would allow me to get close to the Krell performance at a lower cost. 

I ended up replacing the Nords with a Parasound JC-5 which I'm enjoying very much. A little different sound than the Krell (almost a year between listening to the Krell and JC-5 and I was using a different preamp), but the JC-5 is a beautiful sounding amp with effortless power that is also emotionally engaging. 

I wouldn't rule out Class D in the future, but probably not any time soon. 

@jaytor That's what I was after! Some real world, hey I tried this but didn't like it because, straightforward honest first hand experience. I must admit, I have heard/read a lot about class d build, specs. and prices but not much of anyone extolling their virtues. Thank you for your response!

jaytor138 posts

 These amps replaced a Krell FPB-300

I setting here looking at a pair of KSA-100 mk2s, that I LOVE, thinking do I want to listen to ANY, class a, tube, or other HOT running thing.. LOL.
87 degrees here, now.  In a month over 90, then over 100. 

Class d has its place. But it's not a Krell, Pass, Mark L and few more. BUT some of these class d manufactures sure have a hefty price tag. Considering, what's in the box, I think some of the binding post are more expensive than the whole amp module.. 

A majority of my listening is on multi planars, and ribbons, systems. No large surface systems. Different results, compared to most round speaker setups. Class d does the planars justice, for sure, to what degree, is the question..How good is good? it's not perfect, but pretty darn good, it's just COOL..

Regards

About this time last year, I purchased a Digital Amplifier Company class D amp.  It was used, about ten years old and the most expensive amp I have ever purchased.  I have many different class A/Bs from a multitude of US manufacture's and a couple of Japanese built, all at 200 wpc or greater.  The DAC 4800a was the first amp to let my speakers sound their best.  I use Magnepans and Martin Logan's.  From first listen, it was the absolute quietest amp ever.  Put a disc on walk away-and suddenly sound just erupted from my speakers, whether Greig or Steely Dan, it was incredible.  The sound from deepest notes to highest were clear, single notes lost in the A/B fog now had their own voice.  Soundstage and depth was wide and deep.  In January of this year I purchased 2 DAC Maraschinos, one used and one from DAC direct.  I could not be happier, the build quality is old school USA.  The amps do not use modules from other companies, instead they build it from their own design.  Most of the A/B amps were made at ATI.  Give the Digital Amplifier Co. web site a look see.  Just another opinion.

The best at giving great detail without fatigue I have heard are amps with Purifi 

Sorry maybe you missed that in my post I get carried away sometimes. I think these Class D amps are very good but I went back to Class AB. I liked the amps I heard with Purifi and Hypex but from just my subjective opinion I like the sound of AB. I've had McIntosh, B&K old ones, Micromega, Anthem. I'm  not getting into an OP Amp discussion,  I've heard different ones I couldn't tell the difference the measurements are within 1% of each other on the ones mentioned here. Maybe my ears aren't good enough.  Nords are good but I would advise if you get one to try, take the cover off and make sure they didn't wire the speakers wrong, yes I've seen that. March Purifi is good VTV is another I would look inside the XLR might have pin 1 wired wrong and no ground on the mains. NAD doesn't sound bad good detail  and soundstage they're coming out with a new Purifi the M33? Need to watch their build quality as well. 

I Know you said the Rowlands are out of your price range, but I would like to recommend the 535. One of them new is in your price range. I have a pair as mono's (they are designed to be used that way if you choose). I had a Rowland Model 2 (A/B) for 25 years, and replaced it with a pair of 535's. Voicing is virtually identical but the 535's have audibly less noise, more dynamics (there is a considerable power difference), and a positively huge sound stage. Using a hybrid line stage - PS Audio BHK. Driving Totem Forest Signatures. I am quite happy with them.

Speaking of PS Audio, anyone have any comments on the M700's?

Also Elac has some low profile Class D amps out there these days.
Anyone heard and able to comment?

I picked up a pair of Nuprime 9 running bridged into electrostatics to replace a ML 336 that died. Maybe not as sweet, but overall I do not feel like I am missing that much. I have since played with a VAC Avatar and Marsh A400s and feel that I am still getting more from the class A front/class D output of the Nuprime. Do I want more-of course, that is why I rummage these forums and wait impatiently for the LSA and Atmasphere GaNFET designs.
The Nuprime do seem to respond to clean AC and I have tried direct from PS Audio outlet, APC and Shunyata filters. The old APC seems to be the best so far. I have not tried anything from this century yet!!

" That’s why it’s best to not generalize. No two amps of any particular type are created equal. They all run the gamut."

As above, but it should be " No two  S Y S T E M S  of any particular type are created equal."

What many Class-D haters fail to realize is that they all have an LP output filter. Any filter in series with another filter, read cables & loudspeaker, has a different response than with another, read cables & loudspeaker.

I have a NuPrime ST-10 which has strengths and and weakness that vary with the LS & cables used, just like every other amplifier.

It's currently on woofer duty in a tri-amped system and it's bloody brilliant!

How it might fair driving some Himalayan impedance nightmare is unknown.

Because of their high frq noise, Class D amps can be a problem for tweeters with wide band frequency response and high frequency break up. Excess energy (not music related) can cause the breakup to induce distortion.

Another Class D that looks like it could drive most any speaker but I know nothing about is the Anthem M1.  They look interesting.  Pair of monoblocks are $7000. 

“Speaking of PS Audio, anyone have any comments on the M700's?”

I gave them a try but they didn’t do it for me. Not bad, but not what I was looking for. The price was certainly right.

One more thing about the Rowland 535s: don’t use any kind of power conditioner, filter, or regenerator. It really messes with them. Makes them hard and shrill. The rest of the system yes, but not the Rowland’s.

@markmuse Can you expand upon your comments about the M700's? In what way did they not work for you?

...I'm just happy to read a Positive forum on class D units....*S*

Maybe the detractors realize that they'd be overwhelmed here....

Good.

Carry on, J

RE: EVS 1200

Ric promotes adding weight to all equipment. Due to tight space in the rack I could only slide a 5 pound divers weight which has been there as long as I have had the 1200. He also would not sell me the 1200 without the Cubes: one each affixed to each Ice module.


Since getting the 1200 I have made many cable upgrades as well as adding Core Power 1800. Now, I want to remove the Cubes, but it’s a 2 person job to remove from the rack, and reinsert. When I do this I am going to leave the top off too

In the meantime, in one of the forums the other day someone mentioned Shungite, which I bought from a company who has the authentic Shungite from the meteor that crashed in Russia decades ago, I did not purchase Shungite for audio, but have 4 chunks not being used that easily fit in the palm of my hand weighing less than 2 ozs, so I decided to put them on top of my 1200 at the back near the power cord.

I forgot about it, and while watching the draft last night I was listening to an old GRP digital remaster: Dave Grusin Gershwin Connection, but it sounded flat (the leading edge top end was lopped off) I cleaned the disc to no avail. As I watched the draft it occurred to me that I had put Shungite on the amp. I removed it and the leading edge was back in full


Just amazing

@tweak1 Wow, that's out of this world! .....thank you, thank you, I'll be here all week.

Does anyone have experience with Pascal? How does it fit into the class D lineup - does it sound significantly different, from Hypex? 

Class-D is more system dependent than tube or bipolar.

It's imperative to know what it is driving and if what you want to drive is similar or wildly different.

+1 bryfi

Underwood HiFi has an incredible special right now on 2 new W4S integrated amps

Anyone using the Crown 1002 class “d” amps.Several you tube reviews like it.

Because of their high frq noise, Class D amps can be a problem for tweeters with wide band frequency response and high frequency break up. Excess energy (not music related) can cause the breakup to induce distortion.

This statement is entirely mythological. Class D amps do put out a small sine wave called the 'Residual'; even with a powerful amp the residual is of no concern to any tweeter.

Whoever mentioned it I do think you might be  better off plugging class D straight into wall with no filter/ conditioner. At least that was what I found as well.
I dont know much about the technical or engineering arguments but when I listen to mine- Class D definitely has its pluses, and the ones I've used have speed, control, imaging, transparency and detail that is pretty impressive. And you also notice low distortion, what some describe as the sqeaky clean class D sound. Where it can fall a little short is harmonic overtones, I can notice it relative to the tube or class A amps I've had/have but the overall tonality is plenty good enough to me, or more specifically, easier to overlook given its other pluses. Sometimes class D is described as being tube like in sound, I don't think so, at least not in a classic tube sound sense; mine and others I've heard don't have the tonal density usually associated with tubes. The only quality of mine that might be slightly reminiscent of tube is it has an immediacy and neutrality through the mid range that made me think of some single ended triodes I once auditioned.  I don't use one exclusively, but it's good to have one around. 

@falconquest I apologize, just saw your question to me.
The M700's just didn't come alive for me. It has been more than a year, so I'm afraid I can't be as specific as I would like to be. And I readily admit that my expectations were low, so I'm sure my perception was colored by that. However the Rowlands are so spectacular that there is no question in my mind that I made the right choice. I'm trying different tubes in my PS Audio BHK line stage and discovering how much different tubes influence the sound.