Krell Class A iBias Experiences

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BDH55

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I've been searching for new amps for some time and had not even considered Krell (actually, I wondered if maybe they had gone out of business). Then I saw a YouTube interview with their COO and he was talking about their Class A iBias technology (lots of forum members have posted about the magic of pairing Pass Class A amps with ML's but I don't think I can deal with the heat output). Anyway, Krell's claim is their new amps can run in Class A to full rated power by adjusting the current supplying the output transistors to only the current they actually need, thus reducing both the power draw of the amp as well as the associated heat output. They go on to explain that they calculate the bias at the output stage which then makes the real-time demands of the speaker a part of the calculation. I doubt I am explaining this as well as they could so here's a link to their one page explanation of iBias Technology.

I'm not an engineer, and no kind of amplifier expert so I'm trying to figure out if this is just marketing spin, or if this actually works (and specifically, works well with ML electrostats). Also, I'm struggling to understand how if they measure this at the output stage so they can include what the speaker is calling for, it seems that they would be measuring and then sending back instructions to change the bias on the output transistors after the actual signal had already passed through them. IOW, it sounds like they are measuring and changing the bias 'after the fact' if that makes sense. Can someone help me understand this, and whether this sounds like a valid approach?

Also, does anyone have direct experience using one of the Krell amps with the iBias technology to drive their ML electrostats?
 

Robert D

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The price seems comparable to Pass Labs class ab. Pass Labs class A are quite a bit more if I remember right. Seems like a fair price in today's market. I wonder why we don't hear about them much today?

 

Len44

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FWIW, I too was quite concerned about the heat output from the Pass XA160.8, but it was not as much as I had feared. Ran with a fan pointed towards them for a couple of months (my paranoia, I guess), then discontinued the practice. These amps do help downstairs in the cooler months, tho.
 

BDH55

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I wonder why we don't hear about them much today?

Agreed, and that is a concern. If this technology is so good, I would think there would be lots more coverage on them. Not a lot of reviews from the big guys, although there seem to be quite a few reviews of their K-300i integrated that are very good. Just not much coverage on either their mono blocks, stereo or multi-channel amps. Of course some of this is likely related to minimal, if any advertising...

FWIW, I too was quite concerned about the heat output from the Pass XA160.8, but it was not as much as I had feared. Ran with a fan pointed towards them for a couple of months (my paranoia, I guess), then discontinued the practice. These amps do help downstairs in the cooler months, tho.

That is really good to hear! Before I got scared away by the heat, I was considering the X600.8 (I don't really need the extra power for my two channel rig, but would prefer extra power to my front channels when in home theater mode. Not really sure I need that much power though). Your XS160.8 and the X600.8 have the same heat output, so your experience is encouraging. However, if you listen to Jay over on Jay's Audio Lab channel, he makes it sound like Pass amps run really, really, REALLY HOT!!! IIRC, he said something like 'you will have sweat running off you' or something to that effect (and he has dedicated AC for his listening room). While in that video he was talking about the four chassis Xs300, I've heard him in other videos as well, plus I've spoken with him directly where he was basically warning me off due to the heat. In addition, JLasher22443 had an opportunity to audition the X600.8 and he said they 'do run hot enough that you wouldn't want to keep your hand on them.'

BTW, how big is your listening room? Also, I certainly agree with you that a little extra heat in the listening room helps out at this time of the year. In fact, I've been leaving my Para JC-1's on around the clock mostly for that reason. Not sure I could do that with a pair of Pass amps however...
 

Len44

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I took plenty of time to consider various options and did the appropriate "due diligence" win my quest to acquire the best solution (for me). I was determined to get this right the first time, as a re-do can get expensive fast! Spoke with Mark and Kent at Reno HiFi (about the Pass products) a number of times. Asked lots of questions, regarding power consumption and heat generated, leaving amps on all the time (or not), which amps and preamps might be best for my specific rig, etc. They were very patient, and readily answered all my questions without hesitation. All that to say you might want to give Mark a call and discuss. I'm sure you will find him quite forthcoming.

Specifically, regarding my specific experience, the amps do get quite warm, but not to the extent that I fear my hand might get burned. Again, could use a fan (for air circulation purposes), at least at first, until you become comfortable with them.

I will say this -- those Pass amps and preamp) sure do sound terrific with the ML 15A speakers. I do not see this setup being upgraded for quite some time -- if ever.

Best of luck with whatever you decide.
 

BDH55

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I took plenty of time to consider various options and did the appropriate "due diligence" win my quest to acquire the best solution (for me). I was determined to get this right the first time, as a re-do can get expensive fast! Spoke with Mark and Kent at Reno HiFi (about the Pass products) a number of times. Asked lots of questions, regarding power consumption and heat generated, leaving amps on all the time (or not), which amps and preamps might be best for my specific rig, etc. They were very patient, and readily answered all my questions without hesitation. All that to say you might want to give Mark a call and discuss. I'm sure you will find him quite forthcoming.

Specifically, regarding my specific experience, the amps do get quite warm, but not to the extent that I fear my hand might get burned. Again, could use a fan (for air circulation purposes), at least at first, until you become comfortable with them.

I will say this -- those Pass amps and preamp) sure do sound terrific with the ML 15A speakers. I do not see this setup being upgraded for quite some time -- if ever.

Best of luck with whatever you decide.
I hear you on 'wanting to get it right the first time' which is why I've been on this pursuit for quite some time. Other than heat, I haven't heard anything negative on the Pass gear, especially when paired with ML's so they are still on my short list. Also, I have had a couple of conversations with Mark at Reno. He had a pair of demo X600.8 in stock at about a $10K discount that I almost pulled the trigger on. He was very transparent about their heat output though, so I decided to sleep on it, and of course... you snooze, you lose! I've also had conversations with Shawn at DaVinci, as well as GW1800 about the Bricasti M28 or M32 models, and they also sound promising (and without any real heat output).
 

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I run 3) Krell FPB600, 1) FPB300, 2) Krell KAS Monoblock amps (top of rack with meters), 2) Threshold SA/4e (see handles past the rack) & an Anthem STR Power Amp (not shown on rack). The heat from the Full Power Balanced Krell is extreme. I added a second Dyson fan (one is shown in the photo). This rack is in a 6 foot machine room located behind the screen,
IMG_0160.jpeg
open on both ends for flow through ventilation. The heat is not a problem, as this theatre is in a 30 foot X 17 foot room in the basement with HVAC. Martin Logan speakers all around; the Krell amps push them to very satisfying quality & SPL.
IMG_0162.jpeg
 

BigGuy

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I took plenty of time to consider various options and did the appropriate "due diligence" win my quest to acquire the best solution (for me). I was determined to get this right the first time, as a re-do can get expensive fast! Spoke with Mark and Kent at Reno HiFi (about the Pass products) a number of times. Asked lots of questions, regarding power consumption and heat generated, leaving amps on all the time (or not), which amps and preamps might be best for my specific rig, etc. They were very patient, and readily answered all my questions without hesitation. All that to say you might want to give Mark a call and discuss. I'm sure you will find him quite forthcoming.

Specifically, regarding my specific experience, the amps do get quite warm, but not to the extent that I fear my hand might get burned. Again, could use a fan (for air circulation purposes), at least at first, until you become comfortable with them.

I will say this -- those Pass amps and preamp) sure do sound terrific with the ML 15A speakers. I do not see this setup being upgraded for quite some time -- if ever.

Best of luck with whatever you decide.
As stated previously many times, Pass and M-L are like chocolate and peanut butter! So tasty I have been a poster child for both for several decades now.
As also stated previously, IMHO you will be very happy with XA60.8s and the M-L line...unless your sound room is a stadium! ;)
 

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I hear you on 'wanting to get it right the first time' which is why I've been on this pursuit for quite some time. Other than heat, I haven't heard anything negative on the Pass gear, especially when paired with ML's so they are still on my short list. Also, I have had a couple of conversations with Mark at Reno. He had a pair of demo X600.8 in stock at about a $10K discount that I almost pulled the trigger on. He was very transparent about their heat output though, so I decided to sleep on it, and of course... you snooze, you lose! I've also had conversations with Shawn at DaVinci, as well as GW1800 about the Bricasti M28 or M32 models, and they also sound promising (and without any real heat output).

With apologies...my listening room is 34' x 22' w/9' ceiling. I have not listened to, but have heard pretty nice things about Bricasti, and of course hard to go wrong with Shawn. Would be excellent if you could arrange to audition your primary candidates with your speakers.

Also agree with BigGuy -- "Pass and M-L are like chocolate and peanut butter!"

Keep us posted, and best of luck in finding the right amplifier(s) for you.
 

Robert D

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The Pass X amps are hot like their XA amps? I'd think the X amps aren't any hotter than my Aragon class AB amp?
 

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As an owner of Pass XA30.8, I can say that it runs hot but it is not going to burn your fingers. Jay likes to over-exaggerate things. I hope you guys do not get discouraged. For me, this is a very small trade-off considering the level of meat-on-the bone, true to life music you get from a Pass class A amp. I am not sure about Krell's claim. But I have heard their AB amps and they are not my cup of tea.
 

Len44

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As an owner of Pass XA30.8, I can say that it runs hot but it is not going to burn your fingers. Jay likes to over-exaggerate things. I hope you guys do not get discouraged. For me, this is a very small trade-off considering the level of meat-on-the bone, true to life music you get from a Pass class A amp. I am not sure about Krell's claim. But I have heard their AB amps and they are not my cup of tea.
I find your comments spot-on -- in every respect.
 

BDH55

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I run 3) Krell FPB600, 1) FPB300, 2) Krell KAS Monoblock amps (top of rack with meters), 2) Threshold SA/4e (see handles past the rack) & an Anthem STR Power Amp (not shown on rack). The heat from the Full Power Balanced Krell is extreme. I added a second Dyson fan (one is shown in the photo). This rack is in a 6 foot machine room located behind the screen,View attachment 22446 open on both ends for flow through ventilation. The heat is not a problem, as this theatre is in a 30 foot X 17 foot room in the basement with HVAC. Martin Logan speakers all around; the Krell amps push them to very satisfying quality & SPL. View attachment 22445
I'm not an expert on Krell amps, but IIRC, your FPB amps are designed and run in full Class A, and I think would be in a completely different league than the new Krell XD amps with their iBias Technology basically 'simulating' Class A (as I understand it). That's why I was asking if anyone had any experience with these new amps, especially with their ML's. Very nice system though and I can only imagine how this must sound! (y)
 

BDH55

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With apologies...my listening room is 34' x 22' w/9' ceiling. I have not listened to, but have heard pretty nice things about Bricasti, and of course hard to go wrong with Shawn. Would be excellent if you could arrange to audition your primary candidates with your speakers.

Also agree with BigGuy -- "Pass and M-L are like chocolate and peanut butter!"

Keep us posted, and best of luck in finding the right amplifier(s) for you.
I've got a weird room configuration with basically two rooms butted together in an L-shape and completely open between them. It is smaller than your room though (approx 5900 cu ft vs 6700 cu ft).

As for an audition, I can do that as Shawn has a pair of Bricasti M28's he will loan me (I just cover shipping), and Mark at Reno HiFi will also do a demo. The biggest challenge for me is I'm not much for slinging around too many 100# amps anymore which is one reason why I'm trying to collect opinions about the different amps.

I'll certainly let everyone know if I can ever make a decision! :ROFLMAO:
 

BDH55

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Pass/ML Owners:

I just wanted to clarify my concerns over ANY manufacturers amp heat output, as it likely seems that I am obsessed with this... but specifically on Pass Labs...

I am aware of the reputation of Pass and ML, and when I started down this road, I was fairly certain that I would have a pair of Pass amps in my room. It was mostly a question of which model. Unfortunately, there are no Pass dealers within hundreds of miles of me, so initially I was working with the factory (and later, Mark at Reno). My concern about heat came up and they had me use a meter to see what the power consumption of my JC-1's were so we could ballpark how the various Pass amps would compare. Off the top of my head, my JC-1's were pulling 256 watts or 512 watts for the pair at idle. and even the XA30.8 pulls 370 watts, or 740 watts for the pair, with the bigger models pulling significantly more. This is why I'm concerned about heat...

Then I came across Bricasti in GW1800's system. Upon further discussion, one thing I found interesting was that he had also been running Para JC-1 mono blocks but one reason he decided to move away from them was because of their heat! While I don't know all the amps he considered, he did end up with a pair of Bricasti M28's and not only by his comments, but others who have visited his room, it sure seems like everyone loves the sound of his system (understood that it's not just due to his amps, and he's made a big investment in his systems power, grounding, cabling, equipment, room treatments, etc). One question I did ask him was 'how hot do they run?' He basically paused as if he was surprised by the question, but responded 'slightly warm'. Well, that got my attention!

I still could end up with a pair of Pass amps in my room... or Bricasti's... or even something else, which is why I was looking for feedback on the new Krell amps.

I absolutely appreciate everyone's feedback and trust me, the fact that many happy Pass/ML owners have chimed in could make the difference! (y)
 

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BDH55, as Roberto says, "Happy Listening." Go with your gut feeling. If you like the sound of an amp, you just get it. Do not worry about the heat. I find buyer's remorse 1000 times worse than possibility of some degree of uncomfortable heat. When I was choosing the Pass XA30.8 (a true over-achiever in the words of Kent English at Pass Labs), I truly did not care if it was 10 to 15 degrees Celsius (roughly 20-25 F) higher than its surrounding!

Just enjoy the music.
 

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BDH55, as Roberto says, "Happy Listening." Go with your gut feeling. If you like the sound of an amp, you just get it. Do not worry about the heat. I find buyer's remorse 1000 times worse than possibility of some degree of uncomfortable heat. When I was choosing the Pass XA30.8 (a true over-achiever in the words of Kent English at Pass Labs), I truly did not care if it was 10 to 15 degrees Celsius (roughly 20-25 F) higher than its surrounding!

Just enjoy the music.

Amen, Northy! Unless someone is competing in "Mine Is Bigger, some of Pass's lower powered amps sound better than their bigger bros. But as with all things LIFE, YMMV.
 

Len44

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Additional thoughts...Might want to also read some reviews for both Pass and Bricasti. I decided on Pass Class A XA160.8s because I wanted plenty of power (as Mark promised, these amps will drive the 15a speakers "Effortlessly" (asthey most certainly do) Also, I wanted the benefits of SS and as close to the tube sound as I could get. While the Bricasti amps are AB, certainly there is an area of listening that is in the Class A area, but I could not find the level at which Class A changes over to B. Of course, one would expect AB Class amps to run somewhat cooler than A Class amps, not sure by how much.

Either way, I would get some help with moving these heavy amps.

Again, best of luck with your decision. I think you are in great hands given the quality folks (Shawn and Mark) with whom you are working.
 
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BDH55

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Additional thoughts...Might want to also read some reviews for both Pass and Bricasti. I decided on Pass Class A XA160.8s because I wanted plenty of power (as Mark promised, these amps will drive the 15a speakers "Effortlessly" (asthey most certainly do) Also, I wanted the benefits of SS and as close to the tube sound as I could get. While the Bricasti amps are AB, certainly there is an area of listening that is in the Class A area, but I could not find the level at which Class A changes over to B. Of course, one would expect AB Class amps to run somewhat cooler than A Class amps, not sure by how much.

Either way, I would get some help with moving these heavy amps.

Again, best of luck with your decision. Either way, I think you are in great hands given the quality folks (Shawn an Mark)with whom you are working.
Actually, between the Covid lockdowns and fact that I am fairly limited from a mobility standpoint, I think I have read every mono block review written over the last decade or so in the less than $50K range... and some, several times! :ROFLMAO: Of course the challenge with that is reading just isn't the same as listening... plus, I'm not sure I can recall a reviewer that was ever listening thru a pair or ML's.

I won't bore eveyone with the long list of amps I've considered, but for one reason or another I've been knocking them off the list and am getting down to a pretty short list. Really hoping to make a decision in the very near future...
 
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