Ok, the bias current varies with the load current. Here's the story. Stereo Amps
Krell's iBias Class A technology allows our latest amplifiers to run in full Class A mode to full power while minimizing heat generation.
Previous efforts at using a "tracking" bias, while effective, only measured the incoming signal and set bias levels from this information.
Our new patent pending iBias technology significantly elevates the effectiveness of previous designs by calculating bias from the output stage.
This seemingly small change in topology results in a dramatic improvement in sound quality, especially midrange richness and purity.
The core of the technology is an innovative, patent pending design for a dynamic intelligent bias circuit.
Our iBias Class A circuit directly measures the output current of the amplifier and adjusts the bias to the optimum level.
Because iBias Class A measures the output current, the real time demands of the specific speaker connected to the amp are directly
incorporated into the circuit function. In addition, iBias Class A even reduces the bias when the signal is at very low levels,
making its operation undetectable by ear and even by standard amplifier measurements.
In sliding bias schemes, the circuit merely estimates how much bias is needed based on the input signal and an "assumed speaker load."
Compared with iBias Class A, these sliding bias technologies are much less effective - and much less accurate.
Krell iBias Class A amplifiers are the first to deliver the rich musicality of Class A amplifiers, the uncompromised dynamics
of classic Krell amplifiers, and the efficiency and low power consumption of Class G and H amplifiers. Because the iBias
circuit eliminates crossover distortion, the amplifier is able to resolve more of the detail and microdynamics in even the best
analog recordings. Simply put, the music breathes. Whether an iBias amplifier is called on to reproduce the extreme dynamic
range of high-resolution digital files, the minute intricacies of a 45-rpm, 180-gram vinyl record, or the complexity of today’s
latest blockbuster action film, it does so without altering or abating the music in any way.
The iBias amplifiers' unprecedented ability to retrieve the subtlest details gives their sound an incredible dimensionality,
with an ambient, broad and extraordinarily deep soundstage. As spacious as the sound is, though, the amplifiers are still
able to produce pinpoint stereo imaging if the recording calls for it. It's all the power and control for which Krell has
always been famous, with a level of resolution and musicality in the midrange and treble that has simply never been heard
before. In short, the new patent pending iBias Class A Krell amplifers give today's audiophiles and home theater fans
everything they could possibly want in an amplifier.
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Can you pop the hood and show us the mods they did? If they changed to the plastic flat versions of the usual TO3's of old then the new ones don't have the higher SOA ( safe operating area) of the 15024 TO3 versions I believe. The lower bias would reflect all worst case issues then for safety, but not sure without some pics
We would be able to spot if they included the later sliding bias scheme ( highly unlikely though) but a pic would be interesting to this forum.
We could also walk you through increasing bias if you want. A 20$ DVW would do it if you don,t have one.
Regardless at least send some internal pics even if you don't want to fiddle with it
Regards
David
We would be able to spot if they included the later sliding bias scheme ( highly unlikely though) but a pic would be interesting to this forum.
We could also walk you through increasing bias if you want. A 20$ DVW would do it if you don,t have one.
Regardless at least send some internal pics even if you don't want to fiddle with it
Regards
David
Ok David. I can send pictures when I get a chance. The parts they put in are as follows:
4 CAP, RAD 220UF 63V
4 CAP, EL RD 1000UF 20% 35 V
2 CAP, 47 UF 100 V
8 TRANS, MOT #484081 NPN
8 TRANS, MOT #484002 PNP
16 SIL-PAD TO-3
1 SWITCH, Green Air PAX
4 hours of labor
Its possible to do many things but the accepted definition of Class A doesn't cover (most) of those schemes.
And they charged $550 for parts and another $500 for fitting. I know its unfair to comment without knowing exactly all the details but the MJ15024 comes in at less than £2.00 in quantity from an accredited supplier.
This sounds expensive to those of us that can build one. We are not the majority of buyers that will spend for an updated Krell
At the very least he now has paperwork if he does decide to sell that someone will buy with confidence knowing joe six pack hasn't messed with it.
Look at what hi end is charging now for similar amps? It begins to look like a deal to some people out there, not us of course.
The output trans markings are krells special quantity buy from Motorola. Not so sure if it's based on the 15024/25 pair
Don,t see the Power supply caps? You probably mean 22k /63v caps..
Regards
David
At the very least he now has paperwork if he does decide to sell that someone will buy with confidence knowing joe six pack hasn't messed with it.
Look at what hi end is charging now for similar amps? It begins to look like a deal to some people out there, not us of course.
The output trans markings are krells special quantity buy from Motorola. Not so sure if it's based on the 15024/25 pair
Don,t see the Power supply caps? You probably mean 22k /63v caps..
Regards
David
Well, the big man just replied to me himself. I sent an email to Dan D'Agostino today and asked his advice. He replied that the guys at Krell "don't know the KSA 100 as it is before their time. Set the idle bias at 650 mills and, as long as the fans are working, all will be ok."
So now all I have to know how to do is set the bias. Yeah, I'm gonna electrocute myself in attempting that. Ok boys, this is where I NEED your step by step guidance. What do I have to buy in order to do this myself.
So now all I have to know how to do is set the bias. Yeah, I'm gonna electrocute myself in attempting that. Ok boys, this is where I NEED your step by step guidance. What do I have to buy in order to do this myself.
First make sure that this is the original circuit, not the new iBias.
It's likely they just rebuilt it to original specs, but they could have installed the newer design.
I have to believe that even with the newer ibias, the thing would still put out some heat when driven. I would have "hoped" that if Krell did do something like an Ibias, they would have mentioned that little fact.
That tells YOU everything. It tells me nothing. It's greek to me. Other than caps and transistors and such, all those parts don't paint as clear a picture for me as you. Now is someone going to tell me how I can easily raise the idle bias to 650 mV, or should I bring it in to a local tech. There's no way in hell I'm going all the way back to Krell, 365 miles away.
A high bias design requires time and patience to get right, and rechecking after some operation to verify correct settings. It would be best to have a local skilled tech
or more knowledgeable audiophile do this, there's too much chance of disaster if you're inexperienced.
Understood. Thank you all for your knowledge and replies. I would like to learn so I'm hoping the local tech will let me watch. Might even be great if they could do house calls because moving this 100 lb beast is no easy task.
I'm sure that they would be willing to do a house call, for a price.
Since it was just from the factory they should be willing to do a field bias adjustment,
as long as you understand that if anything bad happens due to the high heat, it isn't their fault.
Make sure that the emitter resistors are high enough in power rating for the higher current, for example.
Well, I don't see where they changed the emitter resistors, therefore it's the original design that Dan created which can take the 650 mV per output transistor. Dan stated that as long as the fans are operating, which they are, the amp was "designed" with that in mind.
What does a "field bias adjustment" mean? Do you mean Krell sending someone out??? lol. That would be great and is exactly what they should do since I just paid them a $1100. Maybe they could contact a local tech and they pay them. Basically, I felt they were rude on the last email out to me. They are making me feel like an idiot for wanting to raise the bias. The "If you want a toaster" comment bothered me. I'm very close to sharing Dan's email with them. What are they going to say to that? That the original designer doesn't know what he's talking about?
sharing email from Dan with the krell crew probably won't help you much in the long run; i don't remember if dan & krell parted on the best terms - you might need krell again later for something else that might be easier for them to fix to your satisfaction. just keep notes on what they can/can't do and remember your feelings about them when you buy your next amp.
good luck,
mlloyd1
good luck,
mlloyd1
Dan is no longer there and who knows EXACTLY what mod if any the new Krell has.
There's new thinking your dealing with and it wouldn't,t be wise to consider the original designer unless he has seen it personally which is not the case here.
Photos will go along way. Do you have a DVM? We will be your field bias adjustment if you wish.
Remember you said you liked the sound and consider raising the bias will shorten the life span and not necessarily do anything for the sound, but you will find out to your satisfaction.
Regards
David
There's new thinking your dealing with and it wouldn't,t be wise to consider the original designer unless he has seen it personally which is not the case here.
Photos will go along way. Do you have a DVM? We will be your field bias adjustment if you wish.
Remember you said you liked the sound and consider raising the bias will shorten the life span and not necessarily do anything for the sound, but you will find out to your satisfaction.
Regards
David
Hi David. I guess that's the million dollar question on whether or not raising the bias will change the sound. Krell states that it will add distortion. Others have told me that the current idle bias setting of 85 mV is very low, taking the amp away from its true design function of pure class A with all 100 watts. The original design was highly praised. I'm assuming Dan designed it that way for a reason. Today, I'm told that the new power transistors have a much lower THD and don't need high biasing to run in Class A. However, based on the 85 mV bias set on mine, I'm told that translates to my amp only running in Class A for 1.8 watts. I'm then assuming that means after that it becomes a Class AB amp, which historically creates switching distortion that is audible, hence the reason that Dan created full Class A for the entire 100 watts. So, will I hear an improvement by raising the bias in operating in more of the full Class A region? I now ask that of others who have raised and lowered the bias of a Class A amp. What did YOU hear? Indeed, is there an advantage to running an amp with a higher bias? If not, why don't all amps have their biased turned way down? Why don't all amps run cold, such as mine, if the sound is actually less distorted?
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