Krell KSA 100mkII Clone

[PWatts]

Almost all amplifiers are 0degrees phase shift. across the audio band. A minority will have 180 shift, but few will have (mentionable) shift, and definitely not to affect a bi/triamped system where the shifts of the crossover and drivers are far more dominant. The few amps that has 180degrees shift can easily be compensated by wiring them out of phase. At very low frequencies the phase relationships may differ, but then the change of phase (i.e. group delay) of the preceding electronics and electro-mechanical effect of the driver in the box will dominate once more.

In short: don't worry about it. What IS an issue is the different gains of different amplifiers. Most are in the 20dB region, but there's no fixed gain for all amps. Even the Krells differ - the KSA50 has a 23.9dB gain, and the KSA100 28dB; i.e. 4dB higher. That should be compensated for (add/remove gain of one of the two before the amps, or pad the higher gain one if you know what you're doing, or design the crossover with the gain difference calculated in. The last option is the most elegant with no active circuitry or power loss, but naturally limit the speaker to the particular amp combo.

[still4given]

Hi Guys,

Sorry for the Faux pas. I must learn that I don't have to type everything I'm thinking. I surely didn't mean to take the thread off course. I am very interested in the KSA 100 and am looking forward to building one. I built two of the Ksa 50 klones, one with Jan's boards and T-03 outputs and one with the Pinkmouse boards and plastic outputs. I now plan to use the tunnel and outputs from the first unit for one side of the KSA 100. I'll try and keep on subject.

Blessings, Terry

[AndrewT]

Hi MikeB,
I was going to say you are all ears, but now it's EYEs that are leering at me.

[gbyleveldt]

Hi Guys,

I want to start looking for components for this amp and just want to confirm some details here.

Am I correct in assuming that I can use MJL21193 + MJL21194's for the outputs transistors? Should I rather use MJ15003 + MJ15004? I'm thinking of using 4 pairs per channel. For the drivers, I can use MJ15030 + MJ15031 (It looks like that in the previously attached scematic). Do you guys have any idea what kind of heatsink I would need for a channel on this? I had a look what some of our eastern friends use on their amps. They appear to be using the Fischer SK108 or SK109 sinks. These are around $35 unanodised in 100mm lengths each and they use 7 of them for a complete amp. That is quite pricey for heatsinks!!! I don't like the idea of fans, but I might end up having to use them...

Any thoughts would be appreciated!

[AndrewT]

Hi,
building a ClassA amp from scratch is expensive.
Building a big one (KSA100) is much more expensive.

The cost of the "amplifier" is quite (very) small compared to the cost of the transformer + the smoothing capacitance + the case + the heatsinks.

If you want to save significant sums of money then try to source suitable components for the "big costs" secondhand. (I have used Ebay for this).

I would prefer to go with 21193/4 rather than 15003/4 due to the better SOA at the higher voltages found in the KSA100 (for a 50Klone either would do)
They are also more than twice as fast (with half the Cob) and Onsemi divulge more data and that reassures me. ONsemi seem almost secretive about 15003/4 data and that worries me, I begin to wonder what they are hiding.

[Jozua]

Gbyleveldt

If you want to combine your pcb parts order with mine, then you welcome to contact me privately.

Personally I would love to find heat tunnels similar to the ones used by Krell.

Jozua

[PWatts]

Advantage of 15004/3 is their low fT and thus less chance for instability with long wires. The 21193/4 are slightly faster, or else go for the 3281/1302 and all the other newer ones.

MJ15030/15031 are the easiest (and also original) for drivers, or their higher gain 32/33 and 34/35 siblings.

The FET debate is still open, but the board has provision for 3 different types to experiment with.

For LTP transistors the original 2SC/2SA ones or BC546/556 are nice fast choices, slower alternatives would be MPS8099/8599 and MPSA42/92.

For heatsinks you can always use thyristor blocks with slow-moving fans, at low cost and space. Those metal Papst ones are very quiet and cheap at about <$40 each at the agents. Even though they're 20years old, the ones in the original MK2 are so quiet you cannot even hear if the amp's on or off except in the most silent environment.

[gbyleveldt]

@AndrewT
Thanks for your help! I have no doubt that this will be an expensive amplifier. I have not built a Class A yet, so this will be new for me. Unfortunately we have to import everything from Europe and with the excahnge rate as it is things are pretty expensive. I like the look of the Fischer heatsinks, but at that price I'll make another plan, hence I'm wondering what rating is required so that I could try and source something else from a local manufacturer.

@Jozua
We can definately do that, but your PM button is disabled. Pierre has my private E-mail as well. I got the pricing from Electrocomp in Midrand as they import all the Fischer heatsinks. I think if we put our heads together, including Pierre, we could source something locally. I'm going to buy the semi's in bulk, so we could join forces on that as well...

Cheers

Gert

[Flodstroem]

Hello Gert and welcome to the project.

Regarding heat sinks, are your intention to build a stereo amp or two mono-blocks ?
If your intention are to build a stereo amp using no fans it will be a BIG amp due to the heavy heat sinks you will need (total heat dissipating will be >500 Watts). A better choice will be to build two mono blocks but its more expensive as you had to use two totally separated power supplies (double of everything as transformer, caps, soft start etc...).

But if you decide to build mono blocks as I intend to do, then its easier to use natural convection heat sinks. One mono block had to get rid of ca 260W of heat and if using say two heat sinks on each side of the chassis they could have a K-value of ca 0.23. It means the heat sink temperature will rise 0.23 x 130Watts = 30 degrees C above ambient. If your ambient is 22 degrees C, heat sink temperature will then rise to ca 52 degrees C.

This is an example calculated when using this heat sink (MF35, L=151.5 millimeter):

http://www.conradheatsinks.com/produ..._350.html#MF35

This is a very pricey heat sink and you will need four of this model (or a similar sink).

regards

[Mark A. Gulbrandsen]

In order to get the group buy going we need to know what type of PCB everyone wants. I;m am going to order .093 thickness no matter what. I would personally like to see a black board with gold plate traces... no solder mask and white silkscreen for parts placement. I think this type of board would be reminiscent of the boards found in older H-P test euipment. The only thing is that great care neds to be taken while soldering some of the parts in place... mainly the input and mosfet semi's. These pads are VERY close together and the smallest tip available for your iron is required to do this no matter what or you'll end up with a mess. The rest of the board is quite easy to solder with good size solder pads and the through holes are adaquate for up to 1/2 watt resistors.

PWatts would like a black board with soldermask that reveals the whole trace and these traces would also still be gold plated... I think that black with gold would look excellent and typically audiophillic but he points out that black does show the dust very fast so I was wondering about blue.....

At any rate until everyone involved that wants boards agrees I'm not ordering anything.

Lets all battle this out here and make a decision on it by next week so we can get boards made and amps built......

Mark