Krell KSA 100mkII Clone

[Dr_Strangelove]

Now I've got to have...
😀 😀 😀

Hmm.. not enough money. I Know, just skip the vacation. I can do without a vacation. And I think the lady wouldn't mind either staying at home this summer.

 

[TomWaits]

Thanks Chaps for the feedback on the ATI chassis! It is a $1000.00 to ship two of them to my door. Saves a lot of time?

Vacation vs. Amplifier Chassis? Strangelove, that is a good one! Yes I'm certain the wife would prefer another noisy amp in the home vs. 2 weeks chillin' on a cruise ship.😉

Cheers,

Shawn.

 

[Luke]

Shawn,

at least with two of them you can play around with Bias and if you decide later you can use the case to make an even bigger beast amplifier🙂

 

[PhongVuTuan]

Krell??

Hi everybody,
I begin to build this Krell style amp, for the input stage, I don't have a good complement pair of trans (NPN and PNP).

Can I use 2sc2383, 2sa1013. but I'm not sure about whether these trans are faked.

I have genuine too Mpsa 42/92 but gain and noise characteristics is not desirable.

I also have a hundred of genuine 2N5087 and bc546. Can I combine these trans in the input stage, cascoded version.

 

[Jozua]

Group Buy for Chassis ?

Hi

I am keen to have a Krell Clone chassis that looks professionally made and that would not look out of place amongst my other commercial equipment. I also suspect from a sonic perspective this amp is worth the expense of a proper chassis.

The ATI box looks good but personally I would prefer even better heatsinking.

I am very much in favour of exploring the possibility of a group buy. A group buy might just be a cheaper option versus having a chassis build privately.

Alternatively we can decide on a fixed front chassis dimensions and then have a faceplate made in a groupbuy. That could still give a professional look if the amp is rack mounted.

Does anybody have any good contacts in this regard ?


Jozua

 

[PWatts]

Not a bad idea at all about the faceplate. Laser/plasma cutting, brushing, anodizing and silkscreen becomes very cheap in large volumes. A custom-made power switch of aluminium with the same finish embedded in the plate also looks so much more professional than a tacky generic one, and if a proper diffuser can be organised for power LED it would be even better.

IMO something seriously worth considering.

 

[VT67]

Can somebody tell me where R16 (825R) has to be placed on the board?

Regards

 

[AVWERK]

Ge Wa

I'm away from home at present- as I remember, on mine those mount on the bottom of board

 

[VT67]

Thanks AVWERK. Must be something like that because there's no space foreseen on the component side. It's possible that this question was raised before but the thread is becoming a bit long to go back and search for it. It's also not mentioned in the "Everything You Need To Know About The KSA100 Clone Was But Too Afraid To Ask section", or I didn't see it.

Regards

 

[AVWERK]

GeWa,

I guess you found R36 (1.5K) and R37 ( 7.5K) already since you didn't mention them 🙂

Regards

David

 

[jacco vermeulen]

where R16

C4 goes on the top, therefore R16 is on the bottom.
There's a vacant pad between R5 and R6.

 

[PWatts]

It's nice to see people at last starting to build the amp, was wondering when the questions would start coming about the resistors I've placed at the bottom 😉

And yes, there's no support for the 20pF cap since there was no space on the layout when I saw it on the original (not present on the schematic), so it has to be tack-soldered at the bottom too. All mentioned in the FAQ, but I guess the phrase "afraid to ask" should be replaced by "lazy to read"

 

[jacco vermeulen]

Long thread, Walter forgot that Mark switched position of R36/R37 at the board testing time, due to the dual side mounting.
Most people lack 3D memory, i'm still waiting for the turkey for getting the R36 trivia question right.

Aaarghh

 

[Harry3]

It's nice to see people at last starting to build the amp, was wondering when the questions would start coming about the resistors I've placed at the bottom 😉

Some of us are still waiting for boards & diodes

 

[PWatts]

I've received mine last week 😀 Only waiting for a few transistors and ZVN Mosfets and a package from Parts Connexion and I can begin as well. I've milled the driver heatsinks this weekend from old ones, took about 10hours and still not finished since they had to be sawed, drilled, some of the fins milled off clean, anodize removed, re-anodized (almost burnt myself to death with the acid), but they look almost identical to the original ones, just a little thicker 😀

 

[AndrewT]

Hi,
if you have not yet bought VR2 then I suggest some lower values for R36, R37 & VR2.
R36=430r
R37=2k4
VR2=1k
The bias current through Q13 is about 17mA and the resulting base current will be about 0.2mA.
The current through the resistor string R37 VR2 R36 is of a similar value. Ir36=0.65/R36~=0.65/1k5=0.43mA, when bias is set to maximum. Resistor current falls to just 0.2mA when VR2 is set to 1k75.
A small change in Q13 base current will have a very significant effect on the current passing through R37 and the resulting multiplication ratio will swing (unstable?) when Q13 base current varies.

Using reduced values for the resistor string will help to keep the multiplication ratio nearer to a constant value. Reducing R36 from 1k5 to 430r increases the maximum resistor current from 0.43mA to 1.5mA. This is still well within the current limit of a 300mW 1k multi-turn pot.

There may be an advantage to going even lower with these resistor values.

 

[VT67]

Is this correct?

Regards

 

[PWatts]

Yip that's right. On the later iteration of the board (which unfortunately reached Mark too late for manufacture) I made it better laid out. Depending on your predriver heatsink you can mount R37 on top, but if you use foldback type heatsinks as in the original then they'll be in the way.

 

[VT67]

I'm still puzzled with R36 and R37 though and how they are connected. I don't seem to get the correct connections according to the schematic.
Gonna try to figure it out tomorrow with a fresh mind.

Regards

 

[PWatts]

GeWa,
The reason you're puzzled is probably because I've swopped around VR2 and R36 as on the schematic; they're in series so it doesn't matter. In all, just solder the resistors on as you've marked on your picture and you'll be fine.