Krell KSA 50 PCB

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#8,142
Use the default fan cooling , since you have the heat sink for it. FIT a 65C thermostat onto the heat sink that can Cut the primary on the toroidals when heat gets too high.

Example for thermostat: KSD301 Temperature Switch Thermostat 65 °C NC KSD 301 - eBay (item 180549429402 end time Nov-16-10 18:58:11 PST)

Source a pc board that you can fit inside enclosure.

example for pc board: High Power Pure Class A amplifier PCB KSA50 ! - eBay (item 320528350000 end time Dec-02-10 19:47:21 PST)

Source big capacitors:

example: 2 KENDEIL 50V 47000UF CAPACITOR KRELL KSA50 NAIM HICAP! - eBay (item 180557633928 end time Nov-05-10 03:46:35 PDT)


Source 35amp bridge diodes , these should be easily available.

For speaker protect there are endless options and even ready build kits on ebay or you can build it yourself.

For slow start A 10 to 20 ohm 5amp thermistor is the easiest choice. You can add timed relays to short them after a while. Or you can also use one of the many kits on ebay or for sale everywhere.

These are just a few random ideas. and you have A LOT of decisions to make.

One thing though. I think your enclosure is for a ksa 50 mk1 since it only has 1 heat sink en 2 pairs of output devices per channel.

Enjoy!

tang
 
#8,145
piotr_m37 said:
pcb krell ksa 50 - Audiostereo.pl - strona 73
Click to expand...

Hi Piotr,
I'll check the thread out. I may need your help if the translator goes wrong ;-)

I've tried posting a message there, it says "Ten post wymaga zatwierdzenia przez moderatora zanim będzie dostępny i widoczny przez wszystkich użytkowników. To ograniczenie jest ważne do 11.11.2010 - 08:44"

Looks like there is a moderation time.

Regards
fs
 
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#8,146
Tangmonster - thanks for your suggestions, you are right, there are plenty to think about.
Neychi - I have the heatsink and fan already, it will be more practical to use them, but thanks for your comments. I may be asking for help to quietn the fan in the future 🙂
 
#8,147
tangmonster said:
Use the default fan cooling , since you have the heat sink for it. FIT a 65C thermostat onto the heat sink that can Cut the primary on the toroidals when heat gets too high.

Example for thermostat: KSD301 Temperature Switch Thermostat 65 °C NC KSD 301 - eBay (item 180549429402 end time Nov-16-10 18:58:11 PST)

Source a pc board that you can fit inside enclosure.

example for pc board: High Power Pure Class A amplifier PCB KSA50 ! - eBay (item 320528350000 end time Dec-02-10 19:47:21 PST)

Source big capacitors:

example: 2 KENDEIL 50V 47000UF CAPACITOR KRELL KSA50 NAIM HICAP! - eBay (item 180557633928 end time Nov-05-10 03:46:35 PDT)


Source 35amp bridge diodes , these should be easily available.

For speaker protect there are endless options and even ready build kits on ebay or you can build it yourself.

For slow start A 10 to 20 ohm 5amp thermistor is the easiest choice. You can add timed relays to short them after a while. Or you can also use one of the many kits on ebay or for sale everywhere.

These are just a few random ideas. and you have A LOT of decisions to make.

One thing though. I think your enclosure is for a ksa 50 mk1 since it only has 1 heat sink en 2 pairs of output devices per channel.

Enjoy!

tang
Click to expand...

Theres a thermoswitch bolted to the heatsinks already. I should test to see if it works and replace it if necessary.

I'm going to wire the trafos up temporarily to measure the offload V, as there seems to be some variations. This is so I know if I can use 50v caps reliably or I need to use 63V or higher.

How is your KSA50 ?
 
#8,150
My ksa 50 will run on +-35V. so 50V caps are fine for me but test your toroidal AC voltage.

I am going to order the metal for the enclosure in the net week. I had a tube phono riaa circuit i needed to finish before getting back to the ksa 50.

I also bought 2 toroidals at a good price on the swap forum about 5 weeks ago , these where only shipped on the 20th from the UK ,so i am waiting for them.

Most of the metal cutting and bending places close around the 15th of December until 10 Jan so I need to place my order in the net week to get it before closing time 15 Dec.

The attached picture shows you an idea of my enclosure design tested. And also the pdf is the autocad drawing i am busy with for the metal house. I will use 3mm brushed aluminium natural anodized.

with my +-35V and 120mm 12v fan running at around 70 % speed i got a nice 41C heatsinks. With no fan they krept up and up hitting 60C in about 10 to 20 minutes.

The autocad drawing shows the two heat sinks in green and also the two toroidals en 4 capacitors i will be using. Size of enclosure 470mmx220mmx280mm.

I will use 6mm threaded bar to hold everything together as i have been using with all my other enclosures.
 

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#8,151
Hi firestorm

I'm an author of pcb project viewed in #8106 and #8107 posts of this thread and in Polish DIY Audiostereo forum ("pcb krell ksa 50 - Audiostereo.pl - strona 73"). This project was designed with Altium Designer v.6. Up till now I ordered 44pcs of the pcb for Polish DIYers in local pcb manufacturer. It was done in 2 group orders (12pcs + 32pcs).

All details about the pcb you can find in #8106 and #8107 posts.
 
#8,152
Hello JKoch,
thanks for your message.

Am I reading it correct, thats you have designed your clone to the dimensions of the original KSA-50 MK2 ? So it should fit to the original fan tunnel heatsink ?

If so, it looks like the one for me ;-)

Are the parts in your bom easily available still ?

Regards
fs
 
#8,153
KSA50 Avel Lindberg trafo

PWatts said:
Hi all,

Courtesy of Jozua, I removed the board of his original KSA50 Mk2 (fan is bottom-mounted) for some much-needed restoration and tweaking. While busy I thought I'd reverse-engineer the circuit diagram since there are so many KSA50 diagrams and variations floating around. Attached is a picture of the removed board.

Another difference is much higher power rails, at 50V loaded, 52V unloaded. This choice of higher rails could perhaps be due to the higher gain.

As you can see the board's negative section has seen some extensive trauma & prior repair, and the white 2.2uF capacitor at the bottom along with the two tack-soldered resistors are a DC-blocking RC filter at the input. Whether this was a private mod or an afterthought from Krell I'm not sure - on the KSA100Mk2 there also is a tack-soldered capacitor at the bottom of the board so it's not unprecedented.
... some text removed ...

Regards,
Pierre
Click to expand...

Hi Pierre,
I have most of the original bits for a KSA-50 MK2. I have the original Avel Lindberg trafos.

The trafos I have, has two orange wires, 2 pairs of blue and grey, 2 of blue, brown, black and a green/yellow wire.

I guess the green/yellow is for a electrostatic screen. I usually identify the primary by it being thinner gauge wire. For the Avel trafos, they all seem quite thick. So I've measured the inductance, the red to black reads 238mH, red to bown reads 6.3mH, brown to black 163mH. The grey to blue reads over 20H.

Since there are more turns at the primary for a step down trafo, I would guess the blue/grey wires are the primary??

I don't want to get it the wrong way !

Since you have seen the original amp, can you tell me the colour codes or post a photo of the wiring harness ?

Thanks
fs
 
#8,157
I've just measured the mounting pillars, they're 135mm x 75mm.

From the photos I've seen and the measurements using the tunnel heatsink, the maximum dimensions should be about 170 x 100mm. The board can be taller, but it depends where the mounting holes are.

I've taken a few photos.

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


http://img227.imageshack.us/img227/8145/p1190236.jpg
http://img130.imageshack.us/img130/3055/p1190237.jpg
http://img841.imageshack.us/img841/1755/p1190238t.jpg
http://img193.imageshack.us/img193/1569/p1190239d.jpg
http://img59.imageshack.us/img59/3449/p1190241.jpg
http://img513.imageshack.us/img513/9931/p1190235b.jpg
 
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