There are good and bad suppliers.
One thing I go by is the 1mm pins going through a 1mm hole, they should be tight.
One chinese manfacturer I sued always had the holes too big and the pins dropped out. They also took upto 2 months for the pcbs to arrive.
My current chinese supplier always has the holes bang on and the pins dont drop out. They also always arrive within 2 weeks which is magic. And on top of that they are cheaper than the other supplier.
Test sequence
A little update. I've got some suitable capacitors Steve @ Apex. Populated Pinkmouse drivers board from VT67 and a draw full of MJ15003/4 from Onsemi.
I've visually checked the driver board, all looks ok apart from a 100n cap thats cracked by the lead.
I believe I should be able to power it up and check voltages etc. Does it need a load for testing ? The offset should work as normal. What will the bias pot do in this situation ? What do I do about the feedback ? I presume the driver transistors need to be heatsinked ?
I've read to post 7100 so far .... its take me months just to read this far, I think I've forgotten some of the stuff I've read ;-)
For those that have read my earlier posts, I still haven't worked out what I'm going to do about the 40V AC output from the original Krell toroids. I'm going to use a variac in series with a 60W bulb for testing purposes. If I stay with the PS rails at 40V AC then I'll need to change the driver board caps, as they are rated for 50V. I don't really want to buy new toroids.
Cheers
fs
A little update. I've got some suitable capacitors Steve @ Apex. Populated Pinkmouse drivers board from VT67 and a draw full of MJ15003/4 from Onsemi.
I've visually checked the driver board, all looks ok apart from a 100n cap thats cracked by the lead.
I believe I should be able to power it up and check voltages etc. Does it need a load for testing ? The offset should work as normal. What will the bias pot do in this situation ? What do I do about the feedback ? I presume the driver transistors need to be heatsinked ?
I've read to post 7100 so far .... its take me months just to read this far, I think I've forgotten some of the stuff I've read ;-)
For those that have read my earlier posts, I still haven't worked out what I'm going to do about the 40V AC output from the original Krell toroids. I'm going to use a variac in series with a 60W bulb for testing purposes. If I stay with the PS rails at 40V AC then I'll need to change the driver board caps, as they are rated for 50V. I don't really want to buy new toroids.
Cheers
fs
Hi fs, one of the nice things about this amp is that you can power up the driver board to check everything is okay without connecting the outputs. IIRC you need about 18V on the rails before everything is operational. Don't worry about bias or feedback from the outputs for now, that's only needed when you fire up the final stage. So fire up your scope and signal generator, plug in the variac, and unleash hell! 
Hi Pinkmouse,
thanks for your input and designing the pcb all those years ago.
I'm using your boards to rebuild an original KSA-50 mk2, ironic !?!
The only thing that is giving me a headache is the higher voltage rails the Krell specced toroids put out just over 40V AC with 242V AC in, so over 55V DC unloaded. I'll have to accept less bias, change the heatsink and use more OP pairs or buy new power transformers. Or I may use a L-C-C type filter arrangement. Not sure if the L will be practical though.
Cheers
fs
thanks for your input and designing the pcb all those years ago.
I'm using your boards to rebuild an original KSA-50 mk2, ironic !?!
The only thing that is giving me a headache is the higher voltage rails the Krell specced toroids put out just over 40V AC with 242V AC in, so over 55V DC unloaded. I'll have to accept less bias, change the heatsink and use more OP pairs or buy new power transformers. Or I may use a L-C-C type filter arrangement. Not sure if the L will be practical though.
Cheers
fs
To see the hardware, take a look here
http://www.diyaudio.com/forums/solid-state/168482-ksa50-amp-new-production-live-42.html
I thought I was going to use Abin's boards, but I managed to get your version fully populated from VT67.
http://www.diyaudio.com/forums/solid-state/168482-ksa50-amp-new-production-live-42.html
I thought I was going to use Abin's boards, but I managed to get your version fully populated from VT67.
I wanted to get a pair to make a KSA25 for bi-amping purposes, but he ran out of boards. I like the built-in DC protection and speaker delay, but as you say there are only 2 output pairs. Your boards are more suited for the purposes of reviving my KSA50. I'm trying to keep it as original as possible.
Hey Pink...
There is obviously still enough interest in this thread to consider me looking into having another fifty to hundred boards to be made... let me look into it in the next week or two... I would NOT have the time to mail them all out though so someone else would have to volunteer to do that. Perhaps I cold get a local electronics place or someone like Apex Jr could do it. As long as I recoup my cost of the boards thats fine... the rest could go to DIY Audio or your favorite charity. Who was the guy that took over the KSA-100 board mailing for me....? i wonder if he'd do it???
Mark
There is obviously still enough interest in this thread to consider me looking into having another fifty to hundred boards to be made... let me look into it in the next week or two... I would NOT have the time to mail them all out though so someone else would have to volunteer to do that. Perhaps I cold get a local electronics place or someone like Apex Jr could do it. As long as I recoup my cost of the boards thats fine... the rest could go to DIY Audio or your favorite charity. Who was the guy that took over the KSA-100 board mailing for me....? i wonder if he'd do it???
Mark
I have two Avel Lindberg transformers made for Krell, rated at 400VA with the following windings
Primary
100V, 110V, 120V x 2
Secondary
12V
0-40V
0-40V
If I used a variac or autotransformer and fed it 180V, the Vout will be 30V and rectified, it will be around 40Vdc?
Would I be right in assuming that I would have to derate the transfomer by the same ratio ? So the 400VA would end up being a 300VA transformer ?
Regards
fs
Primary
100V, 110V, 120V x 2
Secondary
12V
0-40V
0-40V
If I used a variac or autotransformer and fed it 180V, the Vout will be 30V and rectified, it will be around 40Vdc?
Would I be right in assuming that I would have to derate the transfomer by the same ratio ? So the 400VA would end up being a 300VA transformer ?
Regards
fs
That would have been me.....
I would consider doing it again. It is not much trouble if you do all the label printing online and have the USPS deliver envelopes to use. So yes, if there is enough interest to get a GB going I will do it. The KSA100 and 50 were both fun projects. In fact I was just thinking of making a new case for my KSA50 with my new TIG welder.....
Bob G.
Itsmee,
this particular one exactly, or any wing-type binding post ?
The Tiffany style binding posts are made by a number of manufacturers nowadays ; Vampire, Mundorf, Intertechnik, leafshaped cross-section ones by Propeller Post, etc.
Even Hirschmann used to make this type of terminal ('Polklemme' in German )
this particular one exactly, or any wing-type binding post ?
The Tiffany style binding posts are made by a number of manufacturers nowadays ; Vampire, Mundorf, Intertechnik, leafshaped cross-section ones by Propeller Post, etc.
Even Hirschmann used to make this type of terminal ('Polklemme' in German )
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