KSA 100 from Jim's Audio on EBAY

[Kaplaars]

Hi Guys,

Haha maybe David. But summer or not, replies or not Kaplaars is still @work ;-) !

Hmm, I've searched but could not find a checklist Andrew. Hope I did not overlooked a topic that explained it. Maybe I have to ask my questions again on the Dutch equivalent of this DIY-forum, or maybe someone can repeat the explanation because I am pretty curious. The basis of gaining knowledge is repeating knowledge so if someone wants to repeat, please do :-)

I red a few things about the zobel network. Great suggestion from AVWERK. It seems that this network will prevent instability due to the sometimes capacitive character of the loudspeakers. I hate smoking, I hate it even more if my Krell will smoke, so I have to prevent instability!

@Rolandong; that is exactely how I want to mount the fans :-) So push-pull principle. Noise will be far more less when I use two fans because noise is reduced quadratically with fanspeed. Have heard a lot of, sometimes very different, opinions about how to mount the cooling tunnels. I think I leave them the way they are. Please dont think I am stubborn, but I think this will be in my case the best solution. The tunnels are capable to dissipate at least 200W per channel with fans off (tested it with resistors mounted to them). But I am a little confused by now, because some people told me that I should use AC fans and not DC-fans because DC-fans would add distortion. Is there anything against DC-fans if I use brushless fans?

Have a little update, very busy at the moment so not very much progress. Lots of hours @lab (I now know everything about alcohol dehydrogenases... yay). But ontopic again Mr. Kaplaars; I've finished the PSU!!! I added very carefully current to the capacitors with a little stabilised PSU. I did this so the caps could reform their oxide layer back. I added a 1,2K resistor in series with the capacitor to limit current and added 25VDC to the caps. It was really cool to measure that the leakage current caused by the caps became smaller and smaller and the capacitors thus got better and better. After an hour the leakage current was only 3uA (it was 50uA). Very very good for electrolytic capacitors, but hey we don't want anything less than very very good.

Setup:


When I measured that the capacitors were OK I mounted the capacitors to the chassis. I bought realy cool braided hose to cover the cables with. Is is really nice if I mag say so :-) Everytime when I search the internet for parts I am astonished by what there is to buy; there are so much nice parts around.

Mounted AC-cable:


I also replaced the relays from the speaker protection. I've replaced them by Omron G2RL-1's. They should be a little bit better than the ones which came with the kit, and they were not realy expensive, so it was worth a try.

And how the amp is right now:


To be continued.... :-)

[Jozua]

Kaplaars

Looking very good except for my concerns re overheating - so be prepared for a possible desolder and rebuild w.r.t. output stage...

With the modern parts you are using I would not be surprised if your amp sounds better than the original.

Regards

Jozua

[Kaplaars]

Thanks Jozua! That is a concern which I share with you. I try to keep the build as modular as possible, so that in case of failure the amplifier is relatively easy to disassemble. That is why I used for example cable clips at the side pannel instead of tiewraps and faston plugs instead of soldering the wires directly to the bridge rectifiers. From the other hand I have to assemble the tunnel coolers with a lot of bolts, they weigh a lot. So dissassembling the tunnel coolers will not be an easy task.

I realy hope so! I have never heard the original Krell KSA-100. Would be fun to compare it to an original KSA-100.

[Jozua]

Kaplaars

I have the KSA 100 mk1 and mk 2. Subjectively the mk2 is more mellow wheras the mk 1 seems more dynamic in my system.

With my KSA 50 clone top notch resistors (Ricken)were used and subjectively I seem to imagine it having slightly more detail.

When I find some good looking heatsinks, or a KSA 100 box or a spare set of heat tunnels my clone 100 will proceed.

Consider yourself very lucky with your costing. This is a very expensive amp to build.

Regards

J

[AVWERK]

The AC vs DC fan debate is just that a debate. I used both styles because of the ..debate...
Having built 6 Krell monoblocks that use both types, I can not reliably tell a difference switched in or out that it does anything negative to the soundstage or on the scope for that matter.
The zobel is cheap insurance. Bedini never used them thinking I assume it does something negative to the sound. I smoked a 150 mk2 without anything connected to the outputs while changing components and then the phone rang....magic smoke from the distance? It oscillated itself out of exsistance

When you do power up you can use the light bulb method. I haven,t done that but it is excellent.
When I power up I ramp my Variac fairly quickly to about 1/3rd to get the trannies to switch while looking at the DVM set in the milivolt
range hung on the outputs. You can place a 2nd DVM across a emitter also.
Then I wait about 3 seconds while sweating like a dog with knees vibrating, nail bitting..the whole package.. A few beers might help here BTW!
If I haven,t had a heart attack yet and can observe the DVM coming down into the milivolt range then I can start slowly increasing the Variac while looking at both DVM,s and adjusting bias along the road ahead..

My variac gets stiff fairly easily if something is wacked and that why light bulb method is a better item to asist.
If you get this far you need to sit with it awhile and keep an eye, actually both eyes on everything.

Regards
David

[Kaplaars]

Haha yeah I was pretty lucky with obtaining parts Jozua. There are so much details that cost money. For example I had to order all wires, terminal rings, cable clips ed for the amp, costed me another 50 euro's! Bought that stuff new which makes the parts far more expensive than second handed parts. But OK it's great quality cable which can withstand 180 degrees of temperature. No beer this week, but cables instead ;-)

WOW 6 monoblocks! How turned your clones out David? Do you have pictures of yours?

Great to hear I can still use the DC fans. I've bought pretty good ones from Nidec (Beta V). They are dead silence, you realy can't hear them. I am thinking of building PWM-control, but.... I've heard PWM-control was not sane because of distortion. Hope that is a fable too!

Great suggestion. I always use the lightbulb method to start old tube radio's (I collect them) which havent been used for years. This way you can see very fast if something is wrong. The mains electrolytic capacitor has this way also an opurtunity to form it's oxide layer a bit slower back.

Hahaha, will some Russian water, or in other words Vodka also do? ;-)

Okay David, will do, I will slowly increase voltage with my variac hoping it does not go kaboom. I've build my variac in a cabinet and added a fuse of 3A together with a VAC- and ampère meter. This fuse has proven it's value, had once a radio which was completely short circuit. Luckily for me the fuse blew which prevented further damage. I will also measure voltage across the outputs and emitters carefully. Do you attach a dummyload and maybe an oscilloscope to the outputs aswell when you are measuring across the outputs?

[johnbedini]

Avwerk,
Sorry to here that but all Bedini Amps have that network built on the boards, I have always used them. Some of the 150's also had other networks but people removed them.
The other thing is that just not hooking the Amp to the speakers does nothing to the stability. The Amplifiers are stable without load. You either had something else wrong with the Amplifier or some tweak adjustment.

The 25/25 all the way to the 250/250 all had that network in some form or another. The Zobel would have not helped if you caused the Amp to break into Oscillation while changing components. You can find many 150's running to this day with no stability problems even at 2 Ohms.

So please do not say I never used them. There seems to be allot of false assumptions about what I have done in my life in the audio field. Most just condemn because of false information on the Net or You-tube, they really know nothing of my work in any of these fields. In the market place you will find over 3000 Bedini Amps running to this day without what your talking about. I still do the repairs so I see what people try to do with the tweaks. To take this further any amp can do what your talking about and they do, so it's just not mine that does this. Anybody can break anything give enough time. So, just setting the record straight here.
John

Originally Posted by AVWERK

The AC vs DC fan debate is just that a debate. I used both styles because of the ..debate...
Having built 6 Krell monoblocks that use both types, I can not reliably tell a difference switched in or out that it does anything negative to the soundstage or on the scope for that matter.
The zobel is cheap insurance. Bedini never used them thinking I assume it does something negative to the sound. I smoked a 150 mk2 without anything connected to the outputs while changing components and then the phone rang....magic smoke from the distance? It oscillated itself out of exsistance

When you do power up you can use the light bulb method. I haven,t done that but it is excellent.
When I power up I ramp my Variac fairly quickly to about 1/3rd to get the trannies to switch while looking at the DVM set in the milivolt
range hung on the outputs. You can place a 2nd DVM across a emitter also.
Then I wait about 3 seconds while sweating like a dog with knees vibrating, nail bitting..the whole package.. A few beers might help here BTW!
If I haven,t had a heart attack yet and can observe the DVM coming down into the milivolt range then I can start slowly increasing the Variac while looking at both DVM,s and adjusting bias along the road ahead..

My variac gets stiff fairly easily if something is wacked and that why light bulb method is a better item to asist.
If you get this far you need to sit with it awhile and keep an eye, actually both eyes on everything.

Regards
David

[spurlte]

Originally Posted by AVWERK

The AC vs DC fan debate is just that a debate. I used both styles because of the ..debate...
Having built 6 Krell monoblocks that use both types, I can not reliably tell a difference switched in or out that it does anything negative to the soundstage or on the scope for that matter.
The zobel is cheap insurance. Bedini never used them thinking I assume it does something negative to the sound. I smoked a 150 mk2 without anything connected to the outputs while changing components and then the phone rang....magic smoke from the distance? It oscillated itself out of exsistance

When you do power up you can use the light bulb method. I haven,t done that but it is excellent.
When I power up I ramp my Variac fairly quickly to about 1/3rd to get the trannies to switch while looking at the DVM set in the milivolt
range hung on the outputs. You can place a 2nd DVM across a emitter also.
Then I wait about 3 seconds while sweating like a dog with knees vibrating, nail bitting..the whole package.. A few beers might help here BTW!
If I haven,t had a heart attack yet and can observe the DVM coming down into the milivolt range then I can start slowly increasing the Variac while looking at both DVM,s and adjusting bias along the road ahead..

My variac gets stiff fairly easily if something is wacked and that why light bulb method is a better item to asist.
If you get this far you need to sit with it awhile and keep an eye, actually both eyes on everything.

Regards
David

I have to admit.... this is probably why I am doing this project. I don't drink much, don't gamble (If I put out any money, I want something in return quickly), and don't have much luck with the opposite sex. It hard to get me the excitement you describe and I am already sweating about "Are you sure you are ready to plug-in this monster?" Worth every penny!

[AVWERK]

Ok, John, i should have stated my Stock original 150 was modified with dual transformers when you were in Paramount, CA. Back in the 80, s and ran like a top back then without issue, but on this day nothing out of the ordinary except no load and nowhere on the board or output terminals was there a zobel network. That is certain. I ran it for years but this day oscillation took its toll. I still have it and fixed it.
You do remember your ADD,s about high frequency issues and grinding the tops off the TO3's and filling them with a special nonresonant material in this model right? in Stereophile?
I noticed you didn,t carry this over to any other models after that?

It should be noted back then Bedini,s were the amp to use on wicked electrostatic loads and were recommended all the time by dealers who didn,t even carry his line
Regards
David

[AVWERK]

Kap
My first pics I ever posted I think and not to good BTW.. were of my 100 with PMA boards back in Sept 2008 on page 221 #2208 thru 2210 in the Krell ksa100 mkII Clone thread by Mark B.
The other 4 are the 50's and the Synder 150's that haven,t been posted yet

These still run strong today without issue and my prefered amps on my Quad electrostatics. I also have Martin logan Sequel 2's that I switch in and out depending on the mood.
For not much money you could buy 2 more bridges and go dual/dual on the power supplys you hav there.
This eliminates any hum and any imbalanced currents that flow because of any mismatched caps even new caps might have. If you can match the caps then this isn,t really necessary but either way, what you have will work fine. You might place a .1uf mkp caps after the ac leads just before the bridge

Regards
David