KSA 100 from Jim's Audio on EBAY

[Kaplaars]

Hi Friends,

It's a while ago I posted some updates, very busy period. Although I still have vacation, I worked a bit to finance the KSA inter alia to other projects haha.

I've made some progress. I've also red quite a bit of literature to learn more about the stuff.

First I wanted to construct a Zobel network, but I calculated that using an 1 Watt resistor is going to be tight. Although there is some breating space, and 20 KHz at full power (most extreme circumstance for the Zobel when the amp does not oscillate) is not going to occur too often, I really want to make it safe, so I will order some non-inductive resistors which can withstand a bit more power (3W). Devices which can withstand more power are almost always inductive, which is a no-go for the Zobel. Offcourse, when it oscillates bad even the 3 W resistor will go down no matter what, but at least using a 3 W device will buy a bit more time before it goes down.

I've also obtained some nice connectors for the speaker terminals and 6mm thick wires:



And connected the speaker terminals parallel with each other and the speaker protection board (negative leads are not connected in the picture).



I've also bought some more quiet fans. They are absolutely inaudible. They are from Noise Blocker Germany. Got a few rubber rings with it so vibrations can't be transferred to the cabinet. Really nice stuff, but I am afraid airflow is reduced to much, so maybe I change them for fans that have a bit more airflow:



Andddddd I've been thinking about some way of fan controll with temperature readout. I wanted to keep it modular and I wanted to controll 4 fans with it because I want to place two extra additional 12 cm fans underneath the cabinet for extra airflow. I found a nice device called the Scythe Kaze master:



But I did not wanted to add the controller + PSU in the cabinet of the amplifier. I don't think chances of distortion caused by this device are big, but still it is another transformer and a few bits of electronics extra next to the amplifier. So I was thinking and thinking and finally tadaaa I bought an external DVD-RW drive. Not to make DVD's but I could use the cabinet and PSU. It has exactely the PSU I need, 2A @5VDC and 2A @12VDC:



Nice thing about the cabinet is that the Kazemaster fits perfectly in it! But it needed some tweaking; it had some scratches so I sprayed the cabinet over with some silver spray paint and I added some new feet underneath it:



Resulting in:



It is not finished yet. I have to construct a connection between the KSA and this device. I am thinking of using D-sub connectors. Have a lot of them which I collected a few years ago when I repaired and scrapped computers.

Loads of pictures, and a few updates, but it is not finished yet

@ Spurtle: I would say that you don't loose performance. But it can occur that the contacts of the device corrodes which makes the transision resistance a bit higher.

[Kaplaars]

Hi Friends!

How are the other builds progressing? Hope the other builds are progressing prosperous

I've made little progress, progress is going with baby steps right now, new year at university started. We started right away with quantum mechanics, which I have to say is somewhat difficult. But I am lucky, even Richard Feynman said no one could understand quantum mechanics, so it is not entirely my fault But back on topic Kaplaars!

I've added a D-sub connector to the external fan control unit. Therefore I had to cut a little bit out of the backplate which is attached to the cabinet. I also had to solder all the wires to a re-used D-sub connector which I scrapped from an old computer.



Mounted it to the backplate:



And the cabinet:






I am waiting for a thick cable with 25 small wires in it. I will use this cable to form a connection between the KSA chassis and the fan control unit. I also have to add the other D-sub chassis part to the KSA-100 chassis. So still work to do. But if everything turns out right it should be finished before Christmas I hope

[ticknpop]

I had the earliest Krell KSA 100 and they used 15003 / 15004. Late Krell had Motorola run them a special batch ( maybe a million devices ) and label them AA and A - don't know if they were a tighter spec for gain or ?

[Kaplaars]

Hi Friends!

This amp is getting more and more heavy. Who needs dumbells when you got an amplifier like this So I thought some handles would be handy. I also felt like there was something missing at the rear of the amplifier. Some nice handles should not suit ill. 1 + 1 = 2, so I wanted to mount some handles at the rear of the amplifier. A very friendly radioamateur offered me two very nice handles for free! They had some scratches, but they surely had potential. They are really strong, thick, iron handles. So, I sanded and repainted them with silver spray paint. I am very statisfied with how they turned out:



Next step was to mount them to the rear of the cabinet. This is not easy since it is difficult to predict were I had to drill the holes. But after some measurements I got it right. So it was time to drill the holes. Bingo, they fitted like a glove. I think it turned out really nice. The amp is becoming more and more professional

Rear:



And with the backplate mounted to the cabinet:



I am thinking of mounting two more handles at the front too. But I first have to find two nice handles before I, offcourse, can mount them

[Kaplaars]

Wow, it is quiet here, time to shake this treat up

Another update concerning the KSA project, I've finally connected the Zobel network. I received some parts a few days back; two nice 4W MOX 5.6 ohm resistors and two nice 100 nF Audyn caps. I haven't got a clue how the Audyns perform. But hey were not expensive and easy to mount, so I ordered them with the resistors.



Nicest way to mount them would be on a little PCB, but that would made the leads longer, and since the leads of the Zobel need to be as short as possible, I mounted it directly to the speaker terminals:



But the Zobel raised a question: some power amplifier designs don't use a Zobel network, but only mount a capacitor parallel to the speaker terminals. But is this not dangerous? I am asking this because, when an amplifier oscillates at an high frequency, the capacitor gets more and more conductive, thus I would say eventually when the frequency is high enough it can act like a short circuit between the leads. This would be deadly for any amplifier.... well that is what I think. Is there something I am missing in here? Does this work because the speaker itself is still parallel to the Zobel which adds some resistance? And that impedance changes with frequency, so the higher you go in frequency, the more impedance the speaker will have because of it's coil? I would say no, because current takes the shortest lead, which is at high frequency, through the capacitor. Also it would be still dangerous when there is not a speaker connected to the amplifier. Can someone help me out on this one ?

[AndrewT]

the Thiele Network that is added to give the amplifier enhanced HF stability comes in two forms. There is also an infinite range between the two forms.

1. R+C at the amplifier output, then L to the speaker terminal.
2. L//R to the speaker terminals, then C across the speaker terminals

Dr Cherry showed how to calculate the component values for the two Thiele Networks and also how to calculate for the whole range between the two limiting values mentioned above.

Do not simply put a cap across the speaker terminals. That alone will make stability worse, not better.
You must put in the whole Thiele Network.

However, some designers can make their amplifiers stable without needing the Thiele Network. Those designers are clever and don't need DIYaudio to teach them how to stabilise amplifiers.

It's us that need all the assistance that Members provide. Use a full Thiele Network, until YOU can design out some or all of the Thiele components.

[a.wayne]

Chassis does look nice , but IMO your Input and output connectors are two close..

[Kaplaars]

Hellowhellow Andrew, I wondered where you would be.

Tell me something I don't know... I know how the Zobel and Thiele network works, it is not rocket science to calculate it. But I was curious why some designers use just a capacitor, like Denon does in their PMA-1500R. Why would they do that? But like earlier you can't give real explanations. That is OK, some people don't have the capabilities to teach. But just don't reply then...

Krell uses a Zobel network in their original KSA-100. This sentences: 'However, some designers can make their amplifiers stable without needing the Thiele Network. Those designers are clever and don't need DIYaudio to teach them how to stabilise amplifiers' gives a bad taste in my mouth. I tried to be nice in the past, but not now. Ehh, Andrew, so Mr. D'Agostini is dumb in your opinion, because he used a Zobel network? Actually most respected brands are crap because they use a Zobel network? Who are you to even imply this kind of amplifiers needs a Zobel network. It is just for safety. Should I not use fuses too because an well build amplifier could never go short circuit? C'mon man.

Andrew if you are a sort of design god, were are your designs? So you don't need a Zobel network, because you are, well you think you are, smart. Why did I read in another topic that your KSA-100 clone is mere an oscillator? I would say that this would be really not clever. There are loads of people who done it before . Why did the people who wanted to help you and asked for a picture got a lame excuse that you could not post pictures of it? Do you even have build a KSA? Even I can post pictures on DIYaudio and I am not 'clever', well in your eyes... . How hard is it to construct a KSA-100. Even a, in your eyes, stupid chemistry student who is not that far away from obtaining his Bachelors degree, and who likes to post a thing or two on DIYaudio now and then, can construct a KSA-100

Oh and Mister T: the KSA is actually very stable WITHOUT the Zobel, as you could have red earlier. It is just a safety option. It would be a shame if my speakers would go down. They have a bit of a complex filter, so it can be complicated to my amplifier. Safety first Andrew. Or is safety 'not clever' too?

Thanks A. Wayne! Why would that be? I think input and output could not interfere with each other. I am more concerned about the softstart which is a bit closely connected to the speaker terminals. Hope it does not interfere with introducing some hum If that would be the case, I think I will have to construct some iron shielding, but I think it will be ok Keep you all updated about this.

[sippy]

I lived with a real KSA100 for a month years ago.......so I follow this thread when it pops up on the home page.
I noticed your post on handles, http://http://www.hifi2000.it/ have something similar.

[Kaplaars]

Thanks for the hyperlink Sippy! I actually ordered my cabinet from HiFi 2000 They sell very nice cabinets. But I did not really like the handles. In real the handles from HiFi2000 are a bit too large in my opinion. I was searching for something a bit more subtile The handles at the back are in my opinion perfect. I really like them. They came from old 19 inch rack equipment. Hope I will find two more