Ksa 150

[Antonio Carlos]

Good evening friends!
I just write me in this great forum and would like a help if possible. I am born in electronics and I am with an amplifier Krell KSA 150 to repair. The problem is that I can not find the electric scheme. Some of friends have this plan and if so send me or made available in a site?

Thank's,


Antonio Carlos (Brazil - Rio de Janeiro)

 

[StephenR]

Anyone has schematic of KSA-150 and KSA250? I have been searching on google site diyaudio.com and no luck.

Thanks

 

[stoN_Cold]

Anyone has schematic of KSA-150 and KSA250? I have been searching on google site diyaudio.com and no luck.

Send a mail to Krell.

 

[StephenR]

I wrote to Krell, but at the mean time, nobody has the schematic of either the KSA150 or 250?

 

[stoN_Cold]

but at the mean time, nobody has the schematic of either the KSA150 or 250?

Which part?

 

[StephenR]

Which part?

The schematic of the whole amp.

 

[stoN_Cold]

I have but 2 large.

 

[StephenR]

I have but 2 large.

Is it like this one but with more pairs of output transistor?

I am interested in buying one, just want to know the design.

Thanks

 

[AndrewT]

Is it like this one but with more pairs of output transistor?..............

4 pairs of 250W devices not enough for you?

 

[stoN_Cold]

Is it like this one but with more pairs of output transistor?

I am interested in buying one, just want to know the design.

After I repared.

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.

 

[StephenR]

4 pairs of 250W devices not enough for you?

I am looking at the design. I am a DIY, BUT I am actually looking to buy at this moment. I am actually waiting to buy something like the Threshold S300 or similar amp. I have been waiting for a little while, so I am looking for other brand. There are a few Krell KSA on ebay and are about $2000. I want to see what's in the circuits that make them worth that kind of money.

The schematic of KSA100 I have seems very primitive. In fact, it is very similar with some much cheaper amps. It's just complementary IPS with resistor load, simple VAS(no cascode or darlington) and two EF output. If the KSA150 or 250 are like this but only with more pairs of output transistors, I want to know what make them worth that kind of money.

Compare to Threshold S300 or S500, Threshold has FET IPS, cascode VAS and EF driving CFP output stage. That crys "high end" and worth the money!!!

Even the cheaper Nakamichi PA-7A designed by Nelson Pass that is a whole lot cheaper has much sophisticated design very similar to Threshold S300 with 7 pairs of output transistors. And they are going for $800 only.

If KSA150/250 are like KSA100 with more pairs of output transistors, I am not going to pay over $2000 for a used one!!! I don't want to buy just for the name. I just don't see using say bigger transformer, more filter caps can make up for the primitive design.

 

[stoN_Cold]

Threshold & Krell not the same class.

 

[StephenR]

Threshold & Krell not the same class.

You mean Krell is higher class? Judge by the price, seems like so. That's why I want to look at the schematic. Can you look at your schematic and see how it compares to the KSA100?

Thanks

 

[stoN_Cold]

Old school vs new. 100 --> 150/250.

 

[StephenR]

Old school vs new. 100 --> 150/250.

What do you mean? You mean the IPS and VAS is the same, just more pairs fo output transistors? It sure have a lot of big transistors in your picture.

 

[StephenR]

Hi

I have no luck emailing to Krell to get the schematic. Can anyone post the schematic of the KSA150 or 250?

Thanks

 

[StephenR]

Is this the KSA250 schematic? It did not say it, I am just guessing.

 

[stoN_Cold]

Is this the KSA250 schematic?

Nope.

 

[LineSource]

Is this the KSA250 schematic?

There are 5-pages of schematics for the Krell KSA250. Opamps...opto-couplers...relays

If you decide to purchase a used Krell KSA250....Discussion Forums talk about 3 main versions, each with modest improvements/changes in circuits, bias, power supply, soft-start ckt. Try to buy Version 3.
SOME DIFFERENCES I REMEMBER are:
--Version 1 has the speaker binding posts oriented vertically
--Version 2 and 3 have the speaker binding posts oriented horizontally.
--Version 3 has a larger soft-start board which provides "staggered channel power-up"
--Version 3 has a new input circuit providing lower noise, and improved differential input functionality.
--Version 1 is output biased at ~ 120ma/device
--Version 2 is output biased at ~85ma/device
--Version 3 is output biased at ~100ma/device

Replacing major electrolitic capacitors costs ~$600

A modern $1000-in-parts 250W stereo DIY amp design will measure better than the KSA250, and if well constructed, operate for 20 years without needing repair. BUT it will not be a proven reference standard like the KSA250 which keeps its resale value.

 

[StephenR]

There are 5-pages of schematics for the Krell KSA250. Opamps...opto-couplers...relays

If you decide to purchase a used Krell KSA250....Discussion Forums talk about 3 main versions, each with modest improvements/changes in circuits, bias, power supply, soft-start ckt. Try to buy Version 3.
SOME DIFFERENCES I REMEMBER are:
--Version 1 has the speaker binding posts oriented vertically
--Version 2 and 3 have the speaker binding posts oriented horizontally.
--Version 3 has a larger soft-start board which provides "staggered channel power-up"
--Version 3 has a new input circuit providing lower noise, and improved differential input functionality.
--Version 1 is output biased at ~ 120ma/device
--Version 2 is output biased at ~85ma/device
--Version 3 is output biased at ~100ma/device

Replacing major electrolitic capacitors costs ~$600

A modern $1000-in-parts 250W stereo DIY amp design will measure better than the KSA250, and if well constructed, operate for 20 years without needing repair. BUT it will not be a proven reference standard like the KSA250 which keeps its resale value.

Thanks for the detail reply. Can you give me the link of that thread that has the schematic. I have been searching up and down, I use "KSA 150 schematic site diyaudio.com" on google and searched up and down before I posted this thread. I read a lot of the threads and no schematic. They just assume people have the schematic.

I think at this level of quality, distortion measurement really don't tell the story anymore. there must be something about Krell that people are willing to pay so much money for one.

Thanks