Another mod
OK, finally did the Constant current source mod on the 75V zener. Used a simple setup (3 diodes, 1 transistor, 2 resistors, about $0.50 worth of parts).
100V
l
l
1N914
l
l
1n914
l
l
MPSA92 (base to 1n914, emitter to 100V line via 150R resistor)
l
----1n914----75V zener
l
47k resistor
l
l
ground
Another good mod! This seems to remove the hardness I noted in my previous post and lowers the noise floor further.
In comparison, the unmodded channel is now sounding quite "muffled", with lower levels of detail.
Will listen more tonight.
Lastly, if this mod is good for the 75V zener, it will be good for the 39V zener as well. I'll be trying that soon.
OK, finally did the Constant current source mod on the 75V zener. Used a simple setup (3 diodes, 1 transistor, 2 resistors, about $0.50 worth of parts).
100V
l
l
1N914
l
l
1n914
l
l
MPSA92 (base to 1n914, emitter to 100V line via 150R resistor)
l
----1n914----75V zener
l
47k resistor
l
l
ground
Another good mod! This seems to remove the hardness I noted in my previous post and lowers the noise floor further.
In comparison, the unmodded channel is now sounding quite "muffled", with lower levels of detail.
Will listen more tonight.
Lastly, if this mod is good for the 75V zener, it will be good for the 39V zener as well. I'll be trying that soon.
Last mod
Ok, I think this is my last mod to this great amp:
I added a CCS (set for 8mA) to the 39V Zener. This zener reference feeds the input stage of the amp.
There were small gains in detail, not as much as with the 75V zener mod.
I think that's about it from my side, but would be curious to see/hear of any other mods that may bring benefits.
FWIW, I should add that I have been pleasantly surprised by this amp. Despite its 140W rating, it has been more than capable of driving my Apogee Scintilla's to comfortably loud listening levels, with bass remaining deep and detailed and no signs of distress in treble or mids being evident.
Now to mod the other stereo KSA80B and then run the system in vertically biamped configuration....😀
Ok, I think this is my last mod to this great amp:
I added a CCS (set for 8mA) to the 39V Zener. This zener reference feeds the input stage of the amp.
There were small gains in detail, not as much as with the 75V zener mod.
I think that's about it from my side, but would be curious to see/hear of any other mods that may bring benefits.
FWIW, I should add that I have been pleasantly surprised by this amp. Despite its 140W rating, it has been more than capable of driving my Apogee Scintilla's to comfortably loud listening levels, with bass remaining deep and detailed and no signs of distress in treble or mids being evident.
Now to mod the other stereo KSA80B and then run the system in vertically biamped configuration....😀
Just checked-It is 40,000uF at 100V
Also note some additional mods to a ksa80:
I've replaced the polyester 10uF cap being used in the DC servo with a polyprop. Once again, this brings more detail to the fore. No brightness or anything, just more "ambience".
I've also added a separate 300VA transformer for the input/gain stage (100vDC)-appears to lower noise floor even further.
If I were to rank the mods, with best mods first:
1. Add constant current source on 75V DC supply to input stage
2. Replace 10uF cap in DC servo and additional 300VA transformer on input stage
3. Add 10,000uF caps on input stage power supply
Also note some additional mods to a ksa80:
I've replaced the polyester 10uF cap being used in the DC servo with a polyprop. Once again, this brings more detail to the fore. No brightness or anything, just more "ambience".
I've also added a separate 300VA transformer for the input/gain stage (100vDC)-appears to lower noise floor even further.
If I were to rank the mods, with best mods first:
1. Add constant current source on 75V DC supply to input stage
2. Replace 10uF cap in DC servo and additional 300VA transformer on input stage
3. Add 10,000uF caps on input stage power supply
For the record, it looks like KSA100EUR is KSA80. See here:
Index of /home-audio/amps/Krell KSA 100 EUR and also
http://www.amplimos.it/images/Krell KSA100 EUR 1989.pdf
Index of /home-audio/amps/Krell KSA 100 EUR and also
http://www.amplimos.it/images/Krell KSA100 EUR 1989.pdf
Can anyone help in identifying the CCS being used in the 160? Also, how should this be modded? Cascode or something simpler like a diode to replace one of the resistors?
Hi to all,
It was mentioned way back in this thread by K-Amp that the MJ21195/96 power TRs are most likely the replacement for the KAV amplifier custom Krell TRs. Does anyone know what the markings are on the original custom Krell TRs in the KAV amp?
Thanks!
It was mentioned way back in this thread by K-Amp that the MJ21195/96 power TRs are most likely the replacement for the KAV amplifier custom Krell TRs. Does anyone know what the markings are on the original custom Krell TRs in the KAV amp?
Thanks!
circuit boards
Is there any interest in having some of JWB's boards made up?
If I have 10 made cost will be about $35 a board. If I have 20 made it drops down to only $18. I have a 2kva +/-77vdc power supply just begging to become a KSA200 clone🙂
Is there any interest in having some of JWB's boards made up?
If I have 10 made cost will be about $35 a board. If I have 20 made it drops down to only $18. I have a 2kva +/-77vdc power supply just begging to become a KSA200 clone🙂
Well this is interesting. Are there any info in here about the possibility of getting hold of a couple of these boards or maybe the possibility of having them produced.
I did not. They told me that Zip file was incomplete and did not contain the necessary information for production. If anybody were more successful please inform.
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Well, that's odd of course. What zip file did you use? Obviously I sent them something, and tangible goods were returned by mail, so somewhere I have the right zip file.
I have here "manuf/krell.zip" which contains input.bot input.dri input.oln and input.top, which are the bottom, drill, outline, and top shapefile, respectively. Is that the one you used?
I have here "manuf/krell.zip" which contains input.bot input.dri input.oln and input.top, which are the bottom, drill, outline, and top shapefile, respectively. Is that the one you used?
I used the Zip file presented in post 74 : http://www.diyaudio.com/forums/solid-state/42357-reverse-engineering-krell-kma-160-a-8.html. If you can confirm that this file is unchanged compared to the your original zip file I would very much appreciate that. Then clearly the Danish company I sent it to has a problem when unzipping the file. I believe the owner of the company is a member of this forum as well.
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