| jwb |
I was able to acquire a dead Krell KMA-160 for $0. The driver board of the amplifier seems to have set itself on fire. All the components in the vicinity of the last driver stage have been destroyed, including the transistors, several caps, and a few resistors, one of which is merely scorched, the other if which actually exploded. In addition, a diode in a power supply snubber -- the driver board has a power supply separate from the main power supply -- has exploded. Scary stuff indeed.
What's particularly interesting is there's nothing special about this amp. The topology is unremarkable and the quality of construction screams DIY. In fact the build quality of my Aleph-X monoblocks is, IMHO, quite a lot better than this thing.
Of course, the Krell precedes my efforts by 15 years :)
I hope to get photos and schematics up soon. So far I don't see any exotic parts. There's plenty of MJE 15030/15031 driver transistors, as well as A968/C2238 (these are not marked 2SA/2SC but they do have a great big capital "T" printed on the case. Are they Toshiba?) The small-signal BJTs are A970 & C2240 like you might expect. The power supply seems really basic, but I'll report more after I've diagrammed the whole thing.
Oh, and on the back of the board is the gross rework hack. Eww.
Anyone else have experience repairing, or improving, this unit? |
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| jwb |
| PS, the output stage consists of 24 MJ 15024 transistors. I hate metal cans, it feels like working on a first-generation C-130. |
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| X.G. |
| quote: | Originally posted by jwb
There's plenty of MJE 15030/15031 driver transistors, as well as A968/C2238 (these are not marked 2SA/2SC but they do have a great big capital "T" printed on the case. Are they Toshiba?) |
Yes.One type of Janpanese transistor generally only produced by one Janpanese manufactory ,unlike in USA,Europe...etc:D ;) |
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| Zero Cool |
I am VERY interested in seeing the final schematic and any photos you take.
Yes these early Krells like the 80's the 100's and 160's were all hand built if i am not mistaken. Krell was very new at that time. 1984 i think. but then again, look at the very early Levinson stuff as well, they had MFG problems as well.
BUT, Dan D Agostino is still the king of SS amps in my book! I dream of owning a KSA-250 some daY! Droool!!!
Zero :cool: |
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| anatech |
Hi jwb,
There is nothing wrong with the type of outputs used. Just make sure they are matched.
X.G. is correct in stating that Japanese transistors only have one manufacturer per type number. Use real parts, do not go anywhere near ECG's & NTE's. At least you will know what is in your hand for sure. Also, don't use any sub manuals for cross referencing to a different part #. The ECG/NTE manual is known as "the book of lies" up here. For good reason.
The fire is normal when the unit has been struck by technician. Sometimes, amplifiers just die that way. I had a Bryston 4B that went that way, burned a hole in the PCB. The guys at Bryston said this was impossible, their amps never fail. Right.
So, take your time and be careful. Use a variac so you don't lose anything else.
-Chris |
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| jwb |
Okay, now that I've figured out which transistors are B-C-E and which are E-C-B I can get to drawing the schematic ;)
I think the power supply could use some improvement. Diode technology has truly improved in the last decades. |
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| jwb |
I'm almost done with the schematics. Here's a picture I took of the damaged board. Everything to the right of the molex connectors is the regulated power supply. There's two molex connectors because this same board is flipped and installed on the other side of the amp in the stereo model. For the same reason there are empty pads for a trimmer.
Note the scorched transistor and the molten capacitor. I think the upper transistor is a 2SA968, but I can't tell. I'm guessing because it's complementary to the 2SC2238 below it.
The input comes in on the left from the XLR on the rear panel. Note how the amp is DC-coupled and there is no input protection whatsoever. The gates of those poor FETs (2sk163, anybody have a datasheet?) are just asking to get blown up.
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| Zero Cool |
I sure wish i could "Aquire" some dead Krell amps!!!! what a find! I sure hope you bought the person that you got those amps from at least a case or 2 of guiness!!!!
Anyone else want to off load any old Krell, Levinson, Threshold, Classe, Bedini, Sumo, etc etc. power amps for "$0.00" Dollars or very little dollars PLEASE let me know!!!
I will make sure your favorite beverage truck makes a stop by your house!!!!!
And Mondo thanks to JWB for enlightening us with this privvied info! Now if i could just get the schematics for a KSA-250, i would be in heaven!!!!
JWB, please keep going!!! im dying to see those schematics!!! Thanks for the photo. What a great piece of art, you should call it "Amp PCB scorched by fire"
And Please tell me that you plan on rebuilding these babies...right?
Zero :cool: |
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| jwb |
OK, thanks dimitri, this is the datasheet I've been using. I wasn't sure if the sheet for k163 was still available.
PS What's with all these websites that want you to pay for old datasheets? It's a scam! |
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| jwb |
| quote: | Originally posted by Zero Cool
Now if i could just get the schematics for a KSA-250, i would be in heaven! |
My plan is to turn these KMA 160s into a pair of KSA 80. My friend is going to share the cost and he'll keep one. Full instructions will be included here, naturally. |
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| jwb |
I completed the reverse engineering and now I'm just making nicer drawings. Here's the power supply. No surprises, it's a basic zener-regulated supply. Outputs are ±85V and ±38V. This supply runs the frontend and the output drivers, but the output itself runs from a separate, unregulated, bulk supply.
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| jwb |
Here's the output stage. Points A, B, C, and D are driven from the input, a pair of FET followers and dual differential voltage gain stages. There's also a DC servo. Both of those drawings to follow.
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| jwb |
I decided to draw the input stage with the CAD program. Tired hands...
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| jwb |
Here's the servo. That's all the info you need to build your own KMA-160. Just add a suitable power supply for the output stage.
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| jwb |
Some notes:
C1 and C2 in the output appear to have been added as part of a rework. They are on the wrong side of the board and stuck in the holes for some other components.
R3 and R5 in the input were certainly added in the rework. Initially the bases of Q8 and Q18 were driven directly from the divider R1/R2. There is a trace under R3, which has been manually cut to accomodate the change.
R56 is used to adjust the output DC. The 5K pot in the output is used to trim the bias.
The value of the zener on the servo is unknown. It's less than 25V.
There are many places where a 4K7/4K7 divider is used to bias the base of a transistor. For example, R44/R45 in the servo. This divider is shown many times but in the real amp there's only one such pair of resistors for each rail.
The amp I am working with was destroyed when 87V zener in the power supply exploded. Apparently, the amp didn't shut down, and the DC feedback circuit quickly destroyed itself. It might be advisable to use two zeners in the high-voltage supply, for redundancy. Also there should be a shutdown circuit in case of power supply failure. The Krell has neither.
The input of this amp is DC-coupled without protection. You could easily destroy the input FETs with a hot-plugged cable. I would advise adding zener protection on the input, and possibly also coupling capacitors. |
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| X.G. |
The great works!
Thanks a lot,jwb
Could u share the PCB and internal wiring pictures of it?
regards,
X.G. |
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| jwb |
| quote: | Originally posted by X.G.
Could u share the PCB and internal wiring pictures of it? |
OK, here are some pictures. The first is the main circuit board, containing most of the circuits diagrammed here.
This is what a KMA-160 looks like when you take it to pieces.
The main power supply. Note the quad supply, for stereo operation.
Here's one of the four output boards.
And this is another output board mounted on a heatsink.
Enjoy. |
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| X.G. |
Thank you very much,jwb
Encouraging by you,I work hard at writing a post to share my experience/idea which repair/build a normal PP power amp.;)
But my English is poor....:bawling: wish to finish it in a week.:xeye: :hot:
X.G. |
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| Sze |
nice job JWB
What will you use for the power Fets, Q1,2,3,4, in the output stage? Are the VN and VP0210N5 available anywhere?
YOu didn't specify the voltage of the Bulk supply for the output stage. Do you happen to know what it is.
I'd sure like to built this amp but I think I'd better try something a little simpler first. I'll be keep this info you posted for future reference.
Regards, |
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| jwb |
| quote: | Originally posted by Sze
nice job JWB
What will you use for the power Fets, Q1,2,3,4, in the output stage? Are the VN and VP0210N5 available anywhere? |
I haven't looked. Supertex makes a VN2210 which might be a successor to 0210. I'll look around. Surely there's something more modern that can be used there.
| quote: | | YOu didn't specify the voltage of the Bulk supply for the output stage. Do you happen to know what it is. |
I have no idea. Haven't turned on the main supply yet. |
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| jwb |
| It seems the VN2210 is a much bigger device. Much lower Rds(on), higher Vgs(th), much higher capacitance, slower. Maybe not the perfect substitute. |
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| Sze |
JWB, Please keep us abreast of your progress during construction. I am intested to see how this project of yours turns out. Please post any pertinent information or problems that you encounter while you build this amp.
Thanks
Dan. |
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| K-amps |
| quote: | Originally posted by Zero Cool
I am VERY interested in seeing the final schematic and any photos you take.
Yes these early Krells like the 80's the 100's and 160's were all hand built if i am not mistaken. Krell was very new at that time. 1984 i think. but then again, look at the very early Levinson stuff as well, they had MFG problems as well.
BUT, Dan D Agostino is still the king of SS amps in my book! I dream of owning a KSA-250 some daY! Droool!!!
Zero :cool: |
Zerocool,
Just my 2 cents, I own both the KSA-250 and a KAV-250... at the risk of being bashed around, if I were not consider the looks of the amps... the KAV sounds better. ;-). Both clip at around 330w at 8E.
The KSA-250 is supposed to be pure class A to full power but it is not, it is fixed biased class A to about 28 watts, from then on the auto-bias circuit kicks in. This is the same as all the KSA-300S and fpb series except that is NOT a sustained bias implementation. It is dynamic. The KSA-250 has 24 MJ15024/25 devices per channel and a 4.5kVA toroid.
cheers! |
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| Zero Cool |
| quote: | Originally posted by K-amps
Zerocool,
Just my 2 cents, I own both the KSA-250 and a KAV-250... at the risk of being bashed around, if I were not consider the looks of the amps... the KAV sounds better. ;-). Both clip at around 330w at 8E.
The KSA-250 is supposed to be pure class A to full power but it is not, it is fixed biased class A to about 28 watts, from then on the auto-bias circuit kicks in. This is the same as all the KSA-300S and fpb series except that is NOT a sustained bias implementation. It is dynamic. The KSA-250 has 24 MJ15024/25 devices per channel and a 4.5kVA toroid.
cheers! |
My understanding is that the KSA-250 can be upgraded with the Sustained Plateau Bias like the 300 and FPB models have.
A good freind of mine has been following my audio dream and purchased a KSA-250 several years ago. it was just sent in for updates/upgrades at Krell and he had the SPB upgrade added.
Im sure this big amp is not full class A to full power. i never considered that to be a fact. But, many many audio reviews in many magazine, even today still make reference to this amp. I mean were talking about an amp that can deliver 238 Amps peak per channel! can develop 6hp, has 88 joules of storage capacity, can literally deliver more pounds per stoke then a jack hammer!!!
AND, while specs are fun. this has been the amp that all others have been judged by for many years!
Is it a perfect amp? No im sure its not. But it is one of the best amps Dan D'Agostino has ever built. and, let me quailify that a bit more. At just under $3000.00 used. it is the best amplifier that is close to being within my finacial reach as well.
I would love to own a pair of audio standards, but that doubles the price and then some and that is definitly out of my price range.
I was very excited about the KAV-250 when they first came out. But, correct me if i am wrong. But my understanding was the KAV line was produced as a lower cost alternative for the Home theater crowd. and they run full class AB. Isnt that like buying a budget Ferarri??? Somehow that just seems wrong.
I dream of owning a KSA-250 for many reasons. Of all the amps ever built, this one has recieved the most ink as far as i have seen. I would like to own one to uderstand what all the hub bub is about. But, i have to get to that point first, before i can move forward on my audio nirvana path. And at the moment, i cant even afford 2 of the output transistors used in one of those amps, let alone 24, and i cant even think about affording a whole amp.....so for now. its still just a dream.
Thanks for your .02C worth however. i am now that much richer!
Zero |
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| K-amps |
| quote: | Originally posted by Zero Cool
My understanding is that the KSA-250 can be upgraded with the
Zero |
Zerocool,
I am a power freak... hence when I decided on buying amps in 1997, the Sunfires were pretty much hyped, so I got the Sunfire Signature (600w RMS) with B&W 801's.... I was ... disappointed. To me the sound was screechy, thin and fatiguing (no disrespect to Mr. Carver.. but it was not for me.)
I took it back to the dealer who had the FPB-300's, I tried those and liked them a lot, however $6500 was not in my budget, so he said for 1/3rd the price why don't I try the KAV-250? I took one look at it and said... nah, thats not a Krell . However we decided to give it a try.... within 20 minutes I was home with my KAV-250.
I still wanted to get a KSA-250 because of the ads in the early 90's with the amp sitting next to a jack Hammer etc... I called Krell up and asked them about the KAV, they told me it was Class-AB (just like the Classe/ Halcro and some other very nice amps) I was a little put off but then asked him which amp would sound better, the KAV or the KSA... He said the KAV. I got a little suspect of his recommendations.. so he added, most of the sonic signature is determined in the Input and VAS stages, those all run in class A in both amps. He added only the OP stage of the KAV is class-AB rest is class-A. He said because the KAV was built with newer topologies and components it sounded better.
In my tests, the KSa sounds a litle dark, the KAV more detailed. Both sound relatively warm/ soft and pack a killer bass punch.
My tests were done with the 801's.
I suspect at lower than 4 ohm loads, the KSa will come out as the winner.
Also sheers looks, the KAV does not come close to the KSA.
Both are within the $1500 to $1900 range on ebay today.
Yes the KAV-250 does not look like a Krell but it sure as heck sounds like one.
:D
cheers! |
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| jwb |
K-amps,
What does the input stage of the KAV look like? What transistors are used? Perhaps I can adapt any improvements into my KMA-to-KSA project. |
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| K-amps |
Never took it apart, just the top cover. These suckers are not user friendly to dis-assemble, additionally I do not have the right tools. ;-)
The only thing I remember is that it uses 4 paralelled drivers to drive the OP stage (or something.)
Toroid is a custom order from Plitron, 4 pairs of Mj21195/96 class OP devices (actually custom Krell parts but MOT came out with the MJ2119X series shortly after they fulfilled Dan's order for 1 million OP devices. ;-)
8X 4700uF caps. |
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| jwb |
| I'm probably going to AC-couple the input of this amp, and add zener protection on the gates of the input follower. I really don't see why they might have ommitted them in the original design: while I understand the desire to minimize the parts count, this board is not designed under that philosophy. There's already 72 transistors per channel! I don't think zeners are going to harm anything at all. |
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| jwb |
So what is a decent blocking capacitor, anyway? I need something that's not just huge. Something like the MMKP 383 seems decent. 250Vdc/125Vac limits seem, well, quite overspecified.
Anything wrong with these metallized polypropylene boxes? 11x31mm is still a big footprint but these are the most reasonably-sized ones I can find. |
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| K-amps |
Jwb,
I know the KSA-250's are pure DC coupled (unlike many Amps that claim DC coupling but have an input coupler anyway) because I had a malfunctioning pre-amp (1.2vdc at outputs) that nearly took out my woofers, I was close enough to shut the amp down fast. |
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| jwb |
| I'm from the freedom-of-choice faction. Usually I build inputs with a switch to toggle between AC and DC. Here I'll probably use a jumper instead of a switch, given the internal layout of the amp. |
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| jwb |
| There's an error in my drawings. I read the values of the capacitors incorrectly. The ones I labelled 620pF are 62pF, and the 200pF are in fact 20pF. I was confused by the markings: 620 means 62x10E0, not 620. |
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| bear |
FWIW,
Imho, the KSA series sounded awful. Powerful, but awful. Very hard and nasty on the top end, and there was always something wierd happening in the bass with the Krells of that series.
I suspect that the bias circuit wasn't "static" bias at all, btw. No hard evidence there.
Jon Snyder I think was the main designer on that series, and he published some stuff on "similar" designs after he left Krell - haven't heard anything about him since.
My experience is that the best of that era was the "Reference" amps. Dunno what they did differently there, but they were better sonically.
Great handles, big faceplate, big heatsinks, lots of output devices, and a big toroid. Good stuff for building up a real amp?
Ymmv...
(btw, sure wouldn't mind Dan's $$...) ;)
_-_-bear :Pawprint: |
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| jwb |
I have another mystery capacitor. It's a Roederstein KP 1830, in a 4.5mm x 7.2mm x 6.0mm package. It's clearly marked "100V" but in the current datasheet for that series, there's no 100V capacitors (only 63, 250, and 630). Furthermore, the top of the package is marked "680H" which I initially took to mean, perhaps, 68pF. But in the current KP 1830 line, there's no 68pF capacitor, although there are 680pF and 6800pF.
In the time it took me to write his I could probably have measured the value, which I believe I will now do. |
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| K-amps |
| quote: | Originally posted by jwb
I have another mystery capacitor. It's a Roederstein KP 1830, in a 4.5mm x 7.2mm x 6.0mm package. It's clearly marked "100V" but in the current datasheet for that series, there's no 100V capacitors (only 63, 250, and 630). Furthermore, the top of the package is marked "680H" which I initially took to mean, perhaps, 68pF. But in the current KP 1830 line, there's no 68pF capacitor, although there are 680pF and 6800pF.
In the time it took me to write his I could probably have measured the value, which I believe I will now do. |
LOL one mystery component can fry a lot of "known" components. :D |
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| Nickolas K. |
You have a good point there.
Dan's amps looked terrific.
Nelson's amps play music.
My amps (4 diy Aleph 1.2's) are hidden behind the speakers and I listen to music in the dark.
Who gives a 3#$%^+!!! about handles, faceplates and toroids!
It's all about music, not looks.
Regards,
Nick |
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| jwb |
So Nick, does that mean you don't know a good substitute for Supertex VP0210N5?
;)
Seriously, I have a fleet of Aleph-X too, but you'll never know how good an amp is unless you compare it to something else. The -X is a balanced/bridged symmetrical class A topology, while the KMA is a balanced push-pull class A topology. Anybody who doesn't find fun in the comparison must just be intellectually lazy.
PS I'm thinking the IRF610 and 9610 are good replacements for the VN02 and VP02 parts. The IRFs are bigger, but otherwise similar. |
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| bear |
Speaking of big amps bought by the pound and current, how about John Curl's big Parasound?? Lots of output devices, big heatsinks and big *** toroid... The original one was being sold as low as $600 used for a while...
_-_-bear :Pawprint: |
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| jwb |
| By the graces of the almighty 555 timer I have deteremined the mystery capacitor's value is 680pF. Another case solved. |
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| jwb |
I really have to mention that this KMA-160 sample is riddled with manufacturing defects. I just noticed a solder bridge in the Darlington pair that drives the negative power rail. That's on top of the blatant rework on the diff amp and the ridiculous capacitors on the wrong side of the board.
Krell quality? |
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| bear |
I'm curious, how did they accomplish the 160?
One driver board, two sides of ouputs?
Two driver boards, paralleled outputs?
Two driver boards, bridged outputs??
And, why not bridged, if they didn't?
_-_-bear :Pawprint: |
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| jwb |
| One driver board, two sides of outputs, load returned to ground. |
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| audiomatic |
Hello jmb;
read your thread with great interest. Maybe interesting for you that I am currently working on a similar project. I got a faulty KSA-100 EUR for a very (very,very...) small fee. According to Steven Leckrone, this KSA-100 EUR was called KSA-80B when being sold in the U.S.
The driver board which is located in my amp looks very, very similar to yours shown on the picture (fortunately without parts being burnt that much...). Of course my amp does not have symmetrical inputs - only RCA`s.
Due to other important projects (well--- I do have another Krell Power amp here for repair, it is a KSA-100S with sustained plateau biasing... much more complicated circuit :() I did not get very far now with my KSA-100 EUR, but: Both channels are faulty on my amp (of course as I already told my amp wasn`t on fire as was yours...); all output devices are OK; I have strong DC offset @ both outputs; suspecting a fault in the +/- 80 and +/- 40 Volt regulators on the driver boards.
Well maybe we could exchange some information during our project, and both participate from each other`s knowledge. If there are any totally burnt parts on your pcb`s, I can tell you value/types of these.
Please do not hesitate to contact me via pm, if I can do something for you.
cheers, audiomatic |
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| jwb |
Here's my new layout for the input board. It's a 600KB PDF:
Layout
I kept the basic concept of the original layout, but changed a few things. Most obviously, I added the coupling capacitors, and they take up a lot of room on the left. I also changed the input wiring from soldered to a Molex Micro-Fit connector. On the 38V regulators (Q104, Q105) I added substantial heatsinking. On Q25 and Q26 I added heatsinks where before there were none. On the buffer stage (Q201-204) I think my layout makes a lot more sense than the original, and it's also much more compact. I try to keep a consistent distance between the balanced traces driving these gates, whereas Krell let them wander apart somewhat.
All the footprints and pinouts are the same as the original, save for the added heatsinks. If you used regular Yageo or BC 1/4W metal film resistors instead of Dale, you'd save a ton of space. But as we're constrained by the hole pattern here, there's not much sense in doing that.
The only modification I'm thinking of making is to bias two of the current sources with LEDs instead of resistors. I don't think that's really going to take up terribly much room. |
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| anatech |
Hi jwb,
I've always had better luck and performance using LED's as current source references. There was a great series of posts regarding noise levels among different LED's. All in all, the performance is so improved that the noise levels aren't that important.
It sounds like your Krell is getting a performance kick.
-Chris |
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| jwb |
I'm not expecting a big improvement, but LED references are my standard operating procedure for current sources.
Maybe I'll get a bit of a boost in CMRR. |
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| anatech |
More stable operation and much quieter background. I love it when background noise drops away.
I've noticed this about you from previous posts. They also work very well in power supply regulators. |
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| jwb |
Which parts in this design are important to match? I assume the input FETs need to be matched for Idss, and the diff amps need to be matched for Vbe, as well as the resistors in the diff amps. What about Vgs matching for the FETs in the middle stage? Any other parts I'm neglecting?
Nevermind the outputs and the drivers, since I'm using the original parts there. |
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| jcarr |
How about a two-transistor feedback-type current source? Much higher output impedance, and not terribly complicated, either.
Rod Elliot gives it a quick discussion here:
http://sound.westhost.com/ism.htm#real-life
regards, jonathan carr |
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| hjelm |
I have fiddled with a LED biased current source with a cascode and the cascode improved the performance of the current source a lot, sim wise that is. I actually added a second cascode as well just for fun but then the performance was more determined by the voltage reference noise rather than the transistors themselves.
Has anybody tried cascoding a LED referenced current source in real life, it should help if you consider dynamic thermal stability for the current as well. |
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| jwb |
| Yes I have used cascoded, LED-referenced current sources in voltage regulators before. The impedance is absurd (high tens of megaohms). |
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| jwb |
| Great info, sir. D5 and D6 in your amp has been replaced with resistors in my amp. Do you have any idea why they might have done so? I was considering going back to 2-terminal current sources as part of my modifications. |
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| jwb |
The two current sources on the differentials are operating way in excess of their rated power. They idle with 16Vc-e and are programmed for 22mA, or more than 350mW. The max power is 300mW at 20C ambient, which of course is not the ambient temperature inside an amplifier.
Certainly a more manly current source is required here. The C2240 is OK for the amp and the cascode but not for the current source.
ZTX450 seems to have the required SOA. |
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| lmaclean |
| I'm not sure why they switched. There was quite a bit of variation from unit to unit on some older models. |
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| jwb |
| I wonder why they use so much current in the differential (20mA total). With ±39V rails this causes a real power dissipation headache. Doesn't 2mA seem far more reasonable, with all the resistors increased 10x? Does the 20mA current have some kind of natural advantage in terms of noise? |
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| anatech |
2 mA does make more sense, but I think they were going for speed. Still, 20 mA seems a bit high.
-Chris |
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| bear |
I seem to recall that LEDs as current source references etc, were found to not be a good idea because they happen to modulate with a pulsating light source shining upon them! As with a fluorescent light... :bigeyes:
Of the many ways of making a good current source, I think I'd pick some others first, including some of the purpose built references that are cheap and come in the form of a small transistor package...
_-_-bear :Pawprint: |
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| jwb |
| In this case I'm going to use LM329 buried zener, but only because I want 6V and don't want to stack up 4 LEDs. If you worry about the photovoltaic effect of LEDs (and if you were, you'd also be worried about light-coupled crosstalk within your circuit), just put a blob of opaque gunk over them. |
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| jwb |
I posted a new layout. I moved the screened names so they aren't under other parts, and I have changed the 20mA current sources for 2mA cascoded current sources that run within their SOA.
634KiB PDF download |
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| anatech |
Nice and clean. Soooo, how does it sound now?
-Chris |
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| lmaclean |
| Since cleaning it, it sounds real "clean"! (I couldn't resist...) |
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| jwb |
| quote: | Originally posted by anatech
Nice and clean. Soooo, how does it sound now? |
I'm not a miracle worker. It will take me a few weeks to order all the parts and put it together. |
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| anatech |
Hi jwb,
I can wait for that report. Things take me a while these days too.
As far as cleaning amps is concerned, Imaclean and I have a lot in common. I usually make comments like that at work (& I'm not proud of it either, they just come out. :cheerful: ) |
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| jwb |
| I am frustrated in finding replacements for 2sk163 and 2sj44. 2sk170 and 2sj74 look like good substitutes, but I need to find them from a reliable supplier, and both in the BL grade. |
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| thanh |
| in krell's page ,i can't find out krell 160 |
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| anatech |
I have a similar problem. Since the repair trade has been killed, parts distributors have "died" as well. I had a great guy who closed his doors 2 yrs ago. Still looking for a new RELIABLE distributor. Notice I didn't say cheap.
-Chris |
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| jwb |
| In the past, I have fiddled with making my own semiconductor devices. With the current situation it starts to sound like a reasonable thing to do! |
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| anatech |
Sounds more like we may go to custom devices from players like Motorola. Complete with wonderful house numbers.
It's too bad that the general market has no clue what good sound is, they just want to hear "boom" all around them. That and replace the "rig" every few years when some new processing comes out - cheap.
-Chris |
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| jwb |
By reducing the DC current in the dual differential from 20mA to 2mA, I will presumably get a reduction in 1/f noise from that stage's resistors. But to keep the quiescent operating point, I also have to increase the resistors by a factor of 10, meaning more thermal noise. Is this an even trade? Or will I have more resistor noise? Or less?
I'm using Dale RN-60D resistors. |
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| jwb |
Here's the bill of materials I assembled for this design. The order quantities and extended price are for 4 channels.
Bill of Materials |
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| bear |
I have a source for many Japanese parts. JFETs too.
Email me with your wish list and I can figure out what is available at what prices... let me know if you need matched devices - extra.
Some are not available, but there may or may not be suitable subs - some with different packages, some not.
The more interest, if available, the better I can do.
Some devices I have some stock on now. Not all ranges (gr,bl, v etc.) may be available at any given point in time...
I have a number of 2SJ74s here in front of me... mostly GR, iirc.
When tested they range up and down IDSS in the category.
_-_-bear :Pawprint: |
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| jwb |
| Manufacturing data for KMA-160 audio board, as modified and drawn by myself. |
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| jwb |
| I finally found the perfect FET to replace those Supertex FETs: Zetex ZVP3310 and ZVN3310. I don't know why I didn't think of it before, they're very common, but I think I had the TO-220 stuck in my mind. There's no reason for that, since these components dissipate < 200mW in this circuit. |
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| K-amps |
| quote: | Originally posted by jwb
Manufacturing data for KMA-160 audio board, as modified and drawn by myself. |
What do I need to view these drawings? |
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| Zero Cool |
K-Amps, i see you have a KSA-250 up for auction on ebay! wish i had the change for that!
Zero |
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| jwb |
| K-amps, you can use any program that can view Gerber 274-X and Excellon files. An example, for Windows, is Viewmate . For Unix, use gerbv. |
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| jwb |
| UPS came today. 6 channels of Class A differential goodness |
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| K-amps |
| quote: | Originally posted by Zero Cool
K-Amps, i see you have a KSA-250 up for auction on ebay! wish i had the change for that!
Zero |
Honestly I wish you did too ;-), you are a fine conniseur of the 250. Personnally I put it on auction to make a few bucks... saw the market getting heated up... ;-)
As I said I will sell the KSA-250 but keep my KAV-250 which is more revealing, I use B&W 801's with each. ;-) |
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| K-amps |
| quote: | Originally posted by jwb
K-amps, you can use any program that can view Gerber 274-X and Excellon files. An example, for Windows, is Viewmate . For Unix, use gerbv. |
Thanks, but the webpage did not work... it's ok. |
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| jwb |
Sorry, it is (url removed)
Edit: oh I see, they are being jerks about deep linking to their site. In that case, I recommend you do not use their products. Please use anything else. |
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| jwb |
Project is coming along nicely. I repaired the original equipment, and it works great. I'm almost finished with my first board, and the second one has a few parts on it as well.
Full-resolution photo (1.7MB, 2272x1704) |
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| X.G. |
| quote: | Originally posted by X.G.
Post #19
Thank you very much,jwb
Encouraging by you,I work hard at writing a post to share my experience/idea which repair/build a normal PP power amp.;)
But my English is poor....:bawling: wish to finish it in a week.:xeye: :hot:
X.G. |
cause I had no time to write the post in English,I just spent 6 hours to post the thread on here.
Share my methods to repair/build a discrete power amp
sorry for late.
X.G. |
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| jwb |
| Thanks XG, very good information! |
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| Mike Gergen |
| It's been fun following this thread. I still remember many years ago listening to a KSA100 in a local store. I still have dreams about that day. And I still dream about owning one. |
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| jwb |
| Mike, I'll sell you two boards and the schematic, you'll be well on your way to ownership :) |
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| Mike Gergen |
drool! drool!
Let's talk. Don't know the proprieties of a discussion like this are on the thread. Email me if it's a bad thing.
Mike |
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| jwb |
Are we having any fun yet?
A: No, but after I add 14 more parts to this board, then we will be! |
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| jwb |
| Whatever you do, don't shake this piece of paper! |
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| anatech |
Hi JWB,
Ever sneeze after finishing the matching? I have.
-Chris |
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| bear |
| quote: | Originally posted by jwb
I am frustrated in finding replacements for 2sk163 and 2sj44. 2sk170 and 2sj74 look like good substitutes, but I need to find them from a reliable supplier, and both in the BL grade. |
I can supply both K170BL and J74BL (usually).
The 2SK163 also seems available to me, but not the J44, J43 is but grade on these may or may not be selectable and may or may not be the one desired - but this can be checked.
There needs to be a reasonable quantity, unless I already have them in my bins already.
So, let me know
(bear at bearlabs dot com - for email)
_-_-bear |
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| Sze |
Hi JWB
What circuit are you using to match your transistors?
Thanks
Dan. |
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| jwb |
Dan:
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| jwb |
Viva la resistance. It'd done, and it works great. The only hacks I made were where I used a TO-92 (actually E-line) MOSFET where I had put a TO-220 footprint, and I accidentally specified 100V Schottky rectifiers where I really meant to use 200V. In the end I used a 1000V 1N5408G.
Note that my board has substantially better heatsinking than Krell's. The original KMA-160 must have had a reputation for blowing up the drivers. On the board I fixed, the strip of metal that passes for a heatsink runs in excess of 85C.
Full-resolution photograph
Back to the listening. |
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| Mike Gergen |
JWB
You are having WAY to much fun. NOT |
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| bear |
Just checking, and mildly curious...
We want a Krell 160 clone because??
Great work, but still curious.
_-_-bear :Pawprint: |
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| jwb |
Because we got one for free, that was on fire, and would like a stereo amp, and if we can sell it on ebay for $300 we come out even?
Basically, I'll screw around with any circuit that comes along. Otherwise I'd be bored out of my mind. |
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| Mike Gergen |
I'd like to do it for the same reason one of my brothers rebuilt a '70 Dodge Challenger, a friend of mine rebuilt a '69 Camaro or my dad refinishiing antique furniture. Because it's fun, we can and we can enjoy seeing the creativity and construction of the time.
Mike |
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| jwb |
Stick a fork in it, it's done. Kinda hard to see my boards when they are installed, but here's the photos anyway. I couldn't get the older Neutrik connector, so I had to stick the new model in sideways. Alas.
High-res photo #1
High-res photo #2 |
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