I am building a KrellClone KSA100-MKII amplifier and need help deciding on the power supply design. When you make recommendations try to keep within the following scope:
1) Overkill - Keep every part with the thought of "over designed" if it says within the chassis dimensions
2) Quality Number One Importance - I am not concerned with the price, I am concerned with the quality of each part
3) Internal Chassis Dimension 258mm W x 143mm H x 358mm D
Does anyone have a schematic to help me choose the correct parts?
What Transformer do you recommend? What are the "perfect" values on the secondaries?
What Capacitors do you recommend?
What Rectifiers do you recommend?
Thanks!
1) Overkill - Keep every part with the thought of "over designed" if it says within the chassis dimensions
2) Quality Number One Importance - I am not concerned with the price, I am concerned with the quality of each part
3) Internal Chassis Dimension 258mm W x 143mm H x 358mm D
Does anyone have a schematic to help me choose the correct parts?
What Transformer do you recommend? What are the "perfect" values on the secondaries?
What Capacitors do you recommend?
What Rectifiers do you recommend?
Thanks!
Krell KSA100 MKII Schematic
I just wanted to add the schematic I was using just in case it changes anything.
How does the schematic look? I bought the boards from Honk Kong, really nice quality boards with Gold Traces.
I just wanted to add the schematic I was using just in case it changes anything.
How does the schematic look? I bought the boards from Honk Kong, really nice quality boards with Gold Traces.
Attachments
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http://www.diyaudio.com/forums/solid-state/78129-krell-ksa-100mkii-clone.html
Biased to 100W (aka 2.5A) you'd need 700VA/40Vac per channel minimum.
Option 2 is biasing to full output, on 1000VA/ch.
Preferred electrolytics are CG type big cans, 100C minimum, 125C if you can spare the extra dollars and cents.
Superior rectifier bridge diodes are fast/soft recovery types, TO247 package.
Biased to 100W (aka 2.5A) you'd need 700VA/40Vac per channel minimum.
Option 2 is biasing to full output, on 1000VA/ch.
Preferred electrolytics are CG type big cans, 100C minimum, 125C if you can spare the extra dollars and cents.
Superior rectifier bridge diodes are fast/soft recovery types, TO247 package.
The subject of Krell clones and their construction has been well visited in another series of threads. You can use the search function to find the details.
In most cases people opted for the same capacity and quality as stock or better. My personal preference is to keep the capacity of the power supply at or lower than the de-rated thermal capacity of the output transistors. My last build (with Neil Kaye) for 100W class A/8ohm, was a 600W toroid with ~40000uF with 6 output pairs per channel. With fan assisted cooling each channel weighed #35...
In this instance you have not provided enough info for anyone to make informed comments. For instance what goals do you have for this amp? Not deciding this up front will cause you a world of hurt later on...
Some items for you consideration:
Class A output power into what load? (idle current)
Lowest impedance load (peak current)
Class B output power? (rail voltage)
Stereo build, or dual mono? (transformer capacity)
Do you plan on using fans? (mass and volume)
AFAICT your chassis is just large enough for internal passive cooling of a single ~50W channel for 8ohm use or stereo 50w if fans are used.
If you make a stereo 50W amp, in addition to making beautiful music, it will be a very heavy space heater. They only get bigger, heavier and hotter from there.
None of the above is about sound 'quality' per se, rather quality of engineering for the given task.
You can select the 'best sounding' components once you know what values are appropriate for the task you are attempting.
HTH
Stuart
In most cases people opted for the same capacity and quality as stock or better. My personal preference is to keep the capacity of the power supply at or lower than the de-rated thermal capacity of the output transistors. My last build (with Neil Kaye) for 100W class A/8ohm, was a 600W toroid with ~40000uF with 6 output pairs per channel. With fan assisted cooling each channel weighed #35...
In this instance you have not provided enough info for anyone to make informed comments. For instance what goals do you have for this amp? Not deciding this up front will cause you a world of hurt later on...
Some items for you consideration:
Class A output power into what load? (idle current)
Lowest impedance load (peak current)
Class B output power? (rail voltage)
Stereo build, or dual mono? (transformer capacity)
Do you plan on using fans? (mass and volume)
AFAICT your chassis is just large enough for internal passive cooling of a single ~50W channel for 8ohm use or stereo 50w if fans are used.
If you make a stereo 50W amp, in addition to making beautiful music, it will be a very heavy space heater. They only get bigger, heavier and hotter from there.
None of the above is about sound 'quality' per se, rather quality of engineering for the given task.
You can select the 'best sounding' components once you know what values are appropriate for the task you are attempting.
HTH
Stuart
I use same circuit for my KSA50... it sound nice. I use it to replace my Aleph 5. Of course, I am not sure if the circuit is good for the KSA100
Chinese PCBs
Class A output power into what load? (idle current)--Whatever it
takes to power at 100watts.
Lowest impedance load (peak current)--4ohms, but all my speakers are 8 ohms.
Class B output power? (rail voltage) -- Trying to stay at Class A.
Stereo build, or dual mono? (transformer capacity) The Chinese PCBs are for two MONO main boards and four for each main board (each driver PCB has either 2 each 2SC2240s or 2SA970S). I attached a photo of the PCBs.
Do you plan on using fans? (mass and volume)--I hope not. I read that fans break down easily and spread dust everywhere.
Class A output power into what load? (idle current)--Whatever it
takes to power at 100watts.
Lowest impedance load (peak current)--4ohms, but all my speakers are 8 ohms.
Class B output power? (rail voltage) -- Trying to stay at Class A.
Stereo build, or dual mono? (transformer capacity) The Chinese PCBs are for two MONO main boards and four for each main board (each driver PCB has either 2 each 2SC2240s or 2SA970S). I attached a photo of the PCBs.
Do you plan on using fans? (mass and volume)--I hope not. I read that fans break down easily and spread dust everywhere.
Attachments
I meant 4 driver boards for each of the 2 main boards. 2 driver boards are either V+ or
V- oriented. You can use only 2 driver boards for each main board if you want a KSA50 setup. I really wanted to try for the KSA100 MKII setup. I want to "FEEL" the music in my bones. I am wondering if anyone might have a schematic and parts list for a workable power supply and where I might obtain a soft-start for this setup.
V- oriented. You can use only 2 driver boards for each main board if you want a KSA50 setup. I really wanted to try for the KSA100 MKII setup. I want to "FEEL" the music in my bones. I am wondering if anyone might have a schematic and parts list for a workable power supply and where I might obtain a soft-start for this setup.
offer
hi
ive read youre posts but,dont buy these boards thery are not ok for the task
i have 2 pairs very well made,that were perfected here on diyaudio.com
an i saw on ebay, look for it
i will sell these for 100 usd free shipping, -they can take pwoer caps on the pcb
ive built mine using 1x 2kw transformer ,and very good resistors
2sa1943 2sc5200 ,excellent choice ,buy the right one not that cr,p
you will have problems and youll be forced to do it from the begining
hi
ive read youre posts but,dont buy these boards thery are not ok for the task
i have 2 pairs very well made,that were perfected here on diyaudio.com
an i saw on ebay, look for it
i will sell these for 100 usd free shipping, -they can take pwoer caps on the pcb
ive built mine using 1x 2kw transformer ,and very good resistors
2sa1943 2sc5200 ,excellent choice ,buy the right one not that cr,p
you will have problems and youll be forced to do it from the begining
yours are ksa 100 not ksa 100 Mk II
send private message,will include files to help built it,ONLY mainboards for a stereo amp
send private message,will include files to help built it,ONLY mainboards for a stereo amp
An externally hosted image should be here but it was not working when we last tested it.
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Spurite
On both my 50wt mono,s and the 100w Krell clones I used dual bridge Power supplys.
With one bridge you really need matched caps that no one ever does anyway. The dual bridge design takes care of this right away and more.
The cost is only 1 extra bridge Use at least 35a 600v
For slow start keep it simple and use a CL 60 in line. They limit current somewhat but you,ll never notice it
This is the least costly route that works really well
The mention of fans as unreliable is bogus..., your favorite girlfriend or wife should be replaced with the word "fan" for a more accurate sentence!
Regards
David
On both my 50wt mono,s and the 100w Krell clones I used dual bridge Power supplys.
With one bridge you really need matched caps that no one ever does anyway. The dual bridge design takes care of this right away and more.
The cost is only 1 extra bridge Use at least 35a 600v
For slow start keep it simple and use a CL 60 in line. They limit current somewhat but you,ll never notice it
This is the least costly route that works really well
The mention of fans as unreliable is bogus..., your favorite girlfriend or wife should be replaced with the word "fan" for a more accurate sentence!
Regards
David
Decisions
Well, if you want 100W RMS, class A into 4 ohms, as well as 100W class A into 8 ohms you are going to have a very large power supply and heat-sinks to match:
Here's a beer mat calculation: 100W RMS into 4 ohms needs at least 2.5A for idle current, while 100W RMS into 8ohms needs rail voltages of +/- 40v plus whatever you allow for the output transistors, say 2 more volts top and bottom, so your output stage needs to be capable of continuously dissipating 2.5 * 42 * 2... 210W per channel...and of course that is not including heat from rectifiers, drivers etc.
If you decide you can compromise, you can halve the output stage heat-sinks, transformers etc if you accept class A/B for a 4 ohm load, as Krell did; I don't remember anyone complaining about the low impedance abilities of the Krell amps ;-)
When you try and fabricate the chassis with the heat-sinks required you will being to see why Neil and I chose to use fans...So far my experience with them has been good. In this, as in so many things, I think you get what you pay for, good fans are not cheap and will have ball bearings etc to make sure they last a long time.
A common rule of thumb quoted hereabouts is to allow at least twice as much transformer as the power requirement of the amp, so you'd want at least a 400VA transformer per channel, I chose 600VA basically because I had them sitting around. AFAIK Krell used 400VA per channel of the KSA100, the same as for both channels for the KSA50.
HTH
Stuart
Well, if you want 100W RMS, class A into 4 ohms, as well as 100W class A into 8 ohms you are going to have a very large power supply and heat-sinks to match:
Here's a beer mat calculation: 100W RMS into 4 ohms needs at least 2.5A for idle current, while 100W RMS into 8ohms needs rail voltages of +/- 40v plus whatever you allow for the output transistors, say 2 more volts top and bottom, so your output stage needs to be capable of continuously dissipating 2.5 * 42 * 2... 210W per channel...and of course that is not including heat from rectifiers, drivers etc.
If you decide you can compromise, you can halve the output stage heat-sinks, transformers etc if you accept class A/B for a 4 ohm load, as Krell did; I don't remember anyone complaining about the low impedance abilities of the Krell amps ;-)
When you try and fabricate the chassis with the heat-sinks required you will being to see why Neil and I chose to use fans...So far my experience with them has been good. In this, as in so many things, I think you get what you pay for, good fans are not cheap and will have ball bearings etc to make sure they last a long time.
A common rule of thumb quoted hereabouts is to allow at least twice as much transformer as the power requirement of the amp, so you'd want at least a 400VA transformer per channel, I chose 600VA basically because I had them sitting around. AFAIK Krell used 400VA per channel of the KSA100, the same as for both channels for the KSA50.
HTH
Stuart
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Chinese KSA-50 PCBs
Here is a finished KSA-50 MKII project using only 2 driver boards for each KSA-50 main boards. http://www.diyaudio.com/forums/solid-state/62168-my-completed-krell-ksa-50-clone-pics-2.html
You only have to add 2 150R for R40 and R41 and two more drivers: MJE15032 for Q16 and MJE15033 for Q17 for a complete KSA-100. I purchased the PCBs at this ebay auction:
High Power Pure Class A amplifier PCB KSA100 ! | eBay
I have read someone that the KSA50 or 100 amplifier will sound more correct with a regulated power supply. Any advise on this? And where could I get soft-start for the PS. Then there's talk about temperature sensor for the fan. I am a recently retired tinker-nut who needs occupy myself.
Here is a finished KSA-50 MKII project using only 2 driver boards for each KSA-50 main boards. http://www.diyaudio.com/forums/solid-state/62168-my-completed-krell-ksa-50-clone-pics-2.html
You only have to add 2 150R for R40 and R41 and two more drivers: MJE15032 for Q16 and MJE15033 for Q17 for a complete KSA-100. I purchased the PCBs at this ebay auction:
High Power Pure Class A amplifier PCB KSA100 ! | eBay
I have read someone that the KSA50 or 100 amplifier will sound more correct with a regulated power supply. Any advise on this? And where could I get soft-start for the PS. Then there's talk about temperature sensor for the fan. I am a recently retired tinker-nut who needs occupy myself.
This is the url for the completed project. Sorry, maybe you can only put one url to one post. *http://www.diyaudio.com/forums/solid-state/62168-my-completed-krell-ksa-50-clone-pics-2.html
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May I ask? What PCBs did you use?
I was told the chinese PCBs I purchased will present problems and I will have to start afresh. xSlavic offered a pair, but I need to see other setup before I settle on buying another pair of KSA100 hopefully with driver PCBS, schematics and parts list. May I ask what PCBs did you use for the KSA100?
I have used the PCBs from the original and second group buy, they seemed to work very well.
You asked in a couple of places why someone would build a KSA50 as opposed to a KSA100. AFAIK the main reason is heat, there is an implied scale of construction required in order to dissipate it. I started to construct a passively cooled KSA100, then later I embraced the idea of fans when I realised I would not be able to move the amp on my own.
I did not try a fully regulated power supply, the output capability of the amp is too high to make it practical, the power supply regulator has to have the same or greater current capacity or it will break, or simply not regulate. I tried a CLC power supply and it worked well...but ultimately it was not needed: sonically I did not find any meaningful differences between 40000uF, and 20000u/2mH/20000u, though I did measure lower ripple on the rails.
Soft start is easily achieved with a CL60 thermistor in series with the primary of the transformer. They have high resistance when cold and low resistance when hot. They heat up as a result of the mostly constant current flowing. IIRC the specs for the CL60 are quite appropriate for an amp of this size (50-100W class A), but not too much bigger.
HTH
Stuart
You asked in a couple of places why someone would build a KSA50 as opposed to a KSA100. AFAIK the main reason is heat, there is an implied scale of construction required in order to dissipate it. I started to construct a passively cooled KSA100, then later I embraced the idea of fans when I realised I would not be able to move the amp on my own.
I did not try a fully regulated power supply, the output capability of the amp is too high to make it practical, the power supply regulator has to have the same or greater current capacity or it will break, or simply not regulate. I tried a CLC power supply and it worked well...but ultimately it was not needed: sonically I did not find any meaningful differences between 40000uF, and 20000u/2mH/20000u, though I did measure lower ripple on the rails.
Soft start is easily achieved with a CL60 thermistor in series with the primary of the transformer. They have high resistance when cold and low resistance when hot. They heat up as a result of the mostly constant current flowing. IIRC the specs for the CL60 are quite appropriate for an amp of this size (50-100W class A), but not too much bigger.
HTH
Stuart
xSlavic, could you please post or email to me a photo of your PCBs. Plus, could you please explain why these chinese boards are not up for the task as you say. Please. I spent good money on these and shipping. Could it be the components required for the build? Or, just the boards themselves. I can learn a valuable lesson here. When you mentioned above, "buy the right one not that crap," are you referring to the list you mention above or the PCBs I purchased? I love to read the elelctronic lingo you guys toss around like doctors in a surgery room.
Looking at the boards you found on eBay, I don't see anything that would indicate they are "crap"...that does not mean they work...
However, these are not boards for the KSA50 we made as part of the first and second group buy, they are for the KSA50 ii, technically I suppose it's a better amp. In practice people and reviewers have claimed to prefer the sound of the original.
Beware of very high speed output transistors: the original Krell amps used transistors that were fast enough, 7MHz if I remember correctly, but not as fast as some of the new parts. For a first time build I'd stay close to the original, finding you've made something with stability issues will be expensive in an amp with great current capability ;-)
HTH
Stuart
However, these are not boards for the KSA50 we made as part of the first and second group buy, they are for the KSA50 ii, technically I suppose it's a better amp. In practice people and reviewers have claimed to prefer the sound of the original.
Beware of very high speed output transistors: the original Krell amps used transistors that were fast enough, 7MHz if I remember correctly, but not as fast as some of the new parts. For a first time build I'd stay close to the original, finding you've made something with stability issues will be expensive in an amp with great current capability ;-)
HTH
Stuart