Harry3 said:
You weren't deliberately mislead - that's what we all thought the original was, and a 25-0-25 will still make a very good amp.
edit: and just to clarify, I always intended, (and used) a 30-0-30 traffo, but recommended the 25-0-25 simply because it makes heat management a lot easier, and construction more straightforward. Unless you are an experienced builder, I still recommend 25-0-25. I won't mention my 39-0-39 low biased Class B experiment! 🙂
25-0-25
Harry
My clone is running on a 25-0-25 500 VA transformer. I will look into the possibility of swopping transformers.
However my goal was to replicate a SPECIFIC sonic footprint.
For me the priority should now be to get the correct parts. If the parts can be sourced it will be worthwile to explore a version 3 PCB. I am certain Pierre will be able to produce an high quality procduct. However without the correct parts it might just be simpler to go and buy the real thing.
That means there are two questions the group needs to look at namely:
a) Can the correct parts be sourced?
b) How many people are interested in a version 3 PCB?
Jozua
Harry
My clone is running on a 25-0-25 500 VA transformer. I will look into the possibility of swopping transformers.
However my goal was to replicate a SPECIFIC sonic footprint.
For me the priority should now be to get the correct parts. If the parts can be sourced it will be worthwile to explore a version 3 PCB. I am certain Pierre will be able to produce an high quality procduct. However without the correct parts it might just be simpler to go and buy the real thing.
That means there are two questions the group needs to look at namely:
a) Can the correct parts be sourced?
b) How many people are interested in a version 3 PCB?
Jozua
Hi Al,
I too thought a 25-0-25 Volt 500VA transformer should be ample for a 50W Class A amp and it should. It's just frustrating buying all these expensive components and finding out that something else will make it sound better. In my case I purchased two 25-0-25V 500VA and two 80VA transformers for this project.
I might try using 35-0-35V 80VA for the printed circuit boards and leaving the output devices running on the 25-0-25V 500VA transformer.
Pierre has been wonderful in supplying us with much needed information and advice. I believe that when he draws out the original circuit most of our questions will be answered.
Regards
Harry
PS I hope Dan is not reading these posts and having a laugh at our expense. If you are Dan I will not buy your CD player!
I too thought a 25-0-25 Volt 500VA transformer should be ample for a 50W Class A amp and it should. It's just frustrating buying all these expensive components and finding out that something else will make it sound better. In my case I purchased two 25-0-25V 500VA and two 80VA transformers for this project.
I might try using 35-0-35V 80VA for the printed circuit boards and leaving the output devices running on the 25-0-25V 500VA transformer.
Pierre has been wonderful in supplying us with much needed information and advice. I believe that when he draws out the original circuit most of our questions will be answered.
Regards
Harry
PS I hope Dan is not reading these posts and having a laugh at our expense. If you are Dan I will not buy your CD player!
Harry
I feel exactly like you! For me the 50 watt clone was nearly an open chequebook project.
Yesterday afternoon after work decided to have quick listen before going to a meeting at 19H00. As I listened to Beethoven 9th there were moments I felt my hair standing up in my neck. I could not bring myself to switch off with the result that I was hopelessy late. Now when a amp can create that response in me cost becomes irrellevant.
I dont know how long my existing equipment remaining lifespan is but I still would like to have 50 & 100 watt (replacement) clone that can recreate that experience. I am a consider myself a loyal Krell enthusiast but I have not heard any of their new equipment that appeals so much to me as these amps that was the foundation on which their company was build. I would be the first one to ask Krell to release a modern version of this design.
I am therefore somewhat surprised that nobody seems interested in a V3 replacement board? Unless we first finish the 100.2 project which is 100% exact copy of the orginal. Hopefully the 100 watter might just motivate the group to revisit the 50 watt clone project?
Jozua
I feel exactly like you! For me the 50 watt clone was nearly an open chequebook project.
Yesterday afternoon after work decided to have quick listen before going to a meeting at 19H00. As I listened to Beethoven 9th there were moments I felt my hair standing up in my neck. I could not bring myself to switch off with the result that I was hopelessy late. Now when a amp can create that response in me cost becomes irrellevant.
I dont know how long my existing equipment remaining lifespan is but I still would like to have 50 & 100 watt (replacement) clone that can recreate that experience. I am a consider myself a loyal Krell enthusiast but I have not heard any of their new equipment that appeals so much to me as these amps that was the foundation on which their company was build. I would be the first one to ask Krell to release a modern version of this design.
I am therefore somewhat surprised that nobody seems interested in a V3 replacement board? Unless we first finish the 100.2 project which is 100% exact copy of the orginal. Hopefully the 100 watter might just motivate the group to revisit the 50 watt clone project?
Jozua
Hi Jozua,
there might not be a need to create a V3. If your amp has the same circuit diagram as the one we used for Al's boards it would only be a matter of changing a few of the transistors and increasing the rail voltages.
I have had a quick look at the 2SA968 data sheet and compared it to the MJE15032/33. There are very little differences. However I did notice that the Toshiba transistors "might" be more linear at lower currents. They are also rated at 100Mhz and 30pF. I would appreciate if someone more knowledgeable than I could have a look and make comments!
Also, if someone is going to start this project make sure that you do not buy any filter caps at less that 63V. Unfortunately my UCC 56,000uF caps are only rated at 50V and it seems that I will not be able to use them.
regards
Harry
there might not be a need to create a V3. If your amp has the same circuit diagram as the one we used for Al's boards it would only be a matter of changing a few of the transistors and increasing the rail voltages.
I have had a quick look at the 2SA968 data sheet and compared it to the MJE15032/33. There are very little differences. However I did notice that the Toshiba transistors "might" be more linear at lower currents. They are also rated at 100Mhz and 30pF. I would appreciate if someone more knowledgeable than I could have a look and make comments!
Also, if someone is going to start this project make sure that you do not buy any filter caps at less that 63V. Unfortunately my UCC 56,000uF caps are only rated at 50V and it seems that I will not be able to use them.
regards
Harry
Hi Harry,Harry3 said:
50Vdc smoothing is perfectly OK for use with a 30Vac transformer.
30Vac *1.414*1.06*1.06 -0.6=47Vdc
This calculation allows for maximum mains supply at +6%, transformer regulation of 6% and assumes a single bridge rectifier over the dual secondaries and with the amplifiers disconnected. Anyone building a 50Klone will probably use a transformer with less regulation and once biassed up the running voltage will be about 41 to 42Vdc. That leaves an enormous margin for 50Vdc capacitors. This amp will put out at least 70W on a good 30Vac transformer and may easily exceed 80W into 8r0
The a968/c2238 is very different from the 1503x series.
They do not make good equivalents.
But the 968 is a driver transistor, it is not particularly well suited to VAS or pre-driver duty. The 1503x is even less suited.
If the output devices are 21193/4 then 1503x probably make a good complement for drivers only. The VAS should be a low capacitance device and 968 fails this test. But, there is an EF before it so high capacitance could be tolerated here and that may be why the original got away with that choice (and maybe gave the sound Krell was looking for).
If the output stage were "upgraded" with fast plastic cased devices then the whole mid part of the amp should be redesigned to suit. It is no longer a 50Klone. But there is a possibility it may perform better than the original if the "whole" is optimised to suit the fast plastic devices. I adopted this philosophy with the 100Klone and it has bitten me.
Hi Andrew,
Unfortunately the original amp runs on more than 50Vdc so the caps should be higher.
Thanks for the transistor info, I'll shout you a Tamdhu.
I cannot wait to see the original cct diagram.....hint, hint for our South African mates.
If they come good, we will let them win in cricket.
Regards
Harry
Unfortunately the original amp runs on more than 50Vdc so the caps should be higher.
Thanks for the transistor info, I'll shout you a Tamdhu.
I cannot wait to see the original cct diagram.....hint, hint for our South African mates.
If they come good, we will let them win in cricket.
Regards
Harry
V3
Harry
The 50.2 will be taken apart when the replacement Black Gate PCB capacitors arrive. In the meantime I there is some work on my 100.2 that needs to be done and then the 100.1 conversion with the new clone boards. Last in line is the 50.2 as I want the use the amp present sonic print as a norm to evaluate the changes to the 100.2 and 100.1.
If anybody wants to sell a spare set of resistors for another 50 clone, please contact me.
Regards
Jozua
Harry
The 50.2 will be taken apart when the replacement Black Gate PCB capacitors arrive. In the meantime I there is some work on my 100.2 that needs to be done and then the 100.1 conversion with the new clone boards. Last in line is the 50.2 as I want the use the amp present sonic print as a norm to evaluate the changes to the 100.2 and 100.1.
If anybody wants to sell a spare set of resistors for another 50 clone, please contact me.
Regards
Jozua
I look forward to seeing it. I don't feel any great rush though, this thread has been running for a few years, so a month or so won't make much difference in the grand scheme of things! 🙂
Can I come listen? I have Carlos's DX HDII to bring along for comparison, as well as the Mauro Penasa amp.
Jozua,
thanks for your input it is very valuable. I will put on hold my KSA50 and 100 clone projects until you give us your results.
Best regards
Harry
thanks for your input it is very valuable. I will put on hold my KSA50 and 100 clone projects until you give us your results.
Best regards
Harry
Please dont delay your project !
Harry
No, Nooo No ! This is not what I want to happen.
Please dont delay your project because of me- especially the 100.2 !
My "tweaking" with capacitors and wires-etc. to get a particular sonic footprint applies to the synergy with my speakers and might not even be to your liking.
Jozua
Harry
No, Nooo No ! This is not what I want to happen.
Please dont delay your project because of me- especially the 100.2 !
My "tweaking" with capacitors and wires-etc. to get a particular sonic footprint applies to the synergy with my speakers and might not even be to your liking.
Jozua
Hi Jozua,
the concern I have at this point in time is to pay big bucks for two 37-0-37Vac 1000VA transformers & caps for the KSA100 clone only to find out that the 50W clone sounds better??
But as you stated, there is only one way to find out and that is to compare them for myself. As from tomorrow the wife, kids and pets will go on rations......
Regards
Harry
the concern I have at this point in time is to pay big bucks for two 37-0-37Vac 1000VA transformers & caps for the KSA100 clone only to find out that the 50W clone sounds better??
But as you stated, there is only one way to find out and that is to compare them for myself. As from tomorrow the wife, kids and pets will go on rations......
Regards
Harry
Harry3 said:
Then you just biamp, with the 100 on the bottom, and the 50 doing mid/high duties. 😉
Seriously, as Jozua intimates, a lot of these differences, (apart from raising the bias, the best tweak ever!) are subtle, and down to taste. For instance, I tried three different sets of OP trannies on the prototypes and they all sounded good, but for my taste, the MJL1302/3281 pair fitted the best. The 15003/4 and the 21193/4 didn't sound bad, or even that much different, they just didn't suit me as much.
pinkmouse said:
You might be joking but that is my intention. That is why I bought four boards of KSA50 and four of the KSA100.
Regards
Harry
try a variac...
Hi,
An off the wall idea for those people that want to *try* their Krells with higher voltage rails...borrow or buy a variac...the one I have allows for the output voltage to be higher than line, upto 140v IIRC. My variac is good for 1200va, but they come much bigger if needed. With 120v in giving 37v rails, at 140v in you'd end up with 43v...
I've run mine at lower rail voltages during the bring up, but not paid any attention while it was on the variac, was just for testing.
Obviously if you do this you'd better make sure your voltage ratings on diodes and caps is adequate, heatsinking will need to be even bigger etc...but you'll find out what it could sound like with higher rails...
Stuart
Hi,
An off the wall idea for those people that want to *try* their Krells with higher voltage rails...borrow or buy a variac...the one I have allows for the output voltage to be higher than line, upto 140v IIRC. My variac is good for 1200va, but they come much bigger if needed. With 120v in giving 37v rails, at 140v in you'd end up with 43v...
I've run mine at lower rail voltages during the bring up, but not paid any attention while it was on the variac, was just for testing.
Obviously if you do this you'd better make sure your voltage ratings on diodes and caps is adequate, heatsinking will need to be even bigger etc...but you'll find out what it could sound like with higher rails...
Stuart
nice...
...but definitely not true here, my variac cost less than one of the pair of transformers originally in a ksa100, despite being of higher capacity than the two together.
"Made in China" vs "Made in the US" would probably explain most of the price differential, that and the lack of a secondary, less copper and labor.
If it were not for the lack of isolation (variacs are auto-transformers) I'd probably use them for powering equipment on a permanent basis.
Stuart
...but definitely not true here, my variac cost less than one of the pair of transformers originally in a ksa100, despite being of higher capacity than the two together.
"Made in China" vs "Made in the US" would probably explain most of the price differential, that and the lack of a secondary, less copper and labor.
If it were not for the lack of isolation (variacs are auto-transformers) I'd probably use them for powering equipment on a permanent basis.
Stuart