One last question... I had to increase the value of R-36 to nearly 7.5 K just to get the bias to go low enough. Its low point is now about 50mv and after a half hour warm up it stabilizes really well. I set it to 100mv and still very stable with the drover heatsink getting fairly warm but not so warm that you can't keep your hand on it. I didn't experience this problem with the other channel. It is at 0mv with the pot all the way down. Could the hfe of Q-13 be critical in this amp and causing this problem? I also wonder if Krell selected a resistor to bring the bias within range or would they have selected the device for proper gain?
Thanks!
Mark
Thanks!
Mark
The hfe of Q13 is indeed a large factor regarding bias setting. That's why I mentioned in an earlier post that you should use MJE15030 to keep the original values, or adapt R36/VR2 if using the higher-gain versions.
However, the values you mention are a bit way-out. With simulations using the 15032's I still had to set the trimpot value to below 2k (R36 still 1k5) to achieve 580mA bias per transistor.
That should have brought the same problem in the KSA50 clone, and I'm using 15032/33's thoughout in the MK2 I've rebuilt and did a prelim test yesterday evening with the trimpot maxed out for minimal bias, and it was 0mA.
Note that the drivers' hFE also influences the bias, so perhaps you should try and check all of them (though start with Q13); maybe one's a dud or somehow got damaged.
OK, now that everything seems sorted out, the GB should be ready to progress. I've adressed all the problems and comments Mark had with the design I sent him. We still need concensus over a few things. It looks like we've settled for blue soldermask and gold traces. Concerning covering the traces with soldermask or not: I strongly feel that at least the bottom side shouldn't remain uncoated, it's often very close to metal parts and the close proximity of all the traces will have the risk of thin solder shorts. Besides - once the boards are fixed to the heatsinks or wherever, you'll never see the bottom side again 😉
As a compromise I'd suggest we keep the top layer's traces uncoated. They are the ones in plain sight, and since they're not as densely routed as on the bottom layer the risk is smaller.
However, the values you mention are a bit way-out. With simulations using the 15032's I still had to set the trimpot value to below 2k (R36 still 1k5) to achieve 580mA bias per transistor.
That should have brought the same problem in the KSA50 clone, and I'm using 15032/33's thoughout in the MK2 I've rebuilt and did a prelim test yesterday evening with the trimpot maxed out for minimal bias, and it was 0mA.
Note that the drivers' hFE also influences the bias, so perhaps you should try and check all of them (though start with Q13); maybe one's a dud or somehow got damaged.
OK, now that everything seems sorted out, the GB should be ready to progress. I've adressed all the problems and comments Mark had with the design I sent him. We still need concensus over a few things. It looks like we've settled for blue soldermask and gold traces. Concerning covering the traces with soldermask or not: I strongly feel that at least the bottom side shouldn't remain uncoated, it's often very close to metal parts and the close proximity of all the traces will have the risk of thin solder shorts. Besides - once the boards are fixed to the heatsinks or wherever, you'll never see the bottom side again 😉
As a compromise I'd suggest we keep the top layer's traces uncoated. They are the ones in plain sight, and since they're not as densely routed as on the bottom layer the risk is smaller.
Good job Mark
Now you can relax
Interesting to hear what you think of the anp in Stereo-mode, you must tell us whats your impression.
Yes PWatts I agree to that. It would be fine.
Regards 😎
Now you can relax
Interesting to hear what you think of the anp in Stereo-mode, you must tell us whats your impression.
Yes PWatts I agree to that. It would be fine.
Regards 😎
Who better to show that it's the little things when you're pressed for time than a guy in SLC who's built more amplifiers than killed turkeys.
I'll blend right in with the bird, without reading glasses R36 looks like R38 to me.
I haven't been able to read the newspaper for the last 12 months, suppose it's time to get used to wearing jars again.
Personally, i prefer to switch to the brilliant Sanyo 2SC3955 suggested by Pavel for the KSA50 or try a multi-stage version posted by Mike-K recently.
I find the Vbe-multiplier of the KSA100 kinda odd, and 15030/31s should be on display in a museum.
i prefer to switch to the brilliant Sanyo 2SC3955
I can buye them here for ca € 0,50 and can send them to Mark so he can add it to the collection for the Wiki.
Loek
I can buye them here for ca € 0,50 and can send them to Mark so he can add it to the collection for the Wiki.
Loek
Loeki here,
Now that you're Online:
contrary to my statement i've not had a chance yet to deliver your Sym boxes.
I'm hoping to be able to drop them off at your daycare centre this thursday.
Now that you're Online:
contrary to my statement i've not had a chance yet to deliver your Sym boxes.
I'm hoping to be able to drop them off at your daycare centre this thursday.
Hi,
I can't understand why r36 has to be raised to 7k5 to get the bias to back off.
The voltage across the Vbe multiplier is about 4 Vbe + 2 Vre.
This is about 2.4V @ zero bias rising to about 3.8V @ maximum bias.
That needs a minimum of 3.4times across the Vbe multiplier.
Now working back from r37=7k5, then (pot+r36) = 7.5/(3.4-1)=3k1, with r36=1k5 then pot =1k6.
At the maximum, the ratio needs to be about 6.3times. This needs the (pot + r36) = 7.5/(6.3-1)=1k4. However the r36 value is 1k5 so we cannot guarantee to get 6.3 times out of the multiplier for all types of transistor (high Vbe).
Personally I would lower the value of r36 to 750r and also drop r37 to 5k1 or maybe lower still.
This is to ensure that sufficient current flows through the resistor string when using a low gain transistor for Q13.
I can't understand why r36 has to be raised to 7k5 to get the bias to back off.
The voltage across the Vbe multiplier is about 4 Vbe + 2 Vre.
This is about 2.4V @ zero bias rising to about 3.8V @ maximum bias.
That needs a minimum of 3.4times across the Vbe multiplier.
Now working back from r37=7k5, then (pot+r36) = 7.5/(3.4-1)=3k1, with r36=1k5 then pot =1k6.
At the maximum, the ratio needs to be about 6.3times. This needs the (pot + r36) = 7.5/(6.3-1)=1k4. However the r36 value is 1k5 so we cannot guarantee to get 6.3 times out of the multiplier for all types of transistor (high Vbe).
Personally I would lower the value of r36 to 750r and also drop r37 to 5k1 or maybe lower still.
This is to ensure that sufficient current flows through the resistor string when using a low gain transistor for Q13.
Board Specs
Mark
I would prefer that we have a soldermask on both sides. It prevents solder runs and having open traces adds to the risks of accidently shorting a trace with probe or getting unwanted solder stains/droppings on an exposed trace. The moment you have unwanted solder stains on the board, the whole object of having a professional look is defeated.
Good looks are nice and can give one some temporary pleasure when looking at them. However I would rather want this group to opt for board that complies to the technical specifications you expect to find in any high end amp.
The above does not mean I wish to negate your efforts in assisting this group in having the boards made up or building the prototypes so quickly. We do appreciate it.
Jozua
Mark
I would prefer that we have a soldermask on both sides. It prevents solder runs and having open traces adds to the risks of accidently shorting a trace with probe or getting unwanted solder stains/droppings on an exposed trace. The moment you have unwanted solder stains on the board, the whole object of having a professional look is defeated.
Good looks are nice and can give one some temporary pleasure when looking at them. However I would rather want this group to opt for board that complies to the technical specifications you expect to find in any high end amp.
The above does not mean I wish to negate your efforts in assisting this group in having the boards made up or building the prototypes so quickly. We do appreciate it.
Jozua
I would prefer that we have a soldermask on both sides
Me too, to prevent fingerprints and other effects are making the boards less shiny when stuffing and testing.
Loek
Me too, to prevent fingerprints and other effects are making the boards less shiny when stuffing and testing.
Loek
I'm now wanting to go back to a black solder mask.... Just kidding! I can live with blue and soldermask on bottom but not top, silkscreen on top and gold traces. The Q-1 to 4 pads are so tiny that you all will have to go out and buy new soldering irons and the smallest diameter silver solder available! Soldering the SMT LED and resistors was ALOT easier that Q-1-4 and the MOSFETS.... and just hope you don't have to remove them
I've had everything off this board and back on three times and the board is very good quality and survived as though you'd never know it.
Mark
I've had everything off this board and back on three times and the board is very good quality and survived as though you'd never know it.Mark
Great! Mark, I'll send you the final Gerbers with the changes, including the solder mask agreed on tomorrow.
I can try to shift the TO-92's pads further apart if the soldering seems daunting to some, but would prefer not to. Fortunately for the MOSFET's there are two alternative packages to the TO92's, of which the IRFD's are the easiest - in fact you can use a DIP-4 socket and remove it later on if you like to experiment with the other FET's or if something breaks 🙂
I can try to shift the TO-92's pads further apart if the soldering seems daunting to some, but would prefer not to. Fortunately for the MOSFET's there are two alternative packages to the TO92's, of which the IRFD's are the easiest - in fact you can use a DIP-4 socket and remove it later on if you like to experiment with the other FET's or if something breaks 🙂
Here it is hooked in and playing in my system. Biased to 100mv for now and the sound even from the very wimpy supply is fantastic. I will re-build that supply using the 1.5 KVA Plitron laying on the floor in front of it. If I wire that toroid for 220 volt primary I should get +/- 50 volt rails which is good enough till Flodstroem gets the transformer GB up and running. For now we need someone willing to go in and modify the WOKI to make it a real GB.
Thanks for everyone's help... this has been alot of fun... now I needa visit to my eye doctor to get my eyes plugged back in place !
Mark
Thanks for everyone's help... this has been alot of fun... now I needa visit to my eye doctor to get my eyes plugged back in place
!Mark
Attachments
Al,
I guess we ought to sturcture it along the lines of the KSA-50 WIKI so we can all add info as we go along. We need to get the PCB GB going first so please go ahead and make that page a permanent WIKI for the KSA-100. Once that GB is over then we can erase all that and just keep posting info.
Give me a day or two to get the final gerbers fomr PWatts and get the pricing down firm and then we can all agree on a price vs quantity. The initial pricing was not too bad but we are now adding gold plating(or flashing) to that price.
Have done alot mroe listening and this amp even biased at 100mv it is definately way out ahead of the KSA-50 in terms of clarity from the upper mids on up. The low end is much more stbstantial but I don't want to stop here, I need to get the power supply into a more realistic configuration for this sort of amp.
Thanks!
Mark
I guess we ought to sturcture it along the lines of the KSA-50 WIKI so we can all add info as we go along. We need to get the PCB GB going first so please go ahead and make that page a permanent WIKI for the KSA-100. Once that GB is over then we can erase all that and just keep posting info.
Give me a day or two to get the final gerbers fomr PWatts and get the pricing down firm and then we can all agree on a price vs quantity. The initial pricing was not too bad but we are now adding gold plating(or flashing) to that price.
Have done alot mroe listening and this amp even biased at 100mv it is definately way out ahead of the KSA-50 in terms of clarity from the upper mids on up. The low end is much more stbstantial but I don't want to stop here, I need to get the power supply into a more realistic configuration for this sort of amp.
Thanks!
Mark
I think we also need to add to the Wiki a building guide as done for the KSA50 clone to make it easy for people who joined/join later. Since a lot of it will be repetition of the KSA50 it can just be an addendum listing the changes.
Mark:
1) What's the status of the driver heatsink GB? Will it be possible to include it with the board and for how much? Since everybody using this PCB will need one, a nice fitting one (pref anodized) will make it so much easier and professional than for all to cobble something together by themselves. A blue anodized sink will look like the original and also match the blue solder mask nicely 🙂
2) Going on your comments of the sound quality, would you recommend KSA50 owners to mod theirs in favour of the KSA100? If the same power supply is used and the bias is kept on 50W, it should be fairly easy to just replace the boards and double the output devices on the same heatsink area.
Mark:
1) What's the status of the driver heatsink GB? Will it be possible to include it with the board and for how much? Since everybody using this PCB will need one, a nice fitting one (pref anodized) will make it so much easier and professional than for all to cobble something together by themselves. A blue anodized sink will look like the original and also match the blue solder mask nicely 🙂
2) Going on your comments of the sound quality, would you recommend KSA50 owners to mod theirs in favour of the KSA100? If the same power supply is used and the bias is kept on 50W, it should be fairly easy to just replace the boards and double the output devices on the same heatsink area.
Krell Poster
In the new Stereophile magazine, the Krell ad has the Krell KSA-100
pictured in the background, circa 1980...
And the new gear in the front.
😀
In the new Stereophile magazine, the Krell ad has the Krell KSA-100
pictured in the background, circa 1980...
And the new gear in the front.
😀
Well, this amp is really dynamyte! Much better and much mich more refined than the KSA-50 is. This calls for another Pass shootout at my place within the next month. Bill WW and Luckylyndy let me know what a good date to hold it is.....
Mark
Mark
Mark A. Gulbrandsen said:
Hi Mark,
So converting a KSA 50 over to a KSA 100 would be a good thing?
What do you think for the outputs, T-03 or plastic?
Blessings, Terry