In case anyone scratches the silkscreen of his boards or damages it in any other way at a later stage :
Both board and silkscreen are usually epoxy resin based. Sometimes the silkscreen has a polyurethane base, basically the only other stuff that has a good holding grip on epoxy resin materials.
Both epoxy resin and polyurethane can be given a preferred color by adding the appropriate pigment.
Scratches and bruises can be touched up with a disposable brush.
After the curing time, the touch-up can be polished to look invisible.
Both board and silkscreen are usually epoxy resin based. Sometimes the silkscreen has a polyurethane base, basically the only other stuff that has a good holding grip on epoxy resin materials.
Both epoxy resin and polyurethane can be given a preferred color by adding the appropriate pigment.
Scratches and bruises can be touched up with a disposable brush.
After the curing time, the touch-up can be polished to look invisible.
Exceptional
It has been said already and I don't want to be redundant but the boards are fantastic! No scratches or scuffs on these ones.
I tip my hat toward you folks who put it together and the DIY forum in general as a wonderful place for all things audio.
Now if only my schedule would allow me to get back to finishing the KSA50 then I could get on to it's big brother. I guess I can start sourcing the parts. 😀
Shawn.
It has been said already and I don't want to be redundant but the boards are fantastic! No scratches or scuffs on these ones.
I tip my hat toward you folks who put it together and the DIY forum in general as a wonderful place for all things audio.
Now if only my schedule would allow me to get back to finishing the KSA50 then I could get on to it's big brother. I guess I can start sourcing the parts. 😀
Shawn.
MikeBarton said:
FWIW... I just finished a mod to a power amp whereby the rails are about 58.5 or 59vdc.
I get 190watts per channel before clipping.... that's a very hi rail for a true KSA-100... unless u are building a KSA-150... then it will be on the money... but then jack all power sections up by 50% as well and have preceeding circuitry able to handle it too...
PS: Has anyone compared a finished KSA-50 to the KSA-100? I know Mark liked the 100.... anyone else do it?
Heatsinks
Has there been any recommendations regarding heatsinks for this project?
I have read some of the discussions, but I am not sure if there has been a consensus reached. I am most interested in passive heatsinks. Is there a spec on thermal transfer rate that I could use as a guideline when shopping for sinks? I come across some copper heatsinks may prove interesting for the project.
thanks,
Paul
Has there been any recommendations regarding heatsinks for this project?
I have read some of the discussions, but I am not sure if there has been a consensus reached. I am most interested in passive heatsinks. Is there a spec on thermal transfer rate that I could use as a guideline when shopping for sinks? I come across some copper heatsinks may prove interesting for the project.
thanks,
Paul
Something along the lines of what was used for the KMA-160 would work well. That is what I am going to be using on my monoblocks. 4 sinks per amp. They are available through M&M Metals.....
Mark
Mark
Re: Heatsinks
Hi Kamps,
Since the output (3pair on each driver pair) conveniently groups into 6pairs or 4triplets you can buy either 4 off 0.2 to 0.32C/W or 6 off 0.3 to 0.48C/W
Hi Kamps,
what are the corresponding Vac input and output of the transformer?
0.05 to 0.08C/W.pollypocket said:
Since the output (3pair on each driver pair) conveniently groups into 6pairs or 4triplets you can buy either 4 off 0.2 to 0.32C/W or 6 off 0.3 to 0.48C/W
Heatsink de-rating
I forgot to mention that each manufacturer rates their sinks at a fixed temperature difference above ambient.
As the working temperature moves towards ambient (deltaT<70Cdeg) the C/W drops off. Most manufacturers quote the deltaT and how to correct Rth s-a for lower/higher values.
The Krell 100 Klone dissipation will be about 270W on +-52Vdc supply rails. Heatsink temperature~=270*(0.05 or 0.08) = 14Cdeg to 22Cdeg+ambient (30degC to 40degC). These deltaT values (14 to 22) are very much below 70Cdeg with the result that a specified 0.05C/W will run much hotter than predicted if the de-rating is ignored.
I forgot to mention that each manufacturer rates their sinks at a fixed temperature difference above ambient.
As the working temperature moves towards ambient (deltaT<70Cdeg) the C/W drops off. Most manufacturers quote the deltaT and how to correct Rth s-a for lower/higher values.
The Krell 100 Klone dissipation will be about 270W on +-52Vdc supply rails. Heatsink temperature~=270*(0.05 or 0.08) = 14Cdeg to 22Cdeg+ambient (30degC to 40degC). These deltaT values (14 to 22) are very much below 70Cdeg with the result that a specified 0.05C/W will run much hotter than predicted if the de-rating is ignored.
Re: Re: Heatsinks
117vac prims and 42-0-42 vac secs. At 120v mains about 43.0.43vac. 1-2kva part... never did find the exact rating. Seller claimed 2kva but size is more like 1kva.... at 4 ohm clipping of 330 watts, rails sag to only about 56.5vdc. caps 40kuF per rail. Panasonics.
AndrewT said:
117vac prims and 42-0-42 vac secs. At 120v mains about 43.0.43vac. 1-2kva part... never did find the exact rating. Seller claimed 2kva but size is more like 1kva.... at 4 ohm clipping of 330 watts, rails sag to only about 56.5vdc. caps 40kuF per rail. Panasonics.
Hi,
Kamps' supply rails sitting at near 59Vdc will force about 14% extra dissipation in the output stage. The drivers and some resistors in the voltage amplifier will also run hotter.
If you decide to try transformers above the 37Vac rating them be prepared to check temperatures and selecting bigger heatsinks.
Kamps' supply rails sitting at near 59Vdc will force about 14% extra dissipation in the output stage. The drivers and some resistors in the voltage amplifier will also run hotter.
If you decide to try transformers above the 37Vac rating them be prepared to check temperatures and selecting bigger heatsinks.
The schematic for the KSA specifies 41VAC secondaries, but I doubt that. With the load (amp) disconnected it measured more or less in that area, and dropped about 2VDC with the load on.
41vac seems just about right.
41* 1.1414 = ~58vdc
Less the 1.5v drop of the Bridge =
unloaded rails of 56.5vdc
Loaded with 270 watts of Bias... and you are down 2-3 volts more.
56.5 - 3 = 53.5vdc. This is the exact voltage I measured on my KSA-100mk.II (though my mains was more like 118v).
41* 1.1414 = ~58vdc
Less the 1.5v drop of the Bridge =
unloaded rails of 56.5vdc
Loaded with 270 watts of Bias... and you are down 2-3 volts more.
56.5 - 3 = 53.5vdc. This is the exact voltage I measured on my KSA-100mk.II (though my mains was more like 118v).
Sorry for the offtopic: but this might interest you Krellophiles:
The KAV-250a is perhaps the best sounding krell <$3k that I have heard. (Included the KSA-250 and KSa-100ii's).. This is the closest to a schematic of the KAV that I have found... basically it is just the OP stage... 🙂
http://www.diyaudio.com/forums/attachment.php?s=&postid=1133663&stamp=1171320700
The KAV-250a is perhaps the best sounding krell <$3k that I have heard. (Included the KSA-250 and KSa-100ii's).. This is the closest to a schematic of the KAV that I have found... basically it is just the OP stage... 🙂
http://www.diyaudio.com/forums/attachment.php?s=&postid=1133663&stamp=1171320700
Hi,
during earlier discussion on the 41Vac stated in Krell's schematic, the concensus was that the voltage represented the maximum AC voltage on no load and when mains input was at maximum tolerance.
37Vac + regulation of 4% + mains tolerance of 6% = 40.8Vac,
if regualtion is 4.5% then we hit 41Vac.
If our conclusion was correct then the transformer is 120/240:37+37Vac.
during earlier discussion on the 41Vac stated in Krell's schematic, the concensus was that the voltage represented the maximum AC voltage on no load and when mains input was at maximum tolerance.
37Vac + regulation of 4% + mains tolerance of 6% = 40.8Vac,
if regualtion is 4.5% then we hit 41Vac.
If our conclusion was correct then the transformer is 120/240:37+37Vac.
37vac would give you loaded dc rails of below 50vdc. This is lower than an Actual Krell KSA-100. mkII....
Though the majority can use any voltage they want. 37vac should give you 100watts class-A or more as well.
Though the majority can use any voltage they want. 37vac should give you 100watts class-A or more as well.
Hi Kamps,
My understanding is 37Vac * sqrt2 * unused regulation.
If the quiesecent dissipation is 270W and the de-rated 900VA (70%*900=630) transformer is running at about 40% of capacity. The regulation of 4% will give about an extra 1.48Vac. The unused 60% will result in an extra 0.8 to 0.9Vac.
I reckon the quiescent voltage on the supply caps is about:-
(37+0.8)*sqrt2 -0.7=52.7Vdc when delivering 2.65A to each supply rail. Subtract a bit for the half ripple and it comes close to +-52Vdc
can you explain.
My understanding is 37Vac * sqrt2 * unused regulation.
If the quiesecent dissipation is 270W and the de-rated 900VA (70%*900=630) transformer is running at about 40% of capacity. The regulation of 4% will give about an extra 1.48Vac. The unused 60% will result in an extra 0.8 to 0.9Vac.
I reckon the quiescent voltage on the supply caps is about:-
(37+0.8)*sqrt2 -0.7=52.7Vdc when delivering 2.65A to each supply rail. Subtract a bit for the half ripple and it comes close to +-52Vdc
Andrew:
It depends on the definition of the 37vac rating of the toroid in question. My assumption was that the 37vac is the raw measured output on the secs of the Toroid unloaded.
If the manufacturer specifies (or derates) the rating based on a loading (not everyone does that) then the number would change.
What you mean by 37 vac loaded is the same as what I would call 39vac unloaded... at the secs.
Hope this clears up the assumptions I was working with.
It depends on the definition of the 37vac rating of the toroid in question. My assumption was that the 37vac is the raw measured output on the secs of the Toroid unloaded.
If the manufacturer specifies (or derates) the rating based on a loading (not everyone does that) then the number would change.
What you mean by 37 vac loaded is the same as what I would call 39vac unloaded... at the secs.
Hope this clears up the assumptions I was working with.
Hi Kamps,
thanks for clearing up how you arrived at your measured voltages.
But that leaves us in a quandary.
37Vac = 39Vac depending on how the manufacturer chooses to specify his transformers.
I have not yet come across a manufacturer that quotes open circuit voltage instead of loaded voltage (except on the very rare occasion they specify both).
As an example, in two ClassAb amps, both powered by 35Vac transformers.
230:35Vac, 300VA 7% regulation > Vrail=+-53.5Vdc @Iq=150mA
240:35Vac, 625VA 4% regulation > Vrail=+-50.5Vdc @Iq=40mA
thanks for clearing up how you arrived at your measured voltages.
But that leaves us in a quandary.
37Vac = 39Vac depending on how the manufacturer chooses to specify his transformers.
I have not yet come across a manufacturer that quotes open circuit voltage instead of loaded voltage (except on the very rare occasion they specify both).
As an example, in two ClassAb amps, both powered by 35Vac transformers.
230:35Vac, 300VA 7% regulation > Vrail=+-53.5Vdc @Iq=150mA
240:35Vac, 625VA 4% regulation > Vrail=+-50.5Vdc @Iq=40mA