Thanks Andrew for your reply.
Could you please explain why I should only draw a maximum of 1.6 amps per winding as the secondaries are rated at 6.3 amps each winding and I will be using two transformers, hence four secondaries. I don't doubt you are correct, but I am trying to learn and understand, so all help is greatly appreciated.
Alan.
Could you please explain why I should only draw a maximum of 1.6 amps per winding as the secondaries are rated at 6.3 amps each winding and I will be using two transformers, hence four secondaries. I don't doubt you are correct, but I am trying to learn and understand, so all help is greatly appreciated.
Alan.
Re: Hot amp
Well those MJL21193/94 will not last long at those temperatures.
Either the transistors are poorly mounted (poor thermal conductivity) and/or the heatsinks are inadequate. A 50 watt class A requires some serious heat dissipation capacity. Glad you like the sound...may have to build another KSA 50...or an Alpeph X...
audiophile321 said:
Well those MJL21193/94 will not last long at those temperatures.
Either the transistors are poorly mounted (poor thermal conductivity) and/or the heatsinks are inadequate. A 50 watt class A requires some serious heat dissipation capacity. Glad you like the sound...may have to build another KSA 50...or an Alpeph X...
Spot on zlast
You were right, I checked the mounting screws on the output transistors and they were all too loose. Tightening the hardware lowered the transistor temps over 20F
The hot running driver transistors have no thermal compound under them so I'll re-mount them properly next. I think I'm much closer to having a great amp that won't self destruct!
Thanks for the help.
Jim
You were right, I checked the mounting screws on the output transistors and they were all too loose. Tightening the hardware lowered the transistor temps over 20F
The hot running driver transistors have no thermal compound under them so I'll re-mount them properly next. I think I'm much closer to having a great amp that won't self destruct!Thanks for the help.
Jim
transformer currents
The AC transformer rated at eg. 115:20+20Vac 300VA must be de-rated to ~70% when feeding a capacitor input filter.
This reduces the 300VA to ~200VA @ the smoothing capacitors.
The voltage at the smoothing capacitors when loaded to it's maximum rating is ~20 * 1.4 =+-28Vdc.
200VA / 28+28 = 3.57Adc. (I think it would be valid to use 200/{28.7+28.7} here).
This runs the transformer at maximum rating to match the 300VA AC rating.
The transformer will run HOT. Right up at the manufacturer's maximum temperature.
I and many others recommend that transformer supplying continuous DC current be run at ~ half their maximum continuous rating i.e. 3.57/2 <=1.8A.
Now what is the AC current rating of this 300VA transformer?
it is 300VA / {20+20)V = 7.5Aac.
one quarter of 7.5 is 1.875.
That's a very easy rule to remember that takes account of all the usual de-rating factors for a transformer powering a ClassA amplifier.
Assume the maximum continuous DC current is ~ 1/4 of the max AC current.
So that 6.3Aac transformer comes out at <=1.6Adc continuous.
The AC transformer rated at eg. 115:20+20Vac 300VA must be de-rated to ~70% when feeding a capacitor input filter.
This reduces the 300VA to ~200VA @ the smoothing capacitors.
The voltage at the smoothing capacitors when loaded to it's maximum rating is ~20 * 1.4 =+-28Vdc.
200VA / 28+28 = 3.57Adc. (I think it would be valid to use 200/{28.7+28.7} here).
This runs the transformer at maximum rating to match the 300VA AC rating.
The transformer will run HOT. Right up at the manufacturer's maximum temperature.
I and many others recommend that transformer supplying continuous DC current be run at ~ half their maximum continuous rating i.e. 3.57/2 <=1.8A.
Now what is the AC current rating of this 300VA transformer?
it is 300VA / {20+20)V = 7.5Aac.
one quarter of 7.5 is 1.875.
That's a very easy rule to remember that takes account of all the usual de-rating factors for a transformer powering a ClassA amplifier.
Assume the maximum continuous DC current is ~ 1/4 of the max AC current.
So that 6.3Aac transformer comes out at <=1.6Adc continuous.
Hi everyone,
power supplies,
for the other class A amplifiers I have built I have used a capacitance multiplier circuit following the resevoir capacitors. Are there any views about this for the Krell. It certainly keeps AC ripple to a very low level, but is there any degradation in sound quality. I am trying to construct a "baby" krell with +- 22volt rails.
Any help or advice would be much appreciated.
Alan
power supplies,
for the other class A amplifiers I have built I have used a capacitance multiplier circuit following the resevoir capacitors. Are there any views about this for the Krell. It certainly keeps AC ripple to a very low level, but is there any degradation in sound quality. I am trying to construct a "baby" krell with +- 22volt rails.
Any help or advice would be much appreciated.
Alan
It's my view that it must be an air core inductor.
With that as the prime criteria you will find that the inductor will approach the transformer in size and weight and cost.
It is virtually impossible to build a low budget solid state amplifier with a choke regulated PSU
A CLC may fit your budget but I suspect you will end up with a ClRC (that is a small L in there) and the resistor will do the bulk of the hum reduction work and the small L will add to the HF attenuation.
There is only one way to find if a KSA50 Klone works well with a CRC PSU.
With that as the prime criteria you will find that the inductor will approach the transformer in size and weight and cost.
It is virtually impossible to build a low budget solid state amplifier with a choke regulated PSU
A CLC may fit your budget but I suspect you will end up with a ClRC (that is a small L in there) and the resistor will do the bulk of the hum reduction work and the small L will add to the HF attenuation.
There is only one way to find if a KSA50 Klone works well with a CRC PSU.
Last edited:
Inductors...
Hi,
I tried this (and I wrote about it in this thread) but in a nutshell, technically speaking, it works well. I tried both air cored and iron cored inductors. The air cored inductors were approx. 1.1mH with 68kuF caps. The residual ripple was ~20mv on the rails loaded at ~2A, and there was no ripple measurable at the output of the amp, just the noise one would expect. Using iron cored inductors (Erse) of 2.7mH reduced the ripple to <10mv with no difference on the output or the sound.
To put this into perspective, I did not detect any difference, let alone improvement with the CLC, CRC, or CC so I simply left it out and went with single 68k caps per rail.
BTW Duncans PSU simulator worked perfectly for this task, my simulated and measured results matched within the tolerance of the caps and coils.
HTH
Stuart
Hi,
I tried this (and I wrote about it in this thread) but in a nutshell, technically speaking, it works well. I tried both air cored and iron cored inductors. The air cored inductors were approx. 1.1mH with 68kuF caps. The residual ripple was ~20mv on the rails loaded at ~2A, and there was no ripple measurable at the output of the amp, just the noise one would expect. Using iron cored inductors (Erse) of 2.7mH reduced the ripple to <10mv with no difference on the output or the sound.
To put this into perspective, I did not detect any difference, let alone improvement with the CLC, CRC, or CC so I simply left it out and went with single 68k caps per rail.
BTW Duncans PSU simulator worked perfectly for this task, my simulated and measured results matched within the tolerance of the caps and coils.
HTH
Stuart
Last edited:
To my knowledge there are still a few of the PCB's left from the group buy.
http://www.diyaudio.com/forums/showpost.php?p=1408318&postcount=7521
And we know those work.
http://www.diyaudio.com/wiki/index.php?page=Building+guide
However I am not able to get into it any longer. "Might" be the site upgrade but "probably" user error.
PS- I show 800+ pages...
800+ pages
no one has wiki saved since site is down.?
here is BOM that i found FOXYE.
Here are BOM's from the PCB GB's..
Notice it is TWO pages. On for Jans and one for Al's PCB's.
Follow this link and you will be able to save a copy of the Wiki building guide to your local drive.
http://web.archive.org/web/20080117145909/http://www.diyaudio.com/wiki/index.php?page=Building+guide
http://web.archive.org/web/20080117145909/http://www.diyaudio.com/wiki/index.php?page=Building+guide