Krell KSA 50 PCB

pooge said:
Terry,

Your ground loop is the loop formed by the shields of the right and left channels back through the preamp and back to the power amp. It is not the fault of your preamp.

Try this tip from Leach's site:

If you are sure that the hum is due to an internal ground loop, the procedure for breaking this loop is as follows:

Turn the amplifier off and wait for the power supply to discharge. Do not perform this procedure with the amplifier on.
Cut the wire to the central ground on the input side of one circuit board.
Solder a short circuit jumper wire between the ground lugs on the two input jacks.
The circuit board with the cut ground wire is now grounded back through its input ground lead to the ground of the other circuit board. Use an ohmmeter to verify the new ground connection before turning the amp back on.


Hi pooge,

Thanks for that advise. I will try that tonight. I was just showing the amp to a friend here at work and with either side plugged in the amp is dead quiet until the other side is plugged in. That sounds exactly like what you are talking about.

Blessings, Terry
 
how about...

...we made them because:

With the exception of NPs portfolio of SE amps, these are perhaps the simplest, discrete, known 'good' (ie reviewed widely) power amps you can make.

But, unlike SE amps, properly constructed, the Krell has the ability to drive just about any load, and sound reasonable doing it. They are quite tolerant of changes, ie supply voltage, component values etc. Just about any reasonable output transistor seems to work. They can be built using new or old parts.

Depending on who you ask, there are probably other reasons, but these were enough for me...

Stuart
 
pinkmouse said:


Cos we don't know how the "Sliding Bias" or whatever it's called works? ;)


ohh.....right. It seems to me that all you would need to do is feed the input into a buffer, then to a comparator which activates some relays to bring in different preset bias settings depending on the input level. Along with some kind of timer that is reset by the levels so that when it times out bias drops. Plus you could light some blue LEDs to indicate what bias setting you were on...more LEDs? Yeah, now we are talking! I was actually going to build such a circuit but I'm not that smart, and I had massive heat sinks anyway.

Plus, with my 2 days of experience adjusting 2 levels of bias (low/high bias levels) on the Krell Clone, its tricky and time consuming to get the channels to match up with each other. This sliding bias would move all around and who knows whether your L/R bias levels would track. I may be wrong because in the real deal the bias rarely changes.

Anyone know what happened to our benefactor, "bra"? Is his Krell Clone in progress or not?
 
I had meant to report earlier. As far as comparing my ESP P101 and my Krell KSA50, it was suggested that I use a variac on the P101 to reduce the output to get a more even volume between the two. Well I tried it, and using a variac, the P101 doesn't start making sound until around 50VAC. At that point it is still louder than the Krell. As a matter of fact, at normal listening levels, there is almost no noticible increase in loudness from 50VAC to 120VAC. I would imagine if you pushed the amp harder you would see it but at what I would call a comfortable volume, The P101 sounds fine with only 50VAC applied.

I'm going to have to use two seperate preamps to get the volumes somewhat even. I'll try that.

Blessings, Terry
 
variac...

Terry,

The gain of the amps is fixed by the ratio of a pair of resistors. Literally R130/R129 (14.67x) in the Krell. The maximum power available from either amp is dependant on the voltage fed into the primary, in so much as it varies the voltage coming out of the secondaries. So your variac is not helping in this regard.

If you have the specs for the p101, or a schematic I can tell you the value to use for r130 in the krell to match it...

HTH

Stuart
 
Re: variac...

Stuart Easson said:
Terry,

The gain of the amps is fixed by the ratio of a pair of resistors. Literally R130/R129 (14.67x) in the Krell. The maximum power available from either amp is dependant on the voltage fed into the primary, in so much as it varies the voltage coming out of the secondaries. So your variac is not helping in this regard.

If you have the specs for the p101, or a schematic I can tell you the value to use for r130 in the krell to match it...

HTH

Stuart


Hi Stuart,

I figured it was something like that. The give-away was when it wouldn't even make sound until a certain voltage was reached.

The P101 is rated at 200wpc into 8 ohms with the transformer I used. It is understandable why the Krell is not quite as loud. A twist of the volume knob is all that is required to make the Krell sound as loud, it just takes away the "flip the switch" comparison when using one preamp. I don't really care if they are the same level since They will never be used in the same system. After two days and evenings of listening to the two of them I have concluded that through my JBLs, listening to mostly well recorded jazz, that they are both very pleasing and easy on the ears. If I had to choose one over the other, it would be the P101. Maybe I just got lucky, but to my ears it does everything well for what I use it for. I bet I will be the only guy on my block who will have a Krell driving some JBL's for his garage setup. :D

Blessings, Terry
 
Power testing

Stuart Easson said:
...we made them because:


But, unlike SE amps, properly constructed, the Krell has the ability to drive just about any load, and sound reasonable doing it.***

Stuart

That's why I made one. So lets test the theory. I'd like to power test my amp and see how it drives low impedance loads. I have 4 100W resistors of 4 ohms each, probably closer to 5.

I suppose just hooking them in parallel and cranking up the input to clipping might be dangerous into 1 ohm but that is how I'd measure power into 8 ohms and 4 ohms. So what measurements are people interested in and what is the recommended procedure. Have scope and sig gen, no distortion meter.
 
Well Alright!

Pooge's fix worked like a charm. The hum is gone.

Also, I just measured my JBLs hooked up in parallel and they measure 3ohm. I've got it playing "party loud" right now and it is just cooking along. JBL's are pretty efficient so maybe it doesn't take as much to get them to "party loud". I wish I had the gear to take acurate measurements for you guys but it's playing way louder than I will ever need.

Blessings, Terry
 
Pwr supply caps..

Well lots of people have asked me in PSU kits would be available in the GB.

The answer is no since PSU discussion is like conversation on religion.

But I will note that I bought capacitors from Steve @ APEX.JR To build mine.

50VDC x 68kuF ea. with mounting rings.

The transformer is a 25volt, dual secondary, 800VA Avel
 
Email Quantity

bmxxxs81@ 2
jlexus@ 2
Ki1ohke@ 4
Hugo_bxxxx@ 2
arifh@ 12
hoojoe@ 2
diyaudio@ 2
kwokwinxxxxx@ 2
Abondi@ 4
stgrab@ 5
repute@ 5

Total 42

1 = one channel

The names may have been modified to protect the innocent.... :)


I will be getting pricing today and tomorrow and will post on Thursday.