I know It Is has a variable biasing. I can not comment on the sound difference with the KSA-50. My friend owns one
Eric
Hmmmm.......over 400 pages. I don't know where to start. Anyone can help post the schematic?
My KSA-50 resurrection project has been on hold for the last 3 years for various reasons. To recap, I procured 70% of a genuine Krell KSA-50 mk2, including the full case, 2 x toroidal by Avel-Lindberg, heatsink tunnel, fan, output boards with Krell branded TO-3 transistors, thermal cut-out switch, power switch and part of the wiring loom.
I have since bought 47k uF 100v BHC capacitors with screw top connections, fully populated Pinkmouse designed pcbs with Dale resistors and matched transistors. I have MJE15033/4 driving MJ15003/4 for the outputs. Stuart E helped me with the 0R68 emitter resistors.
(Pinkmouse pcbs)
There are some extra capacitors which are not in the cct diagram, namely c301, c302, c401 and c402. They are 470uF/50v. They look like ps decoupling C to me. Since the trafos are giving out about 42V ac, I'm expecting unloaded B+ to be in the region of 57V. They'll need to be exchanged for 63V capacitors as a minimum.
The 2 caps in series, C102,103 are rated for 16V, do they need to be changed too? I don't expect to see full rail V, I think they can stay.
Now, for C104, there is some damage to the packaging. I'd like to change it, but for the same type.
MKP stands for polypropylene - 160 is 160nF ? I'm expecting it to be 100nF. Do I need to change them all for 100nF or are they ok at 160nF?
Any one know who the manufacturer is ?
Thanks
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I have since bought 47k uF 100v BHC capacitors with screw top connections, fully populated Pinkmouse designed pcbs with Dale resistors and matched transistors. I have MJE15033/4 driving MJ15003/4 for the outputs. Stuart E helped me with the 0R68 emitter resistors.
An externally hosted image should be here but it was not working when we last tested it.
(Pinkmouse pcbs)
There are some extra capacitors which are not in the cct diagram, namely c301, c302, c401 and c402. They are 470uF/50v. They look like ps decoupling C to me. Since the trafos are giving out about 42V ac, I'm expecting unloaded B+ to be in the region of 57V. They'll need to be exchanged for 63V capacitors as a minimum.
The 2 caps in series, C102,103 are rated for 16V, do they need to be changed too? I don't expect to see full rail V, I think they can stay.
Now, for C104, there is some damage to the packaging. I'd like to change it, but for the same type.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
MKP stands for polypropylene - 160 is 160nF ? I'm expecting it to be 100nF. Do I need to change them all for 100nF or are they ok at 160nF?
Any one know who the manufacturer is ?
Thanks
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C102 and C103 is in the signal path and don't see the full rail voltage. They need not be changed. That other cap is an Epcos MKP. I suppose 160nF will be OK. The value of that cap is not that crucial.
I've spent some time tonight going through the bits of Krell KSA50 I have accumulated. I discovered the output stage mounted on the heatsink tunnel quarters. The previous person that had a go wasn't too neat and butchered them. There are 1N5408 diodes tacked on to the trace side. On the original CCT circulated in 2004, they seem to be optional, D201 & D202. Should they be refitted ? Are the 1N5408 a good substitute or are the specs not critical ?
I intend to remove all the components, clean up the boards and remount new components using keratherm pads etc. It'll definitely be neater ....
I'll be using 0r68 5W resistors.
I intend to remove all the components, clean up the boards and remount new components using keratherm pads etc. It'll definitely be neater ....
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'll be using 0r68 5W resistors.
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Hi. I finaly got through the 852 pages and 8512 messages. Outch, that was something special. Congrats for the work you guys achieved!
I now know a lot more about KRELL, KSA50 and class A. Thanks for the teaching. I do really appreciate.
Now, let me tell you that I've bought me an original KSA50 MkII a few days ago and I'm giving it some relaxed listening to let it settle in my environment.
It replaces my all time Stasis2 amp, and feeds a pair of Audio-reference speakers (French company now defunct) whose impedance is about 2 or 3 ohms from 70 to 20.000 Hz. Ruler flat.
My intention is to give the KSA a couple of tests. The usual measurements, V rails, Ve etc.
And determine the bias set by the last serviceman that opened its bonnet.
As for temp, I must say that the air flow is not that hot, about 40/42 ° C, with the probe of my multimetre.
I shall post some pictures as soon as I open it.
How should I know if I've got the mosfets in it if any? A number?
Thanks fot the information.
I now know a lot more about KRELL, KSA50 and class A. Thanks for the teaching. I do really appreciate.
Now, let me tell you that I've bought me an original KSA50 MkII a few days ago and I'm giving it some relaxed listening to let it settle in my environment.
It replaces my all time Stasis2 amp, and feeds a pair of Audio-reference speakers (French company now defunct) whose impedance is about 2 or 3 ohms from 70 to 20.000 Hz. Ruler flat.
My intention is to give the KSA a couple of tests. The usual measurements, V rails, Ve etc.
And determine the bias set by the last serviceman that opened its bonnet.
As for temp, I must say that the air flow is not that hot, about 40/42 ° C, with the probe of my multimetre.
I shall post some pictures as soon as I open it.
How should I know if I've got the mosfets in it if any? A number?
Thanks fot the information.
Hi Doc,
KSA50 shouldn't have mosfets - they have bjts. If you take a lok at the 1st photo in post 8514, you will see the original markings of the Krell branded transistors.
First thing I'd do with an old amp is to visually inspect the amp internally, for bulging or leaking capacitors. Next is to power it up with a lightbulb in series to act as a current limit. After that measure the offset at the speaker terminals, shouldn't be more than a few 10s of mV, otherwise you risk the voicecoil of your speakers. Do this and any offset adjustments without any speakers connected.
The wiring loom from mine has been chopped up. I'm trying to get a better idea of hom Krell wired it up, from the barrier strips to the trafos, rectifier, grounding etc. I understand there are a pair of high wattage resistors that connects the safety ground to the chassis. Can you confirm that ? Or even better if you have the time is to photograph and trace the wiring.
Cordialement, fs.
KSA50 shouldn't have mosfets - they have bjts. If you take a lok at the 1st photo in post 8514, you will see the original markings of the Krell branded transistors.
First thing I'd do with an old amp is to visually inspect the amp internally, for bulging or leaking capacitors. Next is to power it up with a lightbulb in series to act as a current limit. After that measure the offset at the speaker terminals, shouldn't be more than a few 10s of mV, otherwise you risk the voicecoil of your speakers. Do this and any offset adjustments without any speakers connected.
The wiring loom from mine has been chopped up. I'm trying to get a better idea of hom Krell wired it up, from the barrier strips to the trafos, rectifier, grounding etc. I understand there are a pair of high wattage resistors that connects the safety ground to the chassis. Can you confirm that ? Or even better if you have the time is to photograph and trace the wiring.
Cordialement, fs.
Hi Firestorm.
My KSA50MkII seems to have been used till the day I got it. So no hazardous fire up for me, I just use it and it sings...
As for measurements, here they go:
S/N: 2164 set for 220V
Vmains: 232V
Re : 0.5 ohms
Ve :152 mV
V rail: -/+ 49.9V
Offset, input pin grounded: L&R < 0.002V
The biasing seems very conservative, indeed.
And this amp was service by a capable tech about a couple of years ago, and there was no dust inside.
My KSA50MkII seems to have been used till the day I got it. So no hazardous fire up for me, I just use it and it sings...
As for measurements, here they go:
S/N: 2164 set for 220V
Vmains: 232V
Re : 0.5 ohms
Ve :152 mV
V rail: -/+ 49.9V
Offset, input pin grounded: L&R < 0.002V
The biasing seems very conservative, indeed.
And this amp was service by a capable tech about a couple of years ago, and there was no dust inside.
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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