Hi everyone,
I have a small problem with my Krell, a yellow wire broke off the PCB and I'm still puzzeled about that does that wire actually do?
It comes from the positive speaker connector, has a R8 resistor under a piece of heatshrink, goes through something that looks like a fuse holder and ends on the main PCB.
The question is: Why is it only on one channel? I'm sure that's a factory job as I saw more KSA50's with the same thing.
I have a small problem with my Krell, a yellow wire broke off the PCB and I'm still puzzeled about that does that wire actually do?
It comes from the positive speaker connector, has a R8 resistor under a piece of heatshrink, goes through something that looks like a fuse holder and ends on the main PCB.
The question is: Why is it only on one channel? I'm sure that's a factory job as I saw more KSA50's with the same thing.
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.
Could be, I heard it too that has something to do with fixed offset.
But would it leave the factory with something like that? It's also on one channel only.
The yellow wire also goes through this, I have no clue if this is a fuse holder?
Edit: Turns out to be a switch that needs a key to operate:
But would it leave the factory with something like that? It's also on one channel only.
The yellow wire also goes through this, I have no clue if this is a fuse holder?
Edit: Turns out to be a switch that needs a key to operate:
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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Hate to be negative but I would not be happy if I forked over the cash for a Krell and found a kludge of a fix like that. Whatever you do, I wouldn't reconfigure anything just fix it exactly. It is obviously there for a reason, they didn't just feel like giving you a free resistor and needed a place to put it.
Don't forget 20cm of a fancy yellow wire and a switch 
Yes, of course it will be brought back to original condition.
If I only could get in touch with Dan, maybe he could explain the purpose of that yellow wire once for good.
//
Sorry to go a bit off topic but I'm planning to give the Krell some good TLC and was wondering how important for the sound the small 1000uf ROE caps in the feedback loop are and what to replace them with?
Yes, of course it will be brought back to original condition.
If I only could get in touch with Dan, maybe he could explain the purpose of that yellow wire once for good.
//
Sorry to go a bit off topic but I'm planning to give the Krell some good TLC and was wondering how important for the sound the small 1000uf ROE caps in the feedback loop are and what to replace them with?
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Don't forget 20cm of a fancy yellow wire and a switch
Yes, of course it will be brought back to original condition.
If I only could get in touch with Dan, maybe he could explain the purpose of that yellow wire once for good.
//
Sorry to go a bit off topic but I'm planning to give the Krell some good TLC and was wondering how important for the sound the small 1000uf ROE caps in the feedback loop are and what to replace them with?
I fear losing my head for making a capacitor suggestion, every post below this will probably tell me I'm wrong, but I like Nichicon caps. Particularly the Fine Gold series, I have heard them all- including Elnas (Cerafine, Silmic, Silmic II, they all sound harsh to me) and always come back to the Nichicon FG (Fine Gold) and FW (power supply FG equivalent in bigger values/voltages for when you need them). They sound great from the moment they go in, other caps I have tried not so much. People swear they need to "break in" but I think that you just get used to the sound, better or not.
It could be a feedback take off point after some kind of series interrupt device, a fuse, relay.... whatever.... with a view to maintaining some DC feedback when said device operates. But your circuit as drawn shows no such components.
LOOKS LIKE:
1) The output transistors for the KSA50 are located on a physically separate fan cooled heatsink, such that the global negative feedback from the output at the speaker terminal requires a wire to make connection to the differential amp negative input on the physically separate main PCB. You must have this wire on both channels. R8 is the out-to-in global negative feedback resistor.
2) The ratio of R8 / R9 in your schematic sets the amplifier gain.
3) The adjustment Pot1 (R3-R4-Pot1-R6-R5) at the top of your schematic is used at the factory to null out any "native" amplifier DC offset.
4) C3 C4 C5 in your schematic are there to remove additional DC offset that might get generated from you PreAmp.
5) I expect Krell put any speaker fuse or speaker protection relay after this wire connection from "output" on your schematic to final the chassis speaker output terminal. You never want to break the global feedback connection. (output-R8 -diff_pair)
1) The output transistors for the KSA50 are located on a physically separate fan cooled heatsink, such that the global negative feedback from the output at the speaker terminal requires a wire to make connection to the differential amp negative input on the physically separate main PCB. You must have this wire on both channels. R8 is the out-to-in global negative feedback resistor.
2) The ratio of R8 / R9 in your schematic sets the amplifier gain.
3) The adjustment Pot1 (R3-R4-Pot1-R6-R5) at the top of your schematic is used at the factory to null out any "native" amplifier DC offset.
4) C3 C4 C5 in your schematic are there to remove additional DC offset that might get generated from you PreAmp.
5) I expect Krell put any speaker fuse or speaker protection relay after this wire connection from "output" on your schematic to final the chassis speaker output terminal. You never want to break the global feedback connection. (output-R8 -diff_pair)
PERHAPS, the physical mechanical design is NOT stereo symmetrical.
One pair of output transistors on the shared fan cooled heatsink is close enough to the driver circuit PCB to require just a short jumper, and the R8 NFB resistor connects to this short wire on the circuit PCB for that channel.
One pair of output transistors is on the other side of the shared fan cooled heatsink and requires the longer yellow wire to connect the output with R8 to the negative diff-input. The design engineer might have found that it is superior to put the R8 NFB resistor close to the output transistors to immediately attenuate the feedback signal, and thus allow the yellow wire to just carry a low voltage, low current signal.
PERHAPS, some idiot snapped the yellow wire under the fuse so it would not jiggle.
I own two Krell KSA250 rev2 amps. After re-cap'ing both I like to call Krell mechanical design "idiot-savant engineering" In the KSA250, 0.4" high metal screw spacers are used to stack the driver PCB on top of the output PCB. The output feedback signal travels through a screw+metal_standoff between the two PCBs. The shortest path, but a cheap mechanical connection. "idiot-savant engineering"
This Sunday I went to Church and prayed upon your yellow wire.
God told me that Satan is in that yellow wire!
If you fall to temptation and turn the rear switch, Satan will destroy your speakers!!
If you want your speakers free from Satan, you must perform an Exorcism and remove the yellow wire and restore both channels to the standard wiring+feedback. Never touch Satan's switch!!
Can I get an AMEN!
I have seen several Krell KSA50 and KSA100 amps. None had your rear "switch". Your pictures do not show enough details around the switch to trace the circuit.
PERHAPS: A past owner added this switch with the yellow wire and another feedback resistor as a way of setting two different amplifier gains .... two different R8/R9 ratios. i.e. for ONE CHANNEL the switch selects between (a) one resistor = R8; or (b) two resistors in series(or parallel) = R8. This would allow passive Xover circuit bi-amping with different gain for the woofer than for the mid-tweet.
God told me that Satan is in that yellow wire!
If you fall to temptation and turn the rear switch, Satan will destroy your speakers!!
If you want your speakers free from Satan, you must perform an Exorcism and remove the yellow wire and restore both channels to the standard wiring+feedback. Never touch Satan's switch!!
Can I get an AMEN!
I have seen several Krell KSA50 and KSA100 amps. None had your rear "switch". Your pictures do not show enough details around the switch to trace the circuit.
PERHAPS: A past owner added this switch with the yellow wire and another feedback resistor as a way of setting two different amplifier gains .... two different R8/R9 ratios. i.e. for ONE CHANNEL the switch selects between (a) one resistor = R8; or (b) two resistors in series(or parallel) = R8. This would allow passive Xover circuit bi-amping with different gain for the woofer than for the mid-tweet.