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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Krell KBX Crossover Info Needed
Krell KBX Crossover Info Needed
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Old 9th January 2019, 05:21 PM   #1
willcycle is offline willcycle  United States
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Default Krell KBX Crossover Info Needed

Does anyone have a schematic or service manual for a Krell KBX active crossover?
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Old 19th January 2019, 05:25 PM   #2
willcycle is offline willcycle  United States
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Default Finding cause of DC offset

I am trying to find the cause of a very high DC offset on the high pass section of a Krell KBX crossover. Unfortunately no documentation is available. Any suggestions on how to proceed? I did fully recap the unit and the DC offset is still present without the frequency diving board installed (It was there before the recap as well).
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Old 19th January 2019, 05:30 PM   #3
Mooly is offline Mooly  United Kingdom
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Krell KBX Crossover Info Needed
General rules:

1/ Always check supplies are correct. Very high offset could be a missing rail.

2/ If its opamp based then look at the DC conditions around each opamp and apply the rule of 'the opamp output will assume the voltage needed to bring the difference in voltage between the inputs to zero'.

3/ Look for any less obvious causes such as spillage or leakage from caps causing conductive areas on the PCB.

4/ Look for possible external circuitry 'pulling' an output outside what is correctable by the stage concerned... for example faulty muting circuitry.
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Old 24th January 2019, 12:38 PM   #4
willcycle is offline willcycle  United States
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Default Help identifying pot function

I am trying to figure out the function of some pots on a balanced Krell KBX crossover board. The transistors are MPS8099 and MPS8599, NPN/PNP pairs. Shown is the right channel only and the associated caps and resistors that determine the crossover frequency and slope (350 HZ 12 dB/oct). Any ideas?
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Old 25th January 2019, 08:57 AM   #5
Kay Pirinha is offline Kay Pirinha  Germany
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Without the schematics one could also ask a glass bowl...
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"Bless you, Sister. May all your sons be bishops." (Brendan Behan)
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Old 25th January 2019, 09:05 AM   #6
jazbo8 is offline jazbo8
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Krell KBX Crossover Info Needed
Multiple threads on the same topic merged.
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Old 16th February 2019, 12:03 PM   #7
willcycle is offline willcycle  United States
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Here is the schematic I drew to determine the function of pot R107 of the crossover board.
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Old 16th February 2019, 01:29 PM   #8
willcycle is offline willcycle  United States
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I studied the circuit some more and it appears to be a DC offset adjustment. Correct?
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Old 16th February 2019, 08:03 PM   #9
PRR is offline PRR  United States
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Re-Draw the circuit for "stupid eyes": power rails top and bottom, signal from left to right.

Yes, the pot is a DC offset between two emitter followers, one at +0.6V and one at -0.6V.

If you have more than a little offset with pot centered, something has a bad joint or is blown.
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Old 17th February 2019, 04:36 AM   #10
PRR is offline PRR  United States
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Looking at that plan again, it appears either the rails or the NPN/PNP have been switched.
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