Dear members,
I'm looking for a Krell KAV-400Xi KAV 400 XI schematic / service manual.
left power amp is broken.
I'm looking for a Krell KAV-400Xi KAV 400 XI schematic / service manual.
left power amp is broken.
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Hi pwgtang,
Thanks for the reply. I will disassemble the amp and check the capacitors. Next to distortion the left channel also suffers from an output offset of approximately 8 Volt. I will post the results .
Krell KAV-400XI repair update:
- All electrolytic capacitors including the 8 6800uF psu are out of spec. (measured 10u instead of 47u)
- one of the input circuit transistors is out of spec (bc847), replaced both.
- dc unbalance is gone now
Hi Tang/Musical devices,
I hope to recap my kav-400xi and believe many owners will likely have to do the same especially before even transistors are damaged or damaged irreversibly.
Kindly advise the list of capacitors to be changed out, brand, values etc.
Many thanks in advance and cheers.
I hope to recap my kav-400xi and believe many owners will likely have to do the same especially before even transistors are damaged or damaged irreversibly.
Kindly advise the list of capacitors to be changed out, brand, values etc.
Many thanks in advance and cheers.
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Thanks musical device .. thanks Tang.
Aside to Tang, any reason not to recap ? Amp may be working and scope does not show any significant distortion on oscilloscope but I see all these seemingly known failures for my 14 yrs old unit as well as cases of row of transistors failing pushes me to take some preventive actions.
Aside to Tang, any reason not to recap ? Amp may be working and scope does not show any significant distortion on oscilloscope but I see all these seemingly known failures for my 14 yrs old unit as well as cases of row of transistors failing pushes me to take some preventive actions.
Sorry, miss one query .. I see some had replace those what I think are polymer caps in round tin cans with even audio grade thru hole electrolytic ones e.g. nichicon ufg.
Is this advisable as I had tot that polymer ones are more expensive and last longer being solid ?
Thanks again.
Is this advisable as I had tot that polymer ones are more expensive and last longer being solid ?
Thanks again.
Managed to gather recap requirement of 72 capacitors 😱and hope this helps other owners on getting this done due to reported heat and capacitors dying out before more serious damage as well as have some fun doing so .. like for myself especially since a used kav-400xi is not too crazily priced.
Will depart from usual 100% audio grade capacitors at 85degC to try stuffing with 105degC alternatives in view of the already seen heat related failures as well as hopefully sustained sound quality and planned replacement list will keep to same smd and thru hole format per below while subjected to availability:
Thanks for all the info provided here which certainly help and hope to get my modded blue LEDs display and recapped KAV-400xi in due time. Cheers,
Pre:
1. 4X 47uF 25V
2. 20X SMD 47uF 25V
Power:
3. 24X 47uf 63V
4. 8X 6800uf 63V
5. 4X BP 47uf 25V
6. 8X SMD22uf 6.3V
7. 8X SMD 47uf 25
Will depart from usual 100% audio grade capacitors at 85degC to try stuffing with 105degC alternatives in view of the already seen heat related failures as well as hopefully sustained sound quality and planned replacement list will keep to same smd and thru hole format per below while subjected to availability:
- Still audio grade Nichicon KA 105degC instead of planned Nichicon FG 85degC (Stock: unknown Nichicon)
- 15000uf Mundorf Power Gold 105degC (Stock: Nichicon LC 85degC) per Martin Poulin's KAV-400xi mod,
- Well known audiograde Nichicon ES Bipolar or at least Elna RA4 Audio grade of same 85degC but with fitting size unlike oversized ES Bipolar while 105deg versions of VP and EP are of unknown sound quality and not often discussed in forum (Stock: UCC SME-BP 85degC)
- SMD GYA-GYC 105degC or audio grade UCQ/UUQ 85degC (Stock: UUD 85deg C)
Thanks for all the info provided here which certainly help and hope to get my modded blue LEDs display and recapped KAV-400xi in due time. Cheers,
Pre:
1. 4X 47uF 25V
2. 20X SMD 47uF 25V
Power:
3. 24X 47uf 63V
4. 8X 6800uf 63V
5. 4X BP 47uf 25V
6. 8X SMD22uf 6.3V
7. 8X SMD 47uf 25
Attachments
You do a great job, can you measure all those removed caps and list their value to see how many are out of specification?
Hi Tang, Still in the process of getting required capacitors and will do so for removed ones.
Would really appreciate yr help to advise if the diameter of the Nichicon 6800uf 63V is 30mm or 35mm version available while I do not believe 25mm will clear height constraint as the engineer of my repair shop is off for a week and I hope to order them one time with others but need to ensure that they will fit.
Btw, is there any need to replace/reapply any thermal transfer paste of the transistors on the heatsink to request the technician to do so ?
Cheers.
Would really appreciate yr help to advise if the diameter of the Nichicon 6800uf 63V is 30mm or 35mm version available while I do not believe 25mm will clear height constraint as the engineer of my repair shop is off for a week and I hope to order them one time with others but need to ensure that they will fit.
Btw, is there any need to replace/reapply any thermal transfer paste of the transistors on the heatsink to request the technician to do so ?
Cheers.
Attachments
Oops .... made a couple of capacitors as unit is at repair shop not available to me but one more try here as well as included the front panel one.
Had also put in the order of the replacement after days of reading and review of component specification as I hope to have a good mix of sound quality improvement as well as reliability against heat related failures.
Preamp Replacements
20X SMD 68uf/25V Nichicon GYA 125c
4X BP 47uF/25V Nichicon ES 85c
●
Power
8X SMD 47uF/25V Nichicon GYC 125c
8X SMD 22uF/6.3V Panasonic FP 105c
24X 47uF/63V Panasonic FC 105c
4X BP 47uF/25V Nichicon EP 105c
8X 6800uF/63V 4x Mundorf Elytic 125c *
●
Front Panel
2X 1000uF/25V Panasonic FM 105c
4X SMD47uF/25V Nichicon GYC 125c
Please feel free to correct and advise as deemed fit.
Again not aware what is the model of the 4X Bipolar 47uf 25V caps in the preamp while photos gather shows standard Nichicon SME-BP ones in the power amp but seems from all photos seen is that the color is different and probably I am of the same approach by Krell to employ higher SQ ones in the preamp ... I will be using slightly oversized Nichicon ES that is cheap and quite wonderful for input coupling in the past.
Cheers,
Aside to Tang,
---------------
Thanks on the confirmation of d35mm and l30mm for the power cap but decided to go with Martin Poulin's use of Mundorf caps which are at rate at 125c instead of original Nichicon LS 85c or some example of Wurth's, Cornell etc. also of 85c. With appreciation and cheers,
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