Krell FPB400CX Restoration

[BuzzzFuzzz]

1 hour ago, Doug Johansson said:

Better be quick as other amps are on there way...

 

Yeah, don't know about that with the current situation.  I do have to come down and collect a pair of Pioneer speakers from another member, when all settles down again.

 

Cheers.

[GaryT]

This reminds me I need to finish doing this to my FBP200, I have a few caps for it, just need to work up the courage to take out the roughly 400 screws that hold it together.

[Yamaha_man]

27 minutes ago, GaryT said:

This reminds me I need to finish doing this to my FBP200, I have a few caps for it, just need to work up the courage to take out the roughly 400 screws that hold it together.

Bahahahaha, try doing a FPB-600 or KAS, @Baldieman knows all about it.

Edited August 23, 2021 by Yamaha_man

[GaryT]

I don't want to think about it.

 

The 200 is already such a monstrous amplifier for me with so many components that I've been holding off working on for a year. I did the main power caps when I first got it so it's working just fine but I've got the extra parts to finish the job.

[tubularbells]

9 hours ago, GaryT said:

I don't want to think about it.

 

The 200 is already such a monstrous amplifier for me with so many components that I've been holding off working on for a year. I did the main power caps when I first got it so it's working just fine but I've got the extra parts to finish the job.

 

Yeah that's the thing though, is it really working as it should as a full recap on mine clearly revealed things were not as rosy as it seemed.

 

[GaryT]

I doubt it is at 100%, sonically it's fine, but I don't trust it to last too long on the old caps considering how damn hot it runs.

 

It's a job for a couple of weeks time, moving house next week and building out a new listening room and workshop so the refurbishment gets put off another couple of weeks.

[kroozzy]

interesting read

 

well done on the project

 

question

 

did you go with a higher quality on the caps with the same specs

 

or

 

go as exactly recommended

 

if you did not go a higher quality cap, is there a particular reason why

 

 

chris

[tubularbells]

15 hours ago, kroozzy said:

interesting read

 

well done on the project

 

question

 

did you go with a higher quality on the caps with the same specs

 

or

 

go as exactly recommended

 

if you did not go a higher quality cap, is there a particular reason why

 

 

chris

 

Thanks @kroozzy. As is the case with all my repairs/restorations I prefer to keep things as original as possible so did not seek out exotic branded caps and instead opted for high reliability, low impedance & long life Nichicon UHE series caps which have lifespans in the range of 4,000 to 10,000 hours at there rated temperature of 105 degrees C.

 

I also didn't mess with the values keeping capacitance exactly the same as per Krell's original specifications as there is always the temptation to add a bit more (particularly in regards to the filter caps) so basically this is how it should have sounded from the day it left the factory all those years ago. The only slight modifications I did do was replace the handful of values that were only rated to 80 degrees C. with 105 variants as I suspect back then those values were not available in that temp range which should hopefully improve longevity.

[kroozzy]

18 hours ago, tubularbells said:

 

Thanks @kroozzy. As is the case with all my repairs/restorations I prefer to keep things as original as possible so did not seek out exotic branded caps and instead opted for high reliability, low impedance & long life Nichicon UHE series caps which have lifespans in the range of 4,000 to 10,000 hours at there rated temperature of 105 degrees C.

 

I also didn't mess with the values keeping capacitance exactly the same as per Krell's original specifications as there is always the temptation to add a bit more (particularly in regards to the filter caps) so basically this is how it should have sounded from the day it left the factory all those years ago. The only slight modifications I did do was replace the handful of values that were only rated to 80 degrees C. with 105 variants as I suspect back then those values were not available in that temp range which should hopefully improve longevity.

@tubularbells

 

thank you for your reply

 

definitely agreed with keeping the values, especially with krell and sooooo much going on inside

 

and thank you for sharing how you slightly modded a few caps to higher temp values

 

 

i hope you get many decades out of your restoration

 

chris

[Natehack]

I’ll be that guy to bump an old thread!

 

Just wanted to say thank you for documenting this rehab process as I just got into a 400cx that needs some love.

 

Off to search for the schematics…

[Matt Anderson]

I’m ready to take my Krell FPB200c for a full restoration which is long overdue by now. Anyone’s input into where i should get it done would be very much appreciated thanks folks. I live a coupla hours south of Sydney and my main idea was with Len Wallis Audio. Hoping this good thread (thanks Tubularbells) is a good place to ask, or i could open a new thread? Pls feel free to pm me with any opinions, thanks.

Edited August 24, 2022 by Matt Anderson
Better search coverage.

[Yamaha_man]

@Baldieman is your man. A Krell genius. 

[tubularbells]

26 minutes ago, Matt Anderson said:

I’m ready to take my Krell FPB200c for a full restoration which is long overdue by now. Anyone’s input into where i should get it done would be very much appreciated thanks folks. I live a coupla hours south of Sydney and my main idea was with Len Wallis Audio. Hoping this good thread (thanks Tubularbells) is a good place to ask, or i could open a new thread? Pls feel free to pm me with any opinions, thanks.

 

Personally wouldn't recommend LWA mate as they apparently "serviced" my Krell before I received it and all they addressed was one of the 3 blue leds on the front needed replacement (which incidentally did not match the other 2) and didn't address (or notice the bias issues) that also required attention which is what prompted mt to embark on the full re-cap and service myself led's included.

 

 

[tubularbells]

3 hours ago, Natehack said:

I’ll be that guy to bump an old thread!

 

Just wanted to say thank you for documenting this rehab process as I just got into a 400cx that needs some love.

 

Off to search for the schematics…

 

Good luck with the schematics as I searched for months and came up empty handed. Next to no info on this series online however if you do happen to stumble on  them remember sharing is caring 

[Natehack]

On 23/08/2022 at 8:45 PM, tubularbells said:

 

Good luck with the schematics as I searched for months and came up empty handed. Next to no info on this series online however if you do happen to stumble on  them remember sharing is caring 

You bet! Digging in as I type, excited to hear this amplifier at its originally intended spec.

 

Since I’m new-ish to this I’m not afraid to ask questions of those more experienced:

- After doing your 400cx recap, what would you have changed in your process? Would you have matched different caps in different places or are you happy with the UHE’s?? 
- Are the axial caps you used also Nichicon?

- When you do a unit like this and choosing capacitors, are you looking for low impedance, high ripple current, or looking at the ESR?

 

Thanks so much from way up here in Minnesota USA!

[tubularbells]

4 hours ago, Natehack said:

You bet! Digging in as I type, excited to hear this amplifier at its originally intended spec.

 

Since I’m new-ish to this I’m not afraid to ask questions of those more experienced:

- After doing your 400cx recap, what would you have changed in your process? Would you have matched different caps in different places or are you happy with the UHE’s?? 
- Are the axial caps you used also Nichicon?

- When you do a unit like this and choosing capacitors, are you looking for low impedance, high ripple current, or looking at the ESR?

 

Thanks so much from way up here in Minnesota USA!

 

 

The axial caps on the output stage boards were Vishay 119 AHT-DIN series rated at 125C. Below is a list of my 3rd and final parts order. I had purchased 80x of another axial type but realised form factor was an issue so didnt fit hence the order below.

 

http://www.digikey.com.au/short/h78whmdz

 

As for the caps my main consideration was quality, temp rating and longevity. IMO many so called audiophile caps wouldn't work as the environment is simply too harsh and I also wanted it to be as close to original spec as possible so yes im very happy with the UHE series put into it.

 

And finally as for the process, its all very modular so relatively easy to take apart so take your time concentrate on one board at a time paying close attention to value and polarity.

 

 

 

 

 

Edited August 25, 2022 by tubularbells

[Natehack]

Just wanted to say thank you for your documentation in both word and picture form. Your time spent creating this thread gave me the confidence and knowledge to save big $$$ and learn some things along the way. 

The Krell lives! Took my time and tried my best. Replaced all electrolytic caps save the big filter caps as their esr measured low. 

Can’t wait to break this in and soak in some auditory glory!

 

[tubularbells]

Your very welcome and im glad to hear another 400cx is back to its restored glory! Awesome work and well done mate. 

[Metalunatic]

I'm looking into purchasing a 400cx.  Thanks for taking the time with this article to give others an idea on recapping requirements.  Excellent article!

[Massimo]

@Natehack I need your help!

 

First of all HI to everyone, my name is Massimo

This is my first post here, I'm an Italian music-audio lover, just purchased a Krell FPB400CX to drive my MBL 101E, but I would like to check it properly and understand if it is necessary a recapping.

Who can help me?

I have some experience in soldering/desoldering, I've built a tube preamp, replaced and maintened few tube amps, so I think I can do a recapping, but I would like to avoid any unnecessary work and expenses.

I have seen many TP Test Points on the printed board, but no way to get a service manual in which I could find the correct values to measure...definitely I need your help 

 

[Natehack]

4 hours ago, Massimo said:

@Natehack I need your help!

 

First of all HI to everyone, my name is Massimo

This is my first post here, I'm an Italian music-audio lover, just purchased a Krell FPB400CX to drive my MBL 101E, but I would like to check it properly and understand if it is necessary a recapping.

Who can help me?

I have some experience in soldering/desoldering, I've built a tube preamp, replaced and maintened few tube amps, so I think I can do a recapping, but I would like to avoid any unnecessary work and expenses.

I have seen many TP Test Points on the printed board, but no way to get a service manual in which I could find the correct values to measure...definitely I need your help 

 

 

Hello Massimo! Those MBL’s are some bonkers speakers and the Krell should be a great match for them. 
 

I did not obtain the schematics of this FPB, so as far as adjusting bias I did no such thing. I simply deconstructed the amp and slowly checked and rechecked all capacitor values before placing an order. I figured this amp was ready for a capacitor replacement based on age and symptoms of the amp shutting itself off the previous owner admitted to. The FPB can create some heat! Higher temp caps are a great idea.
 

Recapping is not too difficult a job if you take your time, triple check all values of capacitors, and have some confidence! You will be rewarded with years of wonderful music. 

[Massimo]

On 20/04/2023 at 10:08 PM, Natehack said:

 

Hello Massimo

thanks a lot, I will check carefully all caps, but I'm pretty sure that this summer will be dedicated to this job! 

 

better to do it when outside is hot, and use the Krell as heater for the cold winter listening sessions.

 

Another question, sorry, in order to replace the caps on the board where are connected the power transistor (that one connected with the heatsink), is it necessary to remove screws for all power transisitors? Have you seen any problem in doing this?

Thanks again

 

Massimo

[Natehack]

3 hours ago, Massimo said:

thanks a lot, I will check carefully all caps, but I'm pretty sure that this summer will be dedicated to this job! 

 

better to do it when outside is hot, and use the Krell as heater for the cold winter listening sessions.

 

Another question, sorry, in order to replace the caps on the board where are connected the power transistor (that one connected with the heatsink), is it necessary to remove screws for all power transisitors? Have you seen any problem in doing this?

Thanks again

 

Massimo

Just like tubularbells said above, the FPB’s are very modular in their design; if you like/liked Legos and logical sequencing of steps you’ll love these FPB’s!! 

To get at all of the axial caps a person does need to remove the board, but removal truly isn’t something that should give you too much trouble. Every connection that needs to come apart/be moved/pushed aside is able to be. 

 

Have fun with it! There will be ‘pulling out your hair’ moments, but have confidence. Even taking my time as a new learner I was able to have this done from first top plate fastener removal to playing music in less than 2 weeks (including waiting for capacitors). Now our FPB throws our Kef Reference 4.2’s around with so much precision and power it’s difficult to see the need for a different pair of speakers!
 

[tubularbells]

Removal of the transistors isn't necessary. The way I did it was to snip off the axial capacitor leaving the legs still soldered into place (approx 1.5cm). I then removed the remaining legs with my desoldering tool, This method works well and saves you a bunch of time.

[new2hifi]

On 26/04/2023 at 3:46 PM, tubularbells said:

Removal of the transistors isn't necessary. The way I did it was to snip off the axial capacitor leaving the legs still soldered into place (approx 1.5cm). I then removed the remaining legs with my desoldering tool, This method works well and saves you a bunch of time.

Hi Doug;

It seems you never separated the heatsink and just worked on the top side to de-solder and solder the axial capacitors on the output board; right?