Can you help me choose capacitors for my amplifier restoration project? - diyAudio
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Old 9th March 2007, 11:27 PM   #1
Kuja is offline Kuja  Yugoslavia
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Question Can you help me choose capacitors for my amplifier restoration project?

Hi everybody,

I have to choose four big power supply capacitors for my amplifier restoration project.

The amp in question is KA-907, Kenwood's TOTL model from 1979.

On this photo you can see the original capacitors:

Click the image to open in full size.

.


Only capacitors that are of the right size (that can be physically fitted inside the amp) and that are available to me (I live in Europe), are these Panasonics:

.


Click the image to open in full size.

Click the image to open in full size.


Are they OK for this kind of use?


I hope so, since I couldn't find any others that are small enough to be fitted inside the amp.

I'm not sure which ones should I get.

Some people advised me to go for the capacitors with the largest capacitance that can be physically fitted inside the amp (in this case - 33.000 uF, part no. ECEP1KP333HA).

Others told me that I should stick with the original capacitance.

Some told me that I should go for the 80 degree C, others said go for the 100 degree C ... 80V or 100V?

Who should I listen to and why?

I'm kind of a newbie, so little theory wouldn't hurt.

Please tell me what capacitors would you choose from those lists above.
You can use part numbers.

Thanks in advance,

Aleksandar

I'm so sorry for waisting bandwidth, but I also posted the same question in other section of this site, in hope that more people will see it.
I really need to make this decision as soon as possible (while those capacitors are still in stock).

PS
In case this is important, here is also a scan from the service manual, showing the power supply and power amp sections:

http://www.kujucev.com/kx/_amp_web.jpg
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Old 10th March 2007, 02:30 AM   #2
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The 18000uf@80vdc should work just fine.If you have enough clearance the 22,000uf @ 80vdc would work as well.Those particular caps have 5-mounting pins you will probably have to snip off 3 of them to mount on your PC board.Pay close attention to the polarity. You may or may not notice any audio difference going from 18000 to 33000 with exception to low frequencys which I would think would benefit the additional power reserve.


105 degree would be better than 85
100 vdc would give you additional safety margin.
Obviously the the originals worked just fine probably for quite a while.The choice is up to you to spend a little extra for piece of mind.

Dave

After looking at schematic 80 vdc is plenty.
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Old 10th March 2007, 03:10 AM   #3
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If it was up to me I'd go with the ECEP1KA223HA 22000uf@100vdc 105degree because its the largest I could get in the 105 degree.
Dave
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Old 10th March 2007, 03:32 AM   #4
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Default 1979 was a good year...

Xeaglekeeper sounds good to me! I'd place the largest caps I could inside the location you have and try hard to maintain or exceed the temperature rating and voltage rating to acheive long happy life.

While you are at it, you could shop around and pluck out a few more old electrolytics as well. I think I would like a look-see at the schematic first, then I would choose my battles. I'd look for a couple other opportunities while there, like ceramics and such.

Jah to the restoration!

Shawn.
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Old 10th March 2007, 08:01 PM   #5
K-amps is offline K-amps  United States
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22kuF is just fine, any more then u need to worry about the Bridges and AC fuse...

The KA-907 is a great amp. I still have a KA-1100 and a KA-3300 both flagships after the 907.

Ofcourse upping the caps with lower ESR units like the Panasonics and you are making the rails much tighter than spec... one drawback is the SOAR of the current OP stage may factor the droop and hence be ok but now with lessor droop, you may be getting closer to the OP device limits than intended by the designer. I say this because Kenwood usually had low current hi volt supplies in their integrated's and made the OP stage perform accordingly. The simple solution is to use better OP devices to compensate.

I have had excellent results with replacing the OP devices with 2sd424 and 2sb554. Smoother sound, greater SOAR and reliability.

Availability is another issue.

Go one step ahead and use the MJ21195/96's and you have a bullet proof OP stage. These will be drop in subs, no tweaks needed. the originals are 120w devices and the MJ's are 250w with better gain.
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Old 10th March 2007, 09:26 PM   #6
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Can you tell us the dimensions of the original capacitors?Maybe we can recommend something.
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Old 10th March 2007, 09:59 PM   #7
dBfreak is offline dBfreak  United States
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I recently recapped my Pioneer SX-1250 with some Nichicon KG Super series capacitors. You can also look into the Nichicon KG Gold series (these will probably fit into the amp). Very nice capacitors and of the utmost quality.

I would stick with the original cap values because that is what the engineers at Kenwood designed the amp for.
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Old 10th March 2007, 10:52 PM   #8
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.[QUOTE]Only capacitors that are of the right size (that can be physically fitted inside the amp) and that are available to me (I live in Europe), are these Panasonics

The panasonics will do the trick
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Old 11th March 2007, 11:23 AM   #9
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First of all are the power supply capacitors bad? If they aren't bad why replace them? I have some old equipment that has the original power supply caps and still works flawlessly.

Secondly I do NOT agree with gross oversizing the power supply caps because this causes undo stress on the rectifiers and usually means you will need to design a soft start circuit in order to have your diodes survive the turn on cycle. Adding larger sized caps makes the bass response sound very muddy unless you add bypass caps of the correct size.

If your bent on replacing the power supply caps I would suggest caps of roughly the same size and naturally caps that will work within the pyhsical limitations of the chassis. There are tweeks that will make ANY amplifier sound better. An example of one would be to bypass any electrolytics in the signal path with a small mica or mylar cap. Another tweek would be to add bypass caps to the power supply caps. These two tweeks will add far more to the sonic clarity and overall sound than you will ever get from putting huge power supply caps in.

Shawn,

The bypassing of the caps in the signal path and in the power supply works on Crown amps also. I can remember doing this on an Ampzilla that I owned. I did the bypasses on one channel and left the other channel bone stock and then had some people listen to it and watch their faces drop in amazement. I asked which channel sounded clearer and cleaner and it was a no brainer.
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Old 11th March 2007, 04:51 PM   #10
K-amps is offline K-amps  United States
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Quote:
Originally posted by burnedfingers
First of all are the power supply capacitors bad? If they aren't bad why replace them? I have some old equipment that has the original power supply caps and still works flawlessly.
The guy is asking the question on diyaudio.com not mycapsareflawless.com

He wants to tinker... Let him do so within reason... Caps do age... right? The amp's close to 30 yrs old... !! Is there a chance that the caps are not steller? It's an easy upgrade... within reason not an issue yes? Thats why he is asking the collective wisdom.




Quote:
Originally posted by burnedfingers

An example of one would be to bypass any electrolytics in the signal path with a small mica or mylar cap. Another tweek would be to add bypass caps to the power supply caps.
Amen to this... try different caps to see what suits you. Avoid tantalums...
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