Kenwood 700M - replace filter caps?

[davstev]

Hi,

I recapped a 700M a few years ago. I left the original power supply filter caps in- the big ones. I've sometimes wondered if I should spend the money to replace them, and just to complete the job. Looking at $100 minimum, probably.

If the current ones seem to work fine, though they're original, should I replace them? What sonic benefit would come with new caps?

I haven't measured the capacitance on the originals or anything.

Thanks for your opinions.

 

[S.corp.]

There are some cheap eBay devices (like the mega 328) which can measure the capacitance and the ESR of the cap, so you can check if they are still within manufacturer's tolerances.

It would be probably the best to replace them anyway, since they are around 45 years old...

 

[davstev]

There are some cheap eBay devices (like the mega 328) which can measure the capacitance and the ESR of the cap, so you can check if they are still within manufacturer's tolerances.

It would be probably the best to replace them anyway, since they are around 45 years old...

I have a capacitance tester. Not sure about ESR, will check later.

I know what you mean about 45 years old. That's my age; starting to think I could use an upgrade...:0

Cheers.

 

[homebrew]

A cursory examination of the main filter caps would be a place to start. Tops of the caps bulging or leaking? Even if they look and measure OK, a recap still might be desirable. The newer caps are smaller and more efficient so you could notice a difference.

Don't know if you've seen this site, but he does a total rehab of a Kenwood 700. Looks like a beautiful amp.

http://www.cdkands.com/index2.html

 

[mbz]

Not familiar with the 700M but I'd guess that the power transistors are fed directly from the filter caps (ie, unregulated supply).
It's the power amp stage that converts the xxxmW into the watts you hear. Because of this I'm suspecting the main caps
have a roll in sound quality.

Because of it's age and for piece of mind I'd replace them, maybe UCC SMH or KMH series. However if the amp sounds fantastic
(not just good) then you have a tough decision.

 

[ivandezande]

Do it, the new caps will be in better condition and have better specs no matter what the 45 year old originals measure.

 

[Blue Shadow]

don't forget to go about 10% higher than spec to get a big cap close to spec. Seems the regular production is on the lower side of the ±20% spec for large caps since it saves material and meets the specification.

 

[homebrew]

It's OK to use filter caps of a higher value, both voltage wise and capacitance wise. For example, if the originals are 10,000uFd and 63 volts you can upgrade to 12,000uFd and 80V.

 

[davstev]

Excellent advice from all, thanks. I'm going to look into options and likely order something. I think there are also threads on AK about this very topic- about which to select. Still wondering if the replacement might lead to a more refined sound in some way, but one way to find out....

 

[S.corp.]

I have a capacitance tester. Not sure about ESR, will check later.

I know what you mean about 45 years old. That's my age; starting to think I could use an upgrade...:0

Cheers.

Well, 45 is a nice age (for most), but not so much for electrolytic capacitors

 

[davstev]

don't forget to go about 10% higher than spec to get a big cap close to spec. Seems the regular production is on the lower side of the ±20% spec for large caps since it saves material and meets the specification.

I was thinking of these:

https://www.digikey.ca/product-detail/en/nichicon/LNT1K333MSE/493-8972-ND/2549067

Although I have to admit I'm still considering the cost vs. benefit....especially as they're quite costly. I'd do it in a heartbeat if I was certain there'd be an improvement in sound or overall health of the unit.

 

[Blue Shadow]

i got no idea how much better those would be than the ones that are 30000/100V/3" diameter on mouser for about a third of what those go for.

You might need to consider the inrush current and things that will see that spike if you go for caps that are 50% larger than schematic.

 

[Alobar]

Mine were not changed, just the driver boards, protection board and output transistors. It sounds so lovely right now I really don't want to go in there and mess with a good thing. But do let us know how it goes for you and what caps you went with!

 

[davstev]

Mine were not changed, just the driver boards, protection board and output transistors. It sounds so lovely right now I really don't want to go in there and mess with a good thing. But do let us know how it goes for you and what caps you went with!

I hear you on not changing them, especially since they are a bit costly. But logic would tell us that 45 year old electrolytics have degraded. I wonder if I'd need to readjust bias and DC offset after replacing them.

 

[playittwice]

Heres my take on this, if you're changing everything else, why not the filter caps too! Especially if you're doing it yourself, what you save on labor, spend on replacement components. Then you know its done and worry-free. Thats my philosophy.

Yes I would re-check bias and dc offset.

 

[Alobar]

I hear you on not changing them, especially since they are a bit costly. But logic would tell us that 45 year old electrolytics have degraded. I wonder if I'd need to readjust bias and DC offset after replacing them.

Heres my take on this, if you're changing everything else, why not the filter caps too! Especially if you're doing it yourself, what you save on labor, spend on replacement components. Then you know its done and worry-free. Thats my philosophy.

Yes I would re-check bias and dc offset.

I have looked back through all the many emails between myself and EchoWars and couldn't find any discussion on the big cap replacement. I am not an electronics guy, but I do have some education on this stuff from 35 years ago when I did an electrician apprenticeship, but that's it.. Anyway I have since worried a bit about replacement of these big caps. They are not leaking, or expanded, and the amp itself sounds excellent, so am not thinking about further sound quality gains, but strictly reliability. The 'what if' one somehow failed?

I had considerable hand holding when I was installing the new parts and I was quite nervous I was going to for sure smoke something! Now that EW has moved on I don't feel I can lean on him anymore on this as far as the filter caps go. But I do want to watch this thread and see what the results are with replacement. If favorable I will likely go ahead and order the caps and replace them myself. I have all the instructions for setting the bias, so that shouldn't be an issue.

For some reason replacement of these caps never got into the conversation with EW (that I can find through correspondence) so I guess I just figured they would be fine.. Or that they were not available in the rating required..

 

[davstev]

Heres my take on this, if you're changing everything else, why not the filter caps too! Especially if you're doing it yourself, what you save on labor, spend on replacement components. Then you know its done and worry-free. Thats my philosophy.

Yes I would re-check bias and dc offset.

When I recapped mine about three years back, I avoided the filter caps because it was going to be a $200 outlay. I think that was why I avoided it. Now that I've become accustomed to throwing way too much money at audio, it seems a lot more manageable :-0

I'm pretty sure I'll go ahead with it....just a matter of finding enough time to review my options, make a purchase, and do it.

Worry-free, I like the sound of that!

 

[davstev]

I have looked back through all the many emails between myself and EchoWars and couldn't find any discussion on the big cap replacement. I am not an electronics guy, but I do have some education on this stuff from 35 years ago when I did an electrician apprenticeship, but that's it.. Anyway I have since worried a bit about replacement of these big caps. They are not leaking, or expanded, and the amp itself sounds excellent, so am not thinking about further sound quality gains, but strictly reliability. The 'what if' one somehow failed?

I had considerable hand holding when I was installing the new parts and I was quite nervous I was going to for sure smoke something! Now that EW has moved on I don't feel I can lean on him anymore on this as far as the filter caps go. But I do want to watch this thread and see what the results are with replacement. If favorable I will likely go ahead and order the caps and replace them myself. I have all the instructions for setting the bias, so that shouldn't be an issue.

For some reason replacement of these caps never got into the conversation with EW (that I can find through correspondence) so I guess I just figured they would be fine.. Or that they were not available in the rating required..

I think there's a thread here on this very topic, which EW contriubuted to. I'll try to find it and post a link. Btw, he's 'moved on'? That's a shame. For us, anyway. He was impressive.

 

[gort69]

I'd replace them just on the assumption that eventually they'll start leaking. I'm working on a Model 600 that has one of the four leaking - they cause quite a mess and corrode the chassis.

 

[Alobar]

I think there's a thread here on this very topic, which EW contriubuted to. I'll try to find it and post a link. Btw, he's 'moved on'? That's a shame. For us, anyway. He was impressive.

Simply meant he is not active on AK any longer. My hope is he will come back, but he has written a lot here in the past, and the answers to my concerns are probably there somewhere..