Krell KSP-7B, recap or not?

[deerhunt]

I need some advise about the topic.
After trying to find relevant and trustworthy information about any sonic benefits, I came out short.
From "I got a completely new preamp" to "if it works, don't touch it".

I opened and had a look. I already done some changes like replacing volume pot with muses and bypassing gain, balance, phase .
When inspecting I only see one cracked Roe and no leakage.

About the sound, my impressings are that it lacks air and openess in the higher frequencies compared to a DCB1.
But perhaps thats the design itself?
In the bass it's somewhat "stiff" and a bit focus on midbass I would say.
However, it has a nice analogue sound and more width and depth that the DCB1.

Please advise - is it worth the time and effort?
If yes - what (resonable priced) caps do you recommend?

 

[deerhunt]

The silence from the community made me go ahead and order some Panasonic FC...

 

[analog_sa]

FC will dramatically alter the tonal balance imho. It may be for the better, the old bakelite Roe always sounded too dark to me. To keep some semblance to the original sound I would have used fine golds.

 

[deerhunt]

Thanks for your input!
It’s actually the dark tone that is one reason for the swap. I’ll get the FC:s from Mouser end of next week. Let’s hear the outcome but a bit brighter might suit my system well.

 

[deerhunt]

I got some Nichicon MPH. Any ideas if that’s a good replacement for the Electrocube?
Or some other film cap that is recommended and fits in the box?

Thanks

 

[mkc]

Hi deerhunt,

I don't know if you feel like reversing the circuit and draw a schematic? Or perhaps take a bunch of close up photos of bottom and top-layer so we perhaps could revserse it using them?

 

[jean-paul]

Hi those ROE are notoriously unreliable certainly in a warmer environment. I would replace them all. They have a cult following as usual with bad quality stuff but these guys apparently don't repair devices. I know some replace the ROE for NOS ROE to keep the device "original" so changing a flat car tyre for another flat tyre. All I can say is that I started cap replacement long ago specifically because of these ROE EK types. They like to identify themselves as resistors.

Panasonic FC are so good and so affordable that they are victim of their own success. I think you can't go wrong with them when compared to the ROE.

Why would you replace the Electrocube film caps? They fit exactly and these are not known for failure are they?

 

[deerhunt]

I’m not going to draw a schematic, but if someone’s interested I’ve attached 2 pictures.

Thanks for the ROE information. Feels good to know the FC:s should suit well.
The Electrocubes will stay until someone persuades me otherwise.

I tried a couple and the fall out nicely when heating both pads. Measured both and my Fluke says about 1100uF. So a bit more than specs.
Is that normal? Can’t measure esr unfortunately.

 

[jean-paul]

Electrolytic caps are known for high tolerances like -20/+50%. Nothing to worry about. When even a few of the ROE behave like resistors you know for sure you've done the right thing. Your DMM will measure that.

I recall reading here that the ROE were quite low ESR (never bothered to look into that as they work like a red cloth on a bull when I see them). Well so are the FC so things will work out.

 

[deerhunt]

Work in progress…
No damage to the board. Just have to put it all together. Fingers crossed!

 

[jean-paul]

Looks good. I pre-tin the lead wires, bend them slightly, cut them first and then solder them for slightly nicer looking joints (of course with 60/40).

We learnt to cut first and then solder to prevent mechanical stress on the solder joints.

 

[deerhunt]

I get the benefit of pre-tin and cut leads before mounting. Means you need to physically hold the caps with one hand and solder with the other?
I also use 60/40 - love how it flows and becomes very strong, almost a glueing effect.

 

[jean-paul]

Yes. Not a problem when working with the device standing on its side. When you bend the lead wires after inserting and cutting you can do it as used to.

They won’t fall out.

Some detest the bending but I feel better knowing the lead wires make direct contact with the pads and not via just solder tin.

 

[SCompRacer]

Back in 2016 I recapped this old KSL with MM/MC phono board. The phono board is the one they used in the stand alone KPE phono stage. A friend suggested using United Chemi-Con caps. Sounded great, no more hum. I can't comment on any sound change as it hummed badly before. Sold it to a friend, still in use today.

The phono board was really noisy and had excessive DC in one channel output. I had to remove and test all the transistors on the phono stage and replace some bad ones.

 

[deerhunt]

Thanks for your feedback!
Running now since one hour! Happy so far. Quite clear that dynamics and transparency in the upper frequencies has improved!

 

[jean-paul]

Disturbing WAF with those nice loudspeakers

Well, the set as a whole looks impressive.

 

[SCompRacer]

Isn't it great when something you work on still works and is improved? lol Nice system! I spy an old KSA-50. I have a KSA-250. (Our cat likes it hot).

 

[deerhunt]

You have to keep both wife and pets happy right