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Basic C2 resto threads

rickl

rickl

I'm just a bass player
Subscriber
I recently picked up a C2 for my L-07M mono blocks. I can’t afford the L-07C matching preamp and found a C2 from a local AK member at a price I was willing to pay.

I checked it out on the bench and it seemed to work. I hooked it up to my test system (Marantz 250/Infinity speakers/Sony CDP-201) and wasn’t impressed. I tried my little Hafler and the (heavily modified) DH-101 sounded much better.

Time for an update.

I searched AK and found a few threads with updates/known problems and general listening impressions. Consensus is the C2 is a nice pre. Adding new opamps (with 16v Zener updates) and better coupling caps can really improve the sound.

For updates, Leestereo’s C1 thread seems to be the go-to with a lot of similar resto ideas for the C2.

Leestereo’s C1 resto

Kenwood Basic C1 Preamplifier Restoration/Upgrade

Patfont has a nice C2 thread with great pics

Kenwood C2 basic rebuild/refresh

vsat88’s C2 resto is a spinoff of the C1 thread above.

Kenwood Basic C2 Preamplifier Restoration/Upgrade

nadude's updates with Richard's suggestions.

Kenwood Basic C2 Project

Or for our German friends old-fidelity.de

And don’t forget our friends over on diyaudio (complete with more links and a possible pot replacement for the balance pot using one from a KA-51B)

Kenwood Basic C2 preamp mods

There seems to be a lot of problems with the balance pot and I found a few fix ideas.

C2 Balance Pot fix
Kenwood Basic C2 Restoration
and attempted fix and 180k bypass resistors
Help with C2 Basic Balance Pot

Joel_in_OK’s troubleshooting with tips on the balance pot fix

Troubleshooting my Kenwood Basic C2
and
Troubleshooting my Kenwood Basic C2

Dave's replacement pot Kenwood Basic c2 balance adjustment pot

Bert thread with great pics of the balance pot and ideas on several updates
My first Kenwood and first preamp : Basic C-2

Rakz's C2 with cap BOM of Mouser part numbers Kenwood Basic C2 recap BOM

Broesel02's Phono updates

Kenwood Basic C-2 restoration round 2

I did some work on this a while back and installed a bunch of stuff I ordered from DRM when they were still selling the stuff . Now the selector switch is acting up again after spraying it only . I will take it off and apart to clean it properly . And this preamp sounded good but I was thinking...
audiokarma.org

C2 output relay is either a 12v relay 653-G5V-2-DC12 or 9v relay 653-G5V-2-H1-DC9.

Dave99 op amp upgrade
D

Post in thread 'Kenwood Basic C1 Preamplifier Restoration/Upgrade'

I installed the Burson V7C (classic) from Bloom Audio for my C2. It was an instant improvement and more dramatic sound than replacing all the caps a few years ago.
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My plan is to update the coupling caps with bipolars or WIMAs, update PS with 16v zeners/caps, replace op amps with better ones and see how it sounds. I’m optimistic the balance pot won’t be a problem.

Hopefully I can fit this in with the customer gear on the bench and report back my impressions.
 
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Hello rickl,
ther are some more threads in german whith some stuff from my person. But your suggestion for a little brush up is not bad. And if you are not happy: come back, i have some more ideas

Richard
 
I might be back for more ideas. Last night I got the op amps (with sockets) and couping caps added (wima's, bi-polar caps). Need to get the 16v zeners added. I haven't decided if I'll update PS caps (I have them in stock).

I do have 5480DD and 2068DD op amps. I might play around with those too. Plus you give a few tweaks that I might try.

I want to give the pre a listen for a while before spending more time with updates. Summer is here so it is time to spend in the garage or at car shows, not in the basement slinging solder.

Gruß
 
balance pot is broken. I tried to follow ideas listed above to fix it but just ended up using the 180k resistors and removed the pot.

Added a few new caps, new sockets and op amps, 16v zeners while i was in there.

Hopefully I'll get it in a system and see what the hype is about.
 
I've have finally listened to this pre amp for a few days in the main system. It is nice.

I added fresh PS caps, 16v zeners, Wimas and bipolars coupling caps, 2068DD opamps and 33R for R61/62. nothing too crazy or costly.

my remote control trigger cables work much nicer than my other pre. I think the relay in the pre helps. I use a 12v automotive relay and a 12v wall wart plugged into the switched courtesy outlet. I'm using the remote control port to control the power amps. Works slick.
 
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Well, the honeymoon is over. I pulled the C2 out of the main system.

One channel is louder than the other. the other channel audio fluctuates and overall it seems to be more woolly or veiled than I remember when I first added it to the main system. I'm kind of disappointed. I haven't pulled the cover to check things out. The audio fluctuations almost seem like a cold solder joint. It takes time before the problems start.

This might be good time to get the balance pot working too.

I can tell you my little dh-101 sounds much nicer. It has been tweaked a lot so I'm happy with the main rig again.
 
Yeah me too just picked up a second one and plan on doing a full re-cap and change the op-amps/zeners out rebuilt my balance pot on my first c2 and it came out perfectly a dremel is a must for that repair keep us posted on results
 
please post your results. I'm thinking of putting my C2 back in the main rig.

Maybe I had an off day.

I posted this on the C1 resto thread but if you are in there, I'd suggest replacing the black foam blocks. Mine where crumbling and didn't want to get any of the foam bits in the controls.
 
Can anyone recommend someone to work on my C2 in the Los Angeles/So Cal area? mine has a channel dropping out, function selector drops channel some times, mono doesnt work. would like to get it back into top shape.
 
rickl said:
Well, the honeymoon is over. I pulled the C2 out of the main system.
Click to expand...

I found the problem with the C2. I used UVP bi-polars for the 47uF coupling caps (c19,c20,c23,c24). I replaced these with the pretty green ones (UES) and the C2 sounds much better.

I feel like a dope and not really sure why I have UVPs.
 
I have a question I see some Electrolytic are NP and some are just electrolytic can I use Bi-polarized or NP were it asks for electrolytic I hope i'm asking the right way
 
You can use BP anywhere polar capacitors are designated, as long as they match capacitance and voltage. However, these usually cost slightly more, are physically larger, and often will have marginally higher ESL. There have been cases when I've swapped in bipolars where there were originally polar caps, but it's unnecessary.

Rickl, are you sure swapping out those caps was the issue, and not perhaps that the rest "burned in"?
 
ajfink said:
Rickl, are you sure swapping out those caps was the issue, and not perhaps that the rest "burned in"?
Click to expand...

This was the only thing I changed.

It is a real PITA to swap preamps so I've been putting it off. The C2 has been in the workroom testing other power amps (m1, citation 22, marantz 250, and other low fi stuff) so I guess there could have been some "burn in".

I just like the C2 better now than I remember.

Phaceless56 said:
can I use Bi-polarized or NP were it asks for electrolytic
Click to expand...

@ajfink did a good job answering. I try to use film or NP for coupling caps and polars for everywhere else. Also try to find a similar restore on AK to follow.
 
Done I did a complete recap on my C2 and it came out great what I noticed right off was the mid-bass tightened up real nice and well defined I did have to turn down the mids on my Kappa 7.1. It sounds very clean is the best way I can describe the difference.I will try out the phono stage later today it was late when I finished. It was worth the effort also picked up another Basic M2a $75 during the week plan on recapping it some time in the near future
I replaced all the op-amps and zeners put them in sockets so I can roll some op-amps later I read about the Burson op-amps anyone have an opinion of these op-amps
 
Phaceless56 said:
Done I did a complete recap on my C2 and it came out great what I noticed right off was the mid-bass tightened up real nice and well defined I did have to turn down the mids on my Kappa 7.1. It sounds very clean is the best way I can describe the difference.I will try out the phono stage later today it was late when I finished. It was worth the effort also picked up another Basic M2a $75 during the week plan on recapping it some time in the near future
I replaced all the op-amps and zeners put them in sockets so I can roll some op-amps later I read about the Burson op-amps anyone have an opinion of these op-amps
Click to expand...

You picked up an M2A for $75!? That's a great deal.

I also would be curious to hear more opinions of the Bursons, since I'm also considering swapping in two V6 Vivids (can always resell them if I don't love them, right?). A number of reviews out there, but not so much C2-specific.
 
Phaceless56 said:
but has anyone used the Burson op-amp in there Kenwood Basic C2 phono stage ?
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I always wonder if updating the cartridge or turntable would also help. my west german thorens or empire 398 or Yamaha P would hold back any op amp updates. I think my maggies are the weak link in my system but I have some ideas for improving them. updating the pre is not in my plans.
 
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