Kenwood Basic C1 Preamplifier Restoration/Upgrade

Here are a couple of photos. The 2 caps with the marker on top (C25-C26) were the 2 I ordered incorrectly and still the originals.
 

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I just completed the mod. All I can say initially is Wow, what a substantial difference in the sound. I listened to some FM and 2 albums (Heartsfield and the Beatles blue album). Vert crisp, clean highs and smooth bass...

Happy to hear that your C1 restoration/upgrade went well. I wholeheartedly agree that the sound improvement is quite significant.

My only issue I had was I ordered the wrong caps for the Flat amp C25 and C26 so I reused the original caps. I checked and double checked the list before I placed the order with Mouser and still missed them; right size wrong type (should be Nichion Muse). I don't know if the originals have that much effect on the overall sound. I will order the correct ones with my next order and replace them. One other notable issue are the 1uF Panasonic stacked polyester film capacitors are no longer available. Neither Mouser or DigiKey carries them.

The capacitors C25/C26 are the final output coupling capacitors and should definitely be upgraded to Nichicon ES bipolar types (or equivalent); the improvement in sound will be readily noticeable. For the 1µF stacked film capacitors, one can use the Wima MKS2 equivalent or the Kemet R82 equivalent (both are available from Mouser).

I also want to thank Leestereo for all the upfront work to make this mod a reality. Thank you.

You are very welcome, and I thank you for posting your impressions.
 
dave99, no problems and thank you huge ! I am retired so time is all I have on my hands,,Well, that and the new interconnect using SpeakOn connectors I just built for the Polk SDA IIb's . M2 is run with the Sigma Drive to them : )
 
Thanks leestereo, good info to have. I'm ordering some caps for my RT-707 reel deck and will include the c25/c26 bi-Polars in the order.
 
Went over some of my old notes on the Kenwood C1 restoration and there are 2 small electrolytic capacitors (0.33µF) in the subsonic filter that can replaced with same value stacked film types (as of today, Mouser still has some stock of the Panasonic ECQ-V1H334J).

 
In fact I just noticed those today and wondering on the replacement. I'll put those on my order for tomorrow. Thanks
 
For those following this thread I placed my order for the additional Muse ES bi-polar caps for C25 and C26 (that I mis-ordered) plus the 2 new ones by the subsonic filter switch C18 and C19 last night. Once I get those replaced and do another "sonic sound" check :) I'll upload the completed component list. I'm thinking by Friday it will be available. I hope the delay is acceptable.
 
Don't
For those following this thread I placed my order for the additional Muse ES bi-polar caps for C25 and C26 (that I mis-ordered) plus the 2 new ones by the subsonic filter switch C18 and C19 last night. Once I get those replaced and do another "sonic sound" check :) I'll upload the completed component list. I'm thinking by Friday it will be available. I hope the delay is acceptable.
Don't know if you got it Dave but I sent you a PM
 
Sorry I am out of town on business and haven't kept up with my emails. I have another C1 I'm going to mod, plus recap my M2 and it has several 1uF 50v, plus my RT-707 reel needs 4. I am going to hang on to these. On eBay they are 7.99 for 25 that may be better for you if you are modding 3 plus having some spares.

Dave
 
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Sorry I am out of town on business and haven't kept up with my emails. I have another C1 I'm going to mod, plus recap my M2 and it has several 1uF 50v, plus my RT-707 reel needs 4. I am going to hang on to these. On eBay they are 7.99 for 25 that may be better for you if you are modding 3 plus having some spares.

Dave
Sounds good Dave. I was just gonna take em off your hands if you had no use for them. Will do on your above recommendation.
 
Turns out I have to take a trip to the U.S. in two weeks - my route *could* take me through Thief River Falls (home of Digikey) - seriously considering picking up the parts on the way through.

I'm *assuming* that the biggest bank for the buck is doing the C1 updates? Looks like the M1 updates (even though there are fewer parts) are more complex.
 
I'm *assuming* that the biggest bank for the buck is doing the C1 updates?
I have often found that the preamplifer impacts the final "sound" of the system more than the power amplifier. In this particular case, the changing of the active devices (the op amps), probably accounts for most of the improvement/change.

Looks like the M1 updates (even though there are fewer parts) are more complex.
If the main power capacitors are retained, the updates to the amplifier board are quite easy to do and the solder side of the board is more readily accessible in the M1 compared to the C1.
 
I'm putting together a parts list for this and I noticed a discrepancy.
C5 and C6 in the Flat Amp Stage are 10pf not 100pf, according to the service manual (and actual unit). And C9 in the photo is really where C5 is.

Should C5 and C6 be upgraded to 100pf, or stay 10pf ??
 
C5 and C6 on the Tone Board (the low pass input filter) are indeed 10pF; that was a typo on my part. Same for the C9 label in the picture.
 
Here is my BOM for this project.

The attached text file is labeled with the part designators from the service manual.
I've added TA for the Tone Amp Section and PRE for the Preamp Section (phono).

I've also added a part number for the relay, since I'm having issues with the one in my unit.


Copy and paste this into Mouser's Parts List Importer

647-UES1E470MPM|2
575-113308|4
647-UPW1H010MDD|2
647-UFG1C221MPM1TD 2
667-ECQ-V1H334JL|2
505-MKS2B043301HJSSD|2
647-UPW1C222MHD|2
581-SR151A101JAR|2
513-NJM4580DD|1
647-UPW1V221MPD|2
647-UPW1V101MPD1TD|2
78-BZX85B18|2
603-MFR-25FBF52-56K2|4
581-SR151A470JAR|2
647-UES1H220MPM|2
581-SR151A100JAATR1|4
581-SR151A680JAATR1|2
505-MKS2C041001FJC00|10
513-NJM2068DD|2
512-UF4005|2
78-BZX85B16-TAP|2
647-UPW1C101MED|1
647-UPW1C330MDD|1
647-UPW1C470MDD1TD|2
647-UPW1E471MPD|3
647-UPW1V222MHD|2
653-G5V-2-H1-DC9|1
 

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I'm not quite finished with it yet. But before I noticed that the phono section sounded kinda lifeless and dull compared to my Marantz 1060 (using it as a pre).
I will keep ya posted.
 
I've been listening to this unit for a couple days now, and the improvement is quite dramatic. The sound stage seems deeper and wider on both cd and phono. Nice tight bass and more detail in the mid to high end.
The phono section is much improved, with more definition throughout the range. Seems to be a good match to the Ortofon OM10 I'm currently using.

This was well worth the time and effort, and the cost was pretty cheap even with replacing the relay, under $40.

One word of caution.
The subsonic filter switch is kinda delicate and comes apart pretty easy when manipulating the board around. Be careful not to bump it around to much.

Thank you Leestereo for this wonderful mod.
 
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