Kenwood L-07CII Preamplifier Restoration
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- เผยแพร่เมื่อ 23 ก.พ. 2023
- Being the matching preamp to the L-07MII’s I recently restored, this L-07CII preamp received the same restoration treatment. Everything from input to output was overhauled, with no stones left unturned. I’m happy to have this video as a bookend for the L-07MII video as it completes the set.
Sorry for the extremely long-format video… I tried to condense what was done down to a video that would be palpable for most people, but a video pushing over 50 minutes was the best I could do. This restoration was an extremely long and comprehensive job, and even this video hardly shows low long it took to get the job done.
As always, I truly appreciate engagement whether it be a like or a comment on the video. I try to answer all comments too! Thanks for watching.
Relevant links for the Kenwood L-07CII:
Audio Database:
audio-database.com/TRIO-KENWO...
TheVintageKnob:
www.thevintageknob.org/kenwood...
HiFiEngine:
www.hifiengine.com/manual_lib... - วิทยาศาสตร์และเทคโนโลยี
Many salutes to your love and passion in restoring such amplifiers from the glorious past...over and above your technical knowledge and skills!! You make many people happy with your videos. Thanks a lot👌👌👍👍
Many thanks!
Thank you for taking the time to do this restoration and capture it on video, and share it with the rest of the world. I have owned many of the Kenwood L-series pre amps and amps and as a person who does hobby restoration, I ran into the same issues in trying to restore my MKI L07C... the traces lifted and I admitted defeat and ended up scrapping the unit. Damn shame because I got so many years (decades actually) of enjoyment. I also ran into the oscillation issues with the L07MII amps in where I immediately put them up for sale and reverted back to the MKI amps. Even with these issues, they are just such quality pieces of gear and they provide such a beautiful sound. Thinking back I want to say I've gotten about 30+ years of enjoyment out of them before parting ways and going with newer equipment. I ended up replacing the L07C with a Sony TA-E88 which I feel is superior, but still the Kenwood stuff is just great. Thanks again for the video and hard work, it shows!
What a transformation! Excellent work.
Nice video, enjoyed the detail. I think that releasing a single video is better that's searching for all of the episodes
Glad you enjoyed! Cheers!
Love it! A pleasure to watch these amps get restored! And longer the better, look forward tobthe next one.
Thanks! More to come soon 😃
Wow! Incredible restoration. Love the attention to detail.
Thank you! Cheers!
Thank you for sharing and explaining what you're doing. You do a great job filming this. And the tools you share. You're an asset to this field and vintage audio all together. Very professional. 💯
Glad you enjoyed it and found it helpful! Thanks for the kind words 😊 More to come soon.
Great work and thanks for sharing your experience. I’ve been working on gear for about two years and I agree with your approach of replacing to avoid issues rather than only fixing things that have failed. I note the occasional comment from those who believe the opposite.
A couple of things I do as a matter of course, one electronic, one cosmetic. On the rectification circuit, I add R-C snubbers, using price appropriate capacitors and resistors. The switching noise drop is significant in most cases and clearly audible. Having said that, I did have one CD player where it wasn’t the case, so it’s not a universal solution if the circuit already contains suitable noise suppression.
On the cosmetics, it involves addressing the scratches on the paint. I use automotive touch up paint in either a brush form or, if the case has many scratches, I respray it, having first flatted the scratches out with abrasive paper of increasingly fine grades, finishing at 600. It many not be original but it looks factory fresh.
Thank you for the support! Keep up the great work yourself!
What a good looking piece of gear. Glad to see this vintage piece get some work done!
Me too! Thanks for watching 😄
Great video! Always impressed to see what goes behind your restorations, really gives insight to how tedious the process is and makes you appreciate well done work. Getting better every time, nice job man!
Thanks homie, much love ❤
Wow ! Impressive restoration ! ❤
What A fabulous beautiful restoration, what a credit to you. Exceptional.
Another fabulous restoration. Well done king👑
Thanks homie
Masterpiece
Wow amazing restoration 🙏
Excellent work!!
Amazing job and absorbing video.
Thank you! 😊
That was quite the project, great video!
Thanks!! Glad you enjoyed it 😄
Stunning work!
Thank you! Cheers!
Amazing restoration......Congrats man !!!
Thank you so much 😀
@@PrimeHiFi can you please give me your email address....???
Hi, my contact information can be found on my channels “about” section. Thanks!
wow , looks like a fun job.
Very nice work again
Sounds very good...
Great video Connor
Thanks Burt!
Very impressed with your attention to detail! Hope you own your own shop and passing along some skills to others! And I hope your making the money your skill deserves.
Thanks for your support! I do this as a hobby, so no shop -yet-... Thanks again!
Excellent restoration!!! Tee-Jay was right..your skills are top notch.
Kensonic ) Jiro was one of the best Audio engeeners of his time and founder of Accuphase ,Jiro believed in high quality componetes just like the founder of Sansui Mr Kikuchi . Great Job !!
Thanks TeeJay! Kensonic/Kenwood/Trio was one of the best 😄
Très bel appareil, Kenwood démontrait là son savoir faire concernant la Hi-Fi de très haute qualité, merci pour ce reportage ! 😉
Great work.. gotta love some Nichicons
Thanks! Nichicon are some of the best!
Hi Connor
Excellent restoration. It's definitely not a 'run of the mill' kind of work. A lot of thought has gone into it. Never knew people with such passion, skills and patience existed. Congrats sir
What were the diodes, zeners or transistors replaced in this restoration. Please share location and what has been used.
Regards
Miracle Worker.... Amazing.... !
Excellent restoration. I enjoyed this video. I would have loved to see the process of defluxing the board and the chemicals used. I was amazed at how good the board looked after you cleaned it up. I would love to learn that process. The board looks better than factory. I have a L07C mark 1 that I will be restoring soon. Im not looking forward to the double sided solder and weak traces lifting.
Thank you! I have an explanation in my AU-717 video that details the defluxing process. - The L-07C Mk1 is a fair nightmare to work on. Most traces will lift, as they did with me... And I'm about as careful as someone can get with board rework. The traces seemed like they were held down with spit!
Wonderful and clean job, some good ideas to do in my one L-07CII. I have to check the other comments of you already answered but I will like to know the reference for the new voltage regulators and the new feet. The metal polish really enlighten me. Thanks!
Thank you! The regulators are MJE15032 and MJE15033 respectively. They work very well in this application. Much cooler running. The aluminum feet can be found on Amazon. I will see if I can find them and link them in another comment. They are very nice for the money! Oh! And the metal polish I use is called Simichrome. Use it sparingly and lightly with a microfiber cloth - be very careful on anodization and silkscreening.
@@PrimeHiFi Thank you very much! I will change the regulators in mine, I wonderful improve to cool down the unit a little bit. I will also look for the feet's also. And yes, the metal polish is already in my shopping cart.
Just saw you your great video! Upgrade the fuse!! Synergistic purple, you will be astonished!!
Very nice. Yes, very nice. 😁
A real neat job ! Why are most of the capacitors raised up ?
Thanks
very good job! congrats! I wonder how did simichrome not removed the letters on the face plate? isn't that abrasive enough ? thank you !
Thank you! With light pressure and extreme care, it will not damage a faceplate. You mileage may vary...
Wow what a restoration well done
.how many houra work do you estimate in total? Im soon to have one and would like this work done but im in the UK and need to understand the hoursbto work out whatva engineer would charge iver here for the job..and the parts cost too please? Many thanks
I had to clean up & re-cap some boards on a vintage SONY (TA-2000f) pre-amp.
They were all plug-in boards so it wasn't that hard to work on each board.
I've used old analog TV "Contact Cleaner" for the boards and pins.
dam i wish u lived near me or in my country lol u would have been my go t o guy this workmanship is top class
Wonder whats the difference in sound before and after restoration? I have this preamp..Thanks.
Hello, I have a Kenwood L-07CII too and would like to know what this level of restauration cost.
When you are reflowing the board, what temperature do you have your iron set to? thx!
Generally, 400C.
Hi. Where did you purchase the solid aluminum feet for the Kenwood L-07MII Power Amplifier?
Hi, I purchased them on Amazon 😊
Hello!
I enjoyed watching the videos on Kenwood L-07CII & 07MII maintenance. I now have the opportunity to purchase the complete set - TRIO L-07CII & 07MII (exactly Trio). But they will definitely need a maintenance, since the condition is from the manufacturer, 50 years ago. I don’t know how to do this myself, but I want to give it to a specialist. In this regard, I have a question: could you send me a list of those parts (if you still have them) that you replaced in those amplifiers? So that I start looking for them in advance, since here we have a difficulties with this. Will there be a big difference in the components of Trio and Kenwood? I would be very grateful. If necessary, I will write my email. Thanks in advance.
Very nice work! I just finished a Mark I trio (07c and pair of 07m monos) and a trio of the Mark II (same, L07 series) all for the same client. I did roughly the same work, but may I ask, what made you decide to go ceramic for the black flag replacements? Strictly cost?
Any reason you chose not to eliminate the tantalums? This era of tantalum is known for growin tin whiskers and will eventually short. I’ve run into tantalums that have shorted in this series.
And yes, for such a nice preamp that grounding design for the RCAs is one of the worst I’ve seen. I replaced them on the Mark II preamp I just did as the grounding was very intermittent.
Any info on those bookshelf speakers you were using at the end? Just curious as to what they are.
Hey Dan!
I went with ceramic capacitors as they are extremely reliable and are available in precision tolerances. These caps aren't being used in the signal path, so no need to go too fancy with them. I could have gone with silver mica, but there would be no real added benefit, and they cost much more.
I didn't replace the tantalums in the tone stack as I've never seen tantalums with very low applied voltage go bad. In retrospect, I should have replaced them, but they should be just fine for this application. Yes, one of the L series' downfalls was their terrible ground implementations. The idea was good, but execution was poor. It's what kills most of the L-07M/IIs. That and black flag capacitors. The speakers at the end are the Snell Type Q.
@@PrimeHiFi very cool, thanks for the answer. By the way, after watching your video I collected the two preamps back from the client and installed shielded coax as you did from the output RCAs to the pins for the harness. For such a nice preamp it’s weird that they’d use what looks to be cheap looking speaker wire for the outgoing signal.
Looks almost exactly the same as an Onkyo I had many years ago. I recall the Phono input was a little on the noisy side. Not watched the video yet, be interesting if you find this one noisy.
what do you use to deflux? i tried alcohol, but had a really hard time getting the flux off the board, it will always be sticky afterwards.
Acetone.
I recommend using 99% isopropyl alcohol and a stiff brush. It usually takes me multiple stages of cleaning to get them completely clean. Stay away from harsher solvents like Acetone as they will destroy plastics and remove the color bands off of resistors and silkscreening.
@@PrimeHiFi thanks, im trying to get into restoring amplifiers as a Hobby, so your Videos are highly appreciated. it would be awesome if you could show the process of some operations, like how to decide which caps to use for recap (when wima, when electrolytic, when bypass). thanks alot :D
Would metal clad caps be better .
👍👍👍👍👍👍👍👍
Really convenient tool, the Erem 554tx. BUT its price is 130$ and upwards, for this form plier for passive components legs.
Was drooling over your toolbox with weller special hand tools.. got sidecutter and fine plier, but the cost is out of this world as hobbyist..
Check out hakko, they sell similar lead forming tools on their website for 20-30 bucks, I have a few. They import them from some Italian company named Piergiacomi
I agree - they are very expensive. I’ve bought them slowly but I use them all the time. The quality is worth the price of entry for me, but I totally get the opposition when other tools will get the job done too. The internal springs are what seal the deal for me. They’re just awesome. I was planning on doing a short video on the tools I use regularly for restoring and repairing equipment. I have a ton of specialty tools. Thanks for the feedback!
Are not polystyrene caps considered "use for superior sound quality" NOS is still available in canada. Same source has polyprop radial caps. Would not the polystyrene been used in the signal path
PartsConnexion.
I'm a firm believer in film cap use. Ie Sansui B2101 C2101.
I dont think the traces have started bubbling, I think they were like that from new. Lots of old 8 bit computers are like that and they were like that from new.
This was common on Spectrum, Commodore machines even upto the Amiga era with memory expansions.
Yes many pcbs of this rea looked exactly like this from New
I think they they solder flashed the whole copper area of the board before solder masking and subsequent processing such as wave soldering caused the solder to bubble under the solder mask giving that nasty appearance.
Great vid once again, mate. I appreciate that you take the time to show the handy tools you use in your resto's. The wire unwrapper and top flush cutter have given me tool lust ( ͡° ͜ʖ ͡°)
Love your thoroughness and drive to do a quality job.
Thanks! I was thinking about doing a video focused on the tools I use for working on gear. I have a ton of specialty tools I use on a daily basis. Thanks for the feedback 😃
@@PrimeHiFi great idea - I'd absolutely watch that. There's a couple of guys that review high quality exotic tools; mostly from Japanese makers like KTC / Nepros and Koken etc but a lot of it is gear I'm not likely to use very often (e.g. socket sets). The stuff you use is right up my alley I reckon - I just need to exercise some restraint or I'd likely go broke.
My SANSUI AU 717 special snacks on Kenwoods🌚
I have the same preamp I would love to sell it
It's sad to see such a top device from Kenwood being built with such cheap electrolit condensers
Việt nam ok nam👍👍
My opinion - Obsolete. The power supply just isn't clean enough on the output.
If it's not broken, don't fix
regards face plate, after cleaning have a try WD40, I’m using it on brushed aluminium and plastics, it makes black blacker and, in many cases, eliminate the stains which remain after cleaning or old discoloration. have try on any as experiment and you’ll se the different.
The camera moves too fast and too frequently