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Kenwood L-07MII Power Amplifier Repair and Restoration
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Жыл бұрынBeing one of my biggest restoration jobs to date, this beautiful pair of Kenwood L-07MII amplifiers needed a lot of work. Virtually no stone was left unturned. Everything from rear I/O connector replacement to the replacement of almost every capacitor. Also addressed were the issues pertaining to the stability of the high speed circuit. Specialized care and maintenance like this is seldom found, and is never cheap. This job took hours and hours, and I tried my best to condense what was done down into a video for KZfaq.
Thanks for watching, please let me know what you think! Don't forget to like and subscribe for more content like this!
EDIT: A kind person from another form (Restorer-John) brought my attention to the full power test, stating that the output power I achieved was low, and that the asymmetrical clipping was also not normal. I set the amplifiers back up on the bench and retested at full power. This time, both amplifiers achieved 190W/8r @ 1KHz, and 294W/8r @ 1KHz. Also, no asymmetrical clipping was noted. I’m not sure what happened on the video, but if you video something like this, chances are that Murphy’s law will kick in and screw things up. Sorry for the confusion, and thank you John for bringing my attention to this!
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Relevant links for the Kenwood L-07M / L-07MII:
The Vintage Knob:
www.thevintagek...
Audio-Database:
audio-database...
HiFiEngine:
www.hifiengine...
"Black flag" polystyrene capacitor replacement information:
conradhoffman.c...
@AudioElectronicsChicago Жыл бұрын
You find the rarest items on earth! These are great amps!
@talathussainkhan9052 Жыл бұрын
If only I could send you mine.. Ao. Scared for my own project. You did a lot lot more than just recapping and cleaning. I have no idea about all of the smaller components. I need prayers.. Lots of prayers.. Going to have many sleepless nights 😳🙄
@michaeljones19731 Жыл бұрын
Hey Connor! As soon as I had seen your new uploads , I saved them until I Had time to sit & Watch without any disturbances.I always enjoy seeing where you’re next purchase or project takes you. You have great taste & your Workmanship is impeccable. 🎉🎉🎉With all the craziness going on in the world right now ,viewing you’re content & similar is like meditation for me. Good Music , Good Sound & finding & playing on decent components is like my therapy to escape the daily rat race. 😊
@PrimeHiFi Жыл бұрын
Thanks for the kind comment and continued support! Glad you enjoy my videos! There will be more to come soon.
@michaeljones19731 Жыл бұрын
@@PrimeHiFi I'll look out for them Connor! 👍🏻😃🎉
@wonghongkong3206 Жыл бұрын
This not only time consuming but with lots of capabilities and knowledeges. Good jobs. Thanks for sharing.
@uglsas Жыл бұрын
I just finished restoring something similar with same transition from to-3 to to-3p - Sansui AU-X1. I have all 12 original to-3 but didn't want to risk using them. The sound this amp produces is ..... speechless
@zoinkz8188 Жыл бұрын
Awesome work on all fronts, Connor! From the restoration itself, to the camerawork and insight you provided about the amps and process. Your best work to date, can't wait for more.
@PrimeHiFi Жыл бұрын
Thanks homie ❤
@cpg8000 Жыл бұрын
Wish Kenwood still made amps like this. They were a fabulous manufacturer.
@johnroberts4571 Жыл бұрын
Young man..mad respect to guys like u..this is becoming A lost art.. I have a couple of brothers that are also really good at doing this stuff.. awesome video.. thank you for it.. keep up the good work...
@PrimeHiFi Жыл бұрын
Thanks for the kind words. Glad you enjoyed it. There will be more soon!
@lucasrem Жыл бұрын
Japanese AMP on 120 V is a museum Multi phase is the solution!
@wayneg296 Жыл бұрын
👍👍😎✌️🤟 ⭐️⭐️⭐️⭐️⭐️. Better than new. Wish you were located near me! Love to have some old favorites renewed.
@vprosperi Жыл бұрын
Wizard!! The high power transistor replacement. A beautiful device. Thanks for sharing!
@PrimeHiFi 10 ай бұрын
Thanks for watching! Cheers!
@ixfxi 2 ай бұрын
I have had many, and I mean many of these amplifiers... they are fantastic. Unfortunately, the MMII are the worst of the bunch given their defects.... but its great to see that you have come up with a solution for servicing and repairing them. This looks better than new. Over the years the MKI amps were the ones I held onto the longest because they did not suffer from these defects. I was fortunate enough to also own several L09M amplifiers which were built like tanks, but I eventually sold them as they did not perform well at low impedances. L07/09 are absolutely fantastic amps though, if only there were more qualified/skilled technicians out there capable of servicing them..... and enough people with fat enough wallets willing to pay. Really great work though, impressive!
@willemanuel6136 Жыл бұрын
Fabulous work as always. Can't wait to hear a pair myself.
@PrimeHiFi Жыл бұрын
Thanks homie. Soon!
@grattanvaz1614 Жыл бұрын
Love the amp and the construction. Pretty unique for its time. You restoration job also superb.
@PrimeHiFi Жыл бұрын
Thanks! Glad you liked it.
@stevieg2755 Жыл бұрын
Amazing,its good to know theres craftsman like you,all that effort and UPS will drop it anyway
@glenz1975 3 ай бұрын
Great video covering the LO7's. I rebuilt a pair of these a couple of months ago and mine did not have the black flag capacitors just had standard polystyrene types. They are an interesting design construction wise and I found them easy enough to work on. I did find some of the original electrolytic capacitors were actually starting to leak out around the pins (The LO7 preamp was quite bad in some areas due to these caps leaking not to mention that dam glue and this was loaded with blackflags) I love your TO3P modification thats so ingenious and looks very professional. I have I've been restoring vintage audio for years and a new sub to your channel. You do some amazing work and look forward to future videos. All the best! 👍
@Ezees23 Жыл бұрын
I'm lusting for these that I don't really need and probably can't afford. Great work my friend.
@ThomasAndStereo Жыл бұрын
Hey Connor, this is impressive, I wish I had your knowledge and skills.
@PrimeHiFi Жыл бұрын
Thank you Thomas! That means a lot. I’ve watched your videos for a long time now. Cheers!
@Soundfreeek Жыл бұрын
Awesome video ! I have 2 pairs at home waiting for restoration... Can't wait to start the work...! You are inspiration to me ! Thanks !
@PrimeHiFi Жыл бұрын
Thank you! Glad you enjoyed the video. It’s what keeps me motivated to upload. Good luck with your pairs!
@NevynBrett 3 ай бұрын
Such amazing workmanship! A true master! I need my nad 3020 restored but I live in South Africa! But man, I want you to do my restoration
@Stelios.Posantzis Жыл бұрын
Great restoration video. Very thorough overview of the restoration. It's great to see all the details involved. I like the hifi stand at the end. Very fine - very stylish.
@PrimeHiFi Жыл бұрын
Thank you!
@adrieltzu3565 Жыл бұрын
Beautiful work man. It makes me wish I had learned to do stuff like this when I was young given my interest in HIFI. Lol, oh well.
@antizurdosprogresistashern9124 Жыл бұрын
Que Hermoso Amplificador de potencia, Kenwood,Es una gran marca de AUDIO,Lastima que en América latina no llegaban ese tipo de línea,Solo conocí Amplificador receivers,Minicomponentes,car AUDIO o Estereos.Gran trabajo de restauración,felicidades
@cabronesse386 Жыл бұрын
Oh gosh so much love and dedication like it was yours! Love it man! I wish I was that friend of yours. Kudos to you!
@milosevicbojan07 Жыл бұрын
Nice! I like demo,you should always record demo ! sound is really, really good!
@luismelendez5747 Жыл бұрын
I've been wanting to work on a pair of these myself so, I really appreciate seeing that you've gone through the process. It looks relatively straightforward but.. it's just so much work! Thanks for taking the time to document. I'd be curious to find out how much you paid for all the parts and such. If you had a bill of materials that would be amazing. Your friend is lucky guy.
@PrimeHiFi Жыл бұрын
Glad to hear you enjoyed it and found it helpful! That’s why I make these videos. Parts cost for these was roughly $500 including the high end inputs and outputs that were retrofitted. I don’t have a parts list available, but the service manuals are readily available online in which you can find every part needed. Cheers!
@alfonsodelafreg259 Жыл бұрын
Nice work. I had a pair when they were relatively new, way back when. They did sound good, when they worked. I don't remember how many times I had to fix the POSs. I traded them in and good riddance. Don't worry, they won't let you down. They'll break again soon enough.
@acme.videos Жыл бұрын
Wow excellent restoration! Thanks for the painstaking effort on documenting your excellent workmanship!
@PrimeHiFi Жыл бұрын
Glad you enjoyed it! Thanks!
@IqbalKhan-hc1hv Жыл бұрын
Restoration is back breaking job, well done 👍
@franciscorompana2985 Жыл бұрын
Good work. Your explanation is zen for my mind. Congratulations from Portugal. 🇵🇹
@snhongo1 Жыл бұрын
nice work on the power transistors on the heatsink
@michaelbyrne8860 Жыл бұрын
In my minds eye this what I envision when I take my vintage electronics to be repaired and calibrated! But in my heart I feel some soldier monkey just sprayed deoxit in to the pots and cleaned up outside and charged me $300.00 and call it repaired! That type of repairs & replacements are worth every penny! Like a good mechanic they're what ever they charge? Plus a tip! Great sound! That's why I love the vintage stereo equipment! Thanks gonna play the music again! Funny I just bought a used Kenwood dual Cassette player w/auto reverse out a Goodwill bin for $3 or $4 plus some other junk I don't need! And played Cassettes today in both sides and played & sounded like a champ! I forget about the Kenwood quality in their vintage stereo equipment ?!
@Casualfulltime Жыл бұрын
Thanks for a great fix!
@mangojassal Жыл бұрын
👍 from the 🇬🇧 excellent video and workmanship
@syhi7971 Жыл бұрын
Foxwarren. Good Album. Nice job. Restored a reVox A740 this week. So satisfying to work on nice gear.
@BoBo_huh Жыл бұрын
Amazing work as always. Luv to see videos like this
@PrimeHiFi Жыл бұрын
Thanks boss
@pliedtka Жыл бұрын
Raleigh and Spencer sounds really good on your system
@Jason-zh7wo Жыл бұрын
Nice job, they look great 😀😀
@riclambert4291 Жыл бұрын
just found you channel. good work I will be back
@MrBillsmith60 Жыл бұрын
Nice work Conner, your an artist
@PrimeHiFi 10 ай бұрын
Thank you! Cheers!
@billklement2492 Жыл бұрын
Nice job! Great info if I get around to doing mine. At least I know to replace the Black Flags before I power them up again! Thanks for the video!
@PrimeHiFi Жыл бұрын
Good luck with yours! Glad you found the video helpful 😊
@batmanthinks Жыл бұрын
If i may ask, how much does a restoration job cost? This is really good work.
@PrimeHiFi Жыл бұрын
Repair and restoration prices are established on a case by case basis. Good work isn’t cheap and cheap work isn’t good 😊 Thanks!
@batmanthinks Жыл бұрын
@@PrimeHiFi while not exactly the same, I collect antique books, some centuries old, and i always bring them in to this library that does book conservation. I'm always amazed at how amazing the books turn out after conservation. This has a similar feel to it. You're definitely right. Good work isn't cheap and cheap work isn't good.
@GBAL42022 Жыл бұрын
Wow amazing !!!!
@IamWhoIam2023 Жыл бұрын
$2500 on ebay
@anonymousmc7727 Жыл бұрын
200.00
@1957CRAZYDJ Жыл бұрын
Very professional work
@thom9106 Жыл бұрын
Nice!
@Stelios.Posantzis Жыл бұрын
5:03 That's a brilliant idea!
@justicelut Жыл бұрын
Beautiful work, well done!
@rainman3269 Жыл бұрын
Very nice and comprehensive video ... Awesome work Brother ... 😎
@Nalinc33 Жыл бұрын
Wow. Excellent job. You r a real Pro.
@montech5647 Жыл бұрын
Insanely beautiful
@hyperuso800 Жыл бұрын
TORIO L-07MⅡ very nice sound.
@chrisgrenga1595 Жыл бұрын
Best hifi restoration channel on youtube By Far. Detailed explanations, well shot, and immaculate work station. Connor, how does one acquire the skills and expertisd to diagnose and repair these electronics? Are you an electrical engineer by background? Thanks
@PrimeHiFi Жыл бұрын
Thanks for the kind words Chris. I’m slowly trying my hand at making videos like this. I have some bugs to iron out, but judging by the feedback so far, I must be doing something right. I am not an electrical engineer, but I have been interested in electronics for as long as I can remember. I started working on my own equipment a few years ago and slowly started to take in work. I am an aerospace engineer / A&P full time and do this work on the side.
@GBAL42022 Жыл бұрын
@@PrimeHiFi Wow this is a side job !?! ...Simply amazing !!!
@chrisgrenga1595 Жыл бұрын
@@PrimeHiFi outstanding. I look forward to watching and learning from future videos. Thanks for the time and effort you put into these.
@mauriceclemens3286 Жыл бұрын
I have the same Chraftsman Machinists tool chest. Bought it in 1977.
@hom2fu Жыл бұрын
i heard if you have 20+ years car/truck, you need to replace the cap in the ecu. glad someone went through labor intensive work.
@mkach2521 Жыл бұрын
What an awesome Job!
@Buddythunder1 Жыл бұрын
Stellar job.
@albertcalderon3421 Жыл бұрын
Saludos, máquinas soberbias, verdadera Alta Fidelidad, nada que ver, con las mentiras actuales del High End, gracias por compartirlo, abrazos desde Bogotá, Colombia...
@tomasvalentin6896 Жыл бұрын
Hey, great video, thanks you for sharing
@chipmunk6386 Жыл бұрын
Like a pro.! Awesome job.! 👍
@tee-jaythestereo-bargainph2120 Жыл бұрын
Great Job ! Thanks for the video Top Level !!!!!
@01sapphireGTS Жыл бұрын
I don't know where you live, but I wish you were close to my location. Amazing work.
@PrimeHiFi Жыл бұрын
Thank you!
@VinylPro Жыл бұрын
great setup !
@MD1969 Жыл бұрын
Great job man...congrats !!!
@bdg77 Жыл бұрын
Very nice work your doing!!
@ashwinas4506 Жыл бұрын
Thanks for sharing this video Dude ❤
@miscman10000 6 ай бұрын
What incredible work. Hat off to you sir. Love the music at the end too. Who is it?
@user-fe3hs6oc3n Жыл бұрын
Beautiful work!!!
@jked7463 Жыл бұрын
I believe that it is doing crazy things to your system because of the DC coupled design with no caps in the signal path. I have a KA-7100 DC integrated with 60 wpc. They like to call it mid-fi but it does things I never heard any amp do at multiples times its price. I never believed or understood the concept or "pace" until I heard this amp. The mixing of the original recording of take 5 by Dave Brubeck made no sense until I heard it through the 7100. Would love to hear these amps. You did a great job. Whatever it cost, (assuming not gouging) it is worth it. Would love to own a pair myself.
@tottimejdi5820 Жыл бұрын
very clean and nice work
@Stelios.Posantzis Жыл бұрын
21:33 Couldn't the high speed TO3s be replaced with lower speed TO3s saving all that trouble? Was the high speed necessary to the circuit? Presumably, if speed was not needed, lower speed transistors might not go into high frequency oscillation in the first place, right?
@PrimeHiFi Жыл бұрын
Kenwood applied feedback well above the audible band. The high speed nature of these amps doesn’t only come from the high fT outputs, rather the circuit as a whole. Replacing high speed semiconductors comes with the possibility of hurting the performance of the amplifier and can even lead to other issues as well. Putting the amps back together with parts similar to what were used when they were designed is the way to go.
@Stelios.Posantzis Жыл бұрын
@@PrimeHiFi Ah that makes sense then. Thank you for sharing this.
@atelier_HiFi Жыл бұрын
very nice job Connor!
@PrimeHiFi Жыл бұрын
Thank you!
@grahamkent2868 Жыл бұрын
Great work!
@mickbroad2059 Жыл бұрын
Good engineering work...well done...however the camera work makes me feel like Iv'e just got off a roller coaster...LOL
@lbbork Жыл бұрын
Very impressive.
@oldskoolbronco 5 ай бұрын
Excellent!👌
@dikludas 10 ай бұрын
Super , excellent 👏 👌 👍 🙌 ❤❤
@THELIBERAL Жыл бұрын
Very nice work and it is great to see a fully restored set. I owned the whole LO7 set back in the day and used to sell them. The amps where fantastic sounding but they tended to run hot, especially the LO5s . We had very high failure rates and durability issues but boy did they sound good. In this series the amps were fantastic , the pre amp middle of the road, and the turntable was without question fabulous and I think the best of the series. PS Do you have a repair shop?
@PrimeHiFi Жыл бұрын
Thanks for the kind comment! Yes! I’m well aware of the stability issues of these amps. The issues mostly stem from the factory QC and a select few components that end up drifting overtime, killing the amplifiers. It’s a shame, as most of the series suffered a terrible fate because of it. I run a small HiFi equipment lab on the side, yes!
@dennishill290 Жыл бұрын
Damn....you got Talent...very nice presentation.... !
@toneyisaiah3556 22 күн бұрын
It's like working on your car. Mechanics go through the same thing.
@greghamilton297 Жыл бұрын
Very well done!!
@toneyisaiah3556 22 күн бұрын
It takes a long time to put it together.
@bassboyful Жыл бұрын
nice work man 👍
@a.f.1587 9 ай бұрын
Nice amplifiers, it's a shame they have so much design flaws... Nice restoration BTW
@brianwerner6643 Жыл бұрын
Beautiful work. I have a pair of the MkIIs myself. Do you have a list of parts and where you got them that you could post?
@PrimeHiFi Жыл бұрын
Thank you! I don’t have a parts list, but they can be found in the service manual which is available online.
@aegisofhonor Жыл бұрын
I have a pair of L-07M (first iteration), they are very good sounding amplifiers. I have a 3rd one that doesn't work, one of the screws on the top is gutted out and I can't unscrew the top. I have no idea what's wrong with it, but I have a feeling it's a bad relay.
@tommy68boy Жыл бұрын
are they worth the restore as i have ken L0-5 dont how much will it coast to rebuilt it back
@Stelios.Posantzis Жыл бұрын
6:25 This is the most surpising thing I've learnt from this video. I never thought a restoration would result in polystyrenes being replaced by ceramics. Is it just the polystyrenes that are temperature sensitive, seeing that a lot of mylars are still left in there?
@PrimeHiFi Жыл бұрын
Yes, the “black flag” polystyrenes used in many of the high speed amplifiers in the 70’s and 80’s must be replaced to prevent oscillation. They are nasty and drift with age. See here: www.conradhoffman.com/BF_caps.htm
@Stelios.Posantzis Жыл бұрын
@@PrimeHiFi Thanks for the link! It's been some time since I last visited that site. I had forgotten about these. It seems one would provide a great service by cataloguing all those aging components (caps, resistors, semiconductors etc.) in one site. Professionals in the trade of restoring probably know them by heart but it would make a useful reference for hobbyists that unwittingly plug an old piece just acquired in the mains only to watch a puff of smoke be produced from it.
@lohoch5506 Жыл бұрын
Is it fair to say you specifically is integrated and power amps?
@marbru7829 Жыл бұрын
Dear Connor, great job indeed. As introduction, Can you add a short movie related on how to remove the top cover ? Cheers, Massimo
@PrimeHiFi Жыл бұрын
Glad you enjoyed the video! Please reference the service manual for complete disassembly instructions. The service manual offers comprehensive instructions with clear pictures on how to do this. It is available on HiFiEngine
@toneyisaiah3556 22 күн бұрын
Cost to replace everything in the stereo amplifier.
@Jack96993 Жыл бұрын
Would you like to restore a Marantz 2325 reciever? Hey l know good work when l see it, and l must say it doesn't look cheap With the current supply chain issues any problem getting supplies?
@brianmoore8235 Жыл бұрын
AMAZING work my friend excellent note to detail which is hard to find nowadays. I’ve got a klipsh synergy 10 subwoofer and I blew the fuse on it unfortunately I had lost the fuse and the cap that screws on it I guess l should I try contacting Klipsch any thoughts ? Thanks
@PrimeHiFi Жыл бұрын
Thank you! Yes - that will be your best bet. Or bring it to someone local to you to have it repaired.
@dab9742 Жыл бұрын
Kenwood, une grande marque Japonaise, qui n'a rien à envier à Pioneer, Sansui, Sony, Technics, Yamaha, Sony, et autres. Dans les années 80, j'avais le couple Basic C2-M2, un très bel ampli, impossible à mettre en défaut. Dommage que certaines de ces grandes marques aient disparu de la hifi de qualité, alors qu'elles étaient d'aussi bonne facture... 🥲
@salvadorrodenas3071 Жыл бұрын
Amazing job
@ossianhaufe4671 8 күн бұрын
What kind of music did you listen?
@Nickbazukaho3nt Ай бұрын
A1943 & c5200 Work in this amp?
@emmanuelgarrouste7494 Жыл бұрын
What an incredible sound! What kind of speakers are you playing in this video? They really sound awesome!
@PrimeHiFi Жыл бұрын
Thanks! They are Vandersteen 2Ci
@shahzadkhan-nd1jg Жыл бұрын
Nice video sir
@stevesmyth4982 Жыл бұрын
Nice job remounting the TO3P devices, the axial capacitors on the protection board would benefit from the application of a soft adhesive or silicone sealant (Dow Corning RTV3140 does not contain acetic acid) to prevent the soldered connections from failing due to vibration of the capacitors.
@PrimeHiFi Жыл бұрын
Thank you! And yes, I always add a bead of thermoplastic glue to components like this. I ended up doing it after taking the video. Cheers!
@fickfehler3866 Жыл бұрын
What's your opinion on the Revox B242 amplifier ?
@jackflackatari Жыл бұрын
Do you take on work?
@PrimeHiFi Жыл бұрын
Unfortunately I am not taking in any work as my schedule is too full for HiFi repair. Sorry!
@Stelios.Posantzis Жыл бұрын
19:11 So is this varnish thing found everywhere just left over flux? I always thought this was some sort of moisture-proofing varnish used in all old electronics! If it's flux, then must we remove it? and how? Once this is removed, is there something to protect bare copper tracks from corrosion (as in modern pcbs)? Or do we just have to cover them with solder (which is both laborious and very risky on old pcbs)?
@PrimeHiFi Жыл бұрын
The material on the back side of the PCB that covers the solder mask is flux. The flux attracts dirt and dust, and can become corrosive and conductive overtime with moisture. Added to the fact that it could mess with high impedance circuits, I always remove all flux from PCB’s.
@Stelios.Posantzis Жыл бұрын
@@PrimeHiFi I later realised while watching that these pcbs where already coated anyway, i.e. the copper tracks were not exposed to air. Pretty strange for a prestigious manufacturer to leave flux on their boards in their flagship component. I guess back when it was it made they had not had components with pcbs go bad yet as pcbs had been in use for only, what, two decades? I wonder whether this thing had been hand-soldered. I guess it was.