Amp woes and restoring a "vintage" treasure

Discussion in 'DIY' started by dBel84, Sep 30, 2015.

  1. dBel84

    dBel84 Friend

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    I figured I would kick off my transition to this new forum by sticking to my resolution of being more active in the DIY forum. I am a tinkerer by heart and although I preach the "leave well enough alone" "if it aint' broke , don't fixit" truth be told , there is very little I have ever left alone.

    I am not sure I consider myself an audiophile , I love gear, I love music and the reproduction thereof but all in, I am a cheap bastard and that generally doesn't gel with following the pursuit of better and more expensive gear. I have bought a few higher ticket items in the headphone world but in speaker land, that is a very deep abyss.

    So to the point of this tale, my trusty and aging old Cyrus power amp finally began to fade , no fear as I had been building a serious Class A hybrid amp that would see me to the grave

    [​IMG]Power Stacker by dufniall_dihardiyr, on Flickr

    well that was until I somehow pulled the speaker cable loose while still in test bed mode and blew out half the amp along with the trusty test speakers.

    In somewhat of a pinch , I started to look into PASS amps figuring it would be easier to just but an INT30A and be done. While browsing audiogon I stumbled on an ad for a late series mighty KLOUT amplifier. I don't think Linn Audio is all too popular in these woods but having originated in the colonies, I was all too familiar with the Klout and had great respect for this masterpiece of engineering.

    I was also all too aware that these amps are now 20 years young and probably needed a little TLC to keep it going for another 20. The internet is a mighty fine tool and with relatively little fuss, I had a full schematic and managed to track down a service manual , so I bought one. I probably paid on the high end of what they are valued at but I wanted a late series amp and was happy to pick up a pristine amp.

    [​IMG]Klout before recap by dufniall_dihardiyr, on Flickr

    The biggest deal with these amps is that they run hot and their capacitors are known to dry out and result in failure, so I decided to recap the amp before it died and needed much more work from the fallout.

    First step was to buy some audio grade capacitors

    imgur link below

    The entire chassis is milled from a solid billet of aluminium

    [​IMG]recapping klout amp board by dufniall_dihardiyr, on Flickr

    The amp modules are screwed to the side / heatsink and are easily removed with the screws that hold the bracket for the output transistors

    [​IMG]Klout caps removed by dufniall_dihardiyr, on Flickr

    These are thick old boards and removing the capacitors was a challenge even with a high heat soldering iron and sucker.

    [​IMG]Klout board topside by dufniall_dihardiyr, on Flickr

    [​IMG]Klout board by dufniall_dihardiyr, on Flickr

    A little bit of oversight on my part was that the nichicon muze caps are taller than the originals and thus the little daughter control board needed to sit a little higher but still made good contact

    [​IMG]Klout recapped by dufniall_dihardiyr, on Flickr


    other images
    https://imgur.com/a/hezaY

    Once it was all back together, it powered up without a glitch and was back to playing music exceptionally well.

    I persuaded myself that it had improved performance - very articulate top end, good solid bass and well fleshed out mids. If you find yourself in a position to pick one of these up at a good price, well worth the effort of replacing a few capacitors.

    ..dB
     
    Last edited: Nov 13, 2017
  2. Bill-P

    Bill-P Level 42 Mad Wizard

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    Awesome! Great work, Don!

    I'm a tinkerer myself, and during the process of designing my own amp, I've also found that capacitors in the power supply also somehow have an effect on the overall sound characteristics of the amp, and yeah, as you noted, articulated top end. I've also noticed tighter bass as well...

    Though all of that could very well have been my imagination.

    P.S.: Nichicon caps FTW! Hahaha, they are my favorites as well for some reason. I tried the other caps but the Nichicon always seem to be the best compromise in availability, size, capacitance, voltage level, variety, and value to me.
     
  3. fishski13

    fishski13 Friend

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    jolly brill mate. now get yourself an LP12 and a pair of Kans.

    that's a cute PCB btw.
     
  4. dBel84

    dBel84 Friend

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    Thanks C.

    Well I decided rather than creating new threads for other projects, I will just dump a few more in here.

    I built a switch box for a friend who needed the option to switch between 2 balanced sources with multiple output options.

    photobucket blocked all the images

    here is a compiled view of the project
    Can't get the image to load - IMGUR

    This affirmed my complete dislike for casework ;)

    ..dB
     
    Last edited: Nov 5, 2017
  5. dBel84

    dBel84 Friend

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    Harmon Kardon HK-775

    I thought that I would continue on in this thread rather than clutter up the M-22 thread

    (and noticed that all the images from my previous post have been redacted - be damned photobucket! )

    I stumbled on a pair of these while trolling the local Craigslist for an M-22 and recalled that Rex had commented on how much he had liked them. After some research on the interweb I thought I might just like to give them a try.

    This is what The Vintage Knob has to say :
    "The hk775 is a fully symmetrical DC circuit design with quad differential cascode, a big toroidal transformer, two 15,000uF of caps, discrete components only (no ICs), protection circuit which remain out of the signal path and 300Khz of frequency response."

    I auditioned the amps briefly at the sellers house - hung around chatting to him for way too long - he has been collecting analogue gear for 40 years and is thinning out the herd to cover some medical bills. Life sure can suck at times but he was in as positive a state of mind as one could hope to be. The audition was through a set of small desk top speakers which sounded very good being driven by an ipod. He did tell me that he was a little concerned with the sale as one channel had made some scratchy noise when he fired tthe amps up for me to hear and while I was there, he shut them down and fired them up - I heard some crackly but it resolved immediately when he messed with the subsonic filter - I figured an aging cap but as both were apparently working and sounding good enough to risk ending up with a chassis and cool heatsinks, I went ahead with the deal.

    He told me that he bought them in the 80's and had used them on and off for a second system but that they had been at his mother's home for the past 15 years. They looked relatively clean from the outside , a little dust in the heatsink fins but not abused aside from the power switch on one amp which was missing.

    So between fitting a new stove in the kitchen this weekend, I set up shop in the breakfast room
    CD -rom with volume control as source, test bench speakers are an old set of bose , found the service manual and printed it , opened up the amps and found a thick layer of greasy dust covering both insides of the amps - I suspect years of smoke and pan grease with settling dust

    upload_2017-11-5_19-18-30.png

    First things - these amps are built like tanks - seriously hefty heatsinks and major attention to detail with respect to internal organization and ensuring that 35 years after they were assembled - they are still rock solid. Immediate negatives - not grounded, power cable is thin twinflex , speaker binding posts can only take bare wire.

    Fired them up and monitored DC offset which in one was around 150mV but in the other was close to 2V ( this must have been the crunchyness in the speaker that I heard during demo ) One other good thing about the design and build - setring bias and offset is seriously simple - 2 easily accessible trimpots which I at first thought would need a little deoxit but I managed to bring both channels DC offset to as near to zero as possible - a few mV ( service manual suggests to aim for about 10mV ) . I checked the bias and while cold was reading about double what it should . Not being sure if this would drop as the amp warmed up I left the bias where it was set but balanced both channels to match one another.

    Then I just cued up several CDs while I went to work on the kitchen. Music from the Bose was about as good as they were capable of , so at this point I was pretty glad I had opted to give them a try. Total run time was about 7 hours, DC offset remained solid , no drift and no funky crackling or distortion. Bias actually climbed more , so I brought it back down to the recommended bias point but because I like running things hot pushed it up a tad . I had read that the pre-drivers run very hot - some quotes stating above 100deg C , my measurements for the output transistors was about 40degC and the predrivers were 55deg C , plenty good for the transistors and heatsnks barely got warm - literally just warm to touch .

    I am pretty happy that the amps are behaving and will not destroy my Maggies, so next round is to hook them up in the system and see if they are worthy of stripping down, cleaning and recapping.

    If sombody comes across an 80's rectangular power push button from any silver gear, I would love to hear from you. ( even better if HK )

    More to come - just not sure when I will next find some time for this sort of fun.

    ..dB
     
  6. dBel84

    dBel84 Friend

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  7. dBel84

    dBel84 Friend

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    I like holiday weekends

    1 amp resurrected and sitting idling on the test bench to make sure it remains stable.

    I went a little OTT and hooked up 4 multimeters to check various test points and then used a variac to bring it up slowly. After some initial bouncing around, I managed to set the bias and output DC settled at +-2mV.

    [​IMG]

    ( no comments on the messy workbench )

    ..dB
     
  8. Cspirou

    Cspirou They call me Sparky

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    It's cleaner then mine
     
  9. dBel84

    dBel84 Friend

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    Final update - got both working today

    [​IMG]

    Not tested yet because I want to make sure they are stable for a while.

    I have to say, these amps are built very well. Once you figure out how they go together, you can really appreciate the engineering marvel of the original design team.

    looking forward to hooking them into the system to see how they sound = an adventure for another day.

    ..dB
     
    Last edited: May 29, 2018
  10. dBel84

    dBel84 Friend

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    and this is where I loose all respect from the Vintage die hards

    [​IMG]

    simple reality - they had to fit in with the rest of the gear to be tolerated and as I want to give them a fair chance, they will replace my Linn Klout for a few months at least.

    I actually might prefer them black to be honest.

    [​IMG]

    ..dB
     
  11. dBel84

    dBel84 Friend

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    Small update

    [​IMG]

    1. Stuck them into the system and thoroughly enjoyed what they did with the Maggies ?? better than the Linn - different but perhaps not better. The Klout is, not unexpectedly, very good at what it does.
    2. they ran HOT ( 65 deg C on one amp - had me a little concerned )
    3. went away to a meeting and got a concerned call that black smoke was coming out of one of them
    4. well toasted and not able to repair the offending amp
    5. restored one of the other amps - cleaned all boards, reflowed solder, replaced all caps, checked resistors
    6. ran for 3 days and stable, stable under repeated on off cycles
    7. dropped into test system and making sweet music - appear stable.

    happiness is ...
     
  12. bengo

    bengo Friend

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    So the moral of the story is... if you buy vintage gear, always have a hot spare?
     
  13. dBel84

    dBel84 Friend

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    This sorta falls under restoration - @spwath sent me a struggling grado

    I "gutted" it , needed to remove the grills in the process and damaged the cup slightly in the process which forced me to pick up a can of paint.

    Mods - removed all felt like covering behind the driver
    - added some physical damping to the magnet - similar to the HP1K mod
    - lined the inside of the cup with closed cell foam ( 3mm crafting foam )
    - added some very loose stuffing
    - back grill has the same lattice foam used in the HD800/HD600 mods
    - cut the front foam away from the driver

    These actually sound reasonably good - mids still need some fine tuning but fairly well balanced overall.

    not honky at all, if anything I have recessed the mids a little too much , no midbass bloat into other frequencies and top end not sharp at all - I may need to measure them to see what I am hearing but seem fairly balanced overall.


    [​IMG]

    [​IMG]

    [​IMG]

    ..dB
     

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