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Harman Kardon Citation 12 Questions

Discussion in 'Solid State' started by TomHarrison1, Mar 1, 2016.

  1. TomHarrison1

    TomHarrison1 Active Member

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    Hi everyone, just picked up a Cit 12 Deluxe this weekend and have a couple of observations/questions. First, I am seeing a surge on power up/down causing thump, woofer pulse that from what I've read online indicates the power supply capacitors are likely due for replacement. So I have ordered 4 new cans. The originals are Mallory Computer Grade, 6000 uF, 50V, but the closest ones I could fine are Mallory Computer Grade, 6800 uF, 50V. From what I have read, this should be ok. Thoughts?

    Second observation, the externally mounted fuse breakers on my amp are not used. Looking closely, I see no evidence that solder was ever applied to the contacts. In their place, internal fuse breakers have been mounted on the underside as you can see in the attached photo. I can find no other images or write-up online regarding this mod. Can anyone shed more light on this?

    Third observation, the original 6 pin differential amplifier trannies have been replaced with 2 separate trannies along with the 12K resistor swap out for the original 8.2K resistor.

    Finally, this amp really sounds amazing. But I am still making plans to replace the cans, recap the amp board with Nichicon Gold Series caps, and replace the bias trimmer pots.

    Thanks,

    Tom
     

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    Last edited: Mar 1, 2016

     

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  2. gslikker

    gslikker Super Member

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    the fuses I have no idea.
    The following page I found in one of the schematic pages from the internet:

    it looks like the one putting the schematic on the net had one having a 5087 number for the differential pair transistors, maybe the 2n5087 is the same as the HK part number.

    My 12 has no loud power up thump but it does have a little power down thump but not very loud. I did not check behavior of it.

    There is an old AK discussion about the caps already, myself the only ones I could find having the very same diameter size was one type from Cornell Dubilier, but they are that expensive I decided to retain the old ones for now. If you use smaller diameter there is plenty of choice, indeed.


    [​IMG]
     
    Last edited: Mar 1, 2016
  3. Pio1980

    Pio1980 AK Member Subscriber

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    One poster sez the amp sounded better to him with the oem output transistors rather than with more modern replacements.
     
    Last edited: Mar 2, 2016
  4. gslikker

    gslikker Super Member

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    btw the pictures on the internet always show two separate transistors as input transistors, although a manual states " revised" as have two separate AND 12k resistors, mine had separate and 12k resistor.

    The fuses, my guess would be somebody modified it and put in new ones at the front, so look closely if the bolts/nuts are the very same as used elsewhere in the amp.

    capacitors: although power up and down will be influenced by them, it is rather unpredictable how exactly. the total amount of energy of the " thump" may be higher if the capacitors are bigger.
    You will not totally get rid of it, since during power up/down the amp looses its feedback possibilities.
    It is a rather normal situation.
    Indeed use nice big professional capacitors only, for peace of mind.
     
    Last edited: Mar 2, 2016
  5. gslikker

    gslikker Super Member

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    funny is the 2n5807 designation of " commercial equivalent" for q711,712. As a 2N5807 is not a transistor. I wonder if there is an accurate transistor lists which they used to have their own partnumbers on, although the rectangular drivers are rather unique to the RCA devices.
     
  6. TomHarrison1

    TomHarrison1 Active Member

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    Thanks gslikker, I do have the service manual, and if you download the copy from Harman Kardon site, someone has hand written a change to the part number to indicate it was a typo. The transistor should be 2N5087.

    My Cit 12 is either a newer, revised version, or a previous owner did the mod on the differential transistors.

    As far as the power on thump, I see mixed stories about likely cause:

    1. One poster on this thread speaks to replacing power supply caps, electrolytic caps AND all transistors to eliminate the thump. http://audiokarma.org/forums/index....n-citation-twelve-repair-estimate-220.329717/

    I would HIGHLY recommend doing ALL these things to one of these. I'd even go so far as to replace the OTHER small transistors on the circuit board. Did this with mine, and not only did it sound better than I can remember one sounding... but, it also pretty much got rid of the turn-on/turn-off "thump" through the speakers! And that "thump" is something that most ANY Citation 12 will do, stock... this is just about the first time I've ever seen one NOT do that. The newer transistors are much better matched for current draw compared to the ones of that era... the amp will wind up much better "balanced" inside, and will behave significantly better than original...

    2. This one speaks to just failing power caps as the cause. http://www.classicspeakerpages.net/IP.Board/index.php?/topic/6406-receivers/

    Often older receivers have a pair of large value capacitors in the plus and minus power supplies - the Twin Powered Harman/Kardon 930 actually has four large caps because it has separate, dual power transformers, and dual everything else after the power cord and power switch.

    If these big capacitors in the main power supplies happen to charge up at slightly different rates, it causes a temporary DC offset which results in a large excursion, slow woofer movement at turn-on, and possibly a thump at power turn-off. Usually this is not a major cause for concern, but what it does indicate is that those four caps are getting to have increased ESR's (internal series resistances) and at different rates, after 30 to 35 years (and much like the mica pads and dried up silicone thermal grease I already mentioned in my prior response) one should now consider that they should now be replaced.

    My plan is to replace things in this order, so I will post updates on progress and whether I am able to get to the bottom of the thump. If anything, I'm looking to get things back in spec to avoid possible damage to other components down the road.

    1. Measure DC offset at speaker terminals on power on to see what surge level is before any mods
    2. Replace power supply cans (Mallorys have been ordered)
    3. Replace 3 50 uF / 50 V Electrolytic caps on each channel (received yesterday)
    4. Replace the 250 uF / 6V Electrolytic cap on each channel (received yesterday)
    5. Replace the 4.7k trimmer pot on each channel (received yesterday)
     

     

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  7. gslikker

    gslikker Super Member

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  8. TomHarrison1

    TomHarrison1 Active Member

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    Nice restoration gslikker! Thanks for the English translations too! I'll be careful and keep an eye on the contact pins when I replace my board. Thanks for the heads up. Btw, do you still have a power on thump or did that go away with your restore?
     
  9. gslikker

    gslikker Super Member

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    To be frank, I have no idea how it sounded for power up/down before the modification, as I bought it having both channels defective. So at the moment there is no obvious turn-on thump but there is one (not loud) at turn-off..Maybe one day I will check behavior using my oscilloscope.
     
  10. TomHarrison1

    TomHarrison1 Active Member

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    Ok, so tonight I checked the DC offset on Power-up/Power-down. First though...when I bought the amp the seller hooked it up to a pair of Pioneer HPM-100s he had and my Pioneer SA-8500 amp that I brought along and hooked up to the Cit 12 via my amp's pre-outs. We noticed the surge as described above:

    "it causes a temporary DC offset which results in a large excursion, slow woofer movement at turn-on, and possibly a thump at power turn-off."

    And I noticed the same behavior when I brought it home and hooked it up to my SA-8500 and my Pioneer HPM-100s. But it played/sounded really nice for the evening, playing a few LPs. I might add the I have built a speaker protection circuit using 2 6800 uF caps in series (positive to positive) to prevent any DC voltage from hitting my HPMs.

    So...tonight's measurements...of just the Cit 12. Not connected to my SA-8500, not connected to speakers.

    On Power-up, DC offset at speaker output terminals spiked over 100 mV for the first second, then settled down to about 5 mV on both channels. That would explain the "large excursion, slow woofer movement at turn-on".

    But on Power-down things got a bit scary, DC offset:
    1. During the first 1-15 seconds, it rose to about 4 V.
    2. But between 15-20 seconds it spiked to 15V.
    3. Then it dropped under 1 V and took about 10 minutes to completely drop to 0 V.

    I've never measured DC offset on shut down before on any amp, but I'm guessing this isn't good :( Are the steps I have outlined above the right steps to take, or is this looking like something more (with the transistors or maybe the rectifiers). The thing is that it played very well, sounded better than my SA-8500 on its own after the power-up surge. And power-down surging sounded less noticeable than the power-up.
     
  11. dshoaf

    dshoaf That high voltage buzz Subscriber

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    Sounds pretty normal for a 40+ year old power amp that's pretty much unrestored, operating without a preamp with an output mute feature. It was a bit later that power amps and receivers started sporting speaker relays for the reasons you've just measured!

    BTW, the matching Citation 11 preamp, indeed, used a muting circuit that effectively shorts the power amp inputs to ground. Try shorting them then re-run your tests.

    Cheers,

    David
     

     

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  12. TomHarrison1

    TomHarrison1 Active Member

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    Do amplifiers like my SA-8500 have an output mute feature? Is that why it seemed to work fine, apart from the brief surge, with and without the speaker protection circuit I have? Should i not be powering up the amp on its own without an amp or preamp connected?

    When you say try shorting them, do you mean the RCA input jacks before or after pulling the plug? Should I just reconnect the SA-8500 and run my tests again powering it down with the amp connected to the switched 110V outlet on my amp and the pre-outs connected to the amp inputs?
     
  13. dshoaf

    dshoaf That high voltage buzz Subscriber

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    What I was saying, with a bit of tongue planted firmly in cheek, is that try the same measurement you've just done but this time with the 2 input RCA jacks on the Cit 12 amp shorted center pin to ground. This removes any interactions of output voltage that could be generated from the input of the amps. That is, you are removing one potential source of the voltage changes you're measuring.

    I believe you're measuring the turn-on/off 'thump' heard with some solid state amps. On the SA-8500, if you hear a gentle click a few seconds after turn on, this is the speaker protection relay engaging. This relay disconnects the speakers while the amp itself is powering up. Based on a timer and a couple of measurements it makes, the circuit will then connect the speakers _if_ the measurements allow it to do so. Think of it as a safety circuit to save the speakers from the dreaded excessive DC offset. See the stickey thread here at AK, DC Offset....and You for details.

    The Citation 12 does not have such a relay so, with speakers connected, you're going to hear the power up/down thump as the amp becomes fully stable. It was designed to operate that way so don't worry about what it is doing unless there's excessive measured DC offset while the amp has its inputs shorted.

    From the measurements taken thus far, I'd say all is as well as can be for an aged amp.

    As for the discussion on the different circuit topologies, HK made production changes on the fly while amp went down the assembly line. McIntosh as well as others did the same thing as do many companies today. This is nothing new. Most, as HK did, documented the changes with Service Bulletins so that service centers knew how to deal with them. The original topology had dual transistors physically connected in the same package, which helped with thermal stability and gain matching on the same substrate. Later, improvements in transistor production technology allowed them to reconfigure the front end differential circuit to use 2 separate transistors. The changes were issued as the bulletins posted here. Again, normal operating procedure. Don't try to re-engineer either design but accept it as it is.

    The biggest restoration problem is finding replacements for the No Longer Available original RCA transistor parts. You might be interested in the Nelson Pass mods to turn the Cit 12 into a MOSFET amp. That's been out for about 30 years now and it, too, has a lot of NLA parts called for. There are a number of AudioDIY threads on the Cit 12, too. Grab a handfull of beers - its all good reading!

    Hope that helps.

    Cheers,

    David
     
  14. TomHarrison1

    TomHarrison1 Active Member

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    Hi David, yes I'm familiar with protection relays. My Pioneer amps do have them. And have read parts of that DC Offset...and You thread, but heck its up to 211 pages :eek: As for grounding the center pin, I haven't gotten to that, but I did hook it back up to my SA-8500 and got the same measurements.

    So the RCA transistors are NLA, but it appears that gslikker found some replacement equivalents he used in his gutted restore. Gerard, can you describe your mods in a bit more detail. Looking at your updated schematic, you describe swapping a 10 ohm resistor with a 2.2. Where was this done and why? Was this related to the replacement trannies, or for some other reason?

    My RCAs appear to be OK for now since my amp played nicely the other day. I guess I'm just looking to the future and would like to consider acquiring some spares.

    I've also read the Nelson Pass mod, but if it too has NLA/obsolescence issues, then what other options are out there? I came across this site selling new Citation 12-based amplifier boards along with add-on speaker protection boards with relays. Sounds like a serious possibility in the event of major failures and not all that pricey. I'm curious if anyone has tried this kit and if anyone has a write-up installing them in Citation 12 chassis/cabinets or elsewhere. http://analogmetric.com/goods.php?id=1996

    Tom
     
    Last edited: Mar 3, 2016
  15. gslikker

    gslikker Super Member

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    Now here is a long story where I state my assumptions: It is probably interesting how others think about this.


    The power on/off measurements will probably be very different having a speaker attached, as the first DC current appearing will have the low speaker resistance to flow away, and all will be done within about some 5 seconds.
    When powering off, the smoothing caps are discharged by the bias current, until the voltage is too low for the circuit to operate depending on the input stage and voltage amp transistor. Probably the move from 8.2k to 12k will not help here, it will probably enhance something else. The voltage amp transistor (Q703) will shut off and output will go max positive at no load since the caps not depleted yet.

    Second, shorting the input can (and will) make the differential amp "unbalanced" for DC, if one would consider the large input capacitor as a short . Probable the behavior is very different then. Normally, the R703/715 account for differential pair current balance.

    So one can measure four ways, with and without a shorted input, and both situations again having a load attached.


    For transistor choices, I do not think they are critical.
    In the very same amp when used in a Japanese built receiver (I think the HK 930 or 730?? ) they just took the very same schematic and put in Japanese type transistors.
    One has to take care for driver and output transistors having sufficient HFE. You want to convert a few milliamps into some 5 amps when the amp is cranked up using two transistors only. So using modern high power transistors having good HFE at high currents may be beneficial.

    The original rectangular drivers may be obsolete for 30 years already. At my employer, a lot of old obsolete projection systems hardware went into the garbage, so I took some interesting cards and scavenged the MM3007 and MM5007 transistors as well as the input pair transistors. I had enough of them to find two good matched pairs having sufficient HFE, and they came with the nice heatsinks as on my pictures. The same applies for the MJ15001, they were new spares but I could take them as they were not to be used anymore.

    Be aware PROBABLY HK did select transistors manually by then. An audio tech who worked in a repair facility until recently, told me for serious audio the brands would supply selected transistor pairs for replacement. (At least he mentioned Pioneer and Yamaha).

    (edit: took away text I wrote 2 times )
    The 10 ohm resistor.

    Looking back, I really forgot why I did make that decision and I also do not know why this resistor is 10 ohms originally. I think I was thinking for any plus or minus power line fault (cap short) a 10 ohms resistor would just heat up and fry. I guess I might have made some mistake here and got carried away thinking about something I do not understand.
    So, if anybody can explain the 10 ohm thing, please chime in .....


    One more thing: I was wondering WHY the designers did put the input capacitor the "wrong way around", since voltage will be positive at the base of the transistor.

    I have read the interesting FET replacement stories, but as I do not understand the matter enough in case things would not work out right, I did not consider building it.
    (apart from that, the 10KHz square wave on mine looks quite good as can be seen on the picture, so the reason why speeding up the amp even more using FETs looks arbitrary)

    Gerard
     
    Last edited: Mar 4, 2016
  16. TomHarrison1

    TomHarrison1 Active Member

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    Gerard, thanks for sharing your "assumptions" and insight. I'm learning more and more each day about this amp. Thanks everyone. I will look at taking grounded measurements with and without speakers connected over the weekend. As far as input capacitors go...are these the ones mounted on the bottom of the chassis, sealed in white, connect to each of the RCA input connectors (thus "input" cap)? Mine are mounted and I can't see the numbers from my angle.

    On another note, I think I have discovered my fuse issue...maybe. I missed this earlier, but just noticed a light blue sticker on the back of the amp next to the left input jack. I found another citation 12 deluxe online for sale in ottawa with the same sticker. I have attached pix of both. Notice that in the one pic from Ottawa, the 3A - 3AG labels next to the Fuse holder is blacked out with tape. The pic of mine shows a similar sticker and the tape has been removed from those labels.

    The sticker indicates Canada...Certified...Home Entertainment Device...a unique serial number...

    So it appears i have a unit that was originally made for/sent to Canada. If we have an Canadians here on AK, can you shed light on why the fuses would have been relocated to the bottom of the chassis inside the cabinet vs their typical location on the back (front of a non-deluxe model)? Also, the external fuse labels indicate 3A, while the internal ones are 2A along with a small piece of paper next to each fuse that says only use 2A fuses. (see the fist pic I posted in this thread). Since this baby is back in the USA, should I switch back to 3A fuses? I'd rather leave the fuses where they are vs. rewiring things if its not necessary.
     

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  17. daveg3588

    daveg3588 Toy addict Subscriber

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    Welcome to the Harman Kardon fan club! This is a great amp, many moons ago I had the basic one, great sounding amp, but I traded for a Citation V. I recent pulled the V out of storage and had Crispycircuits wake it up for me, I had forgotten how good the V is. Find a reasonable Citation 11 preamp and you will be amazed at the quality of sound the 2 provide. I have my Citation 17 running my V, the range, openness, clarity is not to be believed! or find a 17!
    I'm not a tech, so good luck with your rebuild, but always read and follow anything H/K here.
     
  18. TomHarrison1

    TomHarrison1 Active Member

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    Well, I started to take readings with speakers connected but when I tried grounding the center pin, I got loud static to the speaker I grounded, so I stopped. I don't want to mess anything up on the amp end or my Pioneer HPM-100s. For now, I'm going to have one last listen to the untouched amp tonight, listen to some Pink Floyd, CSN, maybe some 2112 and Led Zep. The PS Caps should arrive this week, so I'll start on them next weekend. More to follow...
     
  19. TomHarrison1

    TomHarrison1 Active Member

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    200
    Location:
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    Progress update...I finally got the power supply caps in and have installed them along with replacing the electrolytic caps and trim pots on amp board. While setting bias, the right channel dialed right in with the 25 turn pot I installed, but the left channel was way off (right side heat sink got very warm). After making quite a few turns, I got voltage down to 10 mV (between .008 and .013 V), but found that a slight turn either direction would change voltage very quickly (up to 1 V). With the right channel, a quarter turn would only change voltage by 1 mV.

    Is this something I should look further into?

    It sounded really nice last night but I'm still seeing power-on/off thump. I also picked up a Monster SS4 speaker switch so that I can hook up both my HPM-100s and a pair of nice AR-4x speakers I found last weekend. I plan to use the speaker switch to turn off all speakers during power-up/down to avoid sending those surges to my speakers.
     
  20. TomHarrison1

    TomHarrison1 Active Member

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    I've got everything all hooked up now and am able to disable all speakers during power-up/down...
     

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