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Left channel quiet on Harmann Kardon 330A

Discussion in 'Solid State' started by Benjamin Le, Nov 8, 2018.

  1. Benjamin Le

    Benjamin Le New Member

    Messages:
    5
    Hello, I saved a really nice Harmon Kardon 330A as it was being carried to the dumpster, it was a really lucky coincidence that I ran into it when I did. Anyways, When I got home and hooked it up to my system, I immediately noticed that the left channel was extremely quiet in comparison to the right channel. The only remedy is to turn the balance knob almost 95% to the left to get them to roughly balance.

    I plugged headphones into the amplifier and the left channel is still quiet. I removed the jumpers from the back of the HK330A and plugged in a preamp from another amplifier and it sounded good. I then wired the preamp of the HK330A and plugged it into the other amplifier, and the channel imbalance is present. This leads me to believe that the preamp is the source of the problem. I tried using deoxit on the switches and pots, making sure to thoroughly clean them all. The problem was still present.

    I then replaced a capacitor on the preamp board that seems to have had leaked at some point in the past. There was a brown stain on the board where the capacitor was, so I replaced that capacitor. But the problem was still present.

    I see two large capacitors on the pre-driver board that seem to have leaked at some point in the past, but as aforementioned, I believe that the problem lies in the preamp section. Should I go ahead and replace the large caps in the pre-driver section anyway? What else should I check/do? I am relatively new to this level of circuitry and only have a basic understanding of vacuum tube amplifiers. Thank you!
     
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  2. audiojones

    audiojones Jonesin' for audio Subscriber

    Messages:
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    Location:
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    Hi and welcome to AK!

    The brown goo is actually just glue used to hold the components in place so the board can be wave-soldered at the factory, not a leaking capacitor. The most common cause of this problem on H/K receivers is the tape monitor switch. It usually has to be cleaned and exercised repeatedly before it starts making contact.

    The contact cleaner has to be sprayed directly into the business end of the switch inside the receiver where the contacts are (some folks spray it in through the front of the switch which does absolutely no good) and the switch has to be worked vigorously over and over again. Your problem could be something else but I'd start there, clean and exercise the tape monitor switch a few times.

    Also read through some of the great threads on the H/K by @dlucy, he knows the various versions of this receiver very well.
     
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  3. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    1,983
    Location:
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    Congratulations on saving a great-sounding receiver!

    You have taken the first diagnostic step and determined the problem is before the power amp board. So, you could have a problem in the preamp (I think the schematic calls it "control amp") or the tone circuit (very small).

    It is unusual for the resistors or film capacitors to go bad, so the most-likely cause would be the electrolytic caps or the small signal transistors. And you've already narrowed it down to the preamp, so you'd be looking for problem ecaps or transistors there.

    There are very few ecaps and transistors on the preamp board and shipping from Mouser.com or Digikey.com is a mininimum of $7.99, so you may want to order all the ecaps and all the transistors (each very cheap) and do all of them in the preamp at once.

    The replacement electrolytic caps would be Nichicon KL series radial leaded at whatever capacitance and voltage (or higher). All the transistors on the preamp board can be replaced with KSC1845.
     
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  4. Benjamin Le

    Benjamin Le New Member

    Messages:
    5
    Thank you guys for getting back to me! I will first try cleaning out the tape monitor switch, if that doesn't do the trick, then I will try replacing the components on the preamp board. I will report back once I have tried these fixes.
     
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  5. Benjamin Le

    Benjamin Le New Member

    Messages:
    5
    Well, audiojones, I have tried your suggestion of cleaning out the tape monitor switch by working it the deoxit into it vigorously and turning it on and off quickly. After the deoxit dried off I tried the amplifier through headphones and the left side is still quieter than the right. I shall now try dlucy's suggestion of replacing the components on the preamp board.
     
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  6. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    1,983
    Location:
    Philadelphia, PA
    A good repair and restore thread of a 330A by @Spenser is here: http://www.audiokarma.org/forums/index.php?threads/hk-330a-repair-and-restore.823100/
     

     

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  7. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
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    Location:
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    The preamp board, called control amp I think, is here:

    benjamin le IMG_3863.jpg

    The transistors in the preamp are here:

    benjamin le IMG_3878.jpg

    The electrolytic caps to replace are here:

    benjamin le IMG_38782.jpg
     
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  8. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    1,983
    Location:
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    The parts to replace, if you want to buy from Mouser, would be as follows:

    ComponentNum Qty Type Subtype Value Value ReplacementPN
    TR501,TR503,TR601,TR603 4 Transistor BJT 2SC644 TO-92 512-KSC1845FTA
    TR502,TR602 2 Transistor BJT 2SC828 TO-92 512-KSC1845FTA
    C501,C502,C503,C506,C601,C602,C603,C606 8 Capacitor Electrolytic 1 uF 50 V 505-MKS2C041001FKI00
    C504,C507,C604,C607 4 Capacitor Electrolytic 10 uF 16 V 647-UKL1C100MDDANATD
    C505,C605 2 Capacitor Electrolytic 100 uF 16 V 647-UKL1C101MPDANA
    C508,C608 2 Capacitor Electrolytic 220 uF 6.3 V 647-UPW0J221MED

    The 1 uF / 50 V electrolytic caps will do better by replacing them with film caps from WIMA as listed above.

    Simple cut-and-paste BOM list (part number, qty):

    512-KSC1845FTA 6
    505-MKS2C041001FKI00 8
    647-UKL1C100MDDANATD 4
    647-UKL1C101MPDANA 2
    647-UPW0J221MED 2

    You may want to bump the close-to-ten quantities up to 10 so you get the qty 10 discount.
     
    Last edited: Nov 10, 2018
    Benjamin Le, Johnny_Law and mbz like this.
  9. Benjamin Le

    Benjamin Le New Member

    Messages:
    5
    Thank you @dlucy! That is quite helpful, I shall order these parts soon and pop them in, also there was another problem I forgot to mention, when I plug in a record player into the phono input, there is only a loud buzzing noise, should I replace some components on the phono preamp board as well?
     
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  10. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
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    Location:
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    Loud buzzing is bad. The phono board, called the EQ board, is small and easy to work on. I would highly recommend you recap that board and replace the transistors. This board has very high gain, so even small problems are audible.

    I can post a BOM parts list later tonight. While you are in there, consider replacing the resistors with modern metal film ones. That will reduce the noise floor audibly.
     
  11. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    1,983
    Location:
    Philadelphia, PA
    Parts on the phono stage / EQ board:

    ComponentNum Qty Type Subtype Value Value ReplacementPN
    C401,C405,C409,C414 4 Capacitor Electrolytic 10 uF 16 V 647-UKL1C100MDDANATD
    C404,C413 2 Capacitor Electrolytic 33 uF 6.3 V 647-UKL1C330KDDANA
    C410 1 Capacitor Electrolytic 100 uF 16 V 647-UKL1C101MPDANA
    TR401-TR404 4 Transistor BJT 2SC644 TO-92 512-KSC1845FTA

    Simple cut-and-paste BOM list (part number, qty):

    647-UKL1C100MDDANATD 4
    647-UKL1C330KDDANA 2
    647-UKL1C101MPDANA 1
    512-KSC1845FTA 4

    You may want to bump the close-to-ten quantities up to 10 so you get the qty 10 discount.

    That list does not include the resistors or the film and ceramic caps that "make" the RIAA curve equalization part of the circuit. If you wanted lowest possible noise and closest-to-correct RIAA curve, you'd replace the resistors and non-electrolytic caps while you were in there. There is not super strong compelling reason to do this part... unless you're crazy like me, have $12 to spare for the parts, and an hour of your time to spare. ;)
     

     

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  12. Benjamin Le

    Benjamin Le New Member

    Messages:
    5
    Thank you @dlucy! I shall try replacing these parts and see how it goes.
     

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