Left channel quiet on Harman Kardon 330A

Benjamin Le

New Member
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!
 
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.
 
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!

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.
 
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.
 
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.
 
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.

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/
 
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
 
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.
 
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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?
 
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?

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.
 
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. ;)
 
I finally found the time to do the work on the amplifier today. I first replaced all the transistors, then started replacing a few capacitors. I tested the amp through the headphone jack and the channel balance issue is no longer there! So it most likely would have been some of the transistors in the preamp section. When I get back home I shall hook up some speakers to the amp and put in a phono into it and see how it goes. It appears promising so far!
 
I finally found the time to do the work on the amplifier today. I first replaced all the transistors, then started replacing a few capacitors. I tested the amp through the headphone jack and the channel balance issue is no longer there! So it most likely would have been some of the transistors in the preamp section. When I get back home I shall hook up some speakers to the amp and put in a phono into it and see how it goes. It appears promising so far!

Terrific! Let us know how it turns out.
 
Alright I believe that it is now fixed for good! I plugged an old phono of mine into the phono Jacks and wired up some speakers to it, and both channels of the phono were coming through loud and clear! It sounds amazing, I can't believe it. I thought I would never be able to get it fixed, but with your help @dlucy, I was finally able to fix it and it has exceeded my expectations. Thank you again, @dlucy
 
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.
Thanks for the suggestion, it was my tape monitor switch, but spraying deoxit D5 was hard. I looked for holes and there were no holes in the switch to spray. So I hit the front of the switch edge with 3 different blasts. After cycling the switch the usual 100 times it was better, but not perfect. However about 20 minutes later it was perfect, maybe the deoxit D5 took hold later. Anyhow am now replacing electrolytics with polypropylenes. This receiver is unusual in that it has the more expensive LC IF section and diode matrix MPX section, so the trumpet blasts should sound superior and much better after the polypropylene upgrade!
 
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