Canceling the balance pot on Harman Kardon receiver

[QuiqueM]

Hi,
I have a Harman Kardon AVR30 receiver, which is about 20 years old. It still works perfectly, but the balance potentiometer cuts off on certain parts of its travel.
This is the second time it fails. The first time I repaired it myself, by replacing the pot with a similar one, but several years later fails again. I wish to cancel the balance function, since I never use it.
Please refer to attached schematic, with balance pots marked VR501/502. If I remove then, can I leave an open circuit? or do I replace them by fixed resistors?

I would be grateful if you could advise me.

 

[crutschow]

Below is a schematic clip of the pot's circuit.
What you replace them with depends upon what the pot settings are normally when using those inputs.

They appear to be dual pots, so if they are normally set at the 50% point (half-way between the pot extremes), then just replace the pots with two 24.9kΩ ±1% resistors in series to ground, with the output taken from the junction of the two resistors.

 

[Nigel Goodwin]

Just disconnect the pot entirely, and wire from R501 to FL, and R502 to FR.

No need to put resistors in (it might be slightly louder, but that's what the volume control is for), and if you did they would't be 50/50 as the pot will be log/anti-log - 50/50 would make little difference.

 

[QuiqueM]

Thank you Gents for your good tips. I will try Nigel's first and see how it goes.

 

[unclejed613]

balance pots are so seldom used (by the user). you could just jumper the wipers to the signal end of each pot.

 

[QuiqueM]

balance pots are so seldom used (by the user). you could just jumper the wipers to the signal end of each pot.

Hi Uncle, thanks for your tip, but I'm not an electronics dud and the only wipers I know are those cleaning my car windscreen. Do you mean I do like Nigel suggested: "Just disconnect the pot entirely, and wire from R501 to FL, and R502 to FR."

 

[Nigel Goodwin]

Hi Uncle, thanks for your tip, but I'm not an electronics dud and the only wipers I know are those cleaning my car windscreen. Do you mean I do like Nigel suggested: "Just disconnect the pot entirely, and wire from R501 to FL, and R502 to FR."

Yes he does, the wiper is the centre contact (the little arrow on the symbol) that 'wipes' along the track.

 

[QuiqueM]

Yes he does, the wiper is the centre contact (the little arrow on the symbol) that 'wipes' along the track.

Hi Nigel, thanks again. But just to play it 100% sure and before I open the unit: if I got it right, I must open the connections in red and rewire them like indicated in green. My question is what to do with the pot end showed with the blue arrows, should I keep it connected, or should I leave it open and floating?

 

[Nigel Goodwin]

That's fine, leave the pot slider floating, and leave the outer two connections in place as it might require the DC connection through the pot.

 

[QuiqueM]

So, it will look like this:

 

[Nigel Goodwin]

Yes, that's perfect.

 

[QuiqueM]

Hi Gents,
I carried out my mod yesterday. It took me a while because the receiver's box is quite tricky to open, with most control pots fixed onto a PCB. I shorted the balance pots as you guys suggested and it works perfectly fine, the balance control is now cancelled and sound levels are equal between both channels. Thanks again for the advice.

 

[unclejed613]

it's always been my opinion that power amplifiers should have no controls except a power switch. all of the control of signal levels, tone/balance/source etc... should be in the preamp. with controls in the amp, you have too much room for human error, such as turning the amp gain down in the amp, and wondering why the preamp no longer drives the amp properly.

 

[Nigel Goodwin]

it's always been my opinion that power amplifiers should have no controls except a power switch. all of the control of signal levels, tone/balance/source etc... should be in the preamp. with controls in the amp, you have too much room for human error, such as turning the amp gain down in the amp, and wondering why the preamp no longer drives the amp properly.

Perhaps you haven't read the entire thread?, we aren't talking about separate preamps and power amps, (which are really pretty uncommon - and usually wouldn't have any controls on the power amp anyway) but an integrated amplifier, like almost all are.

 

[George de Vree]

Hi there,
I am very happy to have found yr thread. I guess 5 minutes later and my wife's HK6100 amplifier would have landed in the garbage. Yr AVR30 solution worked fine for the HK6100 as well. The defect pot led to the total loss of the left channel. I cut both (middle) wiper legs on the upper side with a pair of nail scissors and soldered two tiny cables on the bottom side to get the necessary shortcuts. The old pot stayed in place (having lost his middle legs, poor chap). We are listening to The B52's (Private Idaho, Wild Planet, 1980) on a 30-old device and it sounds better than ever before....
My wife calls me genius now (rare enough!) and I pass the compliment to you, gentlemen!

Tired now, but very happy!
George from the Stuttgart area!

 

[unclejed613]

balance pots often get dirty/oxidized (like every other potentiometer). if they are used a lot, or if there's some DC current flowing through them (there shouldn't be, but it can happen with cheaper equipment) they can develop dead spots in them. another common failure with some potentiometers is the junction between the element and the teminals can get flaky. i once worked for NAD, and while thy probably don't do this anymore, they did it back then (around 1985), used conductive silver paint to fix or prevent failures of some potentiometers in their receivers and integrated amps that regularly developed bad connections.

 

[jock1234]

I used the information in this tread to narrow down the issue (loss of the left channel) in a HK-6250 to a defective balance pot and then to successfully repair (bypass) the balance pot. In this case had to unsolder the balance pot from the circuit board to cut both (middle) wiper legs. I then re-soldered the pot along with two tiny cables on the bottom side to get the necessary shortcuts.

Thank you everyone.

 

[Ylli]

Just to add an alternative to this thread.... Older pots can get cranky. Often all they need is a little cleaning and the go-to cleaner is Caig DeoxIT D-5. https://caig.com/deoxit-d-series/ . Smallest can (which will last a long time) is https://caig.com/product/deoxit-dn5s-2n/ . If the pot is constructed in a way that allows you to get some contact cleaner into it, then a spritz of DeoxIT may be all that is needed.