Bypass balance control on a NAD 7140 reciever.

[Count Yorga]

Hi, I have a NAD 7140 Reciever which has a knackered volume pot. The pot in question is some kind of spasticated coaxial combined volume and balance control, with the two separate pots and a stupid coaxial shaft which runs through the volume pot into the balance pot. The volume section is unserviceable, apparently this was a common problem with this particular unit. There is no direct replacement part available, so my plan is to replace the volume pot and do without a balance control.

I am unclear if this Is just a simple matter of joining the two outer pins together or is it more complicated than that requiring resistors? Could use some advice with this.

Cheers.

 

[Nigel Goodwin]

From the schematic the balance control looks to be a 50K stereo pot, and the volume control a 20K stereo pot, BUT with a tap for a loudness control.

I'd be inclined to remove the balance pot, and wire a 22K resistor from slider to top on each half of where the balance pot was. I'd replace the volume pot, and simply ignore the loudness tap.

 

[audioguru]

if you join the two outer pins together then they Short the channels together that might destroy them and if they still work you will have mono instead of stereo. Don't you like stereo?
You should NEVER simply short two different signals together. Resistors will reduce the current.

I have never used a balance control because I sit exactly between the stereo speakers.

 

[Count Yorga]

Thanks for helping. I certainly wouldn't connect two channels together without a resistor, and yeah I like stereo lol. it's a two channel 6 pin tone pot. 3 pins for each channel. So you suggest two 22k resistors for each channel, connecting the outer pins to the centre pin?

I was hoping to find a volume pot with a loudness tap, but it seems these are damn near impossible to find. I would rather retain the loudness function if possible.

 

[Count Yorga]

Not sure I understand how connecting the outer pins shorts the channels. Each channel has it's own 3 pin connection to two isolated potentiometers. Middle pin is signal input then the right outer pin on one channel and the left pin on the other are the signal out, the remaining pin is the ground connection surely? The two channels individual pots are inverted. So using 22k resistors from the outer pins to the centre pin should work. But do I connect BOTH the ground AND the line out connections with resistors? Or just the signal in to the signal out on each channel?

 

[audioguru]

1st the volume controls were bad, then the balance control is bad. Now the tone control (which one, bass or treble?) is bad.
I assumed the balance control was bad and it has left channel on one end, right channel on the other end (don't short them together) and a resistor to ground on the slider.
The middle pin of most pots is the slider that is usually the output for a volume control.

 

[Count Yorga]

This is a combined volume and balance control with two pots, a 6 pin balance and a 4 pin volume (with loudness) utilising a coaxial shaft, one for volume and the centre shaft runs through the volume pot to the balance pot. This balance/volume control seems to have separate left and right channel pots. Yes centre pin is the slider. So if I connect 22k resistors from both the ground and input pins to the slider for each channel this should work?

 

[audioguru]

Since it uses two pots for balance then they are simply volume controls with one wired backwards. Turn it to the left then the left channel becomes louder and the right channel becomes less. The reverse happens when you turn it to the right.

Do you want to disconnect the balance controls and connect the terminals points with wires?

 

[Count Yorga]

Yes I want to remove the pot completely and bypass it.

 

[audioguru]

Nigel has the schematic so ask him how to connect it.

 

[Nigel Goodwin]

Or just download it, as I did.

 

[Count Yorga]

Download it from where?

 

[Nigel Goodwin]

Download it from where?

There's this wonderful new website - called 'google'

Just enter NAD7140 schematic and follow the links.

We're more than 20% of the way through the 21st century, have you never used a search engine?.

 

[Count Yorga]

Thanks! I have the schematic already. My question was a really simple one. Oddly, the schematic does not explain how to make modifications. I simply wish to remove a pot and bypass it. I am just unsure as to whether or not I can just wire up the signal in and signal out together and leave the ground floating, or if I require a resistor or not.

 

[Nigel Goodwin]

Thanks! I have the schematic already. My question was a really simple one. Oddly, the schematic does not explain how to make modifications. I simply wish to remove a pot and bypass it. I am just unsure as to whether or not I can just wire up the signal in and signal out together and leave the ground floating, or if I require a resistor or not.

As I explained in post #2, I would add a 22K resistor in place of each half of the balance pot, from top of the pot to slider. The resistor is just to keep the volume level similar, if you don't mind it louder then use a piece of wire instead.

On the schematic, 22K resistor from top of R601 to top of R606, and the same on the other channel.

 

[Count Yorga]

Thank you, yeah a few subsequent posts by others got me confused about it. That's ace, thanks. I struggle to read these schematic diagrams as I'm not so technically proficient as others. I was just worried regarding the ground connection and leaving it disconnected. Cheers mate.

 

[Visitor]

There's this wonderful new website - called 'google'

Just enter NAD7140 schematic and follow the links.

We're more than 20% of the way through the 21st century, have you never used a search engine?.

Could you be a little more condescending? It's a frekin' fantastic way to welcome new members!

 

[Jthorpe5150]

What size 22k or doesnt it matter?