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Replacing Naim 32.5 / 72 balance pot with fixed resistors

hifiaf

hifiaf

pfm Member
Hi everyone,

Like many people, to get "balance" on my 32.5, I have to have the balance pot at about 2 o'clock, which for obsessives like me is visually offensive :) I've also been wondering about the potential sonic advantages of using fixed resistors in place of the balance pot.

I found this brief mention of the mod on Acoustica:

remove the balance pot and replace with 2 welwyn rc 55y or any good quality resistors e.g vishay dale cmf55s. Try values around 2k67. Not tried this yet but apparently cleans up the sound a bit.
Thanks to Les Worstenholm
Click to expand...

I also found a thread here on pfm in which there is some debate about the number (2? 4?) and value of resistors (@neiljadman recommends 1K2), and whether you'd need to use resistors at all.

We've been discussing this over on Audioflat, and here's what we figure so far.

Here's how we've numbered the 6 pins on the pot (1, 2, and 3 are the row hidden in this photo).

IMG_7048-1.jpeg


Based on values measured in circuit and on the visible traces in the image below, we figure this is what they all correspond to:

1 and 6 connect to ground (they have continuity in circuit)
3 and 4 are input signal from volume pot
2 and 5 are output from the wiper

IMG_7047-1.jpeg


Last night I removed the pot from my 32.5 (I'm very proud that I was able to do so non-destructively, a feat of solder-sucking!) When I measure the pot, out of circuit, at the 2 o'clock position that gives me more-or-less balance, I get these values:

Between...
1 and 2: 8k18 (this varies from 18.4R to 9k05 L-R; "centre" is 7k20)
1 and 3: 9k02 (this is fixed)
6 and 5: 6k70 (this varies from 8k70 to 18.4R L-R; "centre" is 7k73)
6 and 4: 8k68 (this is fixed)

So to perfectly replicate the effect of the balance pot in the circuit, @nobeone has suggested on AudioFlat, you would do the following:

8.18k resistor in a standard value 8k2 between 1&2,
9.02k - 8.18k = 840 ohm resistor in a standard value 845R between 2&3
6.7k resistor in a standard value 6k65 or 6k8 between 6&5
8.68k - 6.7k = 1.98k in a standard value 1k96 or 2k between 5&4

...BUT it's a bit confusing to me why I would need so many resistors of different values...

...AND this doesn't correspond to what others have done: using only two resistors, and values around 1K2 (@neiljadman) or 2K6 (Acoustica).

Others have also suggested doing away with resistors entirely and linking directly...

So I'm wondering what others have done, what recommendations you'd make. The goal is not so much to replicate the exact effect of the balance pot as to do away with some of its inefficiencies (and not have to look at it cocked over to 2 o'clock all the time!) while also not messing up the circuit.

Of course it's possible the original issue is not the balance pot but some channel imbalance elsewhere in my system...
 
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Just link it out, no resistors necessary - it's just a second potential divider on top of the one that is the volume pot. Of course you could just put the knob in the centre position when it's balanced. There's nothing in the pre amp or amps that can cause a major imbalance so it's really only for room correction.
 
2 resistors per channel. both the same value. anything between about 1k5 and 4k7 will do fine, all that matters is they are all the same. solder between 1 and 2 and then another one from 2 to 3 and do the same on the other channel.

Edit: Or as MJS says! Either way should work fine.
 
Seconding MJS..
Linking 4-5 in the front row and 2-3 in the second row and you should be fine.
 
I really appreciate all the replies! Linking without resistors is an appealingly "clean" solution. That's what I'll try...
 
Well I've done it :)

IMG_7053.jpeg


Two little links added:

IMG_7054.jpeg


On my system, this gives me perfect balance -- and, wow, a new clarity. (Admittedly, I did change a few other things around —— but this certainly didn't hurt anything!)

Over on AudioFlat, @YNWOAN has suggested that you could just link legs 2+3 and 4+5 of the balance pot and leave it in place (maybe that's what you were suggesting too, MJS?). That would save the hassle of removing the pot (and getting the motherboard out), be reversible and less potentially destructive, better for resale value... and also give you something to hold the balance knob in place! You'd be left with the connections to ground via 1 and 6, but that wouldn't make any difference, would it?

Anyway, my balance pot was already out, though, so as a lover of simplicity, I left it out...

Thanks again for the help -- couldn't be happier with this little mod!
 
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I was suggesting exactly what you've done. Leaving the balance pot in and linking it out would just put extra resistance on the volume wiper and alter its characteristics a bit.
 
I'm using the brilliant Ryan sound labs cards so don't need the volume pot either

Guess it's a similar job just to either link that out (might be a bit loud!!) Or put in a couple of fixed resistors to set it ( at the fixed 11 o'clock position) I now use
 
Mynamemynaim said:
I'm using the brilliant Ryan sound labs cards so don't need the volume pot either

Guess it's a similar job just to either link that out (might be a bit loud!!) Or put in a couple of fixed resistors to set it ( at the fixed 11 o'clock position) I now use
Click to expand...

A volume pot would more or less take itself right out of circuit if turned all the way up, wouldn't it?
 
Yes I guess it might

The Ryan cards have three settings for the volume range ...but even on the lowest setting it might be too loud too quickly with the (manual) volume pot at full

It might be ok though..I could try it as I was mistaken....I don't leave it at 11 o'clock it's actually at 1 o'clock and maximum is about 5 o'clock
And I use the middle range on the cards normally
 
hifiaf said:
Like many people, to get "balance" on my 32.5, I have to have the balance pot at about 2 o'clock, which for obsessives like me is visually offensive :) I've also been wondering about the potential sonic advantages of using fixed resistors in place of the balance pot.
Click to expand...
Sorry I'm a bit late on this one (not around here as much as I used to be). But I have seen (and heard) rooms that need a balance pot to correct for some acoustical imbalances. If yours in one then removing the balance pot may not be your best solution. In which case at 2 O'Clock the balance pot is where it needs to be. If you really find this offensive, balance the sound stage, simply loosen the grub screw on the plastic knob, rotae it to cental and tighten. Bingo.

Otherwise I arrived at the 1K2 value by measuring the actual value from input to output through the balance pot when both channels read the same...presumably that is also when centered - or close.
 
I did something similar with my 42 but I wasn't happy having a hole in the front panel so I machined a small piece of delrin rod about 12mm long with a hole in the centre through which I could push the balance knob. I glued the spacer to the back of the front panel and when cured pushed the knob through. The knob is a push fit so it can be turned to the right position.
 
I found that removing the balance pot and linking the terminals gave me dead-even balance -- so in my case setting the balance pot to 2 o'clock seems to have been addressing an imbalance in the pot itself, not an issue with my room. My knob would only attach to the pot in one fixed orientation, so that adjusting the fit with the grub screw wasn't possible. I covered the hole by sticking the balance knob back in and holding it to the front of the case with blu tack :) Overall I'm really happy with this mod -- system's sounding amazing and I have a dummy balance knob pointing straight to the ceiling!
 
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