replacing 10KA slide pot with 100KA - audio mixer

[spy]

Hi,

Unfortunately the master fader potentiometer on my audio mixer broke. One of the tracks is fried exactly at the beginning of it's travel and I can't use one of the submasters of the mixer as it's at maximum level all the time.

The mixer is an old Tascam M35 and it has a quadruple master fader. It's an Alps 10KAx4. Tascam doesn't have it and Alps doesn't make them anymore so eBay is my only choice. There's a seller who sells 10Kx4 linear and 100KAx4 log. I prefer to go with logarithmic but how much the 100K will affect the circuit?

I don't have the service manual and I can't find any schematic. If anyone has it it'll be very helpfull. There's only a block diagram if anyone is interested.

[Leo_Gnardo]

Assuming these faders are potentiometers acting as normal volume controls, I see little diff whether 10K or 100K. Possibly a little more bandwidth as they'll load the driving circuit less. That may or may not be a good thing. If it's a problem tack an 11K or 12K resistor across each hot-to-ground to correct the loading. Old gear like this, sometimes you have to punt.

[spy]

Yes, the master fader acts as a volume control. It's the master volume control of four submaster channels.

If I'll add a resistor across each hot-to-ground, will it be a logarithmic then?

I like the idea of more bandwidth with the 100KA. No problem to punt just not make it worse.

[Leo_Gnardo]

I like the idea of more bandwidth with the 100KA. No problem to punt just not make it worse.

Then leave off the correction resistors, unless it sounds awful or has oscillations.

Sometimes less bandwidth is a blessing: the wider you open the window, the more s#!+ flies in, old sound engineer adage.

Your faders will still be audio/log taper, whatever they were made to be with or without parallel resistors.

[Enzo]

There are two kinds of volume control. One is the common voltage divider like a zillion tube amps use. The other is the gain control in an op amp circuit. In the old voltage divider, you can get away with a wide range of resistance. In the case of the op amp, the value of the feedback resistor (your pot)is part of what determines the stage gain. But changing the pot value by a factor of ten, you will also affect the stage gain. SO if it is a 10k in a op amp feedback loop, it kinda need to swtay 10k. You could make a 100k close to 10k with parallel resistors.

Does your avaialble part have the same footprint as the original?

[spy]

Good point, Enzo but I believe it's a common voltage divider.

Yes the available part has the same footprint. It's exactly the same slide pot except it's 100K. The footprint it's not so critical as it's not on the pcb. Here's a photo of the original slider. The cover is missing in an attempt to clean it but then I discovered the fried track.



And the 3rd track over here,

[Enzo]

Footprint only mattered if it was soldered into a circuit board. Wires trailing, it can be wired to anything.

As long as the dimension is the same to fit your panel, go for it.

[J M Fahey]

And the 3rd track over here,

**Third** track??????
I see 2 or 4 there.

[spy]

**Third** track??????
I see 2 or 4 there.

Sorry, I meant that you can see at the photo the 3rd fried track, if you count them from left to right .
It's a quadruple potentiometer so 4 mono tracks. One track of each of the four submaster channels.