Changing an amp EQ potentiometer value

[cornfarmer]

I have a SS amp with an EQ section that features a knob to select a (high) freq, and a corresponding knob to adjust the level of that freq. 0-10. I assume it's boost type control only.

The pot for the level/boost control is bad, it's value is 10k. The only thing I have on hand is a 50k - would that work or would it be not suitable? The corresponding freq knob's range is 520Hz - 2.2kHz.

Just checking if I need to go buy a new 10k pot tomorrow while I'm out.

 

[agedhorse]

Depends entirely on the circuit, but in general you need to stick with the designer’s choice for both value AND taper.

 

[crazycloud]

Just buy the correct part from Digikey, Mouser, Element14, RS (Radiospares) etc depending on where you are in the world.

 

[cornfarmer]

Taper isn't something I can readily tell. This pot is labeled '25A 10k ohm TE'

 

[agedhorse]

Taper isn't something I can readily tell. This pot is labeled '25A 10k ohm TE'

The taper is in the value, it's an A taper, 25 curve. Generally as along as you choose an A taper, the different curves that MOST designers use are common enough that they are't even specified unless outside the standard value.

Is it 9mm or 16mm? What bushing size and shaft type/length?

 

[cornfarmer]

16mm wide, same for shaft

 

[agedhorse]

Be aware that there are 2 ways to specify shaft length. Be sure you read the specs carefully.

 

[cornfarmer]

No worries. I stopped by my local electronics shop, they scoped it out and got a couple ordered. Linear taper which hopefully works.

 

[6thplanet]

So I thought A was Log taper, B Linear, C Rev Log. Second guessing myself I Googled it. Turns out I'm right...in US/Asia, Europe apparently is opposite for A and B. Never knew that

 

[cornfarmer]

Hmm, so the amp is from Japan - so the pot could be log taper...I know the difference between them, but don't think it will be that radical if it's changed to linear...

 

[agedhorse]

Hmm, so the amp is from Japan - so the pot could be log taper...I know the difference between them, but don't think it will be that radical if it's changed to linear...

It could be radically different if you get the tapers mixed up... to the point of being unusable for this application. The flat position would be anything but flat. This is why it depends entirely on the circuit it's used in. Generally, in a Baxandall style eq circuit, it's a linear taper which we call a B taper or possibly a modified linear taper (W taper). You need to know how the original pot is specified or the circuit that it's used in.

 

[cornfarmer]

A bridge too far....this is a kooky Aria made amp called the 'LOCO Micro Bass Amp'. It's something like 60-70w thru two 6" drivers, with a port on the back. It has an additional 8 ohm speaker out for a blistering 90w. Controls:

 

[agedhorse]

No way to know without the schematic, or measuring the pot and documenting the curve.

 

[Aloe]

Europe apparently is opposite for A and B

I've seen this claim recently on TB several times.
but I've never heard of this before, despite living at the East of Europe.

Europe-made MEC pots use A as log, B as linear.
which manufacturer has them opposite?

 

[agedhorse]

I've seen this claim recently on TB several times.
but I've never heard of this before, despite living at the East of Europe.

Europe-made MEC pots use A as log, B as linear.
which manufacturer has them opposite?

I don't know for sure, but it may be some legacy parts rather than current production.

 

[Aloe]

I don't know for sure, but it may be some legacy parts rather than current production.

hm. I've chatted a bit with an ai on this and I'm not sure on the taper of the '25A' pot above now and I'll just paste it here.

While many modern manufacturers (especially in the audio and guitar world like MEC, CTS, or Alpha) have moved toward the "A = Audio/Log, B = Linear" standard to match Asian/Global markets, TE Connectivity's Citec line is a legacy industrial product.

TE Connectivity (specifically the Citec factory) maintains its original European industrial marking system for its 23, 25, and 27 Series pots. In their current technical datasheets:

• A = Linear
• B = Logarithmic (Audio)
• C = Antilog

You can see this in their modern part numbering (e.g., a 25A103 is a 10k Linear, while a 25B103 is a 10k Log).

Here is the breakdown of why "A" still means Linear in this specific case, even inside an amplifier.

1. The Manufacturer Rules the Code​

In the world of components, the brand determines the code, not the application.

• MEC, Alpha, and CTS (the most common "guitar" brands) use the "A = Audio/Log" standard.
• TE Connectivity (Citec) is an industrial manufacturer. Their parts are found in medical equipment, industrial lathes, and—crucially—pro-audio gear like British-made guitar and bass amps.
• TE/Citec has never swapped their codes. For a Citec "25" series pot, A is Linear and B is Log. If you were to buy a brand new one from a distributor like Mouser today to fix that amp, you would have to order the "A" suffix to get a linear taper.

2. The "British Heritage" Factor​

TE/Citec pots were the "gold standard" for UK-made amplifiers (like Marshall, Orange, and Vox) for decades. Because British engineers grew up with the European standard (A=Linear, B=Log), the schematics for those amps are written that way. TE Connectivity keeps the marking the same so that a repair tech in 2026 can see "25A" on a 1995 Marshall schematic and buy the exact same part today.

The Verdict​

Because it is a TE (Citec) brand pot:

• Marking 25A = Linear
• Marking 25B = Log/Audio

If you are replacing it with a different brand like Alpha or Bourns, you actually have to "flip" your thinking: you would need to buy an Alpha "B10K" to match the performance of your TE "25A 10K".

Quick Tip: If the pot is still functional enough to test, turn it to 12 o'clock. If the resistance is roughly 5k, it's Linear. If it's down around 1k to 1.5k, then I’ll eat my hat—it’s Log!

 

[Passinwind]

hm. I've chatted a bit with an ai on this and I'm not sure on the taper of the '25A' pot above now and I'll just paste it here.

I’ve definitely seen this with some other Euro pots, but like Andy I think they were legacy products and I don’t remember the specific branding.

 

[agedhorse]

Considering that Taiwan Alpha and Noble (plus their numerous knock-offs and counterfeits) literally dominate the audio industry with a 99% market share, I've never worked with any of the other parts.

 

[Aloe]

I’ve definitely seen this with some other Euro pots, but like Andy I think they were legacy products and I don’t remember the specific branding.

it actually seems like the pot in question in OP is also marked by 'A', but is linear.
I think, it qualifies as a legacy product (and frankly I'd expect the EQ pot to be linear).

 

[agedhorse]

it actually seems like the pot in question in OP is also marked by 'A', but is linear.
I think, it qualifies as a legacy product (and frankly I'd expect the EQ pot to be linear).

Without measuring, there’s no way to be sure of the taper unless the manufacturer is known along with the part number.

All 4 taper types are used in various eq circuits, it depends on the circuit and the function of the pot.