Drop THX-789 Volume pot replacement?

[Dreyfus]

I am pretty sure that my unit had this issue even without the DAC connected to the input. But I will check that once again when the issue reoccurs.

Did not hear any cracks since the last cleaning. Knock on wood.

 

[rentaclaus]

Some of the cleaners let the contacts get addictive to use more and often... I have good experiences with Teslanol T6.

https://www.amazon.de/Teslanol%C2%AE-T6-OSZILLIN-Kontakt-Tunerspray-400ml/dp/B001FSXMO2

 

[Dreyfus]

That's the stuff I used, actually. But the newer one w/o the T6.

 

[levimax]

While DC across the pot is the "usual suspect" for crackling it is not always the case. I built a little pre-amp during Covid and was only able to get a cheap pot for it due to supply chain issues and it was noisy within a few months. I was using good op amps with very little DC offset so the first thing I tried was replacing the cheap pot with an ALPS pot and it completely solved the issue. I would try some heat from a heat gun or hair dryer to soften the glue. Not sure what op amps are used in this but if NE5533 op amps, which have relatively high DC offset, I would try a blocking cap first, if using op amps with low DC offset I would try replacing the pot first. Good luck.

 

[Selarom]

While DC across the pot is the "usual suspect" for crackling it is not always the case. I built a little pre-amp during Covid and was only able to get a cheap pot for it due to supply chain issues and it was noisy within a few months. I was using good op amps with very little DC offset so the first thing I tried was replacing the cheap pot with an ALPS pot and it completely solved the issue. I would try some heat from a heat gun or hair dryer to soften the glue. Not sure what op amps are used in this but if NE5533 op amps, which have relatively high DC offset, I would try a blocking cap first, if using op amps with low DC offset I would try replacing the pot first. Good luck.

According to this picture below (source) OpAmps are OPA564, TL062C, OPA1602A (which I've seen in other amps too).

What level of DC offset spec can cause this?

 

[Selarom]

These are the specs of the volume potentiometer inside the THX-789.

[Hot Item] 9mm RV91110g0kq Dual Unit 6pins Volume Control Rotary Potentiometer for Audio/ Amplifier

Resistance: Variable Resistor Function for Resistance: Load Resistor Installation: SMD Resistor Material: Carbon Film Resistor Packaging: Throught Hole Type: Rotary Potentiometer

sannidg.en.made-in-china.com

 

[levimax]

According to this picture below (source) OpAmps are OPA564, TL062C, OPA1602A (which I've seen in other amps too).

What level of DC offset spec can cause this?

NE5533 Vos (offset voltage at 25°C) (max) (mV) 4

OPA 1602 Vos (offset voltage at 25°C) (max) (mV) 1

Assuming the op amps are not "fake" I doubt DC offset is an issue with the OPA1602 but that is just an educated quess.

 

[levimax]

These are the specs of the volume potentiometer inside the THX-789.

[Hot Item] 9mm RV91110g0kq Dual Unit 6pins Volume Control Rotary Potentiometer for Audio/ Amplifier

Resistance: Variable Resistor Function for Resistance: Load Resistor Installation: SMD Resistor Material: Carbon Film Resistor Packaging: Throught Hole Type: Rotary Potentiometer

sannidg.en.made-in-china.com

View attachment 273806

View attachment 273807

This looks OK on paper, I have no idea about this brand and about potential fakes. Since it is sealed not sure how much deoxit will help.

 

[paudio]

This looks OK on paper, I have no idea about this brand and about potential fakes. Since it is sealed not sure how much deoxit will help.

They're about 10-15 times cheaper than a high end Alps pot. Probably worth replacing. Would be good to know if there is a DC issue though as well

 

[Selarom]

Would this one work?

Alps "blue beauty" Potentiometers | HIFICollective

Alps "blue beauty" Potentiometers

www.hificollective.co.uk

 

[levimax]

Would this one work?

Alps "blue beauty" Potentiometers | HIFICollective

Alps "blue beauty" Potentiometers

www.hificollective.co.uk

It will work if you can figure out how to mount it. The original is 9.5mm wide and that Alps is 27 mm wide.... this is a big difference and would require some case work and wiring gymnastics. It is a great pot... quiet and accurate with a great "feel". I don't think Alps makes 9mm pots I have used their 16mm and 27mm. For 9 mm "Alpha" is a well know brand but also lots of "fake" ones. A 9mm pot will never have the feel or performance of a 27 mm pot.