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Drop THX-789 Volume pot replacement?

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. :)
 
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.
 
levimax said:
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.
Click to expand...
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?

index.php
 
Selarom said:
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?

index.php
Click to expand...

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

sannidg.en.made-in-china.com

[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
Click to expand...
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.
 
levimax said:
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.
Click to expand...
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 said:
Would this one work?

Alps "Blue Beauty" Potentiometers | HIFICollective

Alps "Blue Beauty" Potentiometers
www.hificollective.co.uk www.hificollective.co.uk
Click to expand...
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.
 
Bringing back this thread from the dead...
I wonder if anybody ever successfully found a replacement or solution for this?
I've had the crackling problem for a while now. My workaround is to typically just spend a few seconds turning back and forth the knob to "clean it" until it somewhat stops cracking enough in the quadrant I need to not drive me crazy while adjusting volume between tracks....
 
Mimizone said:
Bringing back this thread from the dead...
I wonder if anybody ever successfully found a replacement or solution for this?
I've had the crackling problem for a while now. My workaround is to typically just spend a few seconds turning back and forth the knob to "clean it" until it somewhat stops cracking enough in the quadrant I need to not drive me crazy while adjusting volume between tracks....
Click to expand...
Please be sure to update in case you ever find anything out. Monoprice dropped my THX 889 warranty claim because they were unable to provide a replacement unit (and I preferred to keep the current unit instead of returning for refund since I hadn't found anything better to replace it with).
 
Hello All,

Started this thread and the solution still seems to be to replace the pot, but there’s no same size solution of higher quality. I found some relay based solutions on ebay but haven’t had the time to properly dedicate to it.

Best you can do is find an electronics spray cleaner and a lubricant. Open the unit, spray the cleaner on the pot, move the knob to clean the dirt and then do the same with the lubricant. It will temporarily fix it until it happens
 
For now I opened the chassis and used compressed air and then put a LOT of contact cleaner on the pot itself and through the knob from the front panel side.
It's clean and quiet as on the first day!
 
I am hesitant to by DROP products because of this kind of thing. I wonder how many of these units they sold?
 
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