Drop THX-789 Volume pot replacement?

[Selarom]

Hello!

It's becoming very annoying having to use an electronics cleaner on my Drop THX-789's volume potentiometer every week to clean up the crackling sound. My office room is kept pretty clean and I don't know if it's dust accumulation or what... but after I spray electronics cleaner it works fine. A couple of days later, the crackling is back usually on the left channel and then on to the right channel and gets worse and worse. I've tried going on digital control from Windows, but it's not the same.

Has anyone been successful in replacing the volume pot with something else? Perhaps a relay ladder volume control that's pin compatible with the current pot?

Thanks in advance

 

[Doodski]

I've used several different control cleaners and lubricants. Some clean more than lube and others more lubricate than clean. What are you using?

 

[Dunring]

On Ebay you can find them all the time in protection mode in the not working/parts condition. If you can get one cheap enough it might be worth it for the part.

 

[Selarom]

I've used several different control cleaners and lubricants. Some clean more than lube and others more lubricate than clean. What are you using?

I am just using an electronics safe cleaner from CRC. What would be a good electronics safe lubricant? Perhaps that's what I'm missing

 

[FrantzM]

On Ebay you can find them all the time in protection mode in the not working/parts condition. If you can get one cheap enough it might be worth it for the part.

True, and that worries me. It is one of the few amps capable of powering my HiFiMan HE-6SE.
Does Drop/THX provide repair services?

Peace.

 

[Doodski]

@Selarom this has lubricant and cleaning solvent too. The can comes with a extension tube(s) for easier spraying into stuff.

DeoxIT®, #D5S-6ET - CAIG

DeoxIT, #D5S-6ET. DeoxIT D-Series D5 spray, red extension tube, 5% solution, flushing action, perfect-straw valve, includes 24" extension tube, 142 g

caig.com

 

[Selarom]

True, and that worries me. It is one of the few amps capable of powering my HiFiMan HE-6SE.
Does Drop/THX provide repair services?

Peace.

I don't think so. Technical or repair support is not one of their support options.

The ideal solution would be a pin compatible component replacement of higher quality. Volume control is single ended so it should not be very expensive. A resistor ladder replacement would me awesome though.

 

[Selarom]

@Selarom this has lubricant and cleaning solvent too. The can comes with a extension tube(s) for easier spraying into stuff.

DeoxIT®, #D5S-6ET - CAIG

DeoxIT, #D5S-6ET. DeoxIT D-Series D5 spray, red extension tube, 5% solution, flushing action, perfect-straw valve, includes 24" extension tube, 142 g

caig.com

Thanks!

Will check it out!

 

[paudio]

Seems odd with it's young age. Might be deteriorating internally. First step would be visual inspection to see if you can identify what part is used from the part markings or the board.

Measure pin diameter, pin spacing, shaft size, shaft length
Get number of pins, pin layout, shaft end type (matches pot)
Likely through hole mounted

Likely it's going to say like B50K on it.

You could also ask Drop if they can identify the part number.

Replacing it with a good quality sealed unit would be ideal.

 

[Selarom]

I found this post from the Monoprice THX amp that's almost a clone of the 789. Uses the same volume pot. Interesting information

[owner's thread] Monoprice Monolith THX AAA 887 headphone amp

Creating this thread to have all the owners and members have a place to discuss the Monoprice THX 887 amp without creating extra posts in the official review thread. Feel free to post any questions and concerns that you may have regarding this amp in this thread.

audiosciencereview.com

 

[Dreyfus]

Hey there,

pretty much the same problem with my Monolith AAA 887 here. First run with some cleaning spray did only fix the issue for about two weeks. Then, the crackling got even worse. I disassembled the unit a second time yesterday, placed the unit with the front pointing down on the table and more or less drained the recessed area around the pot with the cleaning solution. I used some Teslanol "Contact and Preservation Spray" (https://www.wentronic.com/en/contact-and-preservation-spray-26026). Not sure if that is the appropriate stuff on the long run.

The issue is gone for the moment, together with the friction of the pot. I guess that's the sign that the solvent properly found its way into the housing this time.

Not sure how long it will survive this time, though. The unit is about 12 months old. Looks like their cheapo pots are a significant weak spot.

Has anyone managed to remove the knob, yet? Is it glued strongly?

I assume its the same thing for the 789.

 

[evalrat]

Hey there,

pretty much the same problem with my Monolith AAA 887 here. First run with some cleaning spray did only fix the issue for about two weeks. Then, the crackling got even worse. I disassembled the unit a second time yesterday, placed the unit with the front pointing down on the table and more or less drained the recessed area around the pot with the cleaning solution. I used some Teslanol "Contact and Preservation Spray" (https://www.wentronic.com/en/contact-and-preservation-spray-26026). Not sure if that is the appropriate stuff on the long run.

The issue is gone for the moment, together with the friction of the pot. I guess that's the sign that the solvent properly found its way into the housing this time.

Not sure how long it will survive this time, though. The unit is about 12 months old. Looks like their cheapo pots are a significant weak spot.

Has anyone managed to remove the knob, yet? Is it glued strongly? I assume its the same thing for the 789.

In the days of tubes, it was always direct current through the potentiometer because the grid had caught cathode material and current would start running. That's why capacitors were always needed in the signal path. I am sure your cracking potentiometer has an anolog cause. It"s a design problem rather than a faulty potentiometer. If you can block DC. into the potentiometer without disabling the amp the cracking stops.

 

[FrantzM]

Hi

Mine is working with no issue (FINGER CROSSED!!). I do like the balanced input and the power. I EQ my headphones and use mostly the HE6SEv2. I do not ever need to turn on the volume past 1 o'clock on the THX 789 with it. Balanced output for the HE6SEv2.
What would be a good replacement for these? With balanced inputs and power with headroom for the HE6SEv2 , serious customer support, under $300?

Peace.

 

[Dreyfus]

It"s a design problem rather than a faulty potentiometer. If you can block DC. into the potentiometer without disabling the amp the cracking stops.

Then why does it get better when I turn the knob a few rounds left and right once the crackling occurs (everytime when changing volume)?

 

[evalrat]

Then why does it get better when I turn the knob a few rounds left and right once the crackling occurs (everytime when changing volume)?

Probably because that way you are polishing the carbon track a little bit. But every irregularity in the the track wil bounce the slider and give a crack when dc current is running through the pot. The problem wil always return. A new pot. wil devellop the same problem after a while. Mayby you could check for zero offset in the inputs and outputs . And there even be a trimmer somewhere to tune out zero-offset,

 

[Selarom]

Hey there,

pretty much the same problem with my Monolith AAA 887 here. First run with some cleaning spray did only fix the issue for about two weeks. Then, the crackling got even worse. I disassembled the unit a second time yesterday, placed the unit with the front pointing down on the table and more or less drained the recessed area around the pot with the cleaning solution. I used some Teslanol "Contact and Preservation Spray" (https://www.wentronic.com/en/contact-and-preservation-spray-26026). Not sure if that is the appropriate stuff on the long run.

The issue is gone for the moment, together with the friction of the pot. I guess that's the sign that the solvent properly found its way into the housing this time.

Not sure how long it will survive this time, though. The unit is about 12 months old. Looks like their cheapo pots are a significant weak spot.

Has anyone managed to remove the knob, yet? Is it glued strongly?

I assume its the same thing for the 789.

Yes, I've tried removing it and it is glued strongly. I would even dare say they used epoxy on this thing. I would love to find something pin compatible. Perhaps a resistor ladder volume controller. that would be awesome. I'm sure it can be done, but I worry it will be more expensive than the price of a new 789 amp. Hopefully I'm wrong.

 

[Selarom]

In the days of tubes, it was always direct current through the potentiometer because the grid had caught cathode material and current would start running. That's why capacitors were always needed in the signal path. I am sure your cracking potentiometer has an anolog cause. It"s a design problem rather than a faulty potentiometer. If you can block DC. into the potentiometer without disabling the amp the cracking stops.

I find this confusing. Because the crackling sound happens when the one changes the volume. Once you set on the desired volume level, the crackling sound stops. I would think that if the issue is DC current going through the volume pot, the crackling sound issue would be a constant rather than when changing volume.

 

[evalrat]

I find this confusing. Because the crackling sound happens when the one changes the volume. Once you set on the desired volume level, the crackling sound stops. I would think that if the issue is DC current going through the volume pot, the crackling sound issue would be a constant rather than when changing volume.

That is correct. The cracking sound occurs when the current is temporarily interupted where the track has faults, when the slider is at rest contact is restored.
The problem is direct current runing through the potentiometer. Wear and tear wil always take its toll. You can try cleaning the potentiometer. I saw a nice clip where someone was sanding the innards with a pencil eraser. Simpler try contactcleaner, it might help for a while and doesn't require taking anything apart. Finally you can try to replace the pot. the pin grids are standerdised so the replacement only needs the same value and fit mechanicaly,if you can't find the same formfactor you can even mount it upside down and make the connections with wires. But again on the internet you can find testimonials where replacement didn't help at all.
I Would accept the cracking until it becomes unbearable and then buy another system from a different manufacturer.

 

[Selarom]

That is correct. The cracking sound occurs when the current is temporarily interupted where the track has faults, when the slider is at rest contact is restored.
The problem is direct current runing through the potentiometer. Wear and tear wil always take its toll. You can try cleaning the potentiometer. I saw a nice clip where someone was sanding the innards with a pencil eraser. Simpler try contactcleaner, it might help for a while and doesn't require taking anything apart. Finally you can try to replace the pot. the pin grids are standerdised so the replacement only needs the same value and fit mechanicaly,if you can't find the same formfactor you can even mount it upside down and make the connections with wires. But again on the internet you can find testimonials where replacement didn't help at all.
I Would accept the cracking until it becomes unbearable and then buy another system from a different manufacturer.

Can you point me to the thread where the pot was replaced and it didn’t help at all?

 

[paudio]

Can you point me to the thread where the pot was replaced and it didn’t help at all?

I'm guessing it deteriorates like the one before it because the design is running DC through the pot? It's cheap to replace. It's kind of crazy to me cause I can't remember the last time I even had a volume pot let alone an analog one. Would drive me bonkers.