Today I took out the Alps volume pot in my TU8600. I soldered the volume in and out pins together--one time on the right channel and one time on the left channel. I left the grounds open.
Disclaimer-- I'm human and guilty of subjectivity and confirmation bias.
That said, the 8600 sounds definitely better without the volume pot. Now, maybe a better resistor based and numerous stepped attenuator wouldn't degrade sound. But, I am confident the amp sounds better without that pot, in my setup and my room.
Disclaimer-- I'm human and guilty of subjectivity and confirmation bias.
That said, the 8600 sounds definitely better without the volume pot. Now, maybe a better resistor based and numerous stepped attenuator wouldn't degrade sound. But, I am confident the amp sounds better without that pot, in my setup and my room.
So here are my subject observations on the sound.
Everything is bigger. The bass is the most noticeable. No MSG bass--as Viktor would say--but it's much more defined and present without being overbearing.
Separation in space is greater. Even though there's a bigger soundstage I'm surprised that nuances and little details are not pushed aside.
I also ditched a bit of the grounding hum I had with grounding the Alps to the chassis. Sanding it down helped but I still had some. My speakers are 102 dB efficient so this matters to me.
Everything is bigger. The bass is the most noticeable. No MSG bass--as Viktor would say--but it's much more defined and present without being overbearing.
Separation in space is greater. Even though there's a bigger soundstage I'm surprised that nuances and little details are not pushed aside.
I also ditched a bit of the grounding hum I had with grounding the Alps to the chassis. Sanding it down helped but I still had some. My speakers are 102 dB efficient so this matters to me.
So volume control at those 2 devices? Maybe changing the Alps for a supposedly better potentiometer would be a safer choice. The risk with "open" power amplifiers is that when something goes wrong at the source (it happens) it will all be amplified to the maximum. The TU-8600 was intentionally designed with volume control as well.
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Hum is another issue than perceived quality of the Alps. Probably a ground loop of sorts with the sources so you may be solving an issue with the wrong solution. Secondly it is not solved, it seems a little less. IMO it should be solved 100% as hum is annoying. So something has been removed and you still have hum. Then removing the potentiometer was not the solution.
Are the sources DIY? TU-8600 is not known for hum AFAIK. First thing I would do is to use a ready made source and I would check the TU-8600 to have been connected to a 3 prong wall socket with PE. Beware of connecting sources with no output level control to "open" amplifiers as the risk is full volume. This is why the clever engineers at Elekit added volume control. It is a protection.
Also now the potentiometer is gone there is full amplification of anything. IMO it would now be better to use an input RC filter to filter HF/RF. In effect you might be steering away from a perfectly fine operating TU-8600 without a good diagnosis what exactly is causing the hum (while still having hum
).
Are the sources DIY? TU-8600 is not known for hum AFAIK. First thing I would do is to use a ready made source and I would check the TU-8600 to have been connected to a 3 prong wall socket with PE. Beware of connecting sources with no output level control to "open" amplifiers as the risk is full volume. This is why the clever engineers at Elekit added volume control. It is a protection.
Also now the potentiometer is gone there is full amplification of anything. IMO it would now be better to use an input RC filter to filter HF/RF. In effect you might be steering away from a perfectly fine operating TU-8600 without a good diagnosis what exactly is causing the hum (while still having hum
).
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Thanks Jean Paul!
Yes, it's not a ton of hum, but it's present.
The sources right now are either Technics Grand Class 1200 GAE feeding Manley Chinook, Doge Audio Tube DAC, Audiolab CD Transport, Tidal feeding Roon, feeding the Doge 7 DAC.
When I use these same sources with two other amps, Primaluna Dialogue HP and Carver Crimson 275--no hum.
Any chance I could have a ground loop in the RCA inputs? The solder connections look great, but they get a lot of work because there is only one set of inputs.
Yes, it's not a ton of hum, but it's present.
The sources right now are either Technics Grand Class 1200 GAE feeding Manley Chinook, Doge Audio Tube DAC, Audiolab CD Transport, Tidal feeding Roon, feeding the Doge 7 DAC.
When I use these same sources with two other amps, Primaluna Dialogue HP and Carver Crimson 275--no hum.
Any chance I could have a ground loop in the RCA inputs? The solder connections look great, but they get a lot of work because there is only one set of inputs.
You do have an issue with hum (and not with volume control) which requires further examination. First would be to check if you built it 100% according the manual, certainly the RCA input grounds need special care. They both need to be isolated from chassis.
BTW since you will be working in it anyway this is an excellent chance to add 2 extra inputs!
BTW since you will be working in it anyway this is an excellent chance to add 2 extra inputs!
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Questions:
1. Is it connected with a 3 prong power cable to a wall socket with PE?
2. Does it hum with nothing but speakers connected? So with not a single source connected!
3. Did you check with another set RCA cables? So now with a source and the output level of the source first set to low volume.
4. It was built pretty well but .... was it in any way modified in the years that followed?
Adding inputs is a nice thing to do but make sure to use a small PCB with relays direct in the vicinity of the RCA plugs. I still think volume control (in any form) should be back where it was, definitely when you have phono/dac/cd inputs later on. If I am not mistaking you can have maximum 3 sets of RCA and then you already need to place them wisely. I would like to advise to use 3 sets (or 4 when it is possible) all of good quality isolated types like CMC or the like. So also to replace the original ones. A small PCB with micro relays is designed in an hour, power can come from the filament supply. Where you will locate the rotary switch is up to you. When placing at the front as is standard then one must work very carefully to avoid damage of the front cover. Always use self adhesive tape when drilling.
I am very sure many TU-8600 owners will like such a PCB as well. It is a good device but it lacks inputs.
1. Is it connected with a 3 prong power cable to a wall socket with PE?
2. Does it hum with nothing but speakers connected? So with not a single source connected!
3. Did you check with another set RCA cables? So now with a source and the output level of the source first set to low volume.
4. It was built pretty well but .... was it in any way modified in the years that followed?
Adding inputs is a nice thing to do but make sure to use a small PCB with relays direct in the vicinity of the RCA plugs. I still think volume control (in any form) should be back where it was, definitely when you have phono/dac/cd inputs later on. If I am not mistaking you can have maximum 3 sets of RCA and then you already need to place them wisely. I would like to advise to use 3 sets (or 4 when it is possible) all of good quality isolated types like CMC or the like. So also to replace the original ones. A small PCB with micro relays is designed in an hour, power can come from the filament supply. Where you will locate the rotary switch is up to you. When placing at the front as is standard then one must work very carefully to avoid damage of the front cover. Always use self adhesive tape when drilling.
I am very sure many TU-8600 owners will like such a PCB as well. It is a good device but it lacks inputs.
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1. Yes, it is. I tried using a two prong to defeat the ground just to see--no change.
2. Yes, it hums all on its own with no source connect.
3. Yes, I checked RCAs and have used generics, Monoprice, Chord Electronics, and DH Labs. The DH Labs are the quietest. All show hum.
4. It has not been modified other than the Alps removal.
Yes, there is space for a second set of jacks in the rear. I think this is the only real sin of omission on this unit.
I did uninstall the screws on the OPTs holding them in place. I rotated them 90 degrees to see if they were singing with the power transformer. Hum seemed to go down a wee bit, but not solved. OPTs are re-oriented and secured to their original spots.
2. Yes, it hums all on its own with no source connect.
3. Yes, I checked RCAs and have used generics, Monoprice, Chord Electronics, and DH Labs. The DH Labs are the quietest. All show hum.
4. It has not been modified other than the Alps removal.
Yes, there is space for a second set of jacks in the rear. I think this is the only real sin of omission on this unit.
I did uninstall the screws on the OPTs holding them in place. I rotated them 90 degrees to see if they were singing with the power transformer. Hum seemed to go down a wee bit, but not solved. OPTs are re-oriented and secured to their original spots.
The answer on question 2 shows your TU-8600 has an issue and it has nothing to do with volume control as previously mentioned (so I don't see the logic to remove the potentiometer). This can be a tough one*, I would first check everything against the manual so cabling, RCA inputs, solder connections, grounds, measure ripple voltage on power supply caps like C116, etc. Especially the ripple filter should be carefully inspected.
*Is it 60 Hz mains hum or 120 Hz hum from the PSU? There are many possibilities. Depending on your experience you might need the help of Elekit or the company that sold the device.
*Is it 60 Hz mains hum or 120 Hz hum from the PSU? There are many possibilities. Depending on your experience you might need the help of Elekit or the company that sold the device.
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