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TU-882 Mods

68.149.183.101

Keith L. Jackson

I thought I would start a thread on modifications and upgrades to the TU-882 headphone amp. I will start off with hum, though any other upgrades might be added here.
Mine has great sound, though I am a little unhappy about hum in some 40 ohm headphones. The hum is pretty low, but clearly audible when there is no source present. The hum is present regardless of the volume setting and remains the same at minimum and maximum.
The wires from the power supply are tightly twisted, and no positional tweaking resolved the hum. In fact, even when the main power wires (grey) is right next to PCB over the signal path the hum is no louder. It seems that twisting these wires is pretty effective and the hum is coming from somewhere else.
I upgraded the B+ bulk capacitor (C14) from 47uF to 120uF, and the hum *might* be slightly less, but not much.
C11,C12,C13 are all 22uF. Sticking the left over 47uF cap into C12 or C13 seems to be the next candidate operation.
Any ideas on reducing hum?

Edits: 03/20/10 03/20/10

Follow Ups:

RE: TU-882 Mods - Keith L. Jackson 14:23:32 03/20/10 (5)
Impedance switch has no effect. Phones are 40 Ohm.

There is ripple current coming through the amp, headphone impedance should have little to do with resolving this. Though less sensitive headphones will make the hum less audible.

I am interested in upgrades to the amp power supply, not reason to get new phones! :)
- RE: TU-882 Mods - vkung 23:13:04 03/20/10 (4)
  When you switch from low to high impedance,the sound will be changed accordingly. If there is no change, check your installation.
  - RE: TU-882 Mods - Keith L. Jackson 02:10:43 03/21/10 (3)
    Um... sound does change accordingly, and hum is present on all settings nonetheless.
    
    Edits: 03/21/10
    - RE: TU-882 Mods - vkung 08:53:40 03/21/10 (2)
      Please compare with the assembly manual step by step. Something wrong with the assembly.
      
      Please call me this afternoon after 2:30pm (Vancouver Time).
      - RE: TU-882 Mods - Keith L. Jackson 00:10:08 03/23/10 (1)
        
        In Reply to: RE: TU-882 Mods posted by vkung on March 21, 2010 at 08:53:40
        
        Assembly is spot on. All components check out as do all voltage test points.
        
        The unit has a noise floor. *ALL* audio equipment have a noise floor. My TU-882's noise floor is low and acceptable.
        
        Nonetheless, I would appreciate any ideas on lowering the noise floor even further.
        
        RE: TU-882 Mods - vkung 08:57:33 03/23/10 (0)
        
        In Reply to: RE: TU-882 Mods posted by Keith L. Jackson on March 23, 2010 at 00:10:08
        
        The only option is to seperate the power supply from the Chassis.
RE: TU-882 Mods - vkung 14:05:28 03/20/10 (0)
Where you set the impedance switch?
Matching the impedance is important only to convey the power of the amplifier to the headset in most effective manner.
However, having the best sound quality is another story.
Matching the impedance could cause distortion and low damping.
You need to see the balance of the impedance matching and good sound quality.
As the said headphone, Senn HD650, seems to convey the power very effectively, it no longer has to be connected to high impedance.
Connect it to low impedance and get the best sound out of it. Low distortion and high damping.
As you know, the vacuum tube amplifier has very low damping, 5 or 10 at most, compared to a semiconductor amplifier having 100-200 damping.
Connecting it to low impedance could lead to high damping and low distortion, a better sound quality, which must be something that all users want to achieve.

Also,
TU-882R/AS is designed to best match commonly used headsets, and focusing only on those high-impedance headsets is not a good idea.

I hope this will answer your question

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