If anyone has a little dot MK III amp for sale, please let me know.
WTB Little Dot MK III Amp
- 102 Posts. Joined 5/2008
- Location: Waterford, MI
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I have a used Little Dot MK III headphone amp in excellent working condition. I am the second owner, The original owner did the following mods as he explains, "I have done the 120ohm resistor mod to use 6H30 power tube instead of the stock 6H6PI tubes. The preamp tube has been changed to very rare find Sylvania 5654W (6AK5W) "Black Plate Round Getter" ones that are considered as the best sounding 6AK5 tube according the head-fi Little Dot MK III tube rolling thread. The four tubes has been perfectly matched and tested with Oscilloscope to make sure both channel output level are same. I have marked "L" and "R" on both tubes for you to insert them to the right socket. Cosmetically the only defect is there are two small dings on the front panel, see the picture yourself.
Guarantee against DOA, I will provide 30 day warranty for this amp. If it's defective and dies in 30 days, I will give you full refund. The original Little Dot MK III also has several design flaws. The two 2W power resistors in the power section are underrated and are known to burn out when running the amp for long time. These same resistors have been changed to 5W in MK IV. I have changed these two resistor to 5W for this MK III amp. The cathode resistors for both preamp tube and power tube are also underrated 1W resistors, I have changed them to high quality Dale 2W metal film resistors.
A more serious issue, especially for US models, is the power transformer input voltage is 110V (China's standard AC voltage is 220V, so having 2 x 110V transformer instead of a custom 120V input one is easier for the manufacture). But in US, the standard AC voltage is 120V and most area has a voltage of 125 - 127V AC. In most of the case, vacuum tubes can stand 10% voltage increase without any issue. However, in Little Dot MK III, (also MK IV), the tube filament is using unregulated AC directly from the transformer. So if it is supposed to be 110V -> 6.3V AC conversion from the transformer, if the input AC increases to 125V, the filament voltage will increase to 7.2V. This will drastically decrease the tube's life, and in some case can burn out the power tube. Little Dot has acknowledged this problem to me, and recommend put a small value resistor in series with filament to reduce the voltage. I have modded this MK III amp to have tube filament in safe voltage range.
For all mods I have done, please check the red circles in the picture."
PM me if you are interested.
Edited by edpoz - 6/29/10 at 9:04pm