HA-INFO (TPA6120) Headphone Amp
Oct 24, 2012 at 11:07 PM Thread Starter Post #1 of 4

fubar3

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This is an economy amp purchased for it's case, not it's contents, thinking it would save casework on the next DIY. However, I find that it is good quality amp worth a look for anyone who wants satisfactory performance on a tight budget.  Found on Ebay = $34.50 + $8.50 air mailed from Hong Kong.
 

 
The amp arrives in a factory box with universal 18vdc supply and phone plug adapter. There are more photos on the HA-INFO site but I include the circuit board which has SMD resistors vs the web site which has axial resistors.
 


Sound:  Initially, this amp sounded "brighter" than my others. It seemed to have voice sibilance and a faint echo on music with cymbals.  For example, turn on your equalizer with flat settings and then boost the 14k-16k frequencies. I tend to dislike sounds in this region. However, after much experimentation with amps, headphones, and music, I could find no conclusive difference. I suppose burn-in might be true after all
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.  Bass output is very good from this amp.
 
Design:  This amp has a minimalist design with only 2 active components. There is a TDA2030 18W amplifier which splits 18vdc to +/-9vdc.  The driver is a TPA6120 which has been discussed on Head-FI in the past.  It is a current-feedback-amplifier, CFA, which gives good performance but requires more sophisticated design skills than the common voltage-feedback amps.  Note the 330pf blue caps on the circuit board. The CFA is very sensitive to capacitance and has a 50ohm resistor between the input pins and the volume control. However, the blue caps shunt the input pins. So I think this might be a mistake. Perhaps I will remove them and test later.
 
This amp has too much gain such that I never turn the volume control more than 1 quarter. At 1 half turn there is 10mv offset on the phone jack. I believe the amp would effectively drive high-impedance phones, mine are 32 or 55.
 
There are slots in the side of the case. Perhaps this is irrelevant to it's purpose.
 
Oct 25, 2012 at 10:19 PM Post #3 of 4
Quote:
Are you able to try different opamp combinations on this one? 


Well, there is only one SMD opamp connected between the volume control and the phone jack so there is nothing swappable and nothing to combine.  Perhaps I misunderstand the question.
 
The TPA6120 is designed for performance and high fidelity. However, it is very sensitive to layout and I/O connectivity. Casual tinkering would not give good results, except by chance.
 
Nov 14, 2012 at 12:32 AM Post #4 of 4
Well, with the touchy volume control caused by high gain, and the possible instability of the CFA design, I decided to use this amp as a DIY experiment. I bypassed the TPA6120 with a 4562 followed by a pair of BUF634T. The existing split-rail power supply remains since I perceive no problem with it.
 

 

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