L. Lahmann headphone amplifier

• General parameters:

1. Applicable earphone impedance range: 16-600 ohms
2. Frequency range: 10Hz-20kHz (-1dB)
3. Distortion: 0.02%@1kHz Vppm=20V（90% power output）
4. Output noise level: -90dB
5. Output impedance: 10 ohms; 
6. Rated output power: 550mW/60Ω;280mW/300Ω; 170mW/600Ω; 
7. Input sensitivity: 300mV rms(-7dB) for rated output; 
8. Gain: low gain 5 times, high gain 12 times
9. Power supply voltage: 220V AC
10. Volume weight and accessories: 160*116*48mm（Length, width, height）, About 1 kg, the random standard power cord without audio line.

     Lehman’s classic circuit is characterized by high density, fullness, balance, looseness, gorgeous sound, high resolution, large dynamics, and good high-frequency extension.Overtonerich,Feeling of airStrong, not tired of listening for a long time, I have been thinking about this completed idea for several years, but the circuit of this amp is simple, and there are many amps based on this circuit on Taobao, so I have not been able to start construction until recently. Lehmann took it out and listened carefully for a few days, and found that its gorgeous tone and precise tuning can indeed be called a generation model, so he still reluctantly disassembled the machine like studying a solo amp, and welded the important components.（Including main capacitors, power output tubes, push tubes, etc.）Test the working points one by one, and then carefully study the current trend and wiring design concept of the original amp PCB, and finally L. Lahmann can be put on the shelf!

design concept

1. Unlike most merchants on Taobao, the pursuit of appearance, component color, location and other aspects are consistent with the original version, just like my Solo amp, and strive to make the sound style as close as possible to the original version, so if you need to hear as much as possible To restore the original sound of the amp, you can place an order with confidence. If you like the appearance of the original version, it is not suitable, because I don''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''t like to put the cost of audio equipment on the appearance.

2. The basic circuit structure of this amp is the original cable, but the following improvements have been made:

     . Increase the supply voltage and quiescent current by about 30%, increase the output power by about 70%, and because of the increase in current, headphones with an impedance of 60 ohms or more will always work in Class A State, solve the problem that the original thrust is slightly insufficient.

     . did not use the original heat dissipation method, because the area of ??the horizontal heat sink is too small, because of the increased current, the heat sink is changed to a vertical type, and the power dissipation can be larger Times more.

     . Although this circuit has been very perfect and stable, I still stubbornly added a protection circuit to solve the problem of the original switch machine impact, and I can protect the earphones as much as possible.

3. The original version is almost useless with 0 gain options. Only medium and high gains are retained. The factory default is high gain. It is suitable for large headphones such as HD650 and K701. If you are pushing high-sensitive headphones or small earbuds, you can change Put the two red switches on the main board to the off position to set the amplifier to low gain（Use a longer toothpick to move it easily through the vents）.

4. Remove one of the original two-way headphone output. Actual test also found that there will be a lot of uncertain distortion factors when two headphones are plugged into the amp at the same time to listen to songs.

Regarding the freight: the amp is heavier, and the logistics weight is more than 1.8 kg. Fans in Beijing and Tianjin have contacted me to reduce the freight. Friends who are far away from Tianjin such as Xinjiang, Tibet, and Guangxi, please contact me, and the freight will increase. Otherwise, pay directly, and the seller has the right not to ship the goods!

This machine provides a one-week trial and can be returned within one week. If there is no quality problem, the buyer only needs to bear the round-trip freight.

This machine is guaranteed for one year, and there is no service fee for repairs within one year. The buyer and the seller will bear half of the freight. Repairs outside the warranty period only charge the cost of the components, and the buyer will bear the freight.

Disassembling the machine and changing the circuit will void the warranty service.

Please do not disassemble the machine without the buyer''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''s consent before confirmation, otherwise the seller has the right to refuse the return.