TH-200SE DIY 100W power amplifier.

07 Feb. 2012 by Thanaporn, 618 views.

TH-200SE DIY HiFi 100W power amplifier.
This 100Wrms power amplifier was designed and construction since 1999. It was the first power amplifier I designed my own. It is the second power amplifier I built. The first one is power amplifier by kit which when I was a student. During that time the concept was to designed and constructed by pickup up my stock electronic parts as much as possible such as a transistor, resistor, capacitor and others.

DIY Amplifier TH-200SE

TH-200SE power amplifier design.
The designed is like the most popular amplifier schematics. Differential amplifier circuit is used in the first stage. And of course, for me, a cascode circuit is used for this differential stage in order to increase linearity of the audio signal. Because I do not want to use many small signal transistors. So it is not fully-complementary differential amplifier in this section. The second stage is also the voltage amplifier which working with the differencial amplifier stage. And once again, the cascode circuit was used in this second stage as well in order to have more linearity. The third and fourth stages are the current driver stage and output stage.
No more voltage amplification on these both stages because of we have to produce the much more current feeding capability to the low impedance load like sound speaker.
Actually almost no one uses a cascode circuit for the current amplifier or emitter follower amplifier, but I used it for the current driver stage.
For the power output stage it is similar the ordinary power amplifiers, but for TH-200SE I choose not to use a resistor to the emitter pin of power transistor such 0.22 ohm resistor and so on.
Therefore, the signal from the emitter pin of power transistor will be transmitted directly to the speaker cable with ultra-low output impedance, so we have very high damping factor power amplifier.
Now you may have a question. How to manage the working temperature of power transistor and avoiding overheat. The bias circuit was designed to help control the increase of the power transistor temperature.(negative coefficient).

No global feedback power amplifier circuitry.
I designed this TH-200SE power amplifier without the feedback loop from a power transistor output stage to the differential stage. Negative feedback will be made ??from the current driver stage to a differential amplifier stage. The transmission of audio signal to loud speaker should be in the single direction so from power amplifier to loud speaker only. But actually in the world of reality. Speakers can generate the amount of voltage during the speaker diaphragm is moving. This voltage can feedback to the differential amplifier input stage and generates of the distortion.

There are some more interesting of my designed as following.
- No capacitor in the signal path, there is no any kind of capacitor coupling the audio signal to the circuits.
- Very low output offset(0.2mV), because of using DC servo biasing.
- High power high FT Sanken power transistor pairs are used.
- Class A bias for the current driver stage.
- Speaker protection modulus.

Special Edition (SE).
TH-200SE is actually an upgraded version of the TH-200 in 2000. It was added some upgrade parts such:
- The dedicated voltage regulation power supply to the voltage gain stage..
- The dedicated transformer for the regulation power supply.
- Adds medium size 2,500uF capacitor arrays to the unregulated power supply.
- Internal wired with Furukawa uS3 speaker cable.
- Internal wired with Van Den Hul Thunderline interconnects cable.(2011)

DIY Amplifier TH200se2

This TH-200SE was still constructed as a prototype. The main amplifier circuits are assembled without PCB, each of electronics devices and wires are soldered directly because it is easier and faster to constructed for me. But it can be interference from noises if the connections are too long. There are only speaker protection, regulation power supply and DC servo biasing circuit are assempled in PCB.
Because I need to know how sound quality will be and also watch the stability as well. So I need some couple of month to do testing. But really now I was very satisfy, So far today, I do not think to rebuilt it.

Sound Test.
I am very satisfied with the sound quality of TH-200SE. Upgrading helps amplifier to generate much more details, sounding very excellent. Identifying and defining the positions of the piece of music is much better.
More dynamic sound stage, even if many pieces of musical instruments are played simultaneously. Singers voice is very clear. The bass is deep and precise.

Although it was my first power amplifier I constructed and designed long time ago. But I'm very proud of it that way. The sound quality is comparable to or better than similar products I have ever heard. About 12 year's time, it has been proven that it works well and reliably.