Hi, I am new here but would like to share the modification that we designed for the TU-8200. The idea was to lift the performance and musicality of the amp, in a simple and inexpensive way. We go further than just exchanging recommended parts like caps, VR and tubes, we really change the electrical design, though in a safe way and considering the power supply capacity.
Elekit's products are absolutely fine as they come. The designs are good and so are all components. You won't find any imbalance there. The price/quality ratio is simply great. Because of this we think they are nice platforms to do something interesting with. So what did we do ?
- Although very commonly applied, also in high-end amplifiers, we find the 12AU7 sounding somewhat dull, and often the circuits around it are a bit slow and therefor the powertubes aren't driven well. We use NOS 6n6p tubes, which are rarely applied, but in fact combine good performance with a great musical quality. The 6n6p tube is a different type than the 12AU7, and therefore we rewired the tube sockets to the PCB. This implies that afterwards no other type of pre tube can be used !
- We power the 6n6p tubes in the anode circuit with a cascade type Constant Current Supply, using 10M45 mosfets. This brings 3 great advantages:
1. It gives a lower load to the 6n6p tube which results in a very good linearity.
2. There is a lower output impedance and by that a lower Miller effect in the power-tubes. This is an excellent way to drive the power-tubes !
3. And last but not least, it improves the PSRR significantly, which results in much less distortion and better sound quality.
- We took out the overall feedback system. Overall feedback makes an amplifier sound dull.
- We added local feedback on the power-tube 6L6GC.
- We took out the switching possibility for triode/ ultra linear/ pentode mode, and fixed it to pentode mode. This gives the maximal power output for this amplifier. With our modification, the pentode tubes behaves like a linear triode because of the local feedback. This type of set-up is called super triode connection amplification. This combines the higher pentode output power capacity with the more musical ability of a triode.
- In this configuration, we found that the original Electro Harmonix 6L6 tubes can outcompete other possible tubes like the KT88, in this amplifier. The combination 6n6p + 6L6 is fixed. Tube rolling with other type power tubes is not advised because the voltages and currents will not match or not be sufficient. And as already mentied it is certainly not possible to apply any other pre tube. The EH 6L6GC is in the top of new 6L6 tubes. Of course, with NOS tubes like the Sylvania or even the Philips 6L6, the amplifier will give an even more refined sound. Output power : 2x 6,5W
- We upgraded the coupling capacitors, but we don’t see this as a tuning matter; we don’t apply typical ‘audiophile’ (expensive) capacitors. Those often come with certain sound characters and colorization. To us, the components in this function need to be neutral, and we have spent many time and effort to source for this quality. We have a rather unique process of defining the sound quality or grade of neutrality when comparing capacitors.
