My new hybrid amplifier

[sajti]

I'm workign to build a new hybrid amplifier with tube input stage, and ss buffer. The estimated output power is 300W/4ohms, and the output buffer design based on Marantz PM11S1 output stage. But my version use more and different output devices.
The voltage gain of the buffer is 3. Simulated distortion is 0.003% at 300W output power.
The input stage based on single 6H30P for both channels. Voltage gain is approx. 6.

Sajti

 

[padamiecki]

I'm workign to build a new hybrid amplifier with tube input stage...

wow!
please show!

 

[sajti]

The schematic of the output stage, with the protection.

Sajti

 

[VladimirK]

I'm workign to build a new hybrid amplifier with tube input stage, and ss buffer. The estimated output power is 300W/4ohms, and the output buffer design based on Marantz PM11S1 output stage. But my version use more and different output devices.
The voltage gain of the buffer is 3. Simulated distortion is 0.003% at 300W output power.
The input stage based on single 6H30P for both channels. Voltage gain is approx. 6.
Sajti

If that buffer is push-pull and includes several stages, emloying tube input stage will insignificantly improve the final sound, it is already determined by the buffer, IMHO.

 

[padamiecki]

 

[sajti]

If that buffer is push-pull and includes several stages, emloying tube input stage will insignificantly improve the final sound, it is already determined by the buffer, IMHO.

Hi,

yes it can be. I want to try.
The THD of the output stage is 100 times lower than the THD of the tube driver stage. And the distortion mainly 2nd harmonic.

Sajti

 

[padamiecki]

Aikido or White follower at the input?

 

[sajti]

Aikido or White follower at the input?

You can use any of them, but not necessary. The input impedance of the buffer is 100kohms, with only few pF input capacitance. I plan to use simple common cathode stage.

Sajti

 

[sajti]

The PCB with some emitter resistors.

Sajti

 

[sajti]

The heatsink with the mounted output devices, drivers, and Vbe multiplier.

Sajti

 

[sajti]

And finally the PCB over the heatsink.

Sajti

 

[sajti]

The power transformer is toroidal, 90VCT, 1000VA, wounded on 1500VA iron for low leakage, and low noise.

Sajti

 

[AKSA]

Beautiful design, Sajti. I see the output buffer is error corrected, wow!

Hugh

 

[sajti]

Beautiful design, Sajti. I see the output buffer is error corrected, wow!

Hugh

Hi Hugh

thanks! Unfortunately the quality of the schematic is not quite good, because I have to reduce the size, for another forum. So there is no error correction at the output. The small transistors are working as overcurrent protection.

Sajti

 

[sajti]

There are some difference between the posted schematic, and the final PCB. So the small signal stage contains 2SC2240/2SA970 instead the KSC1845/KSA992

Sajti

 

[sajti]

Some more changes: I reduced the value of the feedback resistors to 4x221ohms. I did it, because of the simulation results. The voltage gain is 2, and the distortion falls to 0.0012%, and the 2nd harmonic is 0.001%, the 3rd is 0.00069%.

Sajti

 

[sajti]

The final schematic.

Sajti

 

[AKSA]

I see now, it's a conventional EF3 output stage, with EF input stage to a complex complementary singleton drive via a current mirror and a cascode to the pre-driver. Fascinating protection system! Not simple at all, I assume very high OLG and very low THD? How does it sound, does it make you tap your feet and bring out a smile?

Hugh

 

[sajti]

I see now, it's a conventional EF3 output stage, with EF input stage to a complex complementary singleton drive via a current mirror and a cascode to the pre-driver. Fascinating protection system! Not simple at all, I assume very high OLG and very low THD? How does it sound, does it make you tap your feet and bring out a smile?

Hugh

So, the OLG is about 500. It can be higher, but I don't think that it's necessary. The OLG distortion is 0.22%, with 4ohm load, and 300W output. Mainly 3rd harmonic. Interesting that the closed loop distortion contains mainly 2nd harmonic.
The protectione system is my own development, and contains delayed switch ON, overcurrent, overtemperature, low voltage protection. Self reseting, and the amplifier can handle the short circuit for long time.
The circuit based on Marantz PM11, or MA9, but I try to use better passive components.
Not yet listened, I need some more time to build the PSU, and the tube input stage.

Sajti

 

[AKSA]

Make it as linear as possible, then apply minimal feedback? I see around 48dB of loop gain, with very, very low open loop distortion. It should sound very good indeed, and the protection circuits are a tour de force. Congratulations Satji!

Hugh