Symphony Amplifier

[Hennady Kovalsky]

back to The Leach Amp

ok, here is my vision of the correction of this amplifier.
P.S. the initial current of each pair of output transistors is 110 mA.

 

[OnAudio]

🤦‍♂️

Each to his own then.

Not really, tech is tech sometimes it denies us an opinion, sometimes you want to think one way then the project expands your mind and you think another way, watch the video and see the phase lag oscillation

 

[OnAudio]

ok, here is my vision of the correction of this amplifier.
P.S. the initial current of each pair of output transistors is 110 mA.

Thanks for sharing your ideas your recipe just like the original recipe are all valid.

 

[EdGr]

See pages 19-23 in the link below. Although this mainly concerns itself with small signal buffers, the theory applies to power buffer stages as well, and especially in the case of EF2/3 and CFP.

https://worldradiohistory.com/UK/Wireless-World/00s/Electronics-World-2003-10-S-OCR.pdf

The article is describing a known weakness of emitter followers: they are bidirectional. Some output gets fed back to the input.

ok, here is my vision of the correction of this amplifier.

You, me, and Rotel all fixed the Leach amp in similar ways.
Ed

 

[OnAudio]

Quasi complementary stages and CFP stages issues to note, the funky business around Q4. 390pF on R27 should take care of it

 

[OnAudio]

Who can make an educated guess at what was found to have caused the 8MHz oscillation, quite interesting find, and no its not the Zobel, video loading soon

 

[maxlorenz]

On my own amp experiments, I suspect that mounting the outputs (and the drivers) on the same HS may cause (another) unwanted parasitic C, so I make changes in that regard....
Also, big C near the outputs may cause big currents to run on G and couple to other paths--> I decouple the G to HS.
But I am only a dilettante....

Best of wishes for your project!
M.

 

[OnAudio]

Thanks @maxlorenz, good ideas there that actually work great for CFP, yes the grounds are decoupled.
The video is loading soon and its interesting what solutions do work

 

[OnAudio]

The debugging video is out, check post 1, its actually a rather too common symptom

 

[OnAudio]

You can now access the corrected schematic

 

[maxlorenz]

Great.
You could try Bootstrapped Darlingtons Just for fun....

Best wishes,
M.

 

[OnAudio]

Thanks, one can also use mosfets with the change of one resistor

 

[OnAudio]

An interesting article about buffers here https://worldradiohistory.com/UK/Wireless-World/00s/Electronics-World-2003-10-S-OCR.pdf

 

[OnAudio]

Symphony Noise at unity 9nV/√Hz which is at par with many low noise opamps

 

[OnAudio]

This amplifier has many pluses including being unity gain stable

 

[OnAudio]

Good stuff here on feedback approximation