My update lin topology

[GEirin]

Hi all.

My mod amplifier.

Guillermo

[linuxguru]

R16 must be 4R7, right?

[GEirin]

Hi Linuxguru.

I will need to arrive at the values empirically for R16; C5; C11-R22.

Regards
Guillermo

[AKSA]

Guillermo,

Try adding 10R of emitter degeneration in Q6 and Q7. This will improve linearity, reduce OLG around the Sziklai pair (already VERY high), reduce bias sensitivity somewhat, and increase input impedance to the Q6/Q7 bases, lightening the load for the VAS.

Otherwise, it's looking good. You will certainly have to fiddle with R16 as LXG says because it will set the slope of the tempco, which is important as only the outputs should be in the thermal loop.

I like it a lot. Simple and very musical. You must design a nice pcb and build it. Up there with the DX amplifier!! Very important to have a long, careful listen.

Congratulations!

Hugh

[destroyer X]

Your amplifier is still very good and will be even better if you accept some of those suggestions people are posting.

I like you ideas...you were selecting, analising and concluded very good things.

Hoje em dia está muito difícil criarmos idéias originais.... muita gente já pensou em muitas coisas....hoje em dia temos mesmo é que selecionar bons subcircuitos e colocá-los para trabalhar juntos, e com isso, descobrir quais combinam melhor.

Now a days we have to select subcircuits and put them to work together to select the best combination...original, new ideas, are difficult and hard to have, as thousands of ideas were already published into the internet.... not easy to create a new circuit, that one nobody had never used...so.... the selection of subcircuits, the best VAS, the best differential, and so on, will result fine...the parts selection is also very important.... the last movement, also important, is the testings and biasing tests.... to tune the unit to best bias.

I think you will finish producing a very special amplifier..... will be SS....not solid state..will be Super Special.

regards,

Carlos

[GEirin]

Hi all.

Thanks very much for yours replies.

Linuxguru: Sorry. Yes: R16 is 4R7. Error of tiping.

Hugh: Very important you help. I improve my project. One question: stopper R in power transistor? Yes or no?

Hermano Destroyer: You DX amplifier and my project amplifier are SS (super special). Mercosul- Mercosur- Sudamericano amplifiers?
Simples y musicales diyamplifiers.

Below attached update my amplifier.

Opinions?

regards

Guillermo.

[AKSA]

Hi David,

The input impedance of a double darlington is a function of the beta product and the load. This is not so with the CFP, which thus isolates the driver from the load more completely.

Guillermo,

Yes, 10R base stoppers on the outputs. Very good idea; prevents any short term oscillation due to occasional instances of base negative impedance, particularly with reactive loads.

Hope this helps.

Now, build your amp and tell us how it sounds!!

Cheers,


Hugh

[linuxguru]

OK, here's something similar, loosely derived from the simplified AKSA schematic posted here a few years ago. I've built a prototype with a few changes from the LTSpice schematic shown (I simulated it with devices for which I had reliable Spice models, and substituted devices with similar specs in the prototype).

The changes are:

Simulated -> prototype
2sa1837 -> 2sa1220a
2sc4793 -> 2sc2690a
2sa1015 -> bc558
2sc2705 -> ksc3953

Edit: The first prototype didn't have R24, Q9 and the miller cap C11. But the gain of the VAS transistor Q3 (ksc3953 in the prototype) is only ~60, so I tried to jack up the open-loop gain with R24 & Q9. That made it unstable in the prototype (although still stable in LTSpice with the 2sc2705 with lower fT than the ksc3953), and it let the magic smoke out of a few resistors, particularly the Zobel. So I bit the bullet and added Cdom, C11. Simulation showed that H2, H3 didn't increase greatly in the range from 12pF to 27pF, but increased by ~10 dB for 47pF. I went with 27 pF, prayed hard and powered it up - no smoke this time! Audible sonics are also exceptional, as suggested by the simulation.

[linuxguru]

Here's a photo of the prototype, built into a stock, off-the-shelf Dexa chassis with a heatsink and other widgets added (the wiring is a bit messy, I'll tidy it up in the next pass):

[linuxguru]

Here's the simulated THD20 FFT plot (H2 is at -77 dB, H3 and higher are below -100 dB) at 50W into 8 ohms: