Navajo - 16 Watt Diamond with low distortion

[FioreDİAlbicocche]

First time I've seen a amplifier/electronic circuit named after a Native American tribe.

The Navajo (Dine) people live in the Four Corners area of the USA. It is the largest tribe in the USA.

Very good THD, but I would have expected more power output for an amplifier named after the biggest Native American tribe in the USA?

I thought it might be because the Americans exterminated the Native Americans. Maybe I'm wrong.

 

[lineup]

It is true that servo will effect the inverted input.
47kohm is effectively parallell to R5 1.8k. This change the gain a little bit.
But as the AC of the servo is below audioband, it will not effect the overall performance of the amplifier.

 

[mz543578854]

My concern is not so much about the gain change, but feeding a DC signal with a significant AC on top of it to the NFB.
Actually the AC frequency is the same as the output signal freq in my sims (I am not speaking about potential really slow frequencies caused by the reaction time of the servo).

 

[jxdking]

I like the TMC compensation.
The servo might not be necessary.
What you could do is to use lower value resistors for the feedback network. Such as 10K with 1K. I notice you got positive input DC impedance matched with that of the negative input. There should not be much DC offset. Well done.
Also I would degenerate the input stage and the current mirror with 47 or 100 Ohm resistors. Without it, the gm of the input stage is not constant.
BTW, the diode D1 is a nice touch.👍

 

[lineup]

@jxdking
Thanks for your comment.
I might implement. These are easy to make changes.
But I want to keep the servo. But I might test the offset without it. Let's see.

 

[mz543578854]

@lineup did you check if you can confirm that the DC servo AC portion indeed is the same freq as the source signal?

 

[jxdking]

@lineup
After inspecting your servo, there are 3 low frequency poles. 2 from your servo, 1 from the feedback network C3. There is a great chance that it will oscilliate. I would say to remove the C3.

 

[lineup]

@jxdking

Done a complete redesign.
1. Removed the servo
2. Added a pot in the input for DC adjustment.
3. Added emitter resistors in input and the mirror.
4. Increased the bias in output.
5. Removed the comp cap across the feedback resistor.
6. Adjusted TMC for low distortion.

Now Gain Margin is 70dB and Phase Margin 54 degrees.