Help me understand this NFB schematic.

[VaporDemon]

In this schematic, can someone elaborate on it further and help me understand how the thump and hair switches are affecting the negative feedback, Obviously the the 4.7nf on the pot is a resonance control, but how do the 39K and 47K resistors and 10pf caps affect things? I would like to try this circuit on an amp with a 100K NFB control pot in series with a 27K NFB resistor, so I have a range ok 27K to 100K. Would I still run my NFB pot off the speaker tap and then into this circuit and eliminate the 27K resistor or is this circuit going to change my minimum NFB resistance? Ultimately I'd like to keep my range the same but also implement this circuit as well. Thanks in advance!

 

[RedPlated]

The 39k and 47k are in series so there’s a total of an 86k NFB resistor. They are split so that the high end can be controlled via each separate resistor. The 10pf over the 39k is cutting high highs in the power section.

The 10pf on a switch over the 47k will allow more highs when open, thus the, “hair” nomenclature. When it’s switched closed, the 10pf parallels the 47k and cuts more high highs.

Leave the 39k replace the 47k with a 100k pot. You’ll have 39k minimum NFB and 139k at max.

I have tested caps over NFB resistors extensively and have never found a scenario where they improve the tone. Cameron uses them frequently. But I don’t like the way they neuter the high end bite. There’s better places to cut highs.

The 47k in the depth circuit is reducing the effect of the depth cap. When the switch closes, the cap bypasses the resistor and is fully in circuit, significantly increasing its effect and “thump.”

 

[VaporDemon]

The 39k and 47k are in series so there’s a total of an 86k NFB resistor. They are split so that the high end can be controlled via each separate resistor. The 10pf over the 39k is cutting high highs in the power section.

The 10pf on a switch over the 47k will allow more highs when open, thus the, “hair” nomenclature. When it’s switched closed, the 10pf parallels the 47k and cuts more high highs.

Leave the 39k replace the 47k with a 100k pot. You’ll have 39k minimum NFB and 139k at max.

I have tested caps over NFB resistors extensively and have never found a scenario where they improve the tone. Cameron uses them frequently. But I don’t like the way they neuter the high end bite. There’s better places to cut highs.

The 47k in the depth circuit is reducing the effect of the depth cap. When the switch closes, the cap bypasses the resistor and is fully in circuit, significantly increasing its effect and “thump.”

Awesome info, thanks man! I realize now I was wrong and my range was actually 27K to 127K on my existing NFB control. I will try the circuit with and without the high frequency caps and experiment a bit to see what the difference is.