How much NFB in a Hiwatt?

[Gaz]

Most of the schematics on Mark Huss' page (MHuss Hiwatt Amplifier Pages - Tech Info) show a 10K feedback resistor coming off the 16ohm tap with a 2.2k shunt resistor. Am I missing something? This seems like way more feedback than what I'm used to seeing in a guitar amp. Thanks for any info!

[Jazz P Bass]

There is more to it than those two resistors.
Like the rest of the Presence circuit.

[frus]

Yeah, Hiwatt has much more elaborate NFB/presence scheme than the simple bassman/marshall type

[Gaz]

Well, gosh, guys, I realize there is more going on in the overall poweramp and feedback network, I'm just trying to figure how much global NFB is actually used. What I was trying to get at with my question, was that it seems like there is a huge amount of NFB, however I was second guessing that presumption based on the fact that there is all that other 'stuff'. Could anyone help explain how that other stuff influences the overall feedback ratio?

[Enzo]

You have a signal voltage at the speaker or other output tap. That feeds through the voltage divider you refer to. I looked at a Marshall 1959HW for comparison (you mentioned none, but if you have some other model you want to compare, tell us) and I see a 47k over a 5k pot. So you see a 5:1 divider versus the Marshall 9:1 divider. That signal is injected into the cathode lead of the phase inverter. In your Hiwatt, the tail resistor is 22k over the 2k2, in the Marshall, the tail is 10k over the 5k pot. That right there is another difference, and affects the OVERALL amount of NFB.