Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: newguitarsmell on June 06, 2019, 10:42:11 pm

Title: NFB
Post by: newguitarsmell on June 06, 2019, 10:42:11 pm: How important is it to hook up the NFB?
I didn't use it on my small watt amps - would I need it on the Plexi style?
https://el34world.com/Hoffman/files/Hoffman_Plexi_6V6-V2.pdf

Thanks
Title: Re: NFB
Post by: sluckey on June 06, 2019, 11:04:38 pm: It has a big effect on the way an amp sounds. How important is that?
Title: Re: NFB
Post by: newguitarsmell on June 07, 2019, 12:42:22 am: I will have to hook it up and give it a listen!
Title: Re: NFB
Post by: Papa Jim on June 07, 2019, 06:06:02 am: It just goes to show ya. :l2:
Title: Re: NFB
Post by: pdf64 on June 07, 2019, 07:29:56 am: Without NFB the presence control won’t have any effect. Of course a Vox style tone cut control arrangement could be used in that front panel location.
Title: Re: NFB
Post by: ALBATROS1234 on June 07, 2019, 09:11:15 am: If I understand nfb right a Marshall without it may sound harsh and distorted in an unpleasant way at least to some extent. And a presence control on a Marshall is basically variable nfb right? That circuit is designed to have that type and value of nfb so without it there's no telling if it would even sold like marshall.
Title: Re: NFB
Post by: vampwizzard on June 07, 2019, 10:02:46 am: Presence control is an eq stage applied in the NFB loop vs a pot which would vary the amount of NFB you inject back into the system.

the Aikenamps article on NFB explains the impact pretty well.. may be worth a search.
Title: Re: NFB
Post by: Jennings on June 10, 2019, 03:44:02 am: I tend to prefer designs without NFB at all...but i like my amps much more organic and chewy than most these days. Worth maybe temporarily hooking up a bit of NFB, playing the amp, then try cutting the NFB and see what you prefer...or simply put a couple of switches in for NFB/no NFB and another for different values of components.