NFB and selectable impedance
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- StrummersOfThunder
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NFB and selectable impedance
Quickie for the venerable amp gurus
NFB circuits when you employ selectable output impedance
If for instance you have a 58k NFB resistor that heads to the 8ohm tap (connected to the output jack) but you interupt that with a switch to select between 8/16 ohm, what should one do with the NFB ? Presumably the value will be incorrect for the 16ohm tap now?
There is an unused 4 ohm tap on the OT . Is that able to be used to connect an adjusted NFB resistor to so that things remain 'stable 'as it were.
Thanks
NFB circuits when you employ selectable output impedance
If for instance you have a 58k NFB resistor that heads to the 8ohm tap (connected to the output jack) but you interupt that with a switch to select between 8/16 ohm, what should one do with the NFB ? Presumably the value will be incorrect for the 16ohm tap now?
There is an unused 4 ohm tap on the OT . Is that able to be used to connect an adjusted NFB resistor to so that things remain 'stable 'as it were.
Thanks
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Re: NFB and selectable impedance
Is the advice within this thread kosher ?
https://el34world.com/Forum/index.php?topic=21511.0
Would that mean leave it attached to the 'hot' of the output jack or to the 8ohm side of the STDP switch?
Im assuming switch lug is the correct answer.
https://el34world.com/Forum/index.php?topic=21511.0
Would that mean leave it attached to the 'hot' of the output jack or to the 8ohm side of the STDP switch?
Im assuming switch lug is the correct answer.
- GrantB
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Re: NFB and selectable impedance
I was trying to find a Ralph Wiggum picture of "my nose makes its own bubble gum".
Mainly to express, despite my desire to help, how utterly lost I am in the electrical theory world.
Mainly to express, despite my desire to help, how utterly lost I am in the electrical theory world.
"Man is the most insane species. He worships an invisible god and destroys a visible nature. Unaware that this nature he's destroying is this god he's worshipping." - Hubert Reeves
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Re: NFB and selectable impedance
Does it change the sound if you plug a speaker into a different tap than the nfb is on? Yes.
You can use that to your advantage though - a JTM45 has the nfb on the 16ohm tap but using the 8ohm give a different tone, bit more grit.
If I was you I would either pick the tap I’m more likely to use OR just build it as stock to hear what it has classically sounded like. I wouldn’t faff about with changing NFB resistors as you change the impedance - you’d likely have to muck around with different values to get it feeling the same anyway
Disclaimer: not a guru
You can use that to your advantage though - a JTM45 has the nfb on the 16ohm tap but using the 8ohm give a different tone, bit more grit.
If I was you I would either pick the tap I’m more likely to use OR just build it as stock to hear what it has classically sounded like. I wouldn’t faff about with changing NFB resistors as you change the impedance - you’d likely have to muck around with different values to get it feeling the same anyway
Disclaimer: not a guru
Utter shill for Kapiti Music – http://kapitimusic.co.nzGrantB wrote:Tony, your taste is, as always, very refined. Or as HG would say, "bloody awful".
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Re: NFB and selectable impedance
Good advice. 8ohm tap it is I thinkTmcB wrote: ↑Fri Nov 15, 2024 6:57 am Does it change the sound if you plug a speaker into a different tap than the nfb is on? Yes.
You can use that to your advantage though - a JTM45 has the nfb on the 16ohm tap but using the 8ohm give a different tone, bit more grit.
If I was you I would either pick the tap I’m more likely to use OR just build it as stock to hear what it has classically sounded like. I wouldn’t faff about with changing NFB resistors as you change the impedance - you’d likely have to muck around with different values to get it feeling the same anyway
Disclaimer: not a guru
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- Reg18
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Re: NFB and selectable impedance
I don’t know anything about the technical side of your question, but I do like the feel of the 68 deluxe and even 68 twin over the 65 versions which from what I’ve read is mostly due to decreased NFB giving it a more aggressive feel. More noise though too!
I’d like the option of switching it personally if I was in your position.
I’d like the option of switching it personally if I was in your position.
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Re: NFB and selectable impedance
Yep thats a big part of the voice (and noise) of those amps. Comes down to taste.Reg18 wrote: ↑Fri Nov 15, 2024 11:23 am I don’t know anything about the technical side of your question, but I do like the feel of the 68 deluxe and even 68 twin over the 65 versions which from what I’ve read is mostly due to decreased NFB giving it a more aggressive feel. More noise though too!
I’d like the option of switching it personally if I was in your position.
Im totally happy to play round with the idea of a switch to have variable NFB
It was more 'where to hang the connection' . But I think I have this sussed now.