Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rockranger on February 09, 2020, 02:12:48 pm
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https://el34world.com/Hoffman/files/Hoffman_5E3.pdf
Looking to add a nfb switch to the Hoffman 5e3, if anyone has any info on this it would be appreciated. Thanks
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there's no nfb for a switch to be added to.
surf up more fender schemo's to find how they did use nfb.
fwiw, the schematic attached has NOT been built/tested, but was stolen um borrowed from the other attached schematic
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see items circled in RED - you need to fiddle with the value of the 1500Ω NFB resistor as shown: it can be anywhere from 820Ω to 5KΩ or more - i chose 1500Ω because it made the paint chop up easier, but is also a good value to start with.
IF you add NFB loop you may need to swap the OT primary leads if the amp squeals on initial power-up. after wiring in, use SW to check - e.g. power up with SW open - if it squeals when SW is closed, then swap OT primary leads.
--pete
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https://robrobinette.com/5e3_Modifications.htm#Switched_Negative_Feedback (https://robrobinette.com/5e3_Modifications.htm#Switched_Negative_Feedback)
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I like Dummyload's version better than Robrob's because Dummyload's has about twice the open-loop gain. If the unbypassed gain stage has 6dB less gain than the bypassed gain stage and the closed-loop gain is -6dB in both cases, then Dummyload's version takes a 6dB hit with NFB and Robrob's takes a 12dB hit.
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> Dummyload's version better than Robrob's
Rob's linearizes the 12AX7. This stage dominates the 2nd harmonic of the otherwise push-pull amp.
Different, not better/worse.
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> Dummyload's version better than Robrob's
Rob's linearizes the 12AX7. This stage dominates the 2nd harmonic of the otherwise push-pull amp.
Different, not better/worse.
Allow me to re-phrase my statement to make it a bit more difficult to quote out of context. "I, and I alone, would prefer to use Dummyload's version rather than Robrob's . . . "
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Allow me to re-phrase my statement to make it a bit more difficult to quote out of context. "I, and I alone, would prefer to use Dummyload's version rather than Robrob's . . . "
I know who "I" is. But who is "I alone"? :dontknow:
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But who is "I alone"?
think it's lyric from a '90s grunge band; "I alone love you I alone......" :icon_biggrin:
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think it's lyric from a '90s grunge band; "I alone love you I alone......"
You got it. I learnt English from a car radio.
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:l2:
Yup, NO spelling tests !!!