Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Misc Schematics and Layouts => Topic started by: tubenit on January 20, 2010, 05:55:27 am
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There was some interest and discussion on these ideas on the forum, so I thought I'd post this. note:(should read "or" NFB not "of" NFB)
Tubenit
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Thanks tubenit.
I upped the smoothie value from 250pF to 560pF on the cathode follower (V2) of the hOsO. It takes off some highs, but the preamp sounds more refined at higher settings.
I have tried the conjunctive filter on the AX84 P1 and I didn't care for how much of the highs were robbed away, no matter what values I used. Maybe it's different on a push-pull?
The others are interesting, so thanks for posting this -
Regards,
Craig
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Thanks tubenit.
I upped the smoothie value from 250pF to 560pF on the cathode follower (V2) of the hOsO. It takes off some highs, but the preamp sounds more refined at higher settings.
I have tried the conjunctive filter on the AX84 P1 and I didn't care for how much of the highs were robbed away, no matter what values I used. Maybe it's different on a push-pull?
The others are interesting, so thanks for posting this -
Regards,
Craig
I have tried a conjunctive filter on a push pull 6L6 amp and it was kind of cool. I really liked the result but I thought it was to hi-fi? I don't if that local feedback on the second triode in his schematic would be a smoothing. More touch responsive I think. I guess you could make it a smoothie and be touch responsive when you dig in more. Plate to cathode works great for taming oscillation while having a different feel than compared to bypassing the plate resistor. Both are good for smoothing. They both have a different feel to me?
Any ways, just my two cents. :smiley:
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could all 3 of you guys discuss these things a little more in depth like your trying to explain this to an idoit :laugh: me.
I have been reading and my overworked brain just cant wrap itself around this concept yet. Thanks Bill
PS and alsop were these things sit in what schematic so I can compare with the original :grin:
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All--
A really great amp design doesn't need much smoothing--usually the catch is:
Bad guitar pickups, cheap long cables, Mismatch of pedals, and too much signal--maybe style of
playing too.
These smoothing traps or filters catch unwanted frequencies (harsh and and transient spikes) on the scope). Personal taste or preference has a lot to do with what sounds good to an individual.
Some amps have used inductors to smooth tone. I have built Bi-amps with a crossover in the tone stack and bi-amped after with two power amps--got a cool different sound--no highs in the bass mid amp.
Anyhow, a lot of the smoothing has been done through the years--some times too make up for inferior design and components.
Mackie2
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Thanks Mackie2
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A really great amp design doesn't need much smoothing...........a lot of the smoothing has been done through the years--some times too make up for inferior design and components.
Yes, so maybe that is why I add the smoothing caps into some of my (inferior) designs.
Or, maybe they're simply another tool to coax great tone out of amp....I dunno.
Personal taste or preference has a lot to do with what sounds good to an individual.
Again, I agree. Which is why I build my amps to my personal taste.
When someone else builds it, they either like it, or don't, & change it to their own personal taste.
Either way, my commission on the project is the same......zero.
Geezer
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For high gain amps or stages, a shunt resistor from grid to ground after the grid stopper is used too. I've installed a couple on V2 of my Bumblewatt amp.
f=1/2pi x input/grid stop R x roll off freq desired, which I used a 47k grid stopper & wanted a roll off of 15k Hz.
This equals 22.575pF so I used 20pF caps on V2a & V2b grid to ground/cathode.
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Some or all of that would work on an EL84 also, right?
As I tinker, what are some common mistakes by new guys that I have to be careful of?
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A really great amp design doesn't need much smoothing
I agree on the "doesn't need much" part. And I firmly believe that it is not the right way to get an otherwise unstable amp stable with smoothing measures. These should only be used for tonal shaping.
I usually do not use smoothing caps in my amps. But a small smoothing cap on the first gain stage plate in my HoSo56 took out the slight harshness and brittleness that was bothering me. And reading Geezer's and Tubenit's threads on the HoSo it should be clear that they used smoothing for tone and not for stability.
Cheers Stephan