Plate resistor more mids?
Moderators: pompeiisneaks, Colossal
Plate resistor more mids?
I've read on this forum that increasing plate resistor values gives more mids. Looking at 12ax7 operating curves the reasoning does not pop out for me. Anyone?
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Bierschinken
- Posts: 26
- Joined: Wed Jan 21, 2009 6:26 pm
Re: Plate resistor more mids?
Hi there,
this is nonsense.
Changing the anode resistors value will change the bias point of that stage.
So there´s two possibilities...
#1 the stage works more linear
#2 the stage produces more distortion
#1 is often described as more dynamic
#2 means more compression
But there is no frequency change.
Swen
this is nonsense.
Changing the anode resistors value will change the bias point of that stage.
So there´s two possibilities...
#1 the stage works more linear
#2 the stage produces more distortion
#1 is often described as more dynamic
#2 means more compression
But there is no frequency change.
Swen
Re: Plate resistor more mids?
Yes, but it may give that impression even though the mids may not be increased, it can make a difference in tone.
What I experience with the higher plate loads is more clarity.
What I experience with the higher plate loads is more clarity.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Plate resistor more mids?
I was under the impression that higher plate load resistors would attenuate the highs slightly. Perhaps, this is perceived as increased mids--relative to the highs.
Don't higher plates also let the gain stage produce more gain in signal before overdiving the tube? Perhaps, this is perceived as more clarity. On the otherhand, I have read that some consider the lower plates to contribute higher clarity, presumably due to more high end.
Don't higher plates also let the gain stage produce more gain in signal before overdiving the tube? Perhaps, this is perceived as more clarity. On the otherhand, I have read that some consider the lower plates to contribute higher clarity, presumably due to more high end.
Re: Plate resistor more mids?
From an earlier post
Plate resistors setup in a typical D-Style/Fender/Marshall.. act as a voltage divider(Tubes plate/plate resistor)..Preamp tubes amplify voltage, output tubes amplify current..The voltage swing across the plate resistor sets the amount of voltage peak to peak..The higher the resistor the larger the swing..Say your typical 100k plate sets the peak to peak voltage at say 100 volts.. 220K doubles this ... More voltage = more gain but most importantly more headroom..(To me this is why some people don't like high plate amps on clean channel..Stiffer with less breakup) If your thinking in terms of transistors.. This sets the rails......The cathode resistor sets the bias..more gain =lower resistor.... With the tube bias set for more gain... the more input voltage (grid voltage) you need to hit the rails....Thats why when you up the plate resistor you need to up the cathode resistor since you still want the tube to clip especially in an OD amp...Plot this on a graph= Transconductance curve.. If you set the operating point closer to the point which the tube starts to clip ie 100K/1.5 RP RK.. (places you closer to the outer edges of the curve or operating point).. when enough voltage, is applied to the grid (less voltage needed in this case with the 100k/1.5's) it hit's the rails tube distorts...appealing anomalies emerge... Compression, touch sensitivity..Playing around with this imaginary boundary makes for a more expressive voice (light touch clean..heavy attack more voltage distortion appears)...For me I don't think in terms of gain anymore as much as where I am in the curve..
Generally speaking 100K/1.5 generates 2nd order harmonics.. 180/220k 2.7/3.3 generate 3rd order harmonics.
Oh also with respect to tone...Raising the value of the cathode resistor decreases gain...Less gain=less bandwidth.. darker on the top..This is why I think 1.5k amps are inherently brighter!!
Plate resistors setup in a typical D-Style/Fender/Marshall.. act as a voltage divider(Tubes plate/plate resistor)..Preamp tubes amplify voltage, output tubes amplify current..The voltage swing across the plate resistor sets the amount of voltage peak to peak..The higher the resistor the larger the swing..Say your typical 100k plate sets the peak to peak voltage at say 100 volts.. 220K doubles this ... More voltage = more gain but most importantly more headroom..(To me this is why some people don't like high plate amps on clean channel..Stiffer with less breakup) If your thinking in terms of transistors.. This sets the rails......The cathode resistor sets the bias..more gain =lower resistor.... With the tube bias set for more gain... the more input voltage (grid voltage) you need to hit the rails....Thats why when you up the plate resistor you need to up the cathode resistor since you still want the tube to clip especially in an OD amp...Plot this on a graph= Transconductance curve.. If you set the operating point closer to the point which the tube starts to clip ie 100K/1.5 RP RK.. (places you closer to the outer edges of the curve or operating point).. when enough voltage, is applied to the grid (less voltage needed in this case with the 100k/1.5's) it hit's the rails tube distorts...appealing anomalies emerge... Compression, touch sensitivity..Playing around with this imaginary boundary makes for a more expressive voice (light touch clean..heavy attack more voltage distortion appears)...For me I don't think in terms of gain anymore as much as where I am in the curve..
Generally speaking 100K/1.5 generates 2nd order harmonics.. 180/220k 2.7/3.3 generate 3rd order harmonics.
Oh also with respect to tone...Raising the value of the cathode resistor decreases gain...Less gain=less bandwidth.. darker on the top..This is why I think 1.5k amps are inherently brighter!!