**MODERATOR EDIT** the links above are no longer workingRoberto wrote:I post just a few documents I've done, to start a little discussion on how gain stages sound and why.
-3dB POINTS FOR Rk AND Ck
SOME GRAPHICS ABOUT GAIN SHAPE
SIGNAL 100k 1k5
FFT 100k 1k5
SIGNAL 100k 10k
FFT 100k 10k
SIGNAL CATHODE FOLLOWER 400V 100k 820R 100k
FFT CATHODE FOLLOWER 400V 100k 820R 100k
SIGNAL CATHODE FOLLOWER 400V 220k 820R 47k
FFT CATHODE FOLLOWER 400V 220k 820R 47k
SIGNAL CATHODE FOLLOWER 400V 100k 1k8 100k
FFT CATHODE FOLLOWER 400V 100k 1k8 100k
SIGNAL CATHODE FOLLOWER AC30 TOP BOOST
FFT CATHODE FOLLOWER AC30 TOP BOOST
Preamp gain stages: how they sound and why
Moderators: pompeiisneaks, Colossal
Preamp gain stages: how they sound and why
Re: Preamp gain stages: how they sound and why
**MODERATOR EDIT** the links above are no longer workingRoberto wrote:Some sweeps on the Rk value of the Cathode Follower from 50k to 110k and the effect on the sound:
SIGNAL CATHODE FOLLOWER 280V 100k 820R 50-110k
FFT CATHODE FOLLOWER 280V 100k 820R 50-110k
SIGNAL CATHODE FOLLOWER 380V 220k 1k8 50-110k 1Vrms
FFT CATHODE FOLLOWER 380V 220k 1k8 50-110k 1Vrms
SIGNAL CATHODE FOLLOWER 380V 220k 1k8 50-110k 4Vrms
FFT CATHODE FOLLOWER 380V 220k 1k8 50-110k 4Vrms
SIGNAL CATHODE FOLLOWER 380V 220k 1k8 50-110k 10Vrms
FFT CATHODE FOLLOWER 380V 220k 1k8 50-110k 10Vrms
Clean, Crunch and Lead channels scope and FFT:
SIGNAL CLEAN PLEXI 1st STAGE + CF
FFT CLEAN PLEXI 1st STAGE + CF
SIGNAL CRUNCH 1st 2nd STAGE + CF
FFT CRUNCH 1st 2nd STAGE + CF
SIGNAL LEAD 1st 2nd 3rd STAGE + CF
FFT LEAD 1st 2nd 3rd STAGE + CF
Re: Preamp gain stages: how they sound and why
Very cool! Thanks for posting these.
Re: Preamp gain stages: how they sound and why
I hope these files will help people better understand how a different polarization will change the frequency (and so tonal) shape of their amps, and also as a different plate resistor will affect the sound and brightness of a stage.mobisimo wrote:Very cool! Thanks for posting these.
On 1st an 2nd gain stages, this influences how the channel will overdrive, on latest stages this influences more the colour/presence of the OD channel.
Take a look also on how a lower Rk on CF will compress the sound (and make it softer.. slower.. less harsh), and how signal evolves inside a plexi clean, crunch and lead channel).
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Re: Preamp gain stages: how they sound and why
Thanks Roberto ! This is great !!! I have been studying tube amp theory the last year,reading Merlin Blencoe,Richard Kuehnel,RDH4 and internet info.These are really gonna help glue all the theory together.
Mario
Mario
Re: Preamp gain stages: how they sound and why
Thank you Mario, hope people start to read them, maybe study them, and then come back to talk about. Could be interesting maybe contribute with samples.
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Re: Preamp gain stages: how they sound and why
Maybe the admins could make this a sticky???
Done!, Structo
Done!, Structo
Re: Preamp gain stages: how they sound and why
I'd be pleased to receive such a gratification for my.. homeworks.
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Re: Preamp gain stages: how they sound and why
Robert,
Beginner's dumb question:
I don't understand the FFT graphs.
Beginner's dumb question:
I don't understand the FFT graphs.
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Re: Preamp gain stages: how they sound and why
FFT is what's known as a Fast Fourier transform. To try to keep things simple, FFTs are used in place of real Fourier transforms because the real ones are very computationally expensive. FFTs are algorithms which can compute the Fourier transform quicker with a slight hit in accuracy depending on how many samples you take.
Why do we care? When you take the FFT of a signal you are looking at on say an oscilloscope, you are looking at the harmonics of the signal. While a purely sinusoidal harmonic is only a single line with amplitude Y (usually in dB), the inherent inadequacies of the FFT makes the harmonics show up as big pointy triangle looking things coming to a point.
To read these, simply ignore the massive "skirts" on each harmonic and look at just where each shape comes to a point. Draw a straight line down to the X-axis and look at what frequency you are at. Now draw a straight line to the Y-axis. Do this for each point. This will tell you the frequency and amplitude of each harmonic. The first point is the fundamental (say 1kHz), the second harmonic is 2kHz, third harmonic is 3 kHz, etc..
We use these harmonics to judge the amount of distortion and filtering we are seeing from our amplifiers, or simply to analyze signals in a manner that is much easier (mathematically speaking) to work with. With some practice you can learn to read the graphs in such a way that you can describe how the distortion will sound before ever hearing anything!
Again this is all a gross oversimplification of what an FFT/Fourier transform can do, it's a very powerful tool once you get to learn it.
Why do we care? When you take the FFT of a signal you are looking at on say an oscilloscope, you are looking at the harmonics of the signal. While a purely sinusoidal harmonic is only a single line with amplitude Y (usually in dB), the inherent inadequacies of the FFT makes the harmonics show up as big pointy triangle looking things coming to a point.
To read these, simply ignore the massive "skirts" on each harmonic and look at just where each shape comes to a point. Draw a straight line down to the X-axis and look at what frequency you are at. Now draw a straight line to the Y-axis. Do this for each point. This will tell you the frequency and amplitude of each harmonic. The first point is the fundamental (say 1kHz), the second harmonic is 2kHz, third harmonic is 3 kHz, etc..
We use these harmonics to judge the amount of distortion and filtering we are seeing from our amplifiers, or simply to analyze signals in a manner that is much easier (mathematically speaking) to work with. With some practice you can learn to read the graphs in such a way that you can describe how the distortion will sound before ever hearing anything!
Again this is all a gross oversimplification of what an FFT/Fourier transform can do, it's a very powerful tool once you get to learn it.
Cliff Schecht - Circuit P.I.
Re: Preamp gain stages: how they sound and why
That's perfect Cliff Schecht,
simple and clear!
simple and clear!
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Re: Preamp gain stages: how they sound and why
Thank you Cliff !!
I kinda tought its content was related to harmonics.I couldn't decipher it because I had no idea about the Fourier Transform concept.I will study some more.
Thanks again Cliff and Roberto.
Mario
I kinda tought its content was related to harmonics.I couldn't decipher it because I had no idea about the Fourier Transform concept.I will study some more.
Thanks again Cliff and Roberto.
Mario
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Re: Preamp gain stages: how they sound and why
This is great info, thanks Roberto. I'm particularly intrigued with how the cathode follower distorts.
It's never too late to have a happy childhood.
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Re: Preamp gain stages: how they sound and why
Yes! Thank you for the research, and the sharing!
This is the kind of thing that makes the wheels in my head spin on the ice lol
This is the kind of thing that makes the wheels in my head spin on the ice lol
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: Preamp gain stages: how they sound and why
This is the reason of sharing: more weels are spinning, more ideas for everyone.Reeltarded wrote:Yes! Thank you for the research, and the sharing!
This is the kind of thing that makes the wheels in my head spin on the ice lol