Preamp gain stages: how they sound and why

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mobisimo
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Re: Preamp gain stages: how they sound and why

Post by mobisimo »

Very cool! Thanks for posting these.
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roberto
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Re: Preamp gain stages: how they sound and why

Post by roberto »

mobisimo wrote:Very cool! Thanks for posting these.
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.

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).
Marioverkill
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Re: Preamp gain stages: how they sound and why

Post by Marioverkill »

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 :D
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roberto
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Re: Preamp gain stages: how they sound and why

Post by roberto »

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.
Marioverkill
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Re: Preamp gain stages: how they sound and why

Post by Marioverkill »

Maybe the admins could make this a sticky??? 8)


Done!, Structo
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roberto
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Re: Preamp gain stages: how they sound and why

Post by roberto »

I'd be pleased to receive such a gratification for my.. homeworks. :wink:
Marioverkill
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Re: Preamp gain stages: how they sound and why

Post by Marioverkill »

Robert,

Beginner's dumb question:

I don't understand the FFT graphs. :oops:
Cliff Schecht
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Re: Preamp gain stages: how they sound and why

Post by Cliff Schecht »

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.
Cliff Schecht - Circuit P.I.
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roberto
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Re: Preamp gain stages: how they sound and why

Post by roberto »

That's perfect Cliff Schecht,
simple and clear!
Marioverkill
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Re: Preamp gain stages: how they sound and why

Post by Marioverkill »

Thank you Cliff !! :D

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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LeftyStrat
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Re: Preamp gain stages: how they sound and why

Post by LeftyStrat »

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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Reeltarded
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Re: Preamp gain stages: how they sound and why

Post by Reeltarded »

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
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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roberto
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Re: Preamp gain stages: how they sound and why

Post by roberto »

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
This is the reason of sharing: more weels are spinning, more ideas for everyone.
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