Guitar Level To RCA Line Level Preamp

Ian0

Joined Aug 7, 2020
10,277
Never heard complaints from anyone about that, and the range where the frequency peaks in the graph is where its typically rolled of in a mix.
But those are the frequencies that contain all the harmonics, which are influenced by the various cone resonances and breakups in the loudspeaker, that give the speaker its tone, and distinguish one speaker from another.
https://celestion.com/product/g12m-greenback/
remember that the loudspeaker is not there to reproduce exactly the tone from the instrument, the loudspeaker is part of the instrument; and so is, unfortunately, the lead between guitar and amplifier.
 

LowQCab

Joined Nov 6, 2012
4,309
The usual, "insisted-upon", "well-everybody-knows-that",
overall Signal-Chain of your "standard" Electric-Guitar, is so convoluted, and just plain atrocious,
that it's almost un-explainable in rational terms.

Guitar-Players should bow at the feet of the exasperated Engineers that gingerly coddled their Massive-Egos,
and even strait-up lied to them,
just to be able to capture a recording that actually sounds good to everyone else.

What a ridiculous drama.

Modern Modeling-Software, and built-in Wireless-Connections, have all but eliminated
all of the absurd, completely "un-adjustable", and cantankerous- ~75-year-old Hardware,
that Guitarists absolutely worship, and just won't let go-away.

It's like trying to answer the question ........ "Do I look Fat in this Dress ?"........ You just can't win.
.
.
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Ian0

Joined Aug 7, 2020
10,277
The usual, "insisted-upon", "well-everybody-knows-that",
overall Signal-Chain of your "standard" Electric-Guitar, is so convoluted, and just plain atrocious,
that it's almost un-explainable in rational terms.
If single-ended pickup circuit wasn't dreadful enough, then they added a so-called "tone stack"!

Compare with the balanced-line microphone and its preamplifiers, which was invented around the same time, but by one of the smartest audio engineers of the era: A.D. Blumlein.
 

Ian0

Joined Aug 7, 2020
10,277
The datasheet's description of the horrible frequency response of the speaker describes the tones that guitar people like to hear.
If ever you get the chance go to a demonstration by Celestion of their various guitar speakers, and the subtle differences in their tones and responses, it's quiet a fascinating experience.
 

LadySpark

Joined Feb 7, 2024
194
The datasheet's description of the horrible frequency response of the speaker describes the tones that guitar people like to hear.
Electric Guitars are a narrow bandwidth device that is rolled off around 2.5K and rolled off around 300Hz. So that is why I tell people there is no real advantage in NOS tubes in a guitar amp. Because the excess bass and treble they have gets EQ out.

But there are other things going on currently with guitar players like thinking their amp + cab is decent much less they will have the typical Celestion speaker that doesn't record well compared to other speaker/cab combinations. Much less a studio amp has been gone through so its very noise free compared to someone else's amp they been hauling around the countryside.

Most pro studios force the guitar player to record a DI signal. Because most of the time their EQ settings are not correct for the mix, which is more important than the player is.
 

LadySpark

Joined Feb 7, 2024
194
I also disagree because all toob amplifiers for electric geetars had a 1M input resistance because the speakers (shriekers) had cone breakup boosted mids (they liked that sound) and a poor high frequency response. Phono preamps for magnetic cartridges (remember them?) used an input resistance of 47k ohms for a flat frequency response.
Disagree all you want. The only time I seen 1M input on a guitar amp was a DIY one that they put the input resistor as the grid stopper.
Attached is a guitar amp schematic with a 47K unbalanced load input. This is standard input design circuit regardless if the output is a grid circuit or a coupling transformer.Screenshot_2024-05-13_20-28-47.jpg
 

Ian0

Joined Aug 7, 2020
10,277
Disagree all you want. The only time I seen 1M input on a guitar amp was a DIY one that they put the input resistor as the grid stopper.
Attached is a guitar amp schematic with a 47K unbalanced load input. This is standard input design circuit regardless if the output is a grid circuit or a coupling transformer.View attachment 322260
That's an input impedance of 1,047,000Ω on Input 1, and 91,890Ω on input 2. (not 47k)
 

Audioguru again

Joined Oct 21, 2019
6,785
I went to a demonstration of a new hifi speaker system. The stereo sounded fantastic with deep low frequencies from the very large speaker enclosures. Then two pretty young ladies removed the large fake enclosure covers revealing small speaker enclosures that were producing the deep low frequencies.
I looked all over for a sub-woofer but there was not one. The surprise caused my skin to turn into goose bumps.
 

LadySpark

Joined Feb 7, 2024
194
That's an input impedance of 1,047,000Ω on Input 1, and 91,890Ω on input 2. (not 47k)
The 1M resistor can be any value, because its the grid self biasing resistor, and sets the gain level in the stage. That is why some use a potentiometer there for a volume control. The Unbalanced voltage source is loaded by the 47K resistor.
 

Ian0

Joined Aug 7, 2020
10,277
The 1M resistor can be any value, because its the grid self biasing resistor, and sets the gain level in the stage. That is why some use a potentiometer there for a volume control. The Unbalanced voltage source is loaded by the 47K resistor.
Where is the return path from the non-signal end of the 47k resistor to the guitar ground?
Through the 1M resistor?
 

LadySpark

Joined Feb 7, 2024
194
Where is the return path from the non-signal end of the 47k resistor to the guitar ground?
Through the 1M resistor?
Since the unbalanced coupling resistor is a series resistor, the voltage from the source is developed across it and there is no current return. Active unbalanced sources are preloaded and do not require any external loading for its operation.
 

Ian0

Joined Aug 7, 2020
10,277
Since the unbalanced coupling resistor is a series resistor, the voltage from the source is developed across it and there is no current return. Active unbalanced sources are preloaded and do not require any external loading for its operation.
How is it going to work without an earth return?
if there is no return current then the impedance is infinite.
 

LadySpark

Joined Feb 7, 2024
194
How is it going to work without an earth return?
if there is no return current then the impedance is infinite.
The source ground is the current return and incorporates the unbalanced coupling resistor as the source resistance in series with finite resistance of the voltage source(usually considered a short in AC analysis).
 

Ian0

Joined Aug 7, 2020
10,277
Isn’t there a path through the other input?
It has high gain and low gain inputs. Low gain giving an attenuation of 6dB.
You can see that the Guitar Input 1 has a grounding contact that is connected to earth and Guitar input 2 doesn't.
If you use guitar input 1 the guitar sees 47k in series with 1M, total input input impedance = 1.047M.
If you use guitar input 2, then input 1 socket's grounding contact connects the input to ground so puts 47k in parallel with 1M.
That combination is then in series with the 47k on guitar input 2, so the signal is attenuated by 6dB.
 

Ian0

Joined Aug 7, 2020
10,277
The source ground is the current return and incorporates the unbalanced coupling resistor as the source resistance in series with finite resistance of the voltage source(usually considered a short in AC analysis).
So the signal sees 1Meg in series with 47k, as I said a few posts ago.
 

LadySpark

Joined Feb 7, 2024
194
So the signal sees 1Meg in series with 47k, as I said a few posts ago.
The 1M resistor doesn't mean anything to it. It could be 1000M or 100 ohms. The unbalanced source resistance is still 47K and thus, the input impedance is still 47K.

If you look at a DC coupled common cathode circuit formula, the input impedance is always the input series input resistor and not the grid to ground resistor. The resistor from grid to ground doesn't have to connect to ground either as it could be connected to a bias voltage instead.
 
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