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JRC 4558D - Guitar preamp
JRC 4558D - Guitar preamp
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Old 14th April 2019, 08:57 AM   #11
Guerilla is offline Guerilla  Denmark
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Quote:
Originally Posted by JMFahey View Post
1)
EDIT: for your intended use, you donīt even need a gain pot, just use fixed 5X gain (say, 100k+22k+1 to 5 uF) and your Guitars will nicely fit the "line level" inputs.
Cool. I didnt know that. Makes it easier/cheaper
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Old 14th April 2019, 11:45 AM   #12
mjf is offline mjf  Austria
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example..........
choose your preferred parts
Attached Images
File Type: jpg guitar pre 1a.JPG (211.6 KB, 50 views)
File Type: jpg guitar pre 1b.JPG (73.4 KB, 47 views)
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Old 14th April 2019, 12:11 PM   #13
Ben Martin is offline Ben Martin  Portugal
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JRC 4558D - Guitar preamp
Hi JMFahey and mjf,

Many thanks you both for your valid input.

JMFahey, I'm curious about your propositions.
Any chance you can put that in a simple schematic so I can be sure about what you mean without any miss interpretation?
Specifically about thid sentence:
Quote:
Originally Posted by JMFahey View Post
EDIT: for your intended use, you donīt even need a gain pot, just use fixed 5X gain (say, 100k+22k+1 to 5 uF) and your Guitars will nicely fit the "line level" inputs.
I'm not sure I understood what you mean with:
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Old 14th April 2019, 12:14 PM   #14
Ben Martin is offline Ben Martin  Portugal
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JRC 4558D - Guitar preamp
Quote:
Originally Posted by mjf View Post
example..........
choose your preferred parts
mjf, is this a DI BOX schematics?
It seems a regular op amp amplification circuitry based on the IC RC 4558D.
I see that the decoupling is done by using 2 capacitor (C3 + C4) in series between pin 4 and 8 ( +12v -12v ).

Last edited by Ben Martin; 14th April 2019 at 12:18 PM.
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Old 14th April 2019, 03:18 PM   #15
Enzo is offline Enzo  United States
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Rather than thinking of C3, C4 in series, just look at them as to ground from either power rail.
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Old 14th April 2019, 04:06 PM   #16
Ben Martin is offline Ben Martin  Portugal
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JRC 4558D - Guitar preamp
Quote:
Originally Posted by Enzo View Post
Rather than thinking of C3, C4 in series, just look at them as to ground from either power rail.
Hi Enzo,
Thank you for your input.
Yes, you are right!
I didn't noticed that in mjf schematic, both capacitors link to GND. Dhooo.
Well, actually, that's what I have in my scheme too. :-)
See attached images;
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File Type: png decoupling.png (7.9 KB, 38 views)
File Type: png PCB.png (9.1 KB, 39 views)

Last edited by Ben Martin; 14th April 2019 at 04:19 PM.
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Old 15th April 2019, 12:39 AM   #17
PRR is offline PRR  United States
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A "DI box" goes to a microphone input.

If you only have Line inputs, all you need is hi-Z gain of 4 to 40 which a '4558 can do (though a TL072 may be better). Then sell your DI box.
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Old 15th April 2019, 06:14 AM   #18
Guerilla is offline Guerilla  Denmark
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Quote:
Originally Posted by PRR View Post
A "DI box" goes to a microphone input.

If you only have Line inputs, all you need is hi-Z gain of 4 to 40 which a '4558 can do (though a TL072 may be better). Then sell your DI box.
I believe a di-box can have gain and even ballanced out, but ben martins doesnt, and I agree I cant see what use he has for it.


Originally Posted by JMFahey View Post
EDIT: for your intended use, you donīt even need a gain pot, just use fixed 5X gain (say, 100k+22k+1 to 5 uF) and your Guitars will nicely fit the "line level" inputs.

I'm not sure I understood what you mean with:

-You dont need a guitar preamp

You only need a surcuit that amplifies the guitars output 5 times (20db?) And change its output impedance to suit the line in on your recorder.

Useualy(cant spell) people use mics in front of guitarspeakers when recording. Nowadays many pedalboards and guitaramplifiers. Have build in guitaramp-(guitarspeaker really)simulation that allows you to record directly without a microphone, or play directly thruu a PA system-without its sounding strange.

You choose to record the clean signal from the guitar and proces it when mixing,which should work fine. Maybe even great.
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Old 15th April 2019, 08:29 AM   #19
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by Ben Martin View Post
Hi JMFahey and mjf,

Many thanks you both for your valid input.

JMFahey, I'm curious about your propositions.
Any chance you can put that in a simple schematic so I can be sure about what you mean without any miss interpretation?
Specifically about thid sentence:

I'm not sure I understood what you mean with:
MJF solved and drew it for you

Just follow his circuit which incorporates all the improvements, specially: ~5X gain and ruler flat from below 40Hz (so it also covers Bass ) to above 10kHz, and with such a degree of NFB itīs practically distortionless.

He was also kind enough to simulate it.

Treat it as a "Black Box" : Guitar/Bass In>Line level Out.

To boot, having very low output impedance, you plug your guitar into it with a not too long cable, output from mixer to Sound Module can use quite a long one, easily 20/30 meters, with no problem, so you can, say, play in the center of a stage and have Module (or a Mixer or a Powered cabinet) at some distance on Stage side with no problems.

Input impedance is perfect for a passive instrument while plugging straight into module would probably be 10k to 20k , too low.
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Old 15th April 2019, 10:06 AM   #20
Ben Martin is offline Ben Martin  Portugal
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JRC 4558D - Guitar preamp
Quote:
Originally Posted by PRR View Post
A "DI box" goes to a microphone input.

If you only have Line inputs, all you need is hi-Z gain of 4 to 40 which a '4558 can do (though a TL072 may be better). Then sell your DI box.
Ah... ah... :-)
I still need my passive DI BOX (4 x instrument level inputs) to when musicians come to my place to record. Sometimes they bring their own preamps and stuff.
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