Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

JRC 4558D - Guitar preamp
JRC 4558D - Guitar preamp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th April 2019, 07:38 PM   #1
Ben Martin is offline Ben Martin  Portugal
diyAudio Member
 
Join Date: Sep 2014
JRC 4558D - Guitar preamp
Default JRC 4558D - Guitar preamp

Hi all,

I have this TDI4 passive DI box that needs a simple guitar preamp to be able to excite my TASCAM 16X08 - line-in TSR ports 11 through 14.
This TASCAM device offers no preamps associated to the ports from 11 up to 16, hence this ports are pure "line-in" channels.

I found a few guitar preamp schematics options.
Some preamps are replicas of guitar stomp pedals that add overdrive and other FX to the signal.

Since I have a few IC "NJM 4885D" around, I noticed that I can use this op-amp to assemble simple electric guitar preamps.

So, I designed a simple solution that allows me preamp 4 electric guitars using 2 IC "NJM 4885D" in the same PCB board.
This should allow me to connect 4 individual electric guitars to the 4 line-in ports of the TDI4 passive DI box (at the same time).

Do you guys have any idea if this is going to work based on my schematics?
What would you do different?
Keeping in mind that distortion is not welcome.
The aim is to get a pre-amplified clear and transparent sound signal able to reach the "line-in" record device with a good signal ratio.

Any sound FX (Distortion, Chorus, Delay, Fuzz, Scream-tube) will be added after record the clean electric guitar signal.
Please care to comment on the schematics.
Many thanks.

Ben
Attached Images
File Type: png GA 4558D 4X.png (22.5 KB, 133 views)
File Type: png GA 4558D 4X PCB Comp.png (137.0 KB, 133 views)

Last edited by Ben Martin; 13th April 2019 at 07:43 PM.
  Reply With Quote
Old 13th April 2019, 08:05 PM   #2
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Quote:
Originally Posted by Ben Martin View Post
any idea if this is going to work based on my schematics? What would you do different?
You'll have some output DC offset (depending on the gain) without output coupling capacitors.
Also normally you would install decoupling capacitors at each op amp rail to ground. In this case
probably a 10uF 25V would be ok. The highs are rolled off at 3400 Hz by the 470pF capacitors.
You can always try other dual op amps as well.

Last edited by rayma; 13th April 2019 at 08:12 PM.
  Reply With Quote
Old 13th April 2019, 10:20 PM   #3
Ben Martin is offline Ben Martin  Portugal
diyAudio Member
 
Join Date: Sep 2014
JRC 4558D - Guitar preamp
Hi rayma,

Many thanks for comment.
About the he highs being rolled off at 3400 Hz by the 470pF capacitors, I guess it is not bad for electric guitars. The golden range for guitars in a mix is from 80Hz up to 1500Hz. The guitar may go up to 5000Hz (maximum) but from 1500 up to 5000Hz it is already considered a "red zone" for guitars and should be avoid into a mix but if you have any other suggestion for this 470pF capacitors, please let me know what values you propose. :-).

About the electrolytic 10uF capacitors.
Well, I'm planning to use the following schematic for Power Supply (see attached please).

I guess the decoupling it was already been taken care off here, right?
Please, let me know what you think. :-)
Attached Images
File Type: png 12v Dual Power Supply.png (10.5 KB, 118 views)
  Reply With Quote
Old 13th April 2019, 10:28 PM   #4
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Quote:
Originally Posted by Ben Martin View Post
if you have any other suggestion for this 470pF capacitors
I guess the decoupling it was already been taken care off here
The particular capacitor type will affect the sound also.
Use whatever pF value you like for the 470pF capacitor,
but choose preferably a polypropylene type, or at least a
COG/NPO ceramic, for the least distortion. No Mylars.

At least a 0.1uF capacitor should be at each IC package supply pin,
even if there is already one by the regulator. The local capacitors bypass
the inductance of the pcb traces between the ICs and the power supply.

Last edited by rayma; 13th April 2019 at 10:30 PM.
  Reply With Quote
Old 13th April 2019, 10:32 PM   #5
Ben Martin is offline Ben Martin  Portugal
diyAudio Member
 
Join Date: Sep 2014
JRC 4558D - Guitar preamp
Quote:
Originally Posted by rayma View Post
The particular capacitor type will affect the sound also.
Use whatever pF value you prefer for the 470pF capacitor,
but choose preferably a polypropylene type, or at least a
COG/NPO ceramic, for the least distortion.

Alright, will go for a polypropylene type, then.


Quote:
Originally Posted by rayma View Post
At least a 0.1uF capacitor should be at each IC package supply pin,
even if there is already one by the regulator.

Ok, going to add that to the schematic and then I'll post it again when it's done.
By the way, ceramic or something else?


Thanks for helping me.

Ben
  Reply With Quote
Old 13th April 2019, 11:08 PM   #6
Ben Martin is offline Ben Martin  Portugal
diyAudio Member
 
Join Date: Sep 2014
JRC 4558D - Guitar preamp
Hi,

I'm back... so it is something like this you are suggesting (capacitors 0.1uF) see the new attached image.

I noticed in the schematics of the Power Supply regulator that, besides the 10uF polarized capacitors there are also 0.1uF capacitors included (before the final points +12v 0 -12v stage).

Despite that, you still recommend to add extra 0.1uF capacitor at each 4 and 8 pins of the ICs 4588D, correct? (like it is now in the schematics).

Ben
Attached Images
File Type: png GA 4558D 4X_V2.png (36.3 KB, 112 views)
  Reply With Quote
Old 13th April 2019, 11:24 PM   #7
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Quote:
Originally Posted by Ben Martin View Post
you still recommend to add extra 0.1uF capacitor at each 4 and 8 pins
of the ICs 4588D, correct? (like it is now in the schematics).
Yes, exactly. This is required universally for most all ICs, linear and digital.
Often an additional 10uF is needed per pin, along with the 0.1uF.
Depends on the loading, etc.

Last edited by rayma; 13th April 2019 at 11:27 PM.
  Reply With Quote
Old 14th April 2019, 02:18 AM   #8
Ben Martin is offline Ben Martin  Portugal
diyAudio Member
 
Join Date: Sep 2014
JRC 4558D - Guitar preamp
Oh, I just noticed that I put the 0.1uF capacitors in "series" with the 4 and 8 pin of the IC, and that is wrong.
I should have put them from the pins to the GND.
Already corrected in this new schematic.


Anyone else has some extra tips to make this 4 channels guitar preamp using only 2 ICs 4558D? By the way, I'm using this IC because I have 8 spare units around from a previous project.
Attached Images
File Type: png GA 4558D 4X_V3.png (28.0 KB, 104 views)
File Type: png GA 4558D 4X PCB 3DV3.png (119.4 KB, 30 views)
File Type: png GA 4558D 4X PCB V3.png (39.2 KB, 14 views)
  Reply With Quote
Old 14th April 2019, 05:14 AM   #9
Guerilla is offline Guerilla  Denmark
diyAudio Member
 
Join Date: Feb 2018
Location: Aalborg Denmark
You may have to make it pretty linear. To make it sound right you will need to use a cabinet-simulator in your mixingsoftware. That would probably not sound right if the input signal is allready rolling off.
I think what you need, would be called a 4 channel di-box -hardly a guitarpreamp You need a gain button for each channel to raise signal from microphone level to a clean line-level, and then use 100 wet signal in the mix
I dont read scematics, so maybe thats what you have already

Last edited by Guerilla; 14th April 2019 at 05:16 AM.
  Reply With Quote
Old 14th April 2019, 08:24 AM   #10
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
1) as is you can ground pin 2 and 6 at some pot settings and get infinite gain, not good.
Add, say, 4k7 or 10k between pot wiper and pins 2 or 6 , that will limit max gain to 20X or 10X tops.

2) also add a 1uF to 10uF electrolytic in series with that gain limiting resistor, currently your preamp amplifies DC and that again is not good.

3) reduce RF rolloff from 470pF to 220pF and even better 100pF which is the unwritten standard value.
a) there is some content "up there" , no need to kill it beforehand.
If you wish, you can do that later.
b) those are "slow" filters, so choosing 1500Hz as you did at the beginning, will start attenuating quite below that; no guitar will have sparkle.

4) for a smooth gain variation related to knob movement, try to get a "C" curve pot (reverse log) .
A Linear one will do very little over most of the range and jump a lot near the end, hard to adjust.

5) supply bypassing is fine, now donīt obsess with capacitor dielectrics, that makes more sense in high quality Audiophile stuff but for Guitar use, Electrolytics, Ceramics and "any" plastic film is way above normal needs.

In fact, although Electrolytics "should" be bipolar when no DC voltage is applied, here applied AC voltage is so small that you can safely use plain ones.
FWIW everybody does (Fender/Marshall/VOX/Laney/Peavey/etc.)

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.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.

Last edited by JMFahey; 14th April 2019 at 08:27 AM.
  Reply With Quote

Reply


JRC 4558D - Guitar preampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
preamp regulated or unregulated 4558d rahulrahullll Analog Line Level 4 3rd January 2018 06:55 PM
Guitar preamp argonrepublic Instruments and Amps 2 30th January 2017 04:29 AM
4558d auto pilot Analog Line Level 4 7th January 2013 07:42 PM
guitar preamp star882 Instruments and Amps 5 1st May 2007 02:37 AM
low THD guitar preamp Antonix Instruments and Amps 4 29th June 2006 04:49 PM


New To Site? Need Help?

All times are GMT. The time now is 05:32 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki