Hey there,
I have here a original Throttle Box from Mesa Boogie that is unbelievable noisy.
The noise reminds me in rain pelting in the wind.
(Sorry for the bad explanation, English is not my native language.)
All pots and switches impacts the noise besides Mid Cut and S2 on the PCB, so I assume that I got the noise quiet early.
I t seems like the previous owner (he sold it as broken) worked on it...at least the power jack had been replaced (but I do not see any other trace of soldering).
I already put a propper jack back in place.
With the schematics I found in a forum, I was already able to nearly track the issue.
https://www.freestompboxes.org/viewtopic.php?t=23189
Tested with a shorted input (Neutrik silent cable), it seems like I have no noise before C7 (input coupling capacitor) but behind it.
So, if I put a GND probe in front of C7 (to silence any noise) nothing happened.
But if I place it behind it (technically it is the input (pin 5) of the 4558D, all the noise went silent.
Unfortunately, my oscilloscope went out of battery, so I could not go on for today.
----------
Thoughts I had within the day without being at the work bench:
I just wonder if I really found the issue here.
My thoughts:
The pedal is already a loud one and I don't know if mine is normal loud or too loud (and it is a loud bad ass but does not sound broken when it comes to the guitar signal itself.
I think it is normal that I have 2V DC behind the capacitor, since it is added via A+, right?
So I could have:
Found the issue and neet to eliminate the noise in front or within the first stage of the IC.
Propably it is then within the mentioned 2V right?
Or:
The noise is normal, but a later stage of the pedal amplifies too much.
To sort this out, I could place a 300mV sinus on the input of the pedal and see if it differs clearly from the 2V background noise, or if the noise is very loud compared to the signal.
If this looks good, I should trace the signal through the stages.
O have the feeling that the noise gets super loud out of IC2D.
But that stage should make the signal loud, so again hen or egg?
Also, if I do Muting on pin 5 of the first IC I propably mess with the power supply of all other stages, right?
I think I should better try pin 3 (input of IC1 second stage), since it is not connected to any power supply.
I think I should also compare the Pin5 noise level with the one of my Tubescreamer clone, since the input section is pretty identical, right?
What would happen if I lift R2, I should still have a signal then going through, right?
Thanks and regards,
Felix
I have here a original Throttle Box from Mesa Boogie that is unbelievable noisy.
The noise reminds me in rain pelting in the wind.
(Sorry for the bad explanation, English is not my native language.)
All pots and switches impacts the noise besides Mid Cut and S2 on the PCB, so I assume that I got the noise quiet early.
I t seems like the previous owner (he sold it as broken) worked on it...at least the power jack had been replaced (but I do not see any other trace of soldering).
I already put a propper jack back in place.
With the schematics I found in a forum, I was already able to nearly track the issue.
https://www.freestompboxes.org/viewtopic.php?t=23189
Tested with a shorted input (Neutrik silent cable), it seems like I have no noise before C7 (input coupling capacitor) but behind it.
So, if I put a GND probe in front of C7 (to silence any noise) nothing happened.
But if I place it behind it (technically it is the input (pin 5) of the 4558D, all the noise went silent.
Unfortunately, my oscilloscope went out of battery, so I could not go on for today.
----------
Thoughts I had within the day without being at the work bench:
I just wonder if I really found the issue here.
My thoughts:
The pedal is already a loud one and I don't know if mine is normal loud or too loud (and it is a loud bad ass but does not sound broken when it comes to the guitar signal itself.
I think it is normal that I have 2V DC behind the capacitor, since it is added via A+, right?
So I could have:
Found the issue and neet to eliminate the noise in front or within the first stage of the IC.
Propably it is then within the mentioned 2V right?
Or:
The noise is normal, but a later stage of the pedal amplifies too much.
To sort this out, I could place a 300mV sinus on the input of the pedal and see if it differs clearly from the 2V background noise, or if the noise is very loud compared to the signal.
If this looks good, I should trace the signal through the stages.
O have the feeling that the noise gets super loud out of IC2D.
But that stage should make the signal loud, so again hen or egg?
Also, if I do Muting on pin 5 of the first IC I propably mess with the power supply of all other stages, right?
I think I should better try pin 3 (input of IC1 second stage), since it is not connected to any power supply.
I think I should also compare the Pin5 noise level with the one of my Tubescreamer clone, since the input section is pretty identical, right?
What would happen if I lift R2, I should still have a signal then going through, right?
Thanks and regards,
Felix
