Behgringer BXL1800A circuit required

[FEZ2]

HI Need the circuit of this base amp in particular the preamp stage,, the fault is that the DI output is not clean seems to be very noisy.

hope someone can help I have had a good look around but this seems to be a rare one,,

rgds
FEZ2

[Jazz P Bass]

All that I have is the BX 1800.
It may be the same.

BEHRINGER+BX1800.zip

[FEZ2]

Hi JAZZ P I have this one and is not the same,,, it has no DI output and no opto coupler .
thank you for trying
FEZ2

[Jazz P Bass]

O/K.
Let's try the BX1200 then.
DI Out & an opto on the power amp.

Behringer BX-1200 Ultrabass (Rev.H) Schematics.zip

[FEZ2]

I have this one also yes has DI but the opto on the BXL1800a is on the preamp PCB and the PA section is discrete parts not I/C as the1200.
rgdsFEZ2

[Enzo]

Is the noise only on the DI? Are any of the schematics close enough to help you identify the IC that drives the DI output? I'd wager that IC is what has become noisy. Try IC13, a TLo72. It appears the signal that feeds the DI driver also goes directly to the LINE OUT jack, so if that jack is not noisy, it reinforces my suspicion.

I can answer any schematic questions, but I am bound by an NDA not to post it.

[FEZ2]

Hello Enzo,,, Completely understand re the NDA,, Yes I have TL072 on order, so will fit when arrives,,, the other reason for the circuit was to figure out the opto function as I have an oscillation of 1.8Mhz yes Mhz on C25 and this might be the cause of the problem by touching around the opto circuit the oscillations cease,, I suspect it should not be there,,, clues how to remove this spuri,,

FEZ2