Bypassing Tube-Saturation Circuit in an EQ.

[Yos]

Hi guys!

By chance I acquired a Behringer T1951 equalizer.
It works flawlessly but it has this useless option (in my opinion), a potentiometer to add tube saturation/harmonics.
The thing is that the tube saturation circuit seems to be messing with the signal even if the potentiometer for the saturation is closed.
It adds clearly audible second and third harmonics (see attached screenshot #2).

My question to you guys is, could someone glance over the schematics, and tell me if there is an easy way to bypass the tube circuit?
Or attenuate it?
Below I attached the schamatics for the tube citcuit.
And here is a download link for the whole schematics for the device:
https://workupload.com/file/RswQAWyNJ45

Thanks in advance!

Rob.

 

[Script]

That peak at 3K could also come from elsewhere in the circuit.

Either way it's low. Do I see correctly, -25dB signal level and 3K peak is at what -116dB or so?

Tube circuit is surely on the front panel assembly. Very likely SMD. And for easy access I'd assume need to disassemble the entire front.

(-Have a broken, lowest-priority T1952 somewhere. I remember that disassembly was a bit of a pita. Knobs didn't come off easily.-)

Could take few components off the board -- at input TO tube circuit & at output FROM tube circuit -- and then bridge (thru equivalent cap) the entire tube section.
C141 100N
R206 10k
C34 47/25

But need to make *absolutely* sure that component designators on the PCB *really* match those in the schematics. So need to trace circuit. (-Designators sure didn't match over here with the T1952.-)

 

[scott2000]

Either way it's low. Do I see correctly, -25dB signal level and 3K peak is at what -116dB or so?

That's with eq off and saturation pot closed. EQ engaged even with saturation off, it's worse...

 

[Script]

That the T series signature sound or whatever then, I assume

 

[scott2000]

I can't tell where the saturation knob is? ..
Immediately thought starving the starving plates by disconnecting them but I'm not so sure...

 

[Script]

IIRC, by just taking out the tubes, output is mute.

 

[freshtapescent]

I believe the signal is applied differentially to two somewhat equally naughty sounding starved plate triodes. With the saturation knob down, the signal is somewhat equally sent in, and recovered, and the receiver amplifier does a remarkable job of subtracting the distortion products. When the saturation knob is turned, you deliberately mis-balance the input signal and that results in more distortion products on the other end. Quite brilliant…?

Your strategy for least distortion may be to figure out how to tweak the saturation pot to be a ‘triode balance’ pot and compensate for the variations in your triodes. Let the thing warm up, then optimize your setting for lowest distortion.

 

[Yos]

@all

Thank you guys for your responses!

So in short, there is no easy way to bypass the tubes.
Solutions like suggested by freshtapescent are over my head.

If there is no easy way, then I will have to live with the slight coloration.

BTW, taking the tubes out makes the unit go mute.

Cheers!

Rob.

 

[Script]

Well, could try to take components off the board...

...or sell this unit and get two of the earlier Behringer mono EQ units (UltraQ). They should be cheap and they are all thru-hole.