Boss CE2

[Tav]

I have placed a Boss CE2 Chorus Pedal right after a Mesa Boogie Studio Preamp, the chorus signal (not the dry part of the sound) seems to be overloaded by the high line output of the preamp. Is there a way to mod the pedal in order to make it accept high power line signal levels since the unit's input is intended to accept instrument signals?
Regards

[Phostenix]

You should first check to see that the DC bias is set properly on the BBD chip. Do you have an oscilloscope & a signal generator?

[Tav]

Unfortunatley no, the effect is working correctly if I plug a guitar direct in it, asi it is intended to be. The problem occurs onlyif I feed a preamp signal in it.

[Phostenix]

It could still be that the bias isn't set properly. Any idea what the signal level out of the preamp is? I can put 1v p-p into my CE-2 before it distorts.

[Mark Hammer]

It is possible you can do what you want by lowering the gain of the input stage that feed the delay chip by lowering R6 from 47k to maybe 39k.

It is also worth considering adjusting the bias, but it is probably simpler to first tack a second resistor in parallel on the copper side to produce a lower resistance. A 220k resistor in parallel with 47k will get you close to 39k.

[Tav]

It is possible you can do what you want by lowering the gain of the input stage that feed the delay chip by lowering R6 from 47k to maybe 39k.

It is also worth considering adjusting the bias, but it is probably simpler to first tack a second resistor in parallel on the copper side to produce a lower resistance. A 220k resistor in parallel with 47k will get you close to 39k.

Thanks, that will only affect the wet chorused portion of the signal or the entire signal path?

[Mark Hammer]

Thanks, that will only affect the wet chorused portion of the signal or the entire signal path?

It will affect the whole shebang....unfortunately. The thing is that this particular op-amp stage not only sets the entire level being fed to the dry side of the output and signal fed to the delay chip, it also produces a sort of "poor man's Dolby" by introducing a treble boost which is counteracted by a symmetrical treble cut on the output stage. There may be two side-effects of doing what I suggested: 1) a possible imbalance in the tone, and 2) a bit more audible noise from the unit.

The good news is that it takes nothing to temporarily tack on the 220k resistor and give a listen to see if it does what you need, and is a very nondestructive and non-intrusive mod...if you want it to be. If it works, we can proceed fro there, and if it bombs, we can simply remove the tacked on resistor and go back to the drawing board.

Worse comes to worse, you could possibly try a simple passive attenuator on the front end of the pedal, hard-wired to the input jack, or even buld the damn attenuator circuit into the phone-plug housing so that the CE-2 remains stock.

[Tav]

It will affect the whole shebang....unfortunately. The thing is that this particular op-amp stage not only sets the entire level being fed to the dry side of the output and signal fed to the delay chip, it also produces a sort of "poor man's Dolby" by introducing a treble boost which is counteracted by a symmetrical treble cut on the output stage. There may be two side-effects of doing what I suggested: 1) a possible imbalance in the tone, and 2) a bit more audible noise from the unit.

The good news is that it takes nothing to temporarily tack on the 220k resistor and give a listen to see if it does what you need, and is a very nondestructive and non-intrusive mod...if you want it to be. If it works, we can proceed fro there, and if it bombs, we can simply remove the tacked on resistor and go back to the drawing board.

Worse comes to worse, you could possibly try a simple passive attenuator on the front end of the pedal, hard-wired to the input jack, or even buld the damn attenuator circuit into the phone-plug housing so that the CE-2 remains stock.

All right, thanks for the tip. Is there a way to bring back the level in the unit if there is a drop in volume, like a resistor change or something similar?

[Mark Hammer]

I'm going to say that you should attempt to create a reciprocal boost to offset the attenuation at the front, via resistors R21 and R22.

Stock, the unit is essentially unity gain. R4 and R6 assure that the op-amp input/splitter stage is unity gain. C3/R5 give a bit of a boost to the top end (above 2.3khz).

R21/22 and R24 assure that the output/mixer stage is unity gain, however C15/R23 provide a complementary treble cut that essentially cancels what C3/R5 did.

If R6 is decreased from 47k to 39k, that changes the stage from a gain of 1 to a gain of .83. To produce the reciprocal gain of 1.20, simply make both R21 and R22 39k. The same arrangement would hold true for whatever value of R6 you eventually settle on. If you go with 36k, then make R21 and R22 36k.

I may be wrong, but I think that the pre-emphasis and de-emphasis will work as intended, albeit with just a bit more noise at the output, since we're adding gain to whatever noise comes from the delay path. Happily, since the gain is only 1.2x that extra noise will be minimal. If you find it objectionable, make C16 220pf-270pf.

[Tav]

All right, thanks, I'll do that