Re: AOUT_LC/CEM3378 voltages confusion (was: Pimp my Behringer)

[NorthernLightX]

Yes, the SSM2044 should do the same, a sound comparison could be interesting.

It is for the CEM filters, and as the negative voltage is available, I'm also using it for the AOUT_LC module.

The CV inputs (of the *external* CEM3378 circuitry -> see datasheet) are working in a range of ca. 1V-7V (CutOff) and 0V-3V (Resonance). In addition to the gain/offset trimmpots of the AOUT_LC module, I'm using 10k trimmpots against ground at the filter CV input side - all 4 AOUT_LC modules deliver the same voltages when the CVs are swept from min to max, and with the additional 10k pots I'm able to fine-adjust the desired maximum resonance and I equalize the CutOff frequencies of all filters on an easier way, than with the non-linear gain/offset pots

Best Regards, Thorsten.

Hi Thorsten,

Please excuse my ignorance, but I thought the AOUT(_LC) and the CEM filter both used 12v and -12v, The datasheet I have on the CEM3378 isn't too clear on this (the pinout says -5v on pin 9, but it isn't explained why the -5v is needed, it just says the operating voltage is between +4,75v and +12,5v.

I ask this because of the PSU I am designing, I never tought of a -5v rail to be necessary, but now this seems useful for the CEM filter option. Will -12v be sufficient, or will an additional 78L12 (or equivalent) be necessary if one would want to connect a CEM3378 filter to a -12v supply?

Cheers,  Alex.

[TK.]

Hi Alex,

the CEM3378 datasheet says, that +12V/-5V is for best performance. +12V/-12V would produce more heat, whereas +5V/-5V doesn't allow to reach the maximum cutoff frequency.

For the AOUT_LC module any voltage can be used within the supported range of the TL072, it's very flexible!

I ask this because of the PSU I am designing, I never tought of a -5v rail to be necessary, but now this seems useful for the CEM filter option. Will -12v be sufficient, or will an additional 78L12 (or equivalent) be necessary if one would want to connect a CEM3378 filter to a -12v supply?

I don't think that you need to take care about such special cases. If somebody needs -5V instead of -12V, he can just replace the 7912 by a 7905, or he has to adapt his circuit...

Best Regards, Thorsten.

[NorthernLightX]

the CEM3378 datasheet says, that +12V/-5V is for best performance. +12V/-12V would produce more head, whereas +5V/-5V doesn't allow to reach the maximum cutoff frequency.

Great! If -12v procudes more headroom, I'd prefer that over -5v, and -12v is already in the current design

I don't think that you need to take care about such special cases. If somebody needs -5V instead of -12V, he can just replace the 7912 by a 7905, or he has to adapt his circuit...

Indeed, if -5v is really needed one could branch off from the unregulated -12v, and then regulate it with a few caps and a 7905 off-pcb. Luckily, untill now I haven't seen interesting designs to add to midibox, where -5v was a must.

Last question: If you already had -12v available, and the CEM accepts that, why did you opt for -5v instead?

Cheers,  Alex.

[TK.]

Sorry, this was a writing error - I meant "heat" and not "head". Hope that this makes clear, why -5V/+12V is the better solution!

Last question: If you already had -12v available, and the CEM accepts that, why did you opt for -5v instead?

I don't have -12V available, only -15V/+15V from the Behringer PSU, and -5V/+5V/+12V from my own regulators...

Best Regards, Thorsten.

[NorthernLightX]

Thanks TK, I understand now. The -12v being available was a reading error from my side, I thought the behringer PSU did +12v/-12v.

I will not add the -5v rail to my PSU design, I believe it would be better to include the -5v power rail on the CEM filter board instead since it is only used there.

Do you plan to release your CEM filter as a midibox module? I definitely would want to build one or more!

Cheers,  Alex.