Hi The original design with 3x75 ohm outputs would be driving a 50 ohm load rather than a 33 1/3 ohm load. That would put it "in spec" for the CLC409 as opposed to just out of spec current limit wise.
Bob On Aug 9, 2013, at 2:48 PM, Charles Steinmetz <[email protected]> wrote: > Bob wrote: > >> Ok, each op-amp drives three loads. Each load has a 50 ohm resistor in >> series with it. Each output could be terminated in 50 ohms. If they all are >> terminated, the op amp is driving three 100 ohm loads in parallel. The op >> amp sees 33 1/3 ohm at it's output in that case. That's way below the 100 >> ohms that the manufacturer seems to be recommending. > > The circuit is basically the same as the Extron ADA 6 Component that I posted > about back in May. I noted: > >> Several units modified as above have been tested and each amplifier drives >> 3x 50 ohm loads to ~ +13dBm (~ 1 Vrms) with harmonics <-65dBc and about 1 dB >> of headroom. Note that this requires peak currents of ±85 mA from the >> CLC409s, which are rated for output currents of ±60 mA “for maximum >> reliability” (also note that the guaranteed minimum current limit value of >> the CLC409 is ±50 mA). Thus, for optimum performance, 50 ohm loads should >> be distributed one or two per amplifier. Note that the reference inputs of >> many devices is higher than 50 ohms (often ~ 1k ohm), so this may not be an >> issue in many applications. > > (see > <http://www.febo.com/pipermail/time-nuts/attachments/20130522/45ae59f8/attachment-0001.pdf>) > > I do not know for how long a CLC409 will drive 3 parallel 50 ohm > back-terminated loads to +13 dBm before failure. My test mule did it > continuously for several weeks, but I would not recommend it. Of course, > some CLC409s (with current limits closer to the minimum spec) may not drive 3 > parallel 50 ohm back-terminated loads to +13 dBm at all. > > The CLC409 is within its +/- 60 mA "maximum reliability" spec driving 2 > parallel 50 ohm back-terminated loads to +13 dBm (peak current +/- 56 mA), > although parts that are right at the 50 mA minimum current limit spec may be > starting to current limit. > > Someone asked how the modified DA performs. In addition to the distortion > data above, I posted: > >> Phase noise of < -155dBc at 10 MHz was observed on the modified units. >> Adjacent-output isolation (same CLC409) was > 30dB. Non-adjacent-output >> isolation was > 90dB. > > Best regards, > > Charles > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
