Pete, Dudley, I used protection circuit outside the SDR-1000 in the both audio cables. It was with a 100 ohm current limiting resistor and two opposite parallel connected strings of 3 silicon diodes (1N4148). Nominally this limits the input voltage to 2.1Vpp.
In my case also the unit from the first production run showed parasitic oscillations that were cured by grinding off some copper foil around the input/output pads to reduce the ground capacitance. Additional 3 units from the later production runs are completely stabile. Ahti On 10/12/2008, Pete Ferrand <[EMAIL PROTECTED]> wrote: > Ahti, Dudley: > > I'm using a Delta 44. That's interesting, I had been thinking the amp failed > due to output issues as I've rarely seen opamps fail due input drive > problems. I hadn't checked the circuit but in most designs the would have > been limited at some earlier stage. > > Ahti, how did you set up the diodes? Back to back from the high side of the > input transformer to ground, or across the differential inputs or? > > While this is an easy fix to implement and does make the circuit more robust > as I asked I doubt it will fix the issue. I will give it a try though. > > In both cases where the chip failed the drive setting was less than 10 and > the rig was in "tune" mode for a few seconds. In addition, for the almost > half year I've had this working the rig was terminated in a 50 ohm resistor > in the linear. In both cases where it failed the radio was working into some > other load. > > If it's extreme swr sensitivity or possibly parasitics I can guess at the > causes but I do not know what the logical troubleshooting procedure would > be. > > -Pete > > > > > > -----Original Message----- >>From: Ahti Aintila <[EMAIL PROTECTED]> >>Sent: Dec 9, 2008 11:54 PM >>To: Dudley Hurry <[EMAIL PROTECTED]> >>Cc: Pete Ferrand <[EMAIL PROTECTED]>, flexradio@flex-radio.biz >>Subject: Re: [Flexradio] blown SDR-1000 final opamp >> >>Dudley and Pete, >> >>The absolute maximum differential input voltage for OPA2674 is >>+/-1.2V. For that reason I used clamping diodes for protection in one >>instrumentation application of SDR-1000 when I was not sure the >>operators remember to keep the sound card output at reasonable level. >>Be careful though not to distort the signal. >> >>73, Ahti OH2RZ >> >> >>On 10/12/2008, Dudley Hurry <[EMAIL PROTECTED]> wrote: >>> Pete, >>> >>> You did not mention what sound card you are using, but if the sound >>> card output is too high you can easily overdrive the low level driver, >>> particularly the PreSonus can drive more than 4 volts peak to peak.. >>> >>> >>> 73, >>> Dudley >>> >>> WA5QPZ >>> >>> >>> >>> Pete Ferrand wrote: >>>> Ahti: >>>> >>>> Thank you for taking the time to reply. My radio has the OPA2674 and >>>> that >>>> is what it had originally. The issue is not one of a short circuit, but >>>> most probably one of dealing with a high impedance load which would send >>>> the voltage up beyond what the part can handle. At least that's what I'm >>>> guessing; I'm not sure of the correct troubleshooting procedure for this >>>> kind of fault. >>>> >>>> My hope was that someone has figured out how to make the circuit more >>>> robust but since yours was the only reply and there's no mention of it >>>> in >>>> the archives I suppose that hasn't happened. >>>> >>>> 73, >>>> -Pete >>>> WB2QLL >>>> Somers, WI >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> -----Original Message----- >>>> >>>>> From: Ahti Aintila <[EMAIL PROTECTED]> >>>>> Sent: Dec 9, 2008 4:54 AM >>>>> To: Pete Ferrand <[EMAIL PROTECTED]> >>>>> Cc: flexradio@flex-radio.biz >>>>> Subject: Re: [Flexradio] blown SDR-1000 final opamp >>>>> >>>>> Pete, >>>>> The very old SDR-1000 units have OPA2677 as the final amplifier and >>>>> cannot stand short circuit. The newer radios use OPA2674 that has >>>>> internal short circuit protection. Anyhow, ask Flex people directly, >>>>> they know better the difficulties with some of the first production >>>>> units. >>>>> >>>>> 73, Ahti OH2RZ >>>>> >>>>> On 09/12/2008, Pete Ferrand <[EMAIL PROTECTED]> wrote: >>>>> >>>>>> Some months ago I blew the final opamp in my 1W SDR-1000 whilst >>>>>> matching >>>>>> it >>>>>> to a linear. Wasn't happy about that but since I accidentally hooked >>>>>> up >>>>>> the >>>>>> attenuator resistors wrong I wasn't too surprised since the rig saw a >>>>>> very >>>>>> high impedance. Worked fine ever since. >>>>>> >>>>>> Unfortunately I'm less happy about blowing the amp this morning, about >>>>>> a >>>>>> half year after that first incident, whilst trying it on six meters >>>>>> for >>>>>> the >>>>>> first time. Without the linear which doesn't cover six. Just wanted to >>>>>> see >>>>>> if I could work a couple locals. As far as the MFJ-269 showed there >>>>>> was >>>>>> a >>>>>> perfect match into the ATU but when I increased the power beyond about >>>>>> a >>>>>> tenth of a watt output the opamp popped again. >>>>>> >>>>>> Besides the time and money aspect, the circuit board clearly can't >>>>>> take >>>>>> a >>>>>> lot of parts replacements. >>>>>> >>>>>> Has anyone figured out how better to protect this part? Or some better >>>>>> solution. This is a four stack including the rfe board, older version >>>>>> with >>>>>> nylon spacers. >>>>>> >>>>>> Thanks. >>>>>> >>>>>> -Pete >>>>>> WB2QLL >>>>>> Somers, WI >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> FlexRadio Systems Mailing List >>>>>> FlexRadio@flex-radio.biz >>>>>> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >>>>>> Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >>>>>> Knowledge Base: http://kc.flex-radio.com/ Homepage: >>>>>> http://www.flex-radio.com/ >>>>>> >>>>>> >>>> >>>> >>>> _______________________________________________ >>>> FlexRadio Systems Mailing List >>>> FlexRadio@flex-radio.biz >>>> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >>>> Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >>>> Knowledge Base: http://kc.flex-radio.com/ Homepage: >>>> http://www.flex-radio.com/ >>>> >>>> >>> > > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
