This is a portion of the output stage of the Boonton 1120 THD Analyzer -- uses a pair of NE5534's to obtain single-ended or balanced output -- was thinking to use the AD825/AD826 compound opamp for this purpose -- i have a spare output stage card from a broken 1120 to play with:
An externally hosted image should be here but it was not working when we last tested it.
jackinnj
I do think, you can have a hard time
by using Op-Amps to try to get the excellent precision
you can get by using a dedicated IC for this.
Analog Devices SSM2142 is such a high performance circuit!
SSM2142 Balance Line Driver Datasheet
Regards
lineup
I do think, you can have a hard time
by using Op-Amps to try to get the excellent precision
you can get by using a dedicated IC for this.
Analog Devices SSM2142 is such a high performance circuit!
SSM2142 Balance Line Driver Datasheet
An externally hosted image should be here but it was not working when we last tested it.
Regards
lineup
I_Forgot said:
It's lifted right from the schematic in their service manual -- there is one source input to a series of FET switches.
there's just a wee bit of 2nd order distortion and I am wondering if the NE5534's are up to the task -- it would seem that a mismatch in the opamps could be part of the problem whether or not one chooses the balanced or grounded option.
I have used the SSM2142 -- it's THD+N% is very low (there is a graph in the PDF) -- but it's voltage swing is less than that of the NE5534 combo. I will try it out this afternoon if I get a few minutes.
by the way, the Super-Oscillator from Linear is balanced -- basically two very high speed, tuned (current feedback) opamps run amock.
turns out that the schematic I showed -- which is what i copied out of the Boonton Manual -- is for an earlier version. when I popped the top and pulled the output card i saw that the driver was a pair of NE5534's, one a follower, which lead to a relay board.
i have also found out that it makes a difference when you are using the thing -- early in the morning before all the activity in the neighborhood gets going the Boonton's distortion is 0.0008% to 0.0010% -- this with no fluorescents going, no other test equipment running except a Tektronix AA501. in the afternoon or early evening it will average at 0.001% to 0.0014%
i'll leave well enough alone for now. i do appreciate the suggestion of the SSM2142 line driver --
i have also found out that it makes a difference when you are using the thing -- early in the morning before all the activity in the neighborhood gets going the Boonton's distortion is 0.0008% to 0.0010% -- this with no fluorescents going, no other test equipment running except a Tektronix AA501. in the afternoon or early evening it will average at 0.001% to 0.0014%
i'll leave well enough alone for now. i do appreciate the suggestion of the SSM2142 line driver --
Hi Jackinnj, Lineup,
I am looking for balanced output conversion for my single ended active crossover to combat a little buzz problem.
I thought about opamp based circuit until I saw Lineup's recommendation, wich is best suited for my limited skills.
I've done a little search and found this one, the DRV134, from Burr Brown:
http://docs-europe.electrocomponents.com/webdocs/0030/0900766b80030148.pdf
It is a little cheaper than SSM2142 (at least at RS components; stock nº 378-2676 )
Says "specified for high performance audio"
Regards,
M
I am looking for balanced output conversion for my single ended active crossover to combat a little buzz problem.
I thought about opamp based circuit until I saw Lineup's recommendation, wich is best suited for my limited skills.
I've done a little search and found this one, the DRV134, from Burr Brown:
http://docs-europe.electrocomponents.com/webdocs/0030/0900766b80030148.pdf
It is a little cheaper than SSM2142 (at least at RS components; stock nº 378-2676 )
Says "specified for high performance audio"
Regards,
M
there are 3 Boonton 1120's for sale on Ebay at the moment.
if you have problems with the 1120 the first thing to check is the power supply -- according to a tech I spoke with (and there are very few of them around from the time the instrument was manufactured) -- the power supply caps are prone to failure.
if you have problems with the 1120 the first thing to check is the power supply -- according to a tech I spoke with (and there are very few of them around from the time the instrument was manufactured) -- the power supply caps are prone to failure.
I have examples of both the realier and the later version of the 1120. The later version has a completely floating oscillator with opto-isolated connections to the controller. It also has bipolar output transistors to boost the available drive to 50 Ohms source at 16V RMS. It is still at the same .0007-.0009% THD at best. I think the limit is in the oscillator circuit itself.
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