Dealing with higher output amps-
It has a differential input on an XLR/TRS connector so why not a passive 10X "probe" to handle the higher voltages. Some resistors and a trimmer cap and its possible to scale accurately. However safety considerations need to be addressed. the days of exposed bananas and HV are long gone. Series 1 Meg resistors on each leg would actually do the job. A cap would be necessary to compensate for shunt capacitance in the cables.
It has a differential input on an XLR/TRS connector so why not a passive 10X "probe" to handle the higher voltages. Some resistors and a trimmer cap and its possible to scale accurately. However safety considerations need to be addressed. the days of exposed bananas and HV are long gone. Series 1 Meg resistors on each leg would actually do the job. A cap would be necessary to compensate for shunt capacitance in the cables.
Early in the development I looked at including an additional 1Meg input for measurements in tube amps at high impedance points.
But getting it flat to 100kHz+ and relatively accurate made the whole thing exponentially more complex and calibration becomes also more involved.
So I let that be.
After the AR my next project may be a high impedance audio floating differential probe
Jan
But getting it flat to 100kHz+ and relatively accurate made the whole thing exponentially more complex and calibration becomes also more involved.
So I let that be.
After the AR my next project may be a high impedance audio floating differential probe
Jan
> A transparent, wideband 60dB attenuator that can be adjusted in a typical DIY shack is no-go.
Can't you just include an additional, switchable, 10x attenuator in cascade for the few occasions one needs -40~-60dB ?
(Probably up front, since you want to have higher impedance for 100V anyhow.)
Patrick
Can't you just include an additional, switchable, 10x attenuator in cascade for the few occasions one needs -40~-60dB ?
(Probably up front, since you want to have higher impedance for 100V anyhow.)
Patrick
The Zin is actually 100k. But if you add something in front of it, it may be OK with the -40dB setting but all others will be way off because there is a new Zin! So it would only work for one setting and I don't think that would be good.
Edit: Of course if you redesign all attrenuator steps it could work, but that makes it more complex. Currently I have a 40dB and a 20dB atten, in combination with 4dB steps. Your solution would probably double the number of relays and drivers and a lot more special value 0.1% resistors or combinations.
I don't really want to go into details of the design so you need to trust me on this ;-)
Jan
Edit: Of course if you redesign all attrenuator steps it could work, but that makes it more complex. Currently I have a 40dB and a 20dB atten, in combination with 4dB steps. Your solution would probably double the number of relays and drivers and a lot more special value 0.1% resistors or combinations.
I don't really want to go into details of the design so you need to trust me on this ;-)
Jan
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Jan,
Is this similar to what you have now ?
http://www.diyaudio.com/forums/pass...ce-relay-resistor-logarithmic-attenuator.html
(Scale up resistor values by 10x)
Patrick
Is this similar to what you have now ?
http://www.diyaudio.com/forums/pass...ce-relay-resistor-logarithmic-attenuator.html
(Scale up resistor values by 10x)
Patrick
Jan,
Thank you for clarifying that the AR does calculate and display input voltage.
The AR displays the level being sent to the soundcard, displays the attenuation / gain setting, and from that calculates and displays the input voltage to the AR.
The DUT output voltage is not measured.
Minus any inserted attenuators, amplifiers or filters the calculated input of the AR is the output of the DUT.
DT
I think I have converged to a solution to offer jumper-selected sweet spots of 1V and 0.316V. I need to book another half day with Guido Tent at the Tent Labs AP SYS2722 to verify performance.
If it pans out I can finalize the design and get the data package together for the Kickstarter project.
Thanks to the inspiring discussion here!
Ohh and by the way, if you know of a FET input opamp with the same or better distortion performance as the OPA2134 but able to drive lower load impedances, do let me know!
Jan
If it pans out I can finalize the design and get the data package together for the Kickstarter project.
Thanks to the inspiring discussion here!
Ohh and by the way, if you know of a FET input opamp with the same or better distortion performance as the OPA2134 but able to drive lower load impedances, do let me know!
Jan
OPA1642 is a bit better in terms of noise and THD+N into 600 Ohm load. OPA1688 has similar specs (at least in numbers) to OPA2134 but can drive loads down to 32 Ohm. It is also cheaper than OPA2134.
You, know, that is what I like about this forum. The aggregate knowledge and experience is enormous!
Thanks,
Jan
Yes the OPA2172 is a BJT but has very low input bias, and very low distortion.
