Wayne
You may be surprised that the Opa1612 is producing a tad more noise, despite its lower Vnoise of 1.1nV/rtHz.
The reason however is of course the added current noise of 1,7 pA/rtHz injecting into the 1K collector resistor and also into the Vref divider.
Hans
Search found 73 matches
- Tue Sep 18, 2018 9:20 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
- Tue Sep 18, 2018 9:10 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Since this is a model and you have the luxury of perfect devices that we don't have in the real-world what happens if you model it with the ZTX851 base resistance of 0Ω? Remember my Sim right at the beginning of this thread? Your measured results were even better. My experience with this kind of ci...
- Tue Sep 18, 2018 6:32 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
With 0.47uF the bump is close to 0.2dB@50Hz and with 1uF below 0.1dB@50Hz, not really a problem, but less elegant. With Rg as well as Rsource being 1 Ohm, Noise from 20 Hz to 20 Khz is 49,3 nV, as opposed to 52.6 nV with Rsource = 1 Ohm / Rg = 2 Ohm A single 1 Ohm resistor produces 18.2 nV from 20 H...
- Tue Sep 18, 2018 5:06 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Here some additional info taken from the circuit.
The only deviation from Wayne's design is the 1uF cap before the servo, because a 0.47uF in combination with the 100nF in the voltage divider caused a bump in the FR between 10Hz and 200Hz.
Hans
The only deviation from Wayne's design is the 1uF cap before the servo, because a 0.47uF in combination with the 100nF in the voltage divider caused a bump in the FR between 10Hz and 200Hz.
Hans
- Mon Sep 17, 2018 3:18 pm
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
I posted the set of noise figures with a typo.
The first set was for Rsource 10 Ohm, but the second set was for Rsource 1 Ohm and not the 10 Ohm that I mentioned.
Hans
The first set was for Rsource 10 Ohm, but the second set was for Rsource 1 Ohm and not the 10 Ohm that I mentioned.
Hans
- Mon Sep 17, 2018 2:10 pm
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
For using the That1240, I made a subcircuit with four 9k resistors around a configurable OPA, the combination tuned to exactly the specified -104dBu noise. U1 to U4 are also making use of this configurable OPA, now set as an Opa1642. I also inserted a voltage source between one emitter to simulate a...
- Mon Sep 17, 2018 2:01 pm
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
- Mon Sep 17, 2018 1:59 pm
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Wayne, I finalized my Sims. A few remarks: 1) I mentioned the need to go with Vref from 7.5V to 5.5V. Initially I overlooked R17 R18 from the Servo being in par. to R15 R16 , so we landed at exactly the same point. 2) I was not sure what OPA you used for the input pair. Since I could only find a ref...
- Mon Sep 17, 2018 9:07 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
But the OPA1612 has a diff Rin of only 20K, creating trouble with the high ohmic voltage divider R13-R16.
So I switched to an OPA1642, seemingly a better alternative.
Hans
So I switched to an OPA1642, seemingly a better alternative.
Hans
- Mon Sep 17, 2018 8:12 am
- Forum: Pro Audio Design
- Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
- Replies: 499
- Views: 772545
Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
The problem with the OPA2277 is though that it can only supply 10mA, so at this position this amp does not seem the best choice, unless you decrease the current and take the 2dB noise penalty for granted.
The OPA1612 that you initially used, seems a better choice for that matter.
Hans
The OPA1612 that you initially used, seems a better choice for that matter.
Hans