Search found 72 matches

by Hans
Thu Sep 20, 2018 3:26 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

I would strongly advise against making Rg 20 Ohm. It will partly ruin your careful design. With Rg 20 Ohm, Flat noise will be 173.3 nV and after Riaa+A-weight 69.9nV with Rs 40 Ohm and Rload 100 Ohm. Circuit with the DL103 will than have 72.6 dB S/N ref 0.3mV@5mV/sec Keeping the original Rg 2 Ohm, b...
by Hans
Thu Sep 20, 2018 9:23 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Wayne, How do you want to achieve a lower gain from 56 dB to 36 dB, by increasing Rg or by decreasing the 316 Ohm resistors ? When increasing Rg to 20.8 Ohm, there is no difference in noise RTI between a Opa1612 and a noiseless amp. Going to 30.5 Ohm for the current 316 Ohm, gives the same absolutel...
by Hans
Thu Sep 20, 2018 6:06 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Wayne, The amp's noise in the first socket plays hardly a role because of the large feedback. The Opa1612 is giving some 0.1dB less noise contribution than the Opa1642. Replacing the Opa1612 by a completely noiseless amp shows even less than 0.05dB improvement. And with also less than 0.05dB profit,...
by Hans
Wed Sep 19, 2018 10:12 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

What op amp is in the first "socket?" When comparing, only change one component at the time, so for both ZTX851 and ZTX951 an Opa1642 was used. Somewhere I have the idea that you don't like this amp, am I correct ? However, after having corrected the Spice related bug for the Opa1612, I have made t...
by Hans
Wed Sep 19, 2018 7:35 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Just out of curiosity, I changed the ZTX851 for the ZTX951, and turned 11V into -11V.
The result was in all situations, including the quietest version with 500 / 1 / 1 Ohm, less than a percent or > 0.01dB

Hans
by Hans
Wed Sep 19, 2018 7:14 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

I added in the previous posting als the outcome for both Rs and Rg 3.3 Ohm to keeps things together.
And you are still below Doug's 6.4 dB.

Hans

P.S. Rowing was great with 4-6 Bft.
by Hans
Wed Sep 19, 2018 3:57 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Also what does the simulator tell us for 3.3Ω? Self gets a 6.4 dB NF at 3.3Ω with his 3X 2N4401 MC preamp. A 3.3 Ohm Resistor produces 33.1 nV from 20 Hz to 20 Khz With R collector 1K, noise is: Rs 3.3 / Rg 3.3 : 63.1 nV NF=5.6 dB Rs 3.3 / Rg 2 : 59.4 nV NF=5.1 dB Rs 3.3 / Rg 1 : 52.6 nV NF=4.0 dB ...
by Hans
Wed Sep 19, 2018 3:21 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Here is the answer to your first question concerning the ZTX851, noise specified from 20Hz to 20 Khz:

Rsource 1 Ohm/Rg 1 Ohm:
Noise Free Transistor: 48.9 nV
2 ZTX851 : 49.1 nV
1 ZTX851 : 49.3 nV

Rsource 1 Ohm/Rg 2 Ohm:
Noise Free Transistor: 52.3 nV
2 ZTX851 : 52.5 nV
1 ZTX851 : 52.6 nV

Hans
by Hans
Tue Sep 18, 2018 11:08 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

I will comeback to your questions tomorrow.
By now I will have to join my rowing team.

Hans
by Hans
Tue Sep 18, 2018 9:20 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 176137

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

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