Thanks AndrewT. I am just playing with this circuit so it will give me something to do changing values. It just seemed going from 100K to 2K on the top resistor is an extreme difference.
I wonder if the dual gain set up of post4 indicates that the gain bandwidth product of the 2134 ran out of gain with just the first stage and that for adequate output they added in the +20.8dB of gain to get sufficient volume from the RIAA stage?
And to save money they put the line level switching in front of the flat gain stage rather than after to be followed by a line driving Buffer.
And to save money they put the line level switching in front of the flat gain stage rather than after to be followed by a line driving Buffer.
Yes, an extreme change. It shows how wrong I consider that value.
The high value of 100k gives your stage no advantages and has many demerits.
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I'm with Andrew! May be it is time to have a look at the datasheet of the OPA2134, especially Figs. 6 and 7. There you'll see how much noise increases with the source resistance increase. You may also consider reading section 7.4.1 "Noise Performance" in the same datasheet for a detailed explanation. The datasheet also indicates that the OPA2134 can drive 2kOhm loads with no increase in distortion. This includes the following stage input impedance as well as its own feedback network which are electrically parallel to each other. Thus you can easily scale down all your original resistor values aound OPA2134 by at least factor 10 or 20 which will dramatically reduce the noise level.
I made the changes. I had some nice 2.2K 1% resistors and I changed out both the feedback resistors, the 100K and 10K. Much better now. I tried it first on my V-fet and then on the D board that it was unacceptable on to begin with. Works nice and quiet now with it.
To be fair to the designer of the original diagram the values might be best with the phono stage in front of it. As a stand alone preamp I think the changes in the feedback are needed.
Thanks Andrew.
To be fair to the designer of the original diagram the values might be best with the phono stage in front of it. As a stand alone preamp I think the changes in the feedback are needed.
Thanks Andrew.
1) The Meanwell dual output converter needs a small choke on its INPUT.
2) As 00940 suggests, the outputs of the dual converter should have a CLC choke -- try 100uF-300uH-47uF.
Too bad Jan's low noise dual converters aren't yet in production.
2) As 00940 suggests, the outputs of the dual converter should have a CLC choke -- try 100uF-300uH-47uF.
Too bad Jan's low noise dual converters aren't yet in production.
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