All, as this was originally PMA’s thread, I’ve taken the liberty of creating a new thread to discuss Bonsai’s preamp.
https://www.diyaudio.com/forums/ana...sai-altra-mc-mm-phono-preamp.html#post6313472
May I suggest we move discussion of Bonsai’s preamp to its own thread?
Bonsai, I hope that is OK with you?
https://www.diyaudio.com/forums/ana...sai-altra-mc-mm-phono-preamp.html#post6313472
May I suggest we move discussion of Bonsai’s preamp to its own thread?
Bonsai, I hope that is OK with you?
That's not a good idea because there there are less than 10 people that will invade any phono topic in order to fill it with their precious advice...They will turn it into rocket science discussions as soon as possible so that people think they are the best people we should listen in the universe...while its just about another pphono preamp. Even if they have nothing to say, they will make sure they have an intervention on each topic's page so that everybody on Earth should know that they exist...This topic by itself came to live in a very fashionista manner too...It's all about fashion here...
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@dreamth I suggest you stop reading these topics then. And I beg you to stop posting in these threads, because your posts do not add anything useful anyway. We now know you are a frustrated, offended by some, and bored person, no reason to repeat that.
Go search something you can contribute in a constructive manner, if you really feel the need to express yourself.
Go search something you can contribute in a constructive manner, if you really feel the need to express yourself.
Picking up on the noise measurements we discussed the other day, I've had an exchange with Matt.
The noise floor measurements on the QA401 trace are indeed very accurate. We've checked that using resistors and I've reconfirmed that by looking at the 1kHz spot noise with a 10k resistor placed on the input of the phono amp - it calculated out to 1.7uV
The Vrms reading is designed to look at output signal when measuring tones - so I was not using the instrument correctly. I checked the Vrms reading again against the Tek MDO3024 and get the same readings to within a % or two - not bad as I mentioned previously since we are using two totally different measurement systems.
Anyway, the measured specs have been tweaked to reflect reality (some have actually improved) and I remain v. pleased with the result.
I'll sign off on this specific project (X-Altra) - I'll let everyone know when the article is published.
The noise floor measurements on the QA401 trace are indeed very accurate. We've checked that using resistors and I've reconfirmed that by looking at the 1kHz spot noise with a 10k resistor placed on the input of the phono amp - it calculated out to 1.7uV
The Vrms reading is designed to look at output signal when measuring tones - so I was not using the instrument correctly. I checked the Vrms reading again against the Tek MDO3024 and get the same readings to within a % or two - not bad as I mentioned previously since we are using two totally different measurement systems.
Anyway, the measured specs have been tweaked to reflect reality (some have actually improved) and I remain v. pleased with the result.
I'll sign off on this specific project (X-Altra) - I'll let everyone know when the article is published.
Hello Hans,
No worries. Never thought this was anything but an excellent design. Just speculating that it might be possible to squeeze out an extra dB or three of S/N by omitting the MM option.
Best Regards.
No worries. Never thought this was anything but an excellent design. Just speculating that it might be possible to squeeze out an extra dB or three of S/N by omitting the MM option.
Best Regards.
Hi PMA,
Going back to near the beginning of this thread my understanding of noise is limited, however to gain some incite into your graphs how does this relate in comparison to a more modern opamp like the OPA1641? On page 27 Figure 42 it shows noise relative to an output of 1V rms from 10 mVrms at 1KHz (40 dB). The noise level is at -120dB.
In a real world case using an Ortophon 2M blue the output is stated as 5.5mV. For a gain of 34dB (x50) the output would be 275 mV rms or -11dB less than 1 V rms in the graph of the OPA1641. This suggests that the noise level using an OPA would rise to -109dB.
Notwithstanding the incredible "EMIRR vs Frequency" (figure 30) and lack of harmonic distortion suggested by the graph of the OPA, how does noise compare to yours under these circumstances? It seems that yours would be a 20dB improvement.
Just read input voltage noise and current noise from the datasheet and you have the answer. Current noise times 47k gives additional noise to be added to input voltage noise. It si all simple as ABC. In case od JFET devices, no worries about the current noise.