Here is a SOIC 1656 mounted to a DIP8 carrier.
https://www.cimarrontechnology.com/product/soic-dip-adapter-8-pin
Cimarron Technology - home of Browndog adaptors.
https://www.cimarrontechnology.com/
When I buy single OPA627s I get two mounted belly-to-belly with a dual's pin out.
They ship worldwide.
As I said: Cimarron is very expensive.
I want a supplier that is lower in price that will export to Brazil.
The OPA627s I have are DIP8, some OPA637s too. But I wanted to listen to the OPA1656 and OPA1642. They only come in SMD.
I want a supplier that is lower in price that will export to Brazil.
The OPA627s I have are DIP8, some OPA637s too. But I wanted to listen to the OPA1656 and OPA1642. They only come in SMD.
I did not remember you commenting on Cimarron. Sorry, I'm old. Forget 627s. The point was for $13 you can get what you want re a DIP 1656 and same with the 1642 for $13. And as I wrote they ship worldwide. What's not to like..?
Proves that pA matter..? And now when I read that Marcel thinks one topology is inferior to another (a vs. b) b/c it's noisier I gotta wonder whether it's OCD or a real deal. I have never heard system hiss so loud that I could hear it except with my ear to the tweeter. Did you get the files to play? It was revealing. The LT1028 hiss was annoying if loud enough.
I don't know if this helps, but there is also the OPA1655, the single version of the OPA1656. When you use its SO8 version and put it on an adapter board, it will become pin compatible to the OPA627.
I think it was already mentioned here - OPA1655 has about 10x higher input offset voltage than OPA627 (check the datasheet). So, without the DC servo or a big capacitor in the FB to gnd node, there will be a big DC output voltage in case of the RIAA preamp. I use DC servo even for the simplest one-opamp phono pre.
OPA2156, basically an OPA1656 but with very low offset (25uV, four times better than untrimmed 627), R2R input, larger input series resistors (thus a tiny bit more noise), less aggressive loop gain. Noise-wise, like 1656 it is not ideal for MM pre because of high 1/f corner but often still better than a bipolar with high current noise.
If it is the total RIAA- and A-weighted noise you are interested in, there is a break-even point for white and 1/f voltage noise at about 1169 Hz. That is, when you know the density of the equivalent input voltage noise at 1169 Hz, it doesn't matter for the total RIAA- and A-weighted noise what part is white and what part 1/f. (It may sound different, though, due to the different spectral distribution.)
What about the OPA192 that was mentioned on the thread?
What to look on any opamp data specs that is important, besides noise, slew rate and gain bandwidth product?
What to look on any opamp data specs that is important, besides noise, slew rate and gain bandwidth product?
From #457:
These three schematics were meant to be 2nd order HP with direct drive from a MM cart. I don't think that schematic #3 got your full attention. It's a standard S-K but the other two have the +FB for R2 taken from R3 and that was bothersome for you b/c of yes, noise. If you have further thoughts or reminders I'm still interested in ditching a front-end S-K buffer.
From #463
This surprised me. A subsonic filter with 6dB gain before the 40dB RIAA section (a) is better than a flat pre-filter with the 6dB gain moved into the RIAA (b). I like the part about keeping the RIAA EQ from dealing with room-slosh but then you say you liked the post-filter with gain example the best noise-wise and that threw me. Boosting the level of unwanted room-slosh garbage by upwards of +20dB (or more) before inserting that into a -12dB HPF make no sense - to me. Just seems to invite bigger evils than noise I may or may not hear from the couch. I like the "idea" of a direct MM-driven flat front filter w/47K Zin and a 46dB RIAA. The above all has to do with original phono pre c. 2021. I thought you were on to something.
Nothing! I was just getting you to take notice of the $13 1656 and/or 1642 DIP8 shipped to your door ready to rock and roll in Brazil. You were going on about already having DIP8 627s and 637s and that wasn't the point. That's all.
Thanks, JRA!
I was already aware of what Cimarron was offering, and looking for more affordable pricing somewhere else, if available.
The DIP adapters they sell, which would be necessary to try and compare different dual SOIC types, but they do offer pre-assembled versions with different opamps.
The problem with all three circuits of post #457 is that both R1 and R2 contribute to the equivalent input noise current. The lower the parallel value of R1 and R2, the higher their contribution to the equivalent input noise current density √(4kT(1/R1 + 1/R2) becomes. I didn't bother calculating the value for the third circuit, as the parallel value of R1 and R2 is obviously much lower than for the first two.
In general, the more voltage gain up front, the less the effect of the voltage noise of the second stage. As the voltage noise of the second stage is not very large anyway, the difference is only small.
I still think my single-stage circuit is the most suitable, by the way.
👍
This is absolutely correct if you are referring exclusively to the topology - because other component dimensions also lead to the goal.
I don't see the choices as all that difficult. At the input have as little as possible between the source + its load and the dominant noise generating stage and have all large signal overhead issues resolved as soon as possible. Optimally this requires a single stage that does all of the joujou, including a good subsonic filter. Every other stage added diminishes either noise performance or signal overhead capacity. If the subsonic HPF is too early, noise increases. If too late, overhead decreases.
All good fortune,
Chris
All good fortune,
Chris