That's a good start. I'm unfamiliar with the placement of the large e'lytic in the feedback loop. Usually see it in-series with the gain resistor. Where will you get a dual op amp if you don't want to or can't deal with Cimarron? For my proto I realized I didn't have any single DIP8 op amps except for the $39 each OPA627s from eBay. I ain't going to put those in for 1st power-up so I had to go to Digikey and sort through their remaining stock of DIP8 singles and buy a few as fodder. They also have these:
https://www.aliexpress.us/item/2255...=scene:pcDetailTopMoreOtherSeller|query_from:
Wow, their polystyrene caps are cheap and the ones I looked at were 2.5%. No dims are given but they will be big so be aware. That PCB was made for metallized polyester caps which of course are quite small.
For the record, the preamplifier depicted in post #513 does not contain any PCBs, perfboards or breadboards. It's a fully discrete, modular design where each circuit was built in dead-bug style on a cut-open and flattened steel drink can, which was then soldered to the inside of the big can.
I will buy a pair of those pcbs I showed so I can put values to the schematic they show, then we will know what does that electrolytic in the RIAA eq do.
For the precision passive parts, resistors and capacitors, I will try to pick polypropylenes when the polystyrenes are too large, and risk selecting for best precision with my DMM. It's the most I can do.
The single stage version I bought is slightly different in parts quantity.
OPA134 (2134) is good enough for MM phono preamp and capacitor types are unimportant, polyester MKT is enough. You guys are nit-picking for nothing. Rather make a PCB design and proper shielding and wiring. Vinyl replay does not ask for rocket science engineering.
I think the thing about capacitor dialectrics is that there is a little something there, and that little something is mysterious. Everybody knows that a commercial recording has passed through dozens? hundreds? of electrolytic capacitors, sometimes with little bias voltage, but somehow we diyAudio'ers still have a deep aversion to electrolytics, "lesser" films, micas, etc. and a possibly irrational fear of all ceramics.
The cults around coupling capacitors (meaning without signal voltage in band) could be more easily dismissed than filtering capacitors, with significant signal voltage and in the case of phono equalizers very small signal voltages. Are capacitors monotonic enough for us to ignore their tiny signal behavior? Don't know, but nothing is completely monotonic as everything approaches zero, so maybe, maybe not. Doubtlessly a matter of degree. The ambiguity is enough to keep interest alive.
But no one would (?) disagree that signal path wiring is at least as important and usually more. Not the obvious "schematic diagram" wiring, but the unmentioned signal common/return paths and the power supply return paths. The stuff that isn't in the usual LTspice model, but has to be considered in the real world.
All good fortune,
Chris
ps: This won't keep me from using the best capacitors on hand for a phono equalizer, the King of all electronic designs
The cults around coupling capacitors (meaning without signal voltage in band) could be more easily dismissed than filtering capacitors, with significant signal voltage and in the case of phono equalizers very small signal voltages. Are capacitors monotonic enough for us to ignore their tiny signal behavior? Don't know, but nothing is completely monotonic as everything approaches zero, so maybe, maybe not. Doubtlessly a matter of degree. The ambiguity is enough to keep interest alive.
But no one would (?) disagree that signal path wiring is at least as important and usually more. Not the obvious "schematic diagram" wiring, but the unmentioned signal common/return paths and the power supply return paths. The stuff that isn't in the usual LTspice model, but has to be considered in the real world.
All good fortune,
Chris
ps: This won't keep me from using the best capacitors on hand for a phono equalizer, the King of all electronic designs
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Frequency response inaccuracies of 0.2 dB at mid frequencies can be audible in double-blind tests, so it makes sense to try and make the RIAA zero and second pole accurate (even though the inaccuracy of the cartridge is probably worse). In that regard, an OPA134 or OPA2134 is a bit slow for a single-loop RIAA-corrected amplifier with a gain of 200 at 1 kHz. With its gain-bandwidth product of 8 MHz, the magnitude of the loop gain at 2122 Hz and higher would only be about 19, causing an inaccuracy of about -5 % of the second RIAA pole. For the capacitors that set the RIAA zero and second pole, you can best use polystyrene, polypropylene or NP0 a.k.a. C0G ceramic capacitors, as those are available with quite small tolerances. It's indeed not rocket science.
Should the 5% inaccuracy in GBW be weighted as heavily as a 5% tolerance of the capacitor value? If so, is the reciprocal also true, that the capacitor value could be massaged to accommodate the lower GBW product?
All good fortune,
Chris
All good fortune,
Chris
You can simulate the effect of opamp open loop gain transfer on EQ accuracy easily. And measure as well. We usually have loopgain reserve of about 40dB or more with the discussed opamps. This is enough to get appropriate EQ accuracy. Components tolerances count. And, circuit topology. BTW, I do not thing that ((R1//C1)+(R2//C2))/R3 is the optimum topology.
I was hoping to nudge MarcelvdG into doing the work, or even better, to offer a simple to overstand gedanken model for dummies like me. These very recent (to me) ideas, like frequency response sensitivity to servo time constants, amplifier stability sensitivity to source impedance, etc. both open new avenues for thought and leave me far behind the curve.
Much thanks, as always,
Chris
Much thanks, as always,
Chris
My suggestion is simple - always do the job! Debating and reading the debates does not help much, at least such is my experience. Might be good as a hint, but then do it yourself - DIY.
Bode asymptotes:
The attenuation of the feedback network of 200 times stays roughly constant up to 2122 Hz and then rolls off at a first-order rate, so the magnitude of the transfer of the feedback network is f/(200 • 2122 Hz) at audio frequencies above 2122 Hz.
The magnitude of the open-loop gain of an 8 MHz gain-bandwidth product op-amp is 8 MHz/f for frequencies in the region where the open-loop gain drops at a first-order rate, which usually includes all or almost all of the audio band.
Hence, when you use an OPA134 for a single-loop RIAA-corrected amplifier with a gain of 200 at 1 kHz, you have a loop gain of 8 MHz/(200 • 2122 Hz) ~= 19 at audio frequencies above 2122 Hz. Nowhere near 100 (40 dB). The calculation is so simple you don't even need the back of an envelope for it.
Both OP27 and OPA134 have 8 MHz gain-bandwidth product, so you can expect them to have very similar responses. OPA627 has 16 MHz, OPA1656 has 54 MHz. With 40 dB midband gain, you get only half the error you would get with 46 dB.
Many of your posts are indeed pointless nitpicking.
Many of your posts are indeed pointless nitpicking.
And in the other thread (the parallel thingy) I deliberately asked about the SCHEMATIC, the measuring circuit, because we ( EEs) now need this (with the component values) in order to be able to evaluate the result. After all, we want to know why something is the way it appears to be or really is. As long as I can't see the schematic (with component values), I'm not interested in the colorful little picture. You can't do anything with it as an EE.
It looks nice, but nothing more.
kindly,
HBt.
Relative differences between the noise with various opamps remain the same, regardless possible fr errors of 0.1 dB. I think you know. I have always said there was a 40dB 1k gain and 47k cartridge load. Cartridge impedance is 970R + 425m. You do not need to know more to explore input current noise contribution . 100 ohm is fb to gnd. Standard RIAA eq. You do not need to know more, in case you mentioned you are an engineer. We speak about huge differences in noise here. Take or leave, I do not care. I am not going into a nit picking debate on component values and 0.1 dB possible differences.
No problem, I don't want to argue with you. I take the sermon as it stands - and yet I am interested in the exact wiring of the stupid operational amplifier. Why you don't want to provide a sketch is beyond me. We want to know the complex impedances at both inputs. As I said, I'm not questioning the quantitative comparison, I'm just saying that something crucial is missing in the evaluation. Just for the sake of form, if you like.
What about the answer to the network question, the better topology?
I know, and you can rely on it 100%.
HBt.