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Rod Eliot project 88 question
Rod Eliot project 88 question
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Old 18th September 2018, 12:10 PM   #151
Mixi is offline Mixi  Europe
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ok, so i guess both options are equally fine. that's good to hear. and i can save 40 cents on buying fewer caps :-)
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Old 18th September 2018, 04:27 PM   #152
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thread has been moved. finally
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Old 18th September 2018, 08:08 PM   #153
Hicoco is online now Hicoco  France
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Originally Posted by prasi View Post
Hello Mixi,
I always use 0.1uF cap from each supply pin to ground and datasheet recommends it too and generally X7R ceramic are used.

clause 10.2 on page 19 http://www.ti.com/lit/ds/symlink/opa2134.pdf
Hi Prasi,
Do you have any X7R ceramic cap preference?
Thank
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Old 19th September 2018, 02:39 AM   #154
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Rod Eliot project 88 question
Quote:
Originally Posted by Hicoco View Post
Hi Prasi,
Do you have any X7R ceramic cap preference?
Thank
Hello Hicoco,
Generally I use whatever available in parts bin, some times I even use film caps in that position.

here is a mouser results, any of these would be ok .

Radial 0.1 uF 100 VDC X7R Multilayer Ceramic Capacitors MLCC - Leaded | Mouser India

regards
Prasi
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Old 19th September 2018, 07:54 AM   #155
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Originally Posted by ivanlukic View Post
Mixi,

You did it right. Bypass using single 100nF between supply rails is as good as bypass from supply pins to ground. And is much simpler for DIY-ers, and for PCB design. Doug Self recommends it in his Small Signal Audio book.
Do you know which chapter mentions this? I tried to read up on it but couldn‘t find it.
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Old 19th September 2018, 10:29 AM   #156
Hicoco is online now Hicoco  France
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Originally Posted by Mixi View Post
Do you know which chapter mentions this? I tried to read up on it but couldn‘t find it.
Look at the example Figure 2 - Bypassing The Op Amp Supplies and explanation below it
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Old 26th September 2018, 12:17 PM   #157
Hicoco is online now Hicoco  France
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Originally Posted by skrodahl View Post
The schematic above was updated about four years ago, here's the new one:

Click the image to open in full size.
skrodah, look like the gain on the first stage is 30.6db, i try to figure the second stage... is it between 27,5 and 35db ? if yes how could you have 40db total?
As you know this is the input preamp average or may be that i use the wrong formula.
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Old 28th September 2018, 01:32 AM   #158
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Originally Posted by Hicoco View Post
...look like the gain ... is....
Thinking quickly: each gain-stage is gain about 30dB, yes.

The in-between R-C network has loss. How much?

It varies with frequency. According to the RIAA curve.

We usually quote phono preamp gain at 1KHz. This type RIAA R-C network has gain of 0 dB at super low frequency, -3dB at 50Hz, -20dB at 1KHz, and -40dB around 20KHz.

So at 1KHz we have gain of (30dB)+(-20dB)+(30dB), which is 40dB, which is very typical.

Switches in the 2nd stage allow you to trim this up or down as needed to suit your system.
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Old 29th September 2018, 07:13 AM   #159
Hicoco is online now Hicoco  France
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Originally Posted by PRR View Post
Thinking quickly: each gain-stage is gain about 30dB, yes.

The in-between R-C network has loss. How much?

It varies with frequency. According to the RIAA curve.

We usually quote phono preamp gain at 1KHz. This type RIAA R-C network has gain of 0 dB at super low frequency, -3dB at 50Hz, -20dB at 1KHz, and -40dB around 20KHz.

So at 1KHz we have gain of (30dB)+(-20dB)+(30dB), which is 40dB, which is very typical.

Switches in the 2nd stage allow you to trim this up or down as needed to suit your system.
That is not -20dB at 50Hz (Pole#1), 0dB at 1KHz (zero#1), and -20dB around 20KHz (zero #2) ?
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Old 29th September 2018, 10:11 AM   #160
Mixi is offline Mixi  Europe
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hicoco, i believe the poles/zeros are the same relative to each other. bear in mind that pole #1 is usually +20db (you wrote minus). this rc network only attenuates so it can't provide +db. there's +/- 0db at very low frequency and from that point on attenuation increases with frequency.

i guess that's why this kind of network is regarded as not being the best when it comes to noise / headroom. first the signal is amplified, then attenuated, then amplified again.

that being said i use this phono stage quite often and to me it sounds great.
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