the "JB" 3-stage Phono Preamp - diyAudio
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Old 5th February 2015, 05:08 PM   #1
JoeB83 is offline JoeB83  United States
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Default the "JB" 3-stage Phono Preamp

Pretty much as the title states, this is my design for a phono preamp, and while not actually being RIAA standardized, it has a substantial treble cut and bass boost, as well as overall voltage gain of 295x. I originally started this project because I finally got some LPs worth listening to, had a record player, but no preamp to bring it up to line level for either headphones or my power amp. I built the prototype on perfboard, and even with a much-less-than-perfect layout, it sounds great. I decided to go with three separate stages to make the equalization easier and to not place too much strain on one opamp. The prototype originally used LM4562NA x 3, but I've tried out and had success with OPA1612, LME49990, and OPA827. Any suggestions are welcome, I only just finished my first design (a buffered headphone amp) so please feel free to fire away.
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File Type: pdf Three-stage nearly RIAA preamp.pdf (28.1 KB, 137 views)
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Old 5th February 2015, 07:22 PM   #2
mlloyd1 is offline mlloyd1  United States
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search for discussion, schematics, etc. for the hagerman bugle phono preamp.
might be of interest to you.

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Old 5th February 2015, 07:29 PM   #3
JoeB83 is offline JoeB83  United States
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I'll check it out, thanks for the tip!
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Old 5th February 2015, 07:38 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by JoeB83 View Post
Pretty much as the title states, this is my design for a phono preamp, and while not actually being RIAA standardized,
it has a substantial treble cut and bass boost, as well as overall voltage gain of 295x.
This has two poles but no zero, so it's way off the RIAA curve.
If you have to use the two 3.3nF caps, here are the values to get closer to the RIAA curve.

The first RC should be the 75uS for the best overload margin, so with the 3.3nF cap as given, you should have a 22.7k resistor before it.

The second RC should have an R added in series with the C to provide a zero.
With the 3.3nF cap given, the R before the cap should be 867k, and the R in series with the cap should be 96.4k.

Last edited by rayma; 5th February 2015 at 08:00 PM.
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Old 6th February 2015, 10:40 AM   #5
DF96 is offline DF96  England
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Quote:
and while not actually being RIAA standardized,
Nowhere near RIAA. It will probably sound quite muffled, as you are cutting treble in a region where RIAA boosts it! It can't possibly "sound great", unless there is something seriously wrong with your speakers/headphones.

I'm please you are an EE student and still learning. Learn about RIAA networks, then rebuild it.
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Old 8th February 2015, 03:43 PM   #6
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This is the projected response of your makeshift 3 stage RIAA (picture on left) vs. the passive RIAA schematic in the beginning of the LM4562 datasheet. Both circuits have the same input voltage.

I think DF96 has a point. If you think your design sounds great now, when you get it closer to accurate it will sound a lot better. At least as good as your player will allow.

I just finished up a thread about the passive recommendation from the LM4562's datasheet. I learned some things with that project. I ended up doing an A/B test with that circuit and the onboard one that the player had and describing the difference in sound between the 2.

Here is a link to the thread. The summary is at the bottom of the page.
Phono Preamp Question...
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File Type: png 2 Pole RIAA attempt.png (37.3 KB, 97 views)
File Type: png Passive RIAA.png (37.6 KB, 95 views)

Last edited by shredhead; 8th February 2015 at 03:46 PM.
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