DIY turnable amplifier aka RIAA - newbie questions!

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Hi! I'm about to build a preamp for my brothers new LP player, since his amp doesn't have LP player input. I've never done this before, but I've built several Chipamps, so I know what this is all about. I'm planing to use the NE5532, since it's a dual opamp, but I also got access to a ton of other types of opamps (especially LM's an TL's) if there's better alternatives than the NE5532 out there.

Does anybody know how many times the signal from a LP-player is supposed to be amplified to match "ordinary" phono level?
and if someone have a good schematic or any advice, I'll be really happy! :)
 
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Hi! I'm about to build a preamp for my brothers new LP player, since his amp doesn't have LP player input. I've never done this before, but I've built several Chipamps, so I know what this is all about. I'm planing to use the NE5532, since it's a dual opamp, but I also got access to a ton of other types of opamps (especially LM's an TL's) if there's better alternatives than the NE5532 out there.

Does anybody know how many times the signal from a LP-player is supposed to be amplified to match "ordinary" phono level?
and if someone have a good schematic or any advice, I'll be really happy! :)

It not just a case of needing gain (which is around 40 to 60 db depending on cartridge and final output required), but the fact that the response has to conform to the RIAA curve.

RIAA equalization - Wikipedia, the free encyclopedia

The NE5532 is a good choice generally for low noise high gain work.

Hi-Fi RIAA Phono Preamp

Phono Preamplifier Scrapbook
 
ATTENTION

The RIAA designs on Phono Preamplifier Scrapbook are stated as passive, but they are NOT ! They are Active.

Also several of the circuits show either 1k or even worse 10k resistors in series with the power supply to the OpAmps :eek: I know it's for filtering noise etc from the supply, but the values are WAY too high !

The Grado design looks suspect to me as well ! I havn't checked the other designs on there in detail, but Rod Elliott's designs on the other link are known to be fine :)
 
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Thanks! The "RJM Audio - Very Simple Phono Stage" provided in the "Phono Preamp Scrapbook" looked great. Simple design, and with a great RIAA curve! :)

The RJM VSPS is very, very nice indeed. I ordered the kit from him and built it. It is so small I was able to integrate it into my pre-amp, converting one of the inputs to a permanent phono input. I just stole power from my preamp board.

The kit comes with a NE5532, but I find I like the AD8599 better. It is a good idea to install the "optional" bypass caps (C8, C9) if you plan to try different opamps than NE5532.

You could just buy the board from Richard for $15 and then source the components yourself. I decided to keep things simple and order the whole works for $40. Excellent value, IMO.

http://phonoclone.com/pcb.html
 
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Don't like the ESP one for several reasons.

1. 2K2 input resistor adds unnecessary noise making it's noise performance much worse than any other competently designed circuits.

2. Treble cut on the output overloads the opamp at high frequencies resulting in reduced high frequency headroom + high frequency distortion.

3. No need for more than one opamp per stage if it's done in an 'all in one' style like the Beavis circuit.

Go with the Beavis circuit, it looks very competently designed. Passive RIAA networks reduce headroom and are inherently noisier.
 
Alternative OP amp

Hi, I find the OPA2134 to be rather nice in phono preamps. Quiet and stable. I even used one as a reel to reel tape head preamp but altering the equalization to NAB. My biggest concern in any single op amp circuit like this is the gain bandwidth limitation. With a need for around 60 db of gain and a frequency response to 20KHZ or so it gets into to fuzzy territory with many OP amps.
 
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Hi, I find the OPA2134 to be rather nice in phono preamps. Quiet and stable. I even used one as a reel to reel tape head preamp but altering the equalization to NAB. My biggest concern in any single op amp circuit like this is the gain bandwidth limitation. With a need for around 60 db of gain and a frequency response to 20KHZ or so it gets into to fuzzy territory with many OP amps.

I find 40dB of gain just about perfect with MM carts, but the VSPS can easily do 50 with common opamps.
 
Yeah 40dB is just right IMO, for high output carts or 78s I find 37dB is good too.

I think over about 43dB or so is just a bit too much for solid state equipment, however if you're using high impedance tube stuff then it's probably perfect for that sort of application. ;)

I find the OPA2134 to be rather nice in phono preamps. Quiet and stable. I even used one as a reel to reel tape head preamp but altering the equalization to NAB. My biggest concern in any single op amp circuit like this is the gain bandwidth limitation. With a need for around 60 db of gain and a frequency response to 20KHZ or so it gets into to fuzzy territory with many OP amps.

A nice op-amp to be sure but generally suitable only for MM preamps. Would a BJT opamp be better for tape heads due to lower noise at low impedances?

Generally speaking you can probably get away with 60dB gain as the distortion on the tape will be several orders of magnitude either. Did you have to use a low pass filter to get rid of the AC bias?
 
I've built my RIAA preamp, and I chose the recommended beavishifi's design. I haven't tested it on a real LP-player yet, but it's easy to see the RIAA characteristics on the oscilloscope. Thanks so much for the help!

OROOduKl.jpg


An externally hosted image should be here but it was not working when we last tested it.
 
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Out of curiosity I simulated a few of the op amp designs from the beavishifi site in LTSpice (the PAiA, VSPS, and the Grado PH-1) to see how accurate the RIAA equalization was on each of them. The VSPS and Grado are pretty good, but the PAiA had about +/- 4dB deviation. The bass is rolled off and the treble is boosted referenced to 1kHz, so I would say the subjective impression would be "thin" or "bright" based on the frequency response.
 

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Out of curiosity I simulated a few of the op amp designs from the beavishifi site in LTSpice (the PAiA, VSPS, and the Grado PH-1) to see how accurate the RIAA equalization was on each of them. The VSPS and Grado are pretty good, but the PAiA had about +/- 4dB deviation. The bass is rolled off and the treble is boosted referenced to 1kHz, so I would say the subjective impression would be "thin" or "bright" based on the frequency response.

Thanks for posting! Very interesting, indeed. I'm a newbie to this stuff and have never used LTSpice, but I have installed it and opened your attached simulation. After selecting the appropriate visible traces and running the simulation, it is clear what each of these circuits is doing. Note: the default value of the gain resistor in the VSPS is actually 680R, for ~40dB of gain.
 
No, the RIAA equ is the same for mc and mm. Typically the mc input adds another gain stage in front of the mm which contains the equ. Input impedance is generally lower on the mc input also. Look at the specs for some mc carts vs mm and you'll see what I mean. Both desired impedance and capacitance loading will be different.
 
I also made this design in Eagle, and created a one layer PCB, if anyone is interested.
I've also replaced a few components so the preamp is more accurate according to the RIAA curve (thanks cogsncogs!). The PCB size is 72.06mm * 41.6mm and includes an AC rectifier circuit and two voltage regulators (+-12v).
 

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