After checking consumer market of phono preamps, and seeing lots of questionable devices, with a single 9V power supply, or with RIAA tolerance of +/- 0.5 dB. I've decided to design precise and low noise preamp and build a small batch for myself, family and friends. After doing some research, I've found an excellent "Electronics for Vynil" book, written by Douglas Self. Mr. Self made lots of design and research work and published great schematic solutions for RIAA equalisation and subsonic filtration which are precise and low cost.
Here are my design decisions:
* MM-only version,
* Input capacitance to be adjusted by soldering in proper THT capacitor by the owner or me (not ideal, but definitely the best from noise prospective)
* Linear double +/-15V power supply
* Gain +30 dB at 1kHz. To achieve the best headroom
* IEC amendment removed: this is opinionated, but my neighborhood doesn't care
* 3-rd order Butterworth subsonic filter using a single opamp
* NE5532 as first stage
* ADA4075-2 as a subsonic filter buffer and output stage
* Power supply in a separate enclosure, which is meant to be placed at least 1m from preamp
* Anti-interference HF filter in power supply
* 2 x aluminium enclosures of approx. 20x20x4cm
* SMD components
In RIAA EQ network at least 3 x 1% capacitors are used in order to compensate capacity tolerance. Also I'm using multiple 1% resistors in filters. In subsonic filtering I'm using a polypropylene THT caps, they are compact and proven to have no distortion (see the book for a reference on research articles). Aluminium electrolytic caps are used to decouple DC on input and output. Their capacitance is relatively high, so they don't cause audible distortion.
Sonically it is perfect. Dynamics is as great as it can be, drums and classic music when large volume changes are encountered are reproduced perfectly. Bass, thanks to subsonic filter is great too. Drivers are free from 5 and 25 Hz disturbance, and that makes them to operate freely when reproducing program.
I also wanted to build it to last for years. Therefore I'm using components from known manufacturers and wrote a user and service manual, allowing any repair shop to service a device without a problem.
Here are the specs which I managed to measure on a real device:
* RIAA tolerance is 0.2 between 125-12000 Hz
* Gain +32 dB, at 1 kHz,
* Input voltage - 5 mV RMS
* Input resistance - 47 kOhm
* Input capacitance - 100-470 pF, adjusted by (de)soldering,
* Preamp supply voltage - +15V, -15V
* Power supply input voltage - 220-230V, 50Hz,
* Current consumption - 0.9 A
* Maximum output voltage, Headroom 13 VRMS (+25 dBu)
* THD at 1 kHz - 0.003 %
* Noise is -120 dBu at 1 kHz, and -100 dBu at 50 Hz
* Crosstalk at 1 kHz (0 dBu) -66 dBu
Also see pictures attached. THD/Noise/Crosstalk was measured using RME Fireface 400 and DSSF3 Real time analyser software.
Regarding RIAA tolerance. Deviations on low frequencies are caused by subsonic filter, and on high frequencies there is likely a error due to a measurement method. I plan to re-measure and update the post.
Overall my goal was precision, low noise and low cost, and I think these goals were met.
BTW, I'm building these preamps on order. If you're interested see "Ordering" at Phono preamp <<Maria>>: Precise reproduction at affordable price to place the order.
Here are my design decisions:
* MM-only version,
* Input capacitance to be adjusted by soldering in proper THT capacitor by the owner or me (not ideal, but definitely the best from noise prospective)
* Linear double +/-15V power supply
* Gain +30 dB at 1kHz. To achieve the best headroom
* IEC amendment removed: this is opinionated, but my neighborhood doesn't care
* 3-rd order Butterworth subsonic filter using a single opamp
* NE5532 as first stage
* ADA4075-2 as a subsonic filter buffer and output stage
* Power supply in a separate enclosure, which is meant to be placed at least 1m from preamp
* Anti-interference HF filter in power supply
* 2 x aluminium enclosures of approx. 20x20x4cm
* SMD components
In RIAA EQ network at least 3 x 1% capacitors are used in order to compensate capacity tolerance. Also I'm using multiple 1% resistors in filters. In subsonic filtering I'm using a polypropylene THT caps, they are compact and proven to have no distortion (see the book for a reference on research articles). Aluminium electrolytic caps are used to decouple DC on input and output. Their capacitance is relatively high, so they don't cause audible distortion.
Sonically it is perfect. Dynamics is as great as it can be, drums and classic music when large volume changes are encountered are reproduced perfectly. Bass, thanks to subsonic filter is great too. Drivers are free from 5 and 25 Hz disturbance, and that makes them to operate freely when reproducing program.
I also wanted to build it to last for years. Therefore I'm using components from known manufacturers and wrote a user and service manual, allowing any repair shop to service a device without a problem.
Here are the specs which I managed to measure on a real device:
* RIAA tolerance is 0.2 between 125-12000 Hz
* Gain +32 dB, at 1 kHz,
* Input voltage - 5 mV RMS
* Input resistance - 47 kOhm
* Input capacitance - 100-470 pF, adjusted by (de)soldering,
* Preamp supply voltage - +15V, -15V
* Power supply input voltage - 220-230V, 50Hz,
* Current consumption - 0.9 A
* Maximum output voltage, Headroom 13 VRMS (+25 dBu)
* THD at 1 kHz - 0.003 %
* Noise is -120 dBu at 1 kHz, and -100 dBu at 50 Hz
* Crosstalk at 1 kHz (0 dBu) -66 dBu
Also see pictures attached. THD/Noise/Crosstalk was measured using RME Fireface 400 and DSSF3 Real time analyser software.
Regarding RIAA tolerance. Deviations on low frequencies are caused by subsonic filter, and on high frequencies there is likely a error due to a measurement method. I plan to re-measure and update the post.
Overall my goal was precision, low noise and low cost, and I think these goals were met.
BTW, I'm building these preamps on order. If you're interested see "Ordering" at Phono preamp <<Maria>>: Precise reproduction at affordable price to place the order.
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sibiryakov,
You need to post more, so we know more about you. Do you belong to any other audio forums?
You need to post more, so we know more about you. Do you belong to any other audio forums?
audiostar,
Sure, I'm a newcomer here. Unfortunately, no, this is my first DIY forum where I decided to register an account and be proactive.
Just started instagram Login • Instagram, and going to introduce myself in separate area.
Sure, I'm a newcomer here. Unfortunately, no, this is my first DIY forum where I decided to register an account and be proactive.
Just started instagram Login • Instagram, and going to introduce myself in separate area.