High Performance Phono PreAmps




Do you still have a turntable and a lot of old vinyl laying around that you would like to listen to and your stereo does not have a phono input or a good built-in phono pre-amp? Or you don't have a stereo at all and your computer is your stereo? Would you like to hear the best from your vinyl? Most audiophiles believe that vinyl sounds better than digital audio at 16 Bit  44.1 KHz, that is if you have a high quality stylus & cartridge, turntable and a good phono preamp that accurately tracks the RIAA equalization curve with an Op-Amp that has a high enough slew rate that it does not muddy up the high frequencies. Vinyl has the capability to produce frequencies approaching 60 KHz. This extra bandwidth was used to make the CD4 Quadraphonic records where the additional channel information was modulated on a 38 KHz subcarrier with +/-19 KHz sidebands, so it is no wonder that vinyl has a more polished sound for the top end than CD's. Many people notice a harsh, rough, brittle, or crisp, almost too crisp sound that digital audio produces as a result of the quantatizing error. As you approach the highest reproduceable frequency, 22.05 KHz, you have sampling inter-modulation distortion. The modulating frequency is the difference between the signal being sampled and 22.05 KHz and the percent of modulation increases as the sampled signal approaches 22.05 KHz. To alieveate this problem for digital audio you would need to use a 24 Bit  96 KHz sampling. This would make the digital audio files 3¼ times larger than what is used for todays digital audio. This is the next step in digital audio and the Super CD refered to 2496 or 9624 format and would take up over 2 gigs uncompressed for 74 min. Until the recording industry decides on a standard format we are not likely to see this anytime soon. Right now Sony and others are battling it out to have their format adopted. So enjoy your vinyl!

Without having to drag out a receiver with a phono amp you can use this pre-amp to run the signal into the back of your soundcard to play your records. You could also apply digital noise reduction to remove surface noise like pops and clicks caused by scratches or dirt. Given that many titles on vinyl are out of print some would like to be able convert their vinyl to digital to play on their PC or burn the WAV files to a CD or make MP3's out of them.


The schematic below shows the pre-amp circuit. A Signetics NE/SE5532AN op-amp is used for the preamp circuit while the high pass rumble filter uses a Texas Instruments TLO72. You could also use the Signetics amp for the rumble filter but it is the more expensive of the two. You will want to get the 5532AN version as the one with the "A" suffix has guaranteed low noise performance. The low noise version may be hard to find so use tne 5532N if it is the only one available. It still offers good noise performance along with high end clarity, much better than what is used in the todays receivers. In one brand of receiver the 4558DX is used and does not have a high enough slew rate for the use as a phono pre-amp. If your receiver uses a dual op-amp 8 pin DIP package you could just replace it with the 5532 and improve the performance that way although you will not get as low of noise as the feedback components are of a higher resistance and reactance.

A rumble filter is included to help reduce the large signal swings of inaudible noise caused by mechanical vibration or acoustical feedback from high volume levels. This is important because it robs available headroom causing clipping during A to D conversion. Reducing signal input to compensate will reduce the signal to noise ratio of the digital signal. The pre-amp has a maximum gain of 60db at 50 Hz or lower and rolls off @ 6db/octave with a gain of 22db @ 20 KHz. With a gain of a 1000:1 @ 50 HZ or lower you can see why you need to attenuate these unwanted signals.

You can raise the low end roll off frequency by changing the .27µƒ capacitor to a lower value. The chart below lists the approximate roll off frequency for each capacitance value.

  Frequency @ -3db   Capacitance
         ~20 Hz       .27µƒ
         ~24 Hz       .22µƒ
         ~27 Hz       .18µƒ
         ~32 Hz       .15µƒ
         ~38 Hz       .12µƒ

The .01µƒ, .0033µƒ, 24KΩ, and the 300KΩ form the feedback network that preforms the RIAA equalization. It is recomended that you definitely use polystyrene capacitors and if possible match them between the channels. Some digital voltmeters have capacitance testing so if you have one use it to select capacitors. It is also recomended that you use 1% resistors or match them also. Matching of the 300Ω resistors or using 1%ers will guarantee a good match in gain between the channels. Matching the 33µƒ capacitors will guarantee that the low end roll off frequency are close to equal although this is less critical.

Matching the 47KΩ resistors and the 150pƒ capacitors will ensure that cartridge loading between the channels will be balanced.

The .27µƒ capacitors in the rumble filter should be polystyrene also but if you can't find them you can use any High-Q low ESR capacitors like mylars although mylars have poor temperature coeffeceints (tending to drift in value depending on temperature). If you want you can match them also along with the 11KΩ & 62KΩ resistors.

For perfect match in signal response between left & right channels you can match all components between the both channels. The only non-critical compoments are the 100KΩ, 100Ω resistors & 100µƒ capacitor as these are for all pass DC isolation. The only reason to do this is if the program material you want to listen to has any spatial processing so exact phase and amplitude response will equal between the left & right channels. This will help preserve acoustical image of the signal.

If you can't find the larger 33µƒ & 100µƒ tantalum capacitors then use electrolytics although try to get a tantalum for the 33µƒ as they have good temperature coeffeceints and good high frequency shunting.

In the schematic "FB" designates Ferrite Beads. They are used to filter out any radio frequency interference picked up by the wiring from the cartridge to the pre-amp.

The power supply provides a regulated ±15V to the op-amps using half-wave rectification for each regulator. Using a single winding with a 18VRMS output instead of a 36VRMS center-tapped one for full-wave rectification allows easier transformer selection. Each regulator probably draws no more than 25mA of current with circuit load so a 75mA transformer is more than adequate, and you could probably get by with a 50mA one. Finding a 120VAC to 18VAC adapter that plugs into the wall would be ideal as it puts the transformer far enough away from the pre-amp and cartridge so as to not cause 60 Hz interference. If you do put the transformer into the same box as the pre-amp you need to wrap a layer of heavy copper foil around it and solder it as to create a short circuit to dampen the magnetic field that the transformer eminates.

You need to put the pre-amp in a metal box or line the inside of the box with heavy copper foil. The box also needs a ground screw for the turntable ground.

For complete isolation place the power supply in one box and the pre-amp in another box but place the 1µƒ capacitors in the preamp box and not the power supply box. Connect the two boxes with 3 wires +15V,Ground,-15V.

If you do use the 5532 op-amp for the rumble filter you can allow for greater signal voltage swing by increasing the supply voltage supply to ±18V by replacing the voltage regulators with 18 volt versions 78L18 & 79L18. You will also need to increase the transformer voltage to 22VRMS but DO NOT go above 25.2VRMS as the rectified and filtered voltage will be greater than 35V and will damage the voltage regulators.

Phono Preanp Schematic


Here is a versiom with greater eRIAA accuracy (<±.05dB).
OPA2134xA based Phono Preamp
Circuit Board for Simple eRIAA Pre-Amp


If you wish to add a headphone amp for walkman style headphones with a 16Ω impeacance the following circuit should do it. You will need to use a 100mA Transformer and replace the 220µƒ capacitors with 470µƒ ones in the power supply. The output will also drive an 8Ω load @ 70-100mW for small speakers depending on what power supply voltage is used. If you use the ±18V supply for more output power you will want to replace the regulators with 78M18 & 79M18 "M" series for added power handling capability. the "L" series is fine for the ±15V supply as long as you mount them on a heat sink. It wouldn't hurt to put a heatsink on the 5532 headphone amp also.

Headphone Amp
Here is a basic phono preamp using discrete components.
The 2N2222A type transistors used for the differential input pair are suprisingly low noise for being a general purpose device. Sure there are lower noise devices and they would work well here if you can find them but the 2N2222A in the form of the MPQ2222A quad package offers matched pairs and matched between channels also. The 2N2222A has a max noise of 4dB and 0.8nV/√Hz. The output is a class A push-pull current mirror and uses the quad complimentary array MMPQ6842 which are basically 2 pairs of 2N3904 & 2N3906 transistors. Here is a PDF with detailed information.
Here is a through the hole circuit board with the PDF for those who are not into SMD.

The input network and the eRIAA equalization network could also be used with a low noise high performance op-amp.
Discrete Phono Amp
TAPR Open Hardware License

Moving Coil eRIAA Phono Pre-Amp
Version 1


Version 2



In the 2 previous circuits the power supplies for the head amps could be replaced with a 9V battery for each channel for extra low noise operation. The battery supply should be switched or relay controlled when power is delivered to the rest of the circuit. Standard carbon 9V batteries are probably the most economical since current draw is <½mA per channel. The benefit of alkaline or lithium units is for medium to high current uses respectively where the power:cost ratio is well matched but here it would be a waste. The 100K bias resistors can be reduced to as low as 68K to allow for lower voltage operation while maintaining a minimum Vce of 1V on the 2N3904 current regulating transistors. The purpose of the current controlled supply is to regulate r'e of the input transistors which in turn affects gain and input impedance regardless of supply voltage. The input transistors are the readily available classic 2N4401 & 2N4403 general purpose units which have a max. 4dB and 0.8nV/√Hz noise figure. There are quieter units that may be lower noise that could work also.






Here is a more advanced preamp with rumble filter.

The 75µs (2.122KHz) de-emphasis is formed by the .033µƒ, 100Ω, 2.4KΩ, 47KΩ, and the MPSA18's output admittance
(collector resistnace) which is asumed to be ~50KΩ. Small signal transistors can range from 25KΩ to 1MΩ so fine tuning can
be done by adjusting the value of the 47KΩ basing the op-amp. You May want to change the 150pƒ input capacitance
that loads the cartridge to the recomended value. This also applies for the 47.5KΩ load resistance also.



Cartridge Alignment Tools

DUAL 604 Alignment Protractor

Ortofon OM Alignment Tool


Technics SL-1200 Alignment Protractor

Ortofon 2M Alignment Tool


Both Protractors & Cartridge Templates


ALIGNMENT NOTES

These protractors can be used on any deck that has
the same pivot to spindle distance as specified. These
two here will work on various DUALs, Technics, and other
brands/models with equivalent pivot to spindle distance.
Check the documentation of your particular deck.

Placing a coin on the protractor will help prevent it from moving.
Wedging the platter to prevent rotation will also help.

For a better alignment make precise pinholes in the
protractor with a sewing needle for the stylus to sit
in for the points A & B, and inner & outer null points.

If the cantilever does not sit parallel to the direction of
the cartridge then determine the angle of error and make the
correction on the template by drawing new lines. Taking a
closeup digital photo from the bottom of the cartridge with
the cartridge template attached and viewing it in an image
program that has rotation capabilities is one way to determine
angle of error. If the cantilever is off by a great deal or
bent it is not advisable to use a stylus with this great of
defect even though you may get it properly aligned there are
other issues associated with defective stylii that can affect
tracking performance.

For the cartridge alignment tools print on heavy paper or glue paper
template onto poster boad and cut out with an exacto knife making
sure that the cuts are precisely parallel to the lines. Proper fit
is important. Too loose or too tight can cause alignment errors.

These tools were drawn with QCad community edition.
Thanks goes to Vinyl Engine's Tonearm Alignment Comparator
in creating these protractors. To see how these cpmpare to
the other standard protractors plug in the values on the protractor
into the tonearm alignment comparator.


If you wish to draw your own protractors with a CAD program or by hand
my latest optimal inner & outer null points are 67mm & 113.5mm respectively.
Although the templates above do not use these latest null points they will still
provide exceptional results. The only info about your turntable needed is the
pivot-to-spindle distance along with these null points to plug into one of the
many alignment calculators out on the web to get the effective length.
One example is the Arm Data Calculator using the "Null Radii + Mounting Distance" tab.
Pivot-To-Spindle + Overhang = Effective Lenght, the radius of the arc the needle will trace.

DUAL604: Pivot to Spindle = 203mm, Overhang = 17.938, Efective Length = 220.938mm, Offset Angle = 24.11°, Angle Error = 2.52°, Distortion: Max = .867, Avg.RMS = .415
SL- 1200: Pivot to Spindle = 215mm, Overhang = 17.012, Efective Length = 232.012mm, Offset Angle = 22.89°, Angle Error = 2.38°, Distortion: Max = .817, Avg.RMS = .392
Pro-Ject D III: Pivot to Spindle = 200mm, Overhang = 18.185, Efective Length = 218.185mm, Offset Angle = 24.43°, Angle Error = 2.56°, Distortion: Max = .881, Avg.RMS = .422

Active 185Hz 3rd Order High Pass & Low Pass Bi-Amp Filter


Active 3rd Order 30Hz High Pass & 100Hz Low Pass Sub Woofer Filter

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