The XH-A901 Preamplifier

Note that the featured image is for the XH-A901 preamplifier, used to drive the now very popular and very good XH-M542 – using the TPA3116D2 Class D mode power amplifier.

Thousands of these little preamplifiers have been sold, predominantly sourced through the Chinese ecommerce market or market place accounts at local ecomm suppliers. The specific model shown above almost all have a few little caveats before you can get them going though.

The NE5532

The NE5532 is a dual monolithic, bipolar, internally compensated operational amplifier, features from the spec sheet 

• Equivalent Input Noise Voltage: 1 5 nV/√Hz Typ at 1 kHz
• Unity-Gain Bandwidth: 10 MHz Typ
• Common-Mode Rejection Ratio: 100 dB Typ
• High DCVoltage Gain: 100 V/mV Typ
• Peak-to-Peak Output Voltage Swing 26 V Typ With VCC± = ±15 V and RL = 600 Ω
• High Slew Rate: 9 V/μs Typ
• 4-5mA per amplifier current draw at max voltage

The XH-A901A for Turntables and Phono use

These preamplifiers are designed for a higher input voltage, lower input impedance and not the 5mV 47kOhm which is expected from a phono moving magnet cartridge.  Also, the phono output needs to be RIAA equalised.  I’ll give you a circuit at the lower part of this article covering this.

XH-A901A Musicality

I have read lots of negative comments about this, most of them written from the pens of the golden ear brigade. I find it really awful that because the chip has a very modest price tag it will be regarded as being inferior. (many professional R2R recorders used them). I believe many people are buying these preamplifiers to modify the circuitry or even roll the chips – for the price these chips are extraordinarily good BUT not necessarily the other components used.  Before we give specs, in a nutshell the quality of reproduction is good and for the average listener more than adequate.

 However there are some things buyers should be aware of that unfortunately has not been remedied through the ages.

The UX-A901 audio preamplifier – dodgy manufacturing.

Out of the many that I have purchased through Temu all of them had the same fault.  Sadly looking at other forums and posts the same issue comes up and it’s not a little issue.  Here we go:

Customer complains that the chips get hot and crack or they smell something that should not be there.   Yes, the socket for the power has been installed incorrectly – the power supply polarity is reversed to the two chips.  One needs to reverse the socket or the incoming power leads which is what I did.

Loss of audio – one channel, Right channel

Secondly, and this is quite infuriating because this is another long term complaint and for the layman a bigger issue if he or she manged to detect the power polarity problem and repair, is that input 2 (pin 5) of the NE5532 chip is actually at 0V, an obvious layout and manufacture flaw. If the first board was tested then surely the rest would have shown to come up with this error – so obviously they just get released from the factory like this in their thousands because it will cost too much to repair. I actually modified mine to get it working until I found a workaround for the other boards – a big thanks to @bmelectronic.   The YouTube video is below, please click on the LIKE button, much deserved.

The thing I cannot understand is why this has still not being fixed and there are hundreds of complaints on the internet about blowing ICs, channel audio dead etc, etc.

Another interesting one is the input socket middle pin which should be ground unless designed as such floats above ground and is coupled to earth via a capacitor.  Schematic shown below:

XH-A901 preamplifier input open ground.

I could not see whether there are any coupling (DC Blocking capacitors) on the input so enthusiasts may want to put this in preceding the input socket – e.g. 4.7u 35V. 

Thanks goes to Adriano Peres for this snippet of useful information and feedback.

The UX-A901A audio preamplifier – chip rolling.

This one was rather interesting to me because I purchased a few LM4562 chips through Farnell.  Doing a chip swap here didn’t actually show any outstanding changes in audio reproduction.  I’m of the belief in any event that the NE5532 is one of the nicest sounding chips of it’s time (if it is original) – the LM4562 is more an instrumentation device which will show lower distortion than the 5532 although I could not hear this.  I don’t have the equipment – I do have the scope image files which I will share.

For the price I don’t think exchanging the chips will give you that much quality difference, unless the op amp is counterfeit.  (in 2023 I paid about $6.00 each for the LM4562).

The UX-A901A audio preamplifier phono reproduction

There’s a couple of circuit permutations I tackled, the first being the rather excellent design from Elliott Sound Works, coming from Rod Elliott – from my experience the best website around for both students and professionals in the audio design field. (and other)

The project page URL is as below:

https://sound-au.com/project06.htm

Schematic of the one I built.

NE5532 Preamplifier – these chips can be exchanged for the better OPA2134 or LM4562

Just as an aside, I built this on breadboard, the results were exceptional, using the LM4562 which I had in stock.  If you intend to build this preamplifier I recommend you stick to the original PCB design to prevent frustration – https://sound-au.com/pcb/pp06.htm

How to purchase from the ESP website.  All the necessary information on how to purchase from this website shown there.

Another page covering RIAA preamplifiers:

https://sound-au.com/project25.htm

If you would like to stick to the LM4562 chip (which I advise, for the phono preamplifier) there is a spec sheet which you can get from Texas Intruments.

The TI designed preamp circuit is below.

The UX-A901A preamplifier using the LM4562 phono

An enthusiast did build this preamplifier using the same components but complained about the chips running very hot.  On a TI forum a technical expert did try to assist and I cannot remember what the outcome was, if any.  Hence me saying, best to stick to the layout as advertised by Rod Elliott.  These are high gain broad band amplifiers which cannot just be put into any old board.  I built the preamp on breadboard and I can promise you it is very, very good.  I don’t know what the OPA2134 will sound like, there are some enthusiasts that prefer this chip over the LM4562.

OPA2134 spec sheet

Lastly, from Google’s AI: