Ten years ago,I buy a new MUSICAL FIDELITY M1 HPA headphone amp, it’s sound is fine and delicate,I very like it,Recent years I don’t use it, when I use it now,it’s high frequency sound not good,I think mabe the caps of M1 has already aged, change all caps of M1 is a big project, I want to bluntly clone it.
The power of M1 is switch power,I want to use a linear power to replace it,
I buy a set element of SIGMA22 regulation ，and I spend 3 hours to assembled it, it’s sound is similar with M1 switch power.
I draw the circuit diagram of M1 AMP,the diagram is quit simple,maybe it easy to be clone,M1 AMP is A Class AMP,the current of M1 power transistor is 200mA,I need a bit aluminum heat,when I get the heat,I begine to design PCB
View attachment M1.pdf
The power of M1 is switch power,I want to use a linear power to replace it,
I buy a set element of SIGMA22 regulation ，and I spend 3 hours to assembled it, it’s sound is similar with M1 switch power.
I draw the circuit diagram of M1 AMP,the diagram is quit simple,maybe it easy to be clone,M1 AMP is A Class AMP,the current of M1 power transistor is 200mA,I need a bit aluminum heat,when I get the heat,I begine to design PCB
View attachment M1.pdf
Some time ago, I replaced the original M1 switching power supply with sigma22 linear power supply. For the main power filter capacitor on sigma22, I used Philips 10000uf / 63v capacitor, other capacitors used chemical AWJ and lxz capacitors, and all four 100uF decoupling capacitors in M1 amplification part were replaced by chemical lxz100uf / 63v capacitors, and the final output isolation capacitor was used as stepless capacitor by connecting two chemical awj1000uf negative electrodes in series Replacement, equivalent to only a few 10uF and 1uF coupling capacitors, negative feedback capacitor and last stage bias voltage stabilizing capacitor have not been replaced, but the high-frequency sound is still noisy, almost can't hear, I am not confident to repeat. Finally, I bought several 10uF and 1uF tantalum capacitors to replace all the small capacitors on M1. The result was unexpected, the high-frequency noise burr disappeared, the sound The sound recovered the British voice of the original machine. I used a lot of capacitors to replace the four decoupling capacitors in the amplification part. Only the lxz100uf / 63v capacitor of chemical industry can keep the original machine's loose and detailed British sound. Moreover, after the replacement of tantalum capacitor, the sound quality of the original machine has been improved obviously, and other capacitors have not changed much. So far, it can be said that the reason for the decline of sound quality of my 10-year M1 HPA is that The capacitor is aging. Now I'm confident that the M1 HPA is reproduced. It's just the amplifier circuit part. I still don't use the switching power supply of the original machine. I decided to replace it with sigma22 power supply. Now I can start to copy PCB. The M1 HPA has a simple circuit, few parts, low cost of reproduction, and typical British sound quality. This M1 HPA is worth reprogramming. In addition, there is a decoder of pcm2706 synchronous USB chip used in the original machine. I also want to copy it. This decodevery simple and costs tens of yuan（Chinese), Although it is a synchronous USB decoder, as long as the clock stability of the computer USB interface is good (I have used several Apple computers, the USB clock is the most stable, and the sound quality after decoding with pcm2706 is also the best), the final sound quality is still very good, no less than XMOS asynchronous USB decoder.
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