Enquires about Class D Amplifier

Just drop in.....

Balance input does not mean good sound. I think this is a misconception among a lot of people. If the component of the balance circuit is not of premium grade , it is actually worser than normally RCA input. Basically a balance circuit means both positive signal and negative signal was enlarged. in an ideal world which never exist, this should cancel all the distortion and will have low noise. However, the difference in component made it very difficult to achieve it. I have DIY a balance pre-amp, the transistors need to be matched within 0.2% in order to achieve a good result. matching 0.2% means that you need to buy at least 1000 pcs in order to match within the specification and I have 16 pairs need to be matched.

Please correct me if I am wrong.

[quote:ef0382326e="alant"]Dear KK Ho sir,

In additional to the Point #1, I would like to elaborate my concept of “a true balanced stereo HiFi system” to you for review. If something wrong in my concept, please feel free to correct me.
In my concept of HiFi system, every part from source to load in the system is equally important and related to each other with different extent which affects the sound quality. In my goal, I adopt a “Balanced approach” to link each other because a balanced approach will always give you the best sound for the money. Balanced audio technology has been a standard in professional and high-end home audio systems for decades. The advantages are noise and distortion elimination in which the HiFi system can achieve better signal-to-noise performance, greater dynamic contrast, and significantly higher resolution.

In theory of “Balanced signal transmission”, the four signal lines (left - positive and negative) and (right - positive and negative) from source to load must be completely separated and mirror symmetrical such the noise and distortion immunity can be counter eliminated. Please note: (for input voltage “v” and noise “n”)

Left audio channel (+): v (input)  [load]  v+n (output)
Left audio channel (-): -v (input)  [load]  -v+n (output)
Right audio channel (+): v (input)  [load]  v+n (output)
Right audio channel (-): -v (input)  [load]  -v+n (output)

In receiving end (either left or right channel), subtract positive signal to negative signal, we have 2v which can accurately receive the input signal without noise and distortion immunity.

In a stereo HiFi system from source to load, it consists of two parts:
1) Connection cables such as balanced (XLR) and unbalanced (RCA, BNC) cables,
=> In balanced signal transmission in cabling, it uses a 3-pins wiring in which two signals are identical in ever respect with the exception that they are opposite in polarity (+/-). These signals are known by such names as ``inverting and non-inverting'' or ``Live and Return'' - the ``L'' and ``R'' in XLR (the X is for eXternal - the ground).

2) Individual electronic units such and CD transport, DAC, preamp, power amp, etc…

=> In balanced electronic units, it requires to use a balanced circuitry. It sounds simple, but in fact very different in circuit design.
=> Adding a balance driver for output does not mean “completely balanced” if the circuitry in the front is not designed in mirror symmetrical to achieve noise and distortion elimination. This is why KK Ho said “adding a balance driver like DRV136 is not = balance out”. KK Ho, is my interpretation correct?
=> If you want to know whether the circuitry is true balanced or not, by observation, you can see at least 4 OPA chips individually in the circuitry to handle the 4 signals separately. But, it does not 100% guarantee true. Formally, should be tested by complex test equipment, but out of our scope.   

Please comment![/quote]

Your response is quite typical engineering people response, who quote a lot of theory with the real world experience. I have a DIY passkab per-amp with full balance driving a full balance Mcintosh MC275 for at least one year of intensive listening.

My friend using a Mark 380 driving 438 power -amp, they have both balance and unbalance input.

We finally still using unabalance output .


1. For balance circuit, it will have higher distortion and time delay because all the component in the circuit need to be prefecty matched ( that is what I mean premium grade), Given the general compnent is normally withn 5% tolerance, ithen it will means that you have a 5% chance distortion .You can ask a lot of person , 5% distortion is a lot. It is the reason why DIyer have difficult to build distree amps as the transistor need to match to a low tolerance. I built the per-amp based on  1% matching on transistor.We found that the distortion in the upper and lower half wave will not good enough  because differences in component tolerance.
2.  You normally found that the sound of balance is different from unbalance because the output level of the balance circuit is normally double the unbalance level. If you are not using full balance, that means from CD-->pre-amp-->power amp, you are not really enjoy the benefit of balance circuit. I have both balance and unbalance equipment in my system, I did not find balance sound better. My purpose for this responses are to correct misconception that balance will sound better.

I respect your computering knowledge but HI FI is sound, which is quite difference from what you are expert at.

Ha Ha, I always have problems in discussing with engineer with Hi Fi as I found it very difficult to tell them my experience, which may be conradict to a lot of "engineer' belief. Interestingly that Hi Fi is not something that can measure by instrument only or specification only. You can build a top speciifcation machine but sound awful.  The secret of good sound seemed to be much more than those seen on the scope and specification.  I do not mind whether you will accept or not as it is your money and your system. You can take you own route and spent your money that way. I am just here to share  my years of experience in DIY wth people  and hope them they can spend their money wisely.

Alant,

My approach is quite different and I am a practical man. For my hoddy, i just want to achieve the best possible sound for a sum of money that I can afford. Being play with factory made machnes for about 10 years, I decide go to DIY because I really frustrated with those factory made machines. For those factory made machines that I like it, I cannot afford it. In 80's, I am already playing wiht mark's 30.5 + 30.1 and cello performance driving a Duntech. As a result, my ears are very critical. Therefore, I always use listening test as my final decision making criteria. No matter how good a certain technology or products appear on paper, it will be of no value to me if it does not pass the listening test. I hope this will ease your feeling that I am finding trouble with you, it is just our evlauation criteria may be difference.

Go back to your discussion of the power supply unit, both power supply , tranditional transformer and switiching power supply are of different sound characteristic, and it is really important that material like caps, resistor and transformers  that really make up the power supply. I suggest that you should take some time when Hi Fi Fever has a demo of UCD ampifier, you can distinguish the difference in sound characteristic so that you can decide your personal preference.

Agreed , no worry, audio is quite an amazing hobby. One had to pass the listening test. Nice to talk to you.