PO74G38072 and DSIX

The Unsolved Misery

Why the PO74G38072 sounds worse than the DISX with TC74VHCU04/PO74G04 ?

This is the question comes up on my mind after replacing the TC74VHCU04 with PO74G04.

My Own Explanation

Well, I'm just guessing, and I could be wrong, so if you think that I'm saying something stupid, share your comment please, will greatly appreciate for that.

Since in the design of DSIX, the output of the 74HC04 buffer is a combination of 5 sets of inverter. While using PO74G38072 on the DSIX, since the pinout is different from 74HC04 chip, I need to modify the connection. In the end, only one of two PO74G38072 buffer outputs is used. 

Take a look at the oscilloscope graph of PO74G38072.

We can see that the overshoot is very weak, actually we should call it "undershoot".

This is where I suspect the jitter coming from.

So why TC74VHCU04/PO74G04 sounds better?

Let's look at the following graph of the TC74VHCU04.

You'll see that in the waveform above, it might be easier for the DAC to tell if it is a rise or fall, so less chance for the DAc to miss interpret the signal. In other words, less jitter. Pay attention to the waveform, the overshoot is obvious.

Ok, now let's take a look at the DSIX design.

Why Mr. Shibasaki uses all the rest 5 sets of the 74HC04 output for the signal?

I guess he wants to create some reasonable "overshoot", since using only one set of the output will become "undershoot" in the end. By combining all the rest 5 sets, the signal level will be strong enough and the reasonable overshoot will be created.

Basically, this is why TC74VHCU04 sounds better than PO74G38072, however worse than PO74G04A.

Conclusion

I think both PO74G38072 and PO74G04 will have better result than TC74VHCU04, however please note that:

1. Do NOT use the PO74G38072 directly on the DSIX, the signal strength is too weak to create overshoot, jitter will be introduced in the end. With DSIX, use PO74G04 instead.

2. If you prefer to use PO74G38072, the circuit must be redesigned for sure.

DSIX with PO74G04

PO74G04


PO74G04 is an alternative ultra high speed solution for 74HC04, the specification is excellent, supports up to 1.125 GHz bandwidth and the propagation delay is less than 1.4 ns with rise/fall time 0.8 ns.

To me, this is an awesome solution as a replacement for TC74VHCU04.




PO74G04 On the Oscilloscope

PO74G04 @ 100ns/100mV



PO74G04 @ 25ns/100mV


Amazing rise/fall time (compare to the TC74VHCU04 in the following graph).

TC74VHCU04 @ 25ns/200mV


The overshoot and the ringing might be the noise from my power supply, will try to improve this later.

Listening Experience

Noticeable improvement discovered.

1. More silent background, this implies the resolution is greatly improved.
2. More solid bass, even when the bass guitar and the bass drum are played at the same time, you will be able to recognize them respectively.

Conclusion

Highly recommended, what are you waiting for?

PO74G38072 Digital Buffer

Background

Toshiba TC74VHCU04 is a well-known digital audio buffer chip since it was used in the famous DSIX circuit.
The PO74G38072 designed by Potato Semiconductor is a buffer chip for digital signal, supporting up to 1GHz. PO74G38072 was recommended by some DIYers as a alternative solution for digital buffer than the TC74VHCU04 due to the wide-bandwidth and its perfect specifications. I did a simple test, replacing the TC with PO chip, and the following is my discovery.

Listening difference

It was a surprise to me......... Surprise? So, better or worse?

Unfortunately, after swapping TC74VHCU04 with PO74G38072, my system sounds worse.
Actually, the two chips sounds nearly the same, however TC74VHCU04 provides more silent background than PO74G38072.
As a result, the TC74VHCU04 gives more dynamics in general.

Investigation

I then tried to find out the reason technically.

Here's the comparison of the TC74VHCU04 and Po74G38072 on the oscilloscope:

TC74VHCU04@100ns/200mV


PO74G38072@100ns/200mV


Let's take a closer look:

TC74VHCU04@25ns/200mV


PO74G38072@25ns/100mV


As you can see, TC74VHCU04 has less ringing and overshoot than PO74G38072. In other words, less noise.
I think basically that's why TC74VHCU04 sounds better than PO74G38072 on my system.

Conclusion

I do believe that PO74G38072 should have better performance than TC74VHCU04, since it supports more bandwidth than TC. However, wider bandwidth sometimes means that the noise will passthrough the buffer as well. And I think that is basically why PO sounds worse than TC on my system. (Please note what I'm saying - my system)

But if I can decrease the noise on the power supply, I think there is more chance that the PO might sound better than TC for one reason - less jitter. PO is a much faster chip than TC, if we can well control the noise level sourced from the power supply, I do believe that the less jitter characteristics of the PO chip will be easily identified in this case.

I think the power supply will be the next task for me.