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-   -   Potato 74G14 vs Fairchild 74VHC14 (http://www.diyaudio.com/forums/digital-line-level/229849-potato-74g14-vs-fairchild-74vhc14.html)

KlipschKid 12th February 2013 12:54 AM

Potato 74G14 vs Fairchild 74VHC14
 
Hi,

Does anyone know about how to optimise a circuit for the faster Potato ? I recently swapped a 74VHC14 for the Potato 74G14 and the sound is substantially worse. It is used to distribute the output of a Crystek 24.576Mhz CCHD-957. Pin1 is the clock input and pin2 feeds the other sides inputs. Their outputs feed R1-R3 / C2-4.

Thanks !

Tom

canvas 12th February 2013 01:17 AM

Well, I have been using Potatosemi's 74X family for years and found nothing comes close to it. What would be your "substantially worse" sound like?

KlipschKid 12th February 2013 01:25 AM

Sound changes - for example there has been a loss in the urgency/definition/depth in the deep bass, and overall the sound is like added jitter.

I assume I need to change the rc output to get this Potato at its best ? That's what I'm asking.

Tam Lin 12th February 2013 02:17 AM

Instead of using multiple logic gates, why don't you use a fanout clock driver? Let me ask you, what is the pin to pin skew for the 74G14? What is the added jitter? Oh, that's right, they're not published because they're not measured or guaranteed. I wonder why. I would think those would be important characteristics for clock distribution. I suggest you look a little deeper into the PotatoSemi catalog, among others.

canvas 12th February 2013 02:33 AM

Maybe you can try PO38072 1:2 clock distributor. I have one to distribute 33.8688Mhz into digital filter chip and PO74G374 for reclocking. The result is great.
By the way, what is your power regulator for clock?

abraxalito 12th February 2013 03:16 AM

As it looks as though you're using groundfill for your 0V, the worse sound could be arising from common impedance coupling on the 0V. Is the 0V to the potato chip sharing any ground impedance with the clock?

KlipschKid 12th February 2013 03:22 AM

Hi,

As you can see, I need 3 outputs, and pin-for-pin compatible. I'm not hacking a high-speed pcb circuit. The clock has its own regulator, and that area is a common ground for the digital circuit.

So if changing the RC output isn't going to resolve the problem, I'll go back to the 74vhc14. I was just hoping a faster chip would improve, not degrade, the signal. I assume from your answers that the RC filter is not the problem. Besides, I can only listen to so much Massive Attack...

If you want more info about the DAC, its here :

http://www.diyaudio.com/forums/digit...ml#post3250142

Thanks.

abraxalito 12th February 2013 03:25 AM

Higher speed CMOS logic has, IME, always given rise to PSU noise problems. That's why these days I go for the slowest possible one (usually HC, very occasionally 4000 series) and reduce the supply voltage to 2.5V.

Based on my experience with AD1955 DACs from Taobao, if you don't hack the grounding you'll miss out on the best possible sound.

KlipschKid 12th February 2013 03:47 AM

Well, I wanted to try.... and now I'm a believer... slower is sometimes better.

This DAC is not your average Taobao crap. It sounds as good as the ES9018, in everything except dynamics, but it has taken quite a lot of my spare time to make it that way. The seller built it for me w/o the pcm2706 so I can use isolated cm6631.

USB SPDIF PCM2706˫AD1955 384kHz ASRC Ƶ DAC ׼-Ա

abraxalito 12th February 2013 03:59 AM

I agree its very unusual to see an FPGA in a Taobao DAC. But THD+N at -140dB has to be some kind of a joke :D


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