New HQ DIY DAC

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Syd,

ref Alexs post above, this is it on my board...

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Alex, Chris, much praise and as Shaun would say

One AK DAC up and running! I had read about that fault and must have checked the wrong area of the board

Still makes it my most successful build in terms of faults at startup

A respite I think for some music listening then some power supply work next week.

Syd

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Hi Syd

Great news !
Phew, you had me worried there for a bit. Not as much as you would have been worried though !
Kind Regards
Alex

P.S.
Fully tricked out, it should give a full on B2 a run for the money, at a much lower overall cost.

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sandyk said:

Great news !
Phew, you had me worried there for a bit. Not as much as you would have been worried though !

It was the embarassment of yet another failure Considered whether to announce it but its the way I've learned about other faults. It seemed different to anything I'd caused before too.

P.S.
Fully tricked out, it should give a full on B2 a run for the money, at a much lower overall cost.

I'll not object to that! I'm keen to hear it against my AK X-DAC as there is still a powerful edge to some tracks that keep it in my affection

Some more reading I think.

Again, many thanks Alex (and Chris for the pic, zeroed me right in).

Syd

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Hi Syd,
well done on your success with construction, I thought about trying this one but other things got in the way.
Got your PM working on it, be in touch.
Alan

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Ferrite beads where used further back in the thread. Is there a standard size or type? I'm placing an order for other stuff but know nothing about these.

Thanks

Syd

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Nov 12, 2011 12:17:55 GMT @juke said:

Ferrite beads where used further back in the thread. Is there a standard size or type? I'm placing an order for other stuff but no nothing about these.

Thanks

Syd

Hi Syd
Attached is a link to what I used, however there should be similar available worldwide.
Regards
Alex

www.jaycar.com.au/productView.asp?ID=LF1250&keywords=ferrite+bead&form=KEYWORD

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Thanks Alex, that gives me an idea of what to look for.

Syd

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External oscillator modification.
The output from the Xtal oscillator should be connected as shown in the photo. The shield side of the cable is soldered to the original xtal earthing strap's PCB hole.The active of the oscillator connects to the RHS of the removed 33pF ceramic capacitor at the bottom of the PCB.(top in the photo) The other 33pF is also removed. The 100 ohm resistor is replaced by a link.
Please note that although the SC schematic is correct,that pins 7 and 8 on the PCB itself are reversed.
This does not normally matter, but it does when an external xtal oscillator is used.
Alex

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Something else to try, for those who have a PCB drill and are using the G.E. dual JLHs for the + and -15V supply to the DAC PCB.

Drill a suitable sized hole for a PCB pin at the middle lower end of the main large earth trace near where the incoming earth link is.
Expose the copper around the new hole and solder in the PCB pin.Connect a short length of heavy duty lead, such as an offcut from an old 7.5A mains lead between the PCB pin and the spare earth terminal on the JLH.
No test instruments were harmed or abused during the conception of this tweak. ;D
As usual YMMV.
Alex

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No test instruments were harmed or abused during the conception of this tweak.

What about the poor wee PCB?

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Nov 23, 2011 0:55:49 GMT drymdrum said:

No test instruments were harmed or abused during the conception of this tweak.

What about the poor wee PCB?

Hi Alan
It has so many holes drilled in it already, that I doubt one more would upset it too much.
Regards
Alex

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Nov 23, 2011 1:25:44 GMT @sandyk said:

Nov 23, 2011 0:55:49 GMT drymdrum said:

What about the poor wee PCB?

Hi Alan
It has so many holes drilled in it already, that I doubt one more would upset it too much.
Regards
Alex

You have to balance the holes between the input and output. otherwise there will be a imbalance of electrons to holes.

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Nov 23, 2011 4:12:45 GMT @gregerskine said:

Nov 23, 2011 1:25:44 GMT @sandyk said:

Hi Alan
It has so many holes drilled in it already, that I doubt one more would upset it too much.
Regards
Alex

You have to balance the holes between the input and output. otherwise there will be a imbalance of electrons to holes.

Greg
Have you by any chance just visited the Miracle Wraps website ? ;D
Alex

P.S.
As your version of the JLH PCB has an additional earth scew for connecting purposes, it is very easy to try, and easily removed again if desired. I believe that mine has further improved because of this simple modification.

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Hi Alex,

No. I have no interest in such devices. I am sure I be a naysayer and therefore be chastised by the RG community.

On the JLH front, I connect the input to the output terminals so your mod wouldn't have any effect in my particular (or is that peculiar) case.

Regards

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Greg
It doesn't matter which end you have connected to the 3 pin terminal block's 0 volt line on the DAC PCB. It's about reducing the resistance of the present tortuous path from the 0 volt screw terminal via a relatively thin copper trace and a rather long soldered link to the main thick earth trace of the DAC PCB.
Alex

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Hi Alex,

I obviously don't understand your mod. Are we modding the JLH or DAC PCB?

From your description, I thought you were putting the wire from the input to the output of the earth trace on the JLH PCB increasing the current capacity.

Regards

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Are we modding the JLH or DAC PCB?

Greg
It's simply running an additional low resistance earth from the JLH to the central earth trace of the DAC PCB.
The original SC article stated -73dB channel separation at 20kHz.
The use of the low output impedance JLH clearly improved on that.
The recent balanced version was -111dB at 20kHz which is a whopping 38dB better!
The additional direct earth appears to have further improved HF separation in this unbalanced version.My test equipment isn't good enough to measure the further obvious improvement in HF channel separation.


Alex

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hi Alex,

Thanks for taking the time to explain it to me.

It makes a lot of sense now. I needed the picture to get it through my thick skull.

regards

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ERRATA.

From Silicon Chip December 2012.
Stereo DAC (September-November 2009) : the 300 ohm resistor across CON1 should be changed to 82 ohms for improved coaxial cable termination.

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Hi Alex,

Hey I didn't notice the errata but I did notice the schematic on page 30 had the 82 ohm resistor on the input. Made me think (again).

When I originally saw the 300 ohm resistor I thought it was an error because most of the circuits I have seen in the past are usually 75 or 100 ohm. After studying the circuit for a few weeks I realized that the 74HCU04 is used as a amplifier so ideally the input can be considered to be connected to ground. That gave 300 ohm || 100 ohm which gives 75 ohm as per the SPDIF standard, yeah I thought, those SC guys are clever.

How did the SC guys get the fantastic distortion figures when they are now saying there was a signicifant impedance mismatch?

Now I am confused again.

Alex, have you tried it yet?

regards

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the schematic on page 30 had the 82 ohm resistor on the input

Greg
Page 30 ? O.K. You are referring to the new Digital Audio Delay project.All of their previous stuff shows 300 ohms. Schematic, and Part 2 layout which I corrected and posted.
Seems like somebody else must have corrected them !
A SPDIF mismatch will not necessarily cause a change in distortion figures, as "bits are bits" according to some !
It may come down to how well the 74HCU04 etc. does it's job ?
I changed mine to 82 ohms a little while ago, but as my main listening is done via Toslink, all I have done so far is check with my DVD player that I have a proper lock (Green LED) and Audio O.K.
I will need some quiet time to see if I can notice any audible change.

Regards
Alex

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Hi Alex,

Yep, page 30 of the December edition.

Impedance mismatching is probably the reason why people report differences in digital cables. The SPDIF standard calls for 75 ohm impedance. People report that manufacturers are pretty slack when designing cables/connectors and RCA terminations but I don't know if this is true.

AFAIK the SPDIF standard has no error checking as apposed to the "real" digital world of computers and networking.

regards

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Greg
The worst that could happen would be a small amount of added Jitter that the DAC may, or may not, take in it's stride.
I have considered the possibility of replacing the RCA connectors at both the Oppo and the SC DAC with true 75R BNC connectors, but they would need to come from RS or Element 14 as Jaycar doesn't specify whether their BNC sockets are 50 or 75 ohms.
I do however use a Concord (Jaycar) 1.5M 75 ohm "digital" lead made with RG59 coax.
Alex

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Hi Alex,

I may have a very simplistic view of the 74HCU04, but all it does is convert the 0.5V SPDIF signal to 5V. It inverts the signal, so the second gate inverts it again. I guess the second gate acts a abuffer as well. If the signal is stuffed before it enters the 74HCU04, it will be stuffed after it... only bigger. I supposed if the impedance mismatch causes a little attentuation then the 74HCU04 will fix that.

I prefer electrons to photons, but if you feel that the TOSLINK works OK you might be ready to listen to the Lightspeed as it uses photons too.

regards