Upgraded Single Board PCM1794 NOS DDDAC

nige2000,

Since this seems like a good place to discuss your battery scheme - I have a question.

I am going to try Zen Mod's CCS along with carlsor's.

I have found a nimh battery in a 9 volt format to use for the negative supply.

Could one use the same "charger" for this battery? Of course, with the leads oriented correctly.

Can you think of a reason to NOT to do this?
 
I've measured the current feeds 2 boards,
Receiver board # 70mA
Dac board # 60mA
So we can use any super shunt reg power in 100mA ccs range for each board.

No, you can't. I split my analogue and digital supplies. Both analogue and digital used Belleson super SPM super regs rated at 225ma. But the analogue ones failed quickly, Belleson say because the switch on transient with 4 x 47uf would be close to their limits even tho by my calculations the transient shouldn't exceed around 180ma.........Anyway, the normal 0.5a rated ones work perfectly which Belleson kindly substituted
David
 
Hey Rick,

What voltages are the other batteries in use and what charge voltage is the "charger"?

Chuz,

Drew.

nige2000 came up with a version of a scheme used by an Irish DAC to power his computer with the A123 3.3 volts batteries. The charger is a power supply for each voltage needed. For the computer 3.3, 5 and 12 volts. The batteries are constantly being charged when in use, I presume the batteries are acting as giant FAST capacitors in the this application.

Not knowing the provenance of the idea I thought this would be a great way to power the DDDAC. With advice from nige2000 I am using a single battery pack consisting of three cells for the 8 volts analog and a single cells for the 3.3 volts digital. I had intended to use a pack for each channel but nige2000 thought that would be ludicrous. Considering four of these batteries in series can start a car I figured he was correct. Certainly the best best way to begin.

Now with using the blue mainboard I want to use 5 volts for this. So another pack of two cells will be needed to power this. I will be powering WAVE IO with a separate pack of two cells since I think it is worthwhile to keep WAVE IO completely separate from the DAC,

Building a pair of Zen Mods CCSs which require a negative power supply. Easy enough to get the +8 volts from the regular supply. For the negative I am using a 9 volts package NIMH battery. My intention is to use the same charger for the -8 volts but with the leads from the "charger" arranged appropriately to this battery.

I cannot think of a reason this would not be OK but wanted some confirmation.

Using batteries allows getting rid of most of the components off of the DAC board. nige2000 has found caps, even by-pass caps, are not needed - disadvantageous, even.

Using my favorite wood for audio projects, balsa, I have made a three tiered
assembly above the main board to hold the batteries and the switches. Supply wire lengths are minimal and disassembly is fairy easy.

ALL grounds from the DAC are attached to one side of a SPDT switch; all grounds from the batteries are attached to the other. This turns everything on at one time. WAVE IO has its own switch, of course.

The "charger" power supplies are kept a distance from the DAC assembly. Another switch is needed to keep the batteries from discharging when the DAC is not in use. Again, I am tying all of the ground lines together at the switch.

Using my BELLESON regs for the "chargers". 8, 3.3 and 5 volts.

I probably did not make it clear that the chargers keep the batteries at the voltage needed. They are not fully charging the batteries which would blow the DAC up! No need for a regulator after the batteries.

nige2000 says he has listened with the "chargers" not attached (now, he is speaking of a computer setup using lower quality regulators) and hears no difference in the sound.

Yes, it does almost sound too good to be true.
 
I tried doing this with the DAC part but since I am an absolute ZERO when it comes to SMD solderng I gave up.

AS few of the parts as I retain I thought it would make for a more elegant installation. Oh, well ...

AS you can imagine there is not a chance I would try to mimic the mainboard!
 
Ssop28 package like wm8805 and pcm179x is a little bit of hard to work with soldering, but for 74vhc series it is easy for you to do. You can use the magnifier to complete them.

You are kind to be encouraging!

I think I do a good job of soldering but have never successfully soldered an SMD device. Of course, practice would improve my efforts but at the cost of PCM1794s ... No question those 74vhcs are a better/cheaper device to practice with!

Take care,
 
My exps. for SSOP28 package :
- Put IC on the board and align its pin and pad,
- Make 2 soldering points on pin 1 and 15 to fix the chip
- Use small piece of heatsink for chip and hold it by one hand, soldering by other hand.
- Finish soldering job pin by pin, by squeezing solder tip for each pin from chip's edge side.
 
uploadfromtaptalk1417833296963.jpg
 

Now that's my idea of a heatsink!

I never considered using weight to hold the chip to the board.

I thought I was being clever and used some epoxy to glue the chip and then realized after it was too late that this would not allow optimum soldering.

I was using a tiny tip but wonder if it was still too large.

I had been encouraged on the 'net by a technique where you simply ran the iron across the pins. I thought the flux would keep everything from getting messy. I am sure this can work once mastered, but ...

I know I will have to try again. next time with a "heatsink" - thanks!
 
Half clock delay

This upgrade takes most of an afternoon to build and install, but is well worth it.

These are my initial sq impressions from this change: I hear MORE music!
- Cymbals sound 100% right for the first time.
- Voices are more articulate
- Sound is more crisp and vibrant. No smoothing here.
- Same amount of detail, but it sounds more coherent and "right"
- I got drawn into musical nuances of familiar CDs that I never noticed before.
- More focused placement of instruments in the soundstage. I could almost hear the size and shape of instruments.

The board is about $10 usd of parts, but I also bought a 5V Belleson SPM78 regulator ($36 usd) to comply with the Blue Main Board voltage. Yes, a 5V regulator makes the DAC with this upgrade sound more accurate and smooth compared with my original 3.3V Belleson. According to the data sheets the 74VHCxxxx chips switch state many times more quickly when operating at 5.0 volts. Adaptor boards can be bought on eBay but could take a month to receive. 3pcs SMD Converter Adapter PCB SOIC14 LGA14 to DIP14 | eBay

The I2S resistors should all be 100 ohms – the 1000 ohm resistor for DATA must be replaced with 100 ohms! The bottom of the main board had to be modified by cutting BCK foil traces and adding jumper wires. See pictures below. You can see the delayed signal wire from the 2-Chip Board going through one of the clock foil trace holes to the five 74VHC164 chips.

I initially built and installed a 1/2 clock delay circuit above the main board. Later I built a second 1/2 clock delay circuit board but installed it on the bottom of the red main board which puts it out of sight. I think some of the wires lengths may be a little shorter, but this location is no less time consuming to implement. I used 24ga CAT 5e solid wires. For multiple connections I loop a single wire through the points as much as possible.

For the bottom installation I drilled an M3 hole through the adaptor board pair and main board with a plastic nut spacer and screw to hold it firmly in place.

The Belleson and some other Vregs need more load than from the seven 74VHCxxxx chips to provide optimum regulation and sound their best. The connection to the WaveIO isolator provides enough extra load, but if you are using an rpi or reclocker with its own isolator you may need to add a 330 ohm resistor across the Vreg load.

My engineering mind cannot figure out why new components, circuits, PS, etc in the digital domain of 1's and 0's have to go through a burnin period, but my ears tell me this is necessary.

Below is the 74VHCxxxx chips circuit diagram pulled from page 3 of the DDDAC 1794S NOS manual that should be used as a guide for wiring and installing this circuit board. Also included is a BOM and installation pictures.

Hi,

I 'finished' the clock-delay-thing and it gives sound.
Only one channel does 1.2Volts and the other does 2.4Volts.
What did I do Wrong?
Any suggestion is welcome,

Ed


IMG_9515.JPG
 
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I never considered using weight to hold the chip to the board.

I thought I was being clever and used some epoxy to glue the chip and then realized after it was too late that this would not allow optimum soldering.
!
Nope, this heatsink is small piece of aluminum material so it light, the main purpose is protecting chip from overheat.
By using expoxy for gluing chip, it's make you more difficult to rework then if any reason for changing mainboard.
 
clock-delay-thing problem

Ed,

Excellent looking wiring job! Seems correct as far as I can tell. If you messed this up there would be NO sound.

I assume the 2.4V and 1.2V refer to both differential sides of the Rload resistors which are on the analog side. Even with no digital signal these should both be 2.4V. Are you sure these were both 2.4V before you added the 1/2 clock delay?

The PCM1794 in mono mode provides two outputs to each Rload resistor which are combined and the current summed. Maybe the LR signal path for the low voltage side was messed up during this change, but this is the only I2S signal not affected by this upgrade. You did change the Data resistors from 1K to 100 ohms, right?
 
Half clock delay

Ed,

Excellent looking wiring job! Seems correct as far as I can tell. If you messed this up there would be NO sound.

I assume the 2.4V and 1.2V refer to both differential sides of the Rload resistors which are on the analog side. Even with no digital signal these should both be 2.4V. Are you sure these were both 2.4V before you added the 1/2 clock delay?

The PCM1794 in mono mode provides two outputs to each Rload resistor which are combined and the current summed. Maybe the LR signal path for the low voltage side was messed up during this change, but this is the only I2S signal not affected by this upgrade. You did change the Data resistors from 1K to 100 ohms, right?


Hi Carlsor,

Thanks for having a look and thanks for the compliment!

It's always a problem to be shure how the situtation was before the mod?!

I played a 400 herz testtone at a certain level, where I mesured the difference in output between the left and right Dac's pos- and neg posts. This after noticeing the channel difference while playing music material.

I did change the 1K resitors to100 ohms.

I wil take the Dac apart again, and check both decks seperately hehehehe...

Thank you again for the help,
Ed
 
Half clock delay

Ed,

If you have a 2 DAC board stack then it sounds as if one of your DACs has stopped putting out an analog signal from one channel - hence, half the voltage at one Rload. Hopefully its just a connection problem. Doesn't sound like a digital problem.

Hi Carlsor,

You must be right.
I will start playing the decks one by one so the problematic guy will expose himself. After thet it will be much easier to track the problem. Everything will be better in reach then. I let know what I find out,

Ed:)
 
Half clock delay mod

Ed,

If you have a 2 DAC board stack then it sounds as if one of your DACs has stopped putting out an analog signal from one channel - hence, half the voltage at one Rload. Hopefully its just a connection problem. Doesn't sound like a digital problem.

Hi Carlsor,


Problem solved.
It appeared that , with removing the 1 K resistor in order to change for the 100 ohm one, I screwed the foil that makes the connection from the resistor to the DATA connection point. That's all. So my friend is 'singing' again, even better than before.
Thank you for your helpfull how-to!
Up to the pin 20 mod!
Happy Eddie
 
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