A New Take on the Classic Pass Labs D1 with an ESS Dac

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opc

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Hi Guys,

I did read the entire article on the Zen I/V with great excitement, and contrary to Nelson's other designs, I really wasn't all that thrilled with it. I'm pretty confident that the circuit presented here would handily outperform it.

EVUL:

Could you elaborate on why you like the 2SK2013? This circuit could easily be fitted with a pair of jfets, but with significantly lower transconductance, I don't see how they would work any better in this application.

Lauret,

I've attached a rough layout which is as far as I got before I stopped working on it. The problem is twofold:

1. I have a setup that is working very well, so I have very little incentive to put the time and effort into a new PCB.

2. The circuit is very difficult to layout nicely, and people here seem to want different things, so I don't think I can make everyone happy.

I personally prefer to have small board mount heatsinks for each part, but several others have expressed an interest in having the components mount off the side of the PCB so they can be bolted to a bottom plate. Any layout with the components on the side of the board is pretty ugly, and it's not much better with board mount heatsinks.

It's tough because it's low-level circuitry, but with high levels of power dissipation.

Anyhow, the attached layout shows two different options with board mount heatsinks, so let me know which you prefer.

I do have some spare time to dedicate to this over the next little while, so I might just get back to work on it.

Just as an incentive, if I were to get the layout finished, how many people would be interested in boards?

Cheers,
Owen
 

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Owen, I would definitely be interested in at least 4 boards. i'm totally fine witgh onboard sinks, I had just thought with the rather high voltage needed for best performance, that little board mounts would not be all that suitable. but i'm happy if you are happy. as long as there are options to use off board discrete supplies i'm with that no problem.

depending on size I would probably just end up mounting it vertically directly against the wall with the devices underneath
 
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Owen, you could satify both requirements by having a hole drilled in the PCB at the point the screw for mounting it would be when the device is bent to mount on the floor, not off the side, but underneath. or like I do, just mount the devices to the floor first in the correct positions and then place the PCB over and solder them in. best to have the hole there though or you cant get the board off without desoldering them all at once :D

if you look at the sigma22 power supply by AMB you can see this. see the holes right at the edge? you can just use a small screwdriver through here for mounting

An externally hosted image should be here but it was not working when we last tested it.


here they are at the edge too, but this would not have to be the case
 
I think I prefer the right hand side layout. looks to be slightly more compact and with a more logical flow for signal. looks like you have a spdif MUX and simple power supply for the buff on there too. that would be great if I were using it and not the ackodac ;) so yeah as long as its easy for me to use my own power source (ie. easy mounting point for molex after your regs) then i'll be in heaven. if 1 board is stereo balanced, I would want 2, if only a single balanced channel, I would take 4. this is minimum as I may grab some for a friend
 

opc

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Joined 2004
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Hi Guys,

So there's a little more interest than I had initially guessed, which means I'll get my act together and get this thing finished.

I would like to appeal to the greatest number of people possible, but not detract too much from the layout in the process.

I do indeed have provisions for an adjustable 5V reg for the DAC itself, I have all three standard digital input formats (SPDIF, AES/EBU, Toslink) with a 6 pin header to select the desired one (could be wired to a switch).

The board is designed to drop a TP Buffalo II board directly on top, but if someone who owns the ackodac could carefully measure out the input and output connector locations (as well as the board outline, etc.) then I could possibly design it for both providing it doesn't make a complete mess.

I will also include proper connectors for bypassing any of the on-board power supplies if you feel the desire to tinker with that.

One other thing I'm trying to sort out is where to have the boards made, and how much it will cost to go with 4 layers. I always feel that a greater layer count results in better layouts, so I'd like to know if people would be willing to pay a little more for a 4 layer PCB.

Anyone with suggestions on PCB manufacturers who can do reasonably priced 4 layer boards in smaller quantities, please let me know. Any other suggestions for additions to the board are also welcome.

Cheers,
Owen
 

opc

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Joined 2004
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qusp:

One board is indeed balanced stereo output, and I've tried to include everything on board so all that would be needed is a pair of small transformers to make it all functional.

I'll look into your suggestion for under-board mounting of the resistors and transistors, which might actually work for this setup. I'm used to bolting down through the PCB and pinching the transistor between the PCB and the heatsink, but that wouldn't work in this case since both the resistors and the transistors have very different thicknesses. Bolting them down first, and then mounting/soldering the PCB might work well though, and if I place holes at the correct locations, then it might be possible to get everything off without having to de-solder.

I agree with you that the right hand side is the more logical layout, so I'll probably go with that. I'll get rid of the output XLR connector and just come off with a header since having outputs on the side is a little lame. People can wire up their own output connectors, and that leaves more room for output coupling caps.

Looks like we're up to between 15 and 20 boards, so I'll probably put in an order for between 30 or 40 to start. Maybe a group buy for the transformers would be in order as well. I'll look into it.

EUVL:

I'd be shocked if those JFETs had higher transconductance than the FQA32N20's. I measured 0.922 S with 130mA and 25VDS where the Toshiba looks like it'll be around 0.5 S (kudos to Toshiba for actually putting Yfs on the datasheet)

Still, I'll pick up a pair and see how they do. It's always good to try as many different devices as possible.

Cheers,
Owen
 
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Hi Guys,
Anyone with suggestions on PCB manufacturers who can do reasonably priced 4 layer boards in smaller quantities, please let me know.

Gold Phoenix PCB fabricated my D1 boards. Their prices are reasonable for small quantities up to 8 layers, and shipping to Canada is cheap. IMO their quality is acceptable for such simple analog designs.
 
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