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

[buzzforb]

10w with heatsinks. Can always parallel.

[qusp]

ahh OK should be ok then, ~5.5W in the 400R is the most @ +/-45v what sort of heatsink? BGA or something? would be tricky to heatsink an SMD under the board and the PCB wont take anything away.

[Rolle]

Originally Posted by qusp

OK well the heatsink we got, is just comfortable with it inside a case, it does run a little toasty in summer but its still OK. do you know what temp that heatsink rating is given at? heatsinks get more efficient as they get hotter believe it or not; the hotter they get, the more heat they can get rid of. so its important how theyve rated them.

the first one is basically the same dimensions as the conrad unit, but with a thinner base and the depth of the fins is not as much, so for me I would avoid that one if you are mounting in a desk, the wood wont take any heat away from the heatsink either like it does with my current chassis. the heatsinks we have are 0.36C/W for an 80C rise, which translates to ~0.45C/W for the temps i'm running them, which is only about hmm maybe 25C rise above ambient, meaning the heatsink can get up to 65-70C on our hottest days. for an air temp inside the chassis of ~50-60C

so really to be safe I would take the next size up if I were you

Thanks qusb for sharing your experience on this matter - I was not able to see in the Fischer catalogue what temperature it was rated at - but anyway got your point and will probably look for a better rated heat sink - just to be on the safe side

Thanks
Rolle

[MisterRogers]

Just as an aside - I've started discussions with a custom heat pipe design firm. I'm expecting that if I pursue this, it'll result in a custom case. I have the NTD1 in mind, but the design should accommodate components with similar heat dissipation requirements. The basic design will be very similar the Owen's custom case (bottom plate, sinks on the side), with the bottom plate having embedded heat pipes, and the side sinks/radiators dumping the heat. The bottom plate will be marked such that it can be drilled/tapped without getting into the heat pipes.

Anyway, I'm early in talks and it may not come about (cost, etc.). I mention it to gauge any interest, as it's alot of effort for one or two cases. There are cases out there that will work (we're still knocking around one such case in this thread.), but I'm intrigued by the thought of a more compact case that can handle the thermal requirements of this awesome IV.

So it's premature to start any sort of list, but if this is something you'd want - let me know.

[bigpandahk]

Originally Posted by qusp

we are talking about the TPS7A3301 (neg) which is QFN20 and is the matching negative counterpart to the TPS7A4700 youve been using for fifo and is on Ians reg board.

the negative part is not yet available in stock at digikey in the QFN20, will be soon, but the eval board wont cut it for either polarity for the job we have here. I will be doing a PCB shortly for them. with 2 pairs pos and neg, with additional heatsinking possibilities, higher voltage caps, the elevated voltage modification to get them to do +/-45v. I plan to make it so that it can sit under the edge of the IV board and with outputs that match the input positions.

Thanks again qusp.

[qusp]

yeah I looked at and still am looking at the flat cool pipes but I wouldnt want a dac case that looks just like a poweramp if getting something totally custom (as it looks like I am) the heatsink will be milled and not look like a normal finned heatsink. 100W is a lot for a dac, but its not really a lot on the greater scheme of things.

[analog_sa]

Finally got to see the board

And two lamish questions cropped up. Apologies if answers were already provided.

Is there a digikey p/n for the regulator sinks? None of what i have at hand seems to match the footprint well.

How do people mount the output caps? Offboard? None of the caps i have could possibly fit. Questionable if the bypasses for the caps will fit alone Holes too small as well...

As i'm a bit reluctant to solder Wima MKPs i am considering an amorphous Lundahl instead. Has anyone explored a similar route?

[qusp]

in one foul swoop you would decrease bandwidth and distortion performance with the TX, plus finding some that dont mind +/-45VDC across them without saturating.... not always an easy task

the holes are fine for any solid core lead ive got. both of the auricap options will fit the board, the stranded lead option of the auricaps leads may be too thick to fit through because they have 2 paralel stranded leads twisted together to match the 2 parallel caps inside, but are easily soldered on top, the radial lead one has solid core leads and fits. my vcap lead fits, my mundorf cap lead fits...

but ive been using offboard 'clusters' of auricap||VCAP CuTF near the XLRs up till now because I have another platform full of dac stuff that stacks on top so even if the caps fit they would make the whole stack too high and the dac input wiring longer than I would like. offboard is fine for the caps, perhaps the large DC bias on the wiring may even help to keep noise low =) but the IV conversion has already happened and the output is driven by a chunky power mosfet, so I really dont think its any problem just mounting them near the XLR.

if you are mounting off board, just remember not to install the 100K resistors to ground at the output pads and install them across the XLR instead (pin 2->1 and 3->1 and ground pin 1 to chassis ground. this is important to avoid/drain the DC transient you get before the caps are charged.

the heatsinks are just pretty standard EA-T220-38E but you could increase that height a touch.

[analog_sa]

Originally Posted by qusp

in one foul swoop you would decrease bandwidth and distortion performance with the TX, plus finding some that dont mind +/-45VDC across them without saturating.... not always an easy task

Let me guess, transformers are not your favourite coupling devices

Still, the voltage issue you mention is generally a non-issue - there is no dc potential across the windings as the two drains are at the same potential. Not sure if anyone can say exactly by how much this will deviate at different temperatures but i don't anticipate any issues. As for bandwidth and distortion, 80kHz is more that fine with me and i don't really see much point reducing thd below -80db.

Will certainly try it both ways, just have to find some space for the caps.

And thanks for the heatsinks specs.

[qusp]

80kHz is more that fine with me and i don't really see much point reducing thd below -80db.

then forget the IV stage and just connect the transformer to the output directly.... the whole point of this IV stage is to get great performance with only a handful of parts, great length in dissipation, bulk, power supply, heat are gone to, to gain this performance

now do you see my point of view?

actually I have used TX with ESS before (Bud Purvine's Onetics), happily for a while, but I did find they dulled dynamics some, effortless, but too 'smooth' for my liking.

you will still get DC across the windings, they are unlikely to be that symmetrical, even if you match everything on the D1, because they reflect the impedance seen on the other side, which is going to be unbalanced