High Powered HTPC: Broken Krell Preamp Repurposed

[ChairmanDev]

I wasn't sure whether to put this in the build log or modding section but I'll be updating this thread as I make more progress so I guess it goes here.

This won't be the smallest rig on here, but at 30L it matches some of the bigger ITX/mATX cases on the market. However, I feel that it does follow that mantra of stuffing as much as possible into a given space. My past two rigs have been pretty small with a Node 304 and a 6L Wesena. Now I think it's time to make something a little more interesting.

I've been running Krell equipment for years now in my home theater system and I figured that it'd be an awesome project to find a broken, matching preamp chassis for cheap to repurpose into a computer. I've always wanted a high powered living room PC to use as my main rig. I could've easily gotten any off the shelf HTPC case but this option matches perfectly with the power amps I have. Well I finally found one for a good price, roughly $175, and it came in yesterday.

Mocking stuff up - probably gonna be putting an matx board in here.
Dimensions L x W x H: 381 mm x 483 mm x 153 mm
30 liters

Spoiler: Pictures

Don't think I'm gonna be cutting holes for fans anytime soon but there's plenty of ventilation throughout the chassis.

I then started to build the backplate in Inventor after quite a bit of measuring and head scratching. Since the GPU in its standard orientation is too tall for the case, I decided to have the GPUs mounted horizontally, one above each other. With this design, I can stuff in an matx board and honestly I don't need much more than that.

There's not much clearance between the pcie slots and the bottom of the lower card but I still have some room to adjust spacing. I'll have to get my hands on a flexible pcie riser to see what's up. I could flip the graphics cards around and make it a bit easier to route the pcie risers but I think it looks a lot cooler to have them facing up. I probably won't be doing SLI for now but to have the option available would be nice. Plus, this case is too big to only have room for just one graphics card!


Does anyone have any advice as to how I can improve my design? I'm gonna be transferring my main rig into this thing so I'd like it to be as well thought out as possible before I get to actual fabrication. Thanks.


UPDATES:

-7/12​

Spoiler: Possible AIO/watercooling setup?

To avoid cutting the front panel, I've tried to design a duct that routes airflow from the bottom vents. A 240mm radiator could fit but would make cable management even harder. Some cables can be routed behind the duct and looped back out.

Fans only:

With 120mm radiator:

Top mounted 240mm radiator, space is getting tight.

-7/13​

Redesigned back plate for easier manufacturing.

-7/17​

More back plate stuff.

-8/7​

Back plate is in! Thank you Protocase!

 

[msystems]

Wow, nice modeling there. If you do keep the graphics cards like that, allow enough room for your riser to bend and pass under the cards of course to reach the other side. Maybe figure out which riser first. The HDPlex or 3m riser should be well suited.

You also could pass the riser over the top of the card I suppose, and have it sit flush against the bottom of the case for support + heat transfer. You might need to design something to support the weight of the back of the card, because you are taking away the natural support of the PCIe slot.

 

[ChairmanDev]

Wow, nice modeling there. If you do keep the graphics cards like that, allow enough room for your riser to bend and pass under the cards of course to reach the other side. Maybe figure out which riser first. The HDPlex or 3m riser should be well suited.

You also could pass the riser over the top of the card I suppose, and have it sit flush against the bottom of the case for support + heat transfer. You might need to design something to support the weight of the back of the card, because you are taking away the natural support of the PCIe slot.

Hey thanks! And yeah I needa get my hands on a riser first, then I'll mess around with the gpu positioning/spacing. The lower card won't be able to sit on the bottom of the case cause it's an matx board. Pretty much both pcie slots are under the cards. I'll probably make a bracket or something that'll support the other end of the cards. Might also incorporate some of these expansion slot brackets from mountain mods for further support.

I'm thinking about putting in fan ducts for those vents in the front so I can pull in some extra air. Maybe some hard drive cages as well to occupy that empty space.

Also, just started looking through your build log. That's something else LOL. Never would've thought a passively cooled build like that would be possible in such a small case.

 

[iFreilicht]

Hm, it seems like the lower card will have a bit of trouble getting air and will also block the x16 slots you need for actually connecting the cards, so maybe you could do something about that? Any plans about using the front controls of the Pre-amp for something on the PC? That would be pretty interesting.

 

[ChairmanDev]

Hm, it seems like the lower card will have a bit of trouble getting air and will also block the x16 slots you need for actually connecting the cards, so maybe you could do something about that? Any plans about using the front controls of the Pre-amp for something on the PC? That would be pretty interesting.

I'll probably have to push the lower card even further up against the bottom of the upper card if I can't get enough clearance for pcie risers. But as you said, this may choke the lower card even more. Incorporating some fan ducting to pull in air from those front lower vents may help that a bit though.

I'd definitely like to get the front panel working but I have no idea where to even start with that.

To even have that screen working again would be pretty damn cool.

 

[iFreilicht]

Hm, what about watercooling the lower card? Then you could make it single slot. Or watercool both while you're at it

I'd definitely like to get the front panel working but I have no idea where to even start with that.

To even have that screen working again would be pretty damn cool.

Oh that would be so awesome! Well most of the controls are LEDs and buttons it looks like, one could directly solder wires onto those or reverse-engineer the PCB they're sitting on and control that with an Arduino quite easily. The display would be more complicated, but I'm sure that could be reverse-engineered as well. If you found a part-number on the back of the display you might even find the whole datasheet.

It's certainly doable

 

[ChairmanDev]

Hm, what about watercooling the lower card? Then you could make it single slot. Or watercool both while you're at it



Oh that would be so awesome! Well most of the controls are LEDs and buttons it looks like, one could directly solder wires onto those or reverse-engineer the PCB they're sitting on and control that with an Arduino quite easily. The display would be more complicated, but I'm sure that could be reverse-engineered as well. If you found a part-number on the back of the display you might even find the whole datasheet.

It's certainly doable

Watercooling is definitely a possibility that I'll look into. LinusTechTips just put out a video about a kit that EK has that looks promising.

I tried looking up any part numbers on the board and nothing came up. However, I did find this quote from Krell:

"WE DO ALL OF OUR ENGINEERING IN-HOUSE INCLUDING ANALOG, DIGITAL, MECHANICAL, AND SOFTWARE DESIGN. THE TRANSFORMERS ARE ALL CUSTOM MADE FOR THEIR SPECIFIC REQUIREMENTS. EVERY TRANSFORMER IS MEASURED FOR NOISE AND EXCESSIVE MAGNETIC FIELDS WITH THE OUT OF SPEC MODELS BEING DISCARDED VIA RECYCLING. EVERY AUDIO CIRCUIT IS A KRELL DESIGN USING INDIVIDUAL CIRCUIT ELEMENTS. WE DO NOT USE GENERIC OP AMPS OR INTEGRATED CIRCUITS FOR OUR AUDIO SIGNAL PATHS."​

I take that as I'm on my own in terms of reverse engineering this haha.

 

[ChairmanDev]

So I did some tweaking. 3M had 3D files available for their riser cable. I now have a little over a 1/4 inch of clearance. Are the ribbons flexible enough to bend into that space?

 

[iFreilicht]

I tried looking up any part numbers on the board and nothing came up. However, I did find this quote from Krell:

"WE DO ALL OF OUR ENGINEERING IN-HOUSE INCLUDING ANALOG, DIGITAL, MECHANICAL, AND SOFTWARE DESIGN. THE TRANSFORMERS ARE ALL CUSTOM MADE FOR THEIR SPECIFIC REQUIREMENTS. EVERY TRANSFORMER IS MEASURED FOR NOISE AND EXCESSIVE MAGNETIC FIELDS WITH THE OUT OF SPEC MODELS BEING DISCARDED VIA RECYCLING. EVERY AUDIO CIRCUIT IS A KRELL DESIGN USING INDIVIDUAL CIRCUIT ELEMENTS. WE DO NOT USE GENERIC OP AMPS OR INTEGRATED CIRCUITS FOR OUR AUDIO SIGNAL PATHS."

I take that as I'm on my own in terms of reverse engineering this haha.

Meh, this only applies to the audio equipment, which I'd argue the front panel is mostly not a part of. Still, if you don't find any info on top of the display, that doesn't really matter.

 

[msystems]

The 3m riser is very flexible, it also can be bent to an extreme angle (once). I think the spec sheet even goes into the bending.


Ah yeah, here it is:

Static (one-time) fold
Bend Radius: 1.0 mm
Bend Types: 45, 90, 180°
(flat fold)


Meets signal integrity
specifications (impedance,
s- parameters) after a one-
time 1 mm minimum bend
radius fold

http://multimedia.3m.com/mws/media/...ci-express-ext-cable-assembly-series-8kxx.pdf

 

[ChairmanDev]

The 3m riser is very flexible, it also can be bent to an extreme angle (once). I think the spec sheet even goes into the bending.


Ah yeah, here it is:



http://multimedia.3m.com/mws/media/...ci-express-ext-cable-assembly-series-8kxx.pdf

Wow, 3M does not mess around with the details. Thanks for the info.

 

[ChairmanDev]

So I read through a bunch of the info resources Protocase has along with the huge thread Aibohphobia has for his STX 160 build (really should've done that before I designed the backplate but oh well). The original backplate design I had would be annoying to actually make. I did a bunch of tweaking and added more detail. It's not perfect and I probably still have more to adjust but I hope it makes the bending/folding process a bit easier.

Spoiler: Original

Spoiler: Updated

Next step is to measure out all the screw holes. I'm beat for today so maybe tomorrow.

 

[jeshikat]

What CAD program is that?

And it may be a side effect of the feature tree, but I don't see any reason to have the bend relief cutout for the upper PSU mounting tabs since they're not bent.

 

[ChairmanDev]

What CAD program is that?

And it may be a side effect of the feature tree, but I don't see any reason to have the bend relief cutout for the upper PSU mounting tabs since they're not bent.

It's Inventor. I used the sheet metal mode for pretty much all of this, super helpful.

Yeah that relief comes from me just doing it a silly way. I bent the whole lip inwards and then bent the mounting tabs back out. I've now edited that post to reflect the change. Thanks for the tip!

Also, I'd like to thank you for making that build guide. Crazy amount of information in there that helped a bunch with this.

 

[ChairmanDev]

Finally got around to getting mounting holes/nut inserts lined up. It's coming along nicely.

Flattened out with all the bend lines.

EDITED TO REFLECT jtd871's TIPS

 

[jtd871]

Why are you even doing bending at all around the PSU support?! Just do a cutout (I'd suggest rounding the resulting interior corners) and keep the mounting holes.

 

[ChairmanDev]

Why are you even doing bending at all around the PSU support?! Just do a cutout (I'd suggest rounding the resulting interior corners) and keep the mounting holes.

It's quite possible that I got a bit extra with the bending. I thought it looked nice but it's true that it really only serves to make the part more expensive to make.

There, back to practicality haha. Thanks for the tip.

------------------------------------------------

One requirement of this project is to preserve the original front panel for ultimate sleeper status. However, I would like to get some more airflow going through the case. My original idea of using a duct to pull air from the vents on the bottom of the case would work but felt clunky and wasted a lot of space. I've been playing around with different designs and this one seems like it could be the cleanest.

There are two aesthetic pieces on the front that look like this. The originals don't have slots cut into them but I'm hoping to use these slots as intakes.

A duct would then be secured on the backside where fans/radiators can be mounted.

Any thoughts? Could enough air even be pulled through?

 

[Phuncz]

This is coming along nicely, very interesting to see the progress made !

 

[iFreilicht]

Any thoughts? Could enough air even be pulled through?

Sure can, but the slots have way lower surface area than the fans, so airflow would increase rapidly at that point, which would lead to increased noise. Not something you'd want for an HTPC, really. Inside the chamber, air needs to flow quickly as well, and the middle fan would not get any air at all. So maybe just use two fans and make the duct a little deeper?

If you can, rather put vents in the side of the case than the front.

 

[ChairmanDev]

I finally got the backplate in. Big thanks to everyone at Protocase who helped me out with this. It turned out pretty damn awesome. Pictures suck for now cause I'm tired as hell. I'll get some nice ones up sometime later.


I still got a few things left to do. I'll have to get my hands on an mATX mobo when I do my next hardware upgrade... gonna be an ITX board in there for now. That blue LED you see in the fan hole is a power button/LED I scavanged from another case. I won't have a legit power button until I get a redesigned front panel.

Maybe something out of wood?