Millett "Starving Student" hybrid amp - Page 240

Tom,
Outstanding job on the build guide (as usual). Can't wait to see some new build pics in a few weeks.

Thanks, Nate! Comments like that from you and Dsavitsk mean a lot, knowing what great builders you guys are.

More is coming in a couple of hours - I've finished the the "how-to" amp today and will finish up with the pics and posts tonight. The SSMH PCB and case is a rather unique assembly, but you will all find that with a few tricks, it goes together like a no-brainer, with little or no chance for mess-ups.

Thanks for all the hard work Tom. Just for reference, I was easily able to open the sockets by prying them (carefully) open at the seam until the center pin is a little loose. The best place for this is the little notch used for alignment of the halves. Then once you have a little wiggle on the center pin, pry up the pin itself against the bottom half (no longer working on the seam). A very small flathead screwdriver did the job with no damage. This should be useful for those who don't have drills (or live in an apartment where you can't fit a drillpress, like me), or who are adverse to drilling and possible breaking them.

OK - let's finish this thing!

15. Solder the Ground Wire to the Volume Pot -

This will essentially complete construction of the PCB except for the MOSFETs, which we'll leave for fitting up with the case lid in a bit.


Trim a wire so that its length is sufficient to curve over the top of the volume pot from the "G" pad on the PCB. As always, tin the tips of the wire with solder. Strip one end slightly - that one will go into the PCB pad. Strip the other end so that about 1/4" is exposed. That will leave plenty to solder to the metal body of the volume pot.

The metal body of the volume pot has a finish to it that will inhibit sticking with solder. So, we'll file the top a bit so that the solder will have something to stick to -


Once we have a patch filed, it's time to solder the ground wire in place -


16. Clean the PCB of Flux -
At this point - as noted earlier - we're basically finished with the PCB. So, let's clean it thoroughly. I'm a cheap-skate on some things and cleaning solder flux is one of them. Basically, I use some 90 cents a quart, Walmart 90% isopropyl alcohol as the rinse. I pour some in an old plastic butter bowl and use an old toothbrush and a paper towel.


It took me about 5 or 6 rinses, using a paper towel to pat off the alcohol/dissolved flux to get it acceptably clean. There may still be some white spots around the solder joints, but I'm not that picky.

Now on to the custom Beezar/Hammond case!

17. Prepare the Case Lid for Mounting to the PCB -
Dsavitsk's SSMH PCB design depends on mounting the PCB to the case lid - everything is keyed off of that. Pictured below is the underside of the case lid. The first thing we want to do is to stick on the Bergquist thermal pads. These will come in the heat sink mounting kits that come with the SSMH kits -


In this pic, I'm scrapping the anodizing away from the center hole. This hole will be used for a standoff that will be screwed to the center of the PCB. The pad is tied to the ground plane on the PCB, so if we make sure there's good contact with the case lid, that will increase our grounding resource.


Looks terrible and it feels bad to do this to a brand new, custom-mfg'd case, but it's on the inside and no one will see. The benefit is enormous, though, and little touches like these will give us a very quiet amp while many others may have trouble with hum and noise on other P2P tube amps.

Here is the standoff assembly. This will be provided in the kit with several washers. At least one washer is required for spacing along with the standoff - perhaps two. The only caveat to this you'll see in a moment. There are some smaller washers you can pick from and you'll want to use those next to the PCB, or you may short the standoff against the tube LED resistor - more on that later.


Essentially, what you see here (I will draw a detail on the SSMH website.) is a 1/4" socket head screw, washer, and lock washer. Those will go on the parts (capacitors, etc.) side of the PCB. The small washer and standoff will go on the tube socket side. We use a lock washer here because the screw on the PCB will be inaccessible from the outside, so we'll want that one to be locked in place. If it came loose, it might turn forever without un-screwing until we took the case apart. After that, we'll use just a flat washer and a longer screw from the outside to fasten the case lid to the standoff and thereby, the PCB.

This is critical!! Note the spacing between the standoff, washer/spacer and the tube LED resistor lead. Be certain that you have some space here as shown. Otherwise, disaster will ensue. Note also that the flat side of the hex standoff is also facing the resistor lead. This is an additional insurance that a space is maintained. Note that a small washer must be used here - a regular sized flat washer will contact the lead, so don't use one. Nevertheless, the spacing with only the standoff is not sufficient, so some additional spacing is needed and the small washer provides that.


Here we see the other side of the PCB and the pad and snipped lead side of the tube LED resistor. Note the spacing - make sure yours is similar or disaster will ensue!


18. Screw the Case Lid to the PCB -
As mentioned earlier, we use only a screw and a flat washer here - to ensure that if anything comes loose, it's the screw on the outside - the one we can get to! Depending on your build and your Beezar/Hammond custom case, you may need an additional washer/spacer on top of the standoff to make the best fit. I had to use one here, but I didn't on the first two I built. Again, YMMV, and actually - Hammond's MMV - due to extrusion differences, warping, etc.


You'll want to trial fit a few times to get the spacing just right. When you do, the PCB should fit three slots down from the top of the case as shown here in a couple of views:


Note the extra washer I had to use on this one.

Another view from the side:

That's great! I marvel at people such as yourself who are able to do this. I have tried for years and can never get those pins loose without drilling. If you can do it this way, though, by all means - do so!!

OK, so now we have the case lid attached to the PCB with the center standoff! The next thing we want to do now is to complete the MOSFETs and heat sinks. This is much easier now than attempting to do it before, because the center standoff has determined the proper distance between the PCB, MOSFETs, and case lid.

19. Insert the MOSFETs into the PCB Pads -
With the PCB down to the 3rd slot on the case, there is only one way this will work - you must bend the MOSFET leads at 90 degrees directly at the plastic body. The pic shows the MOSFETs before and after:


Here we see one MOSFET inserted into the PCB pads, and one in an inbetween position. Work carefully doing this, or you'll scar up the Bergquist pads and perhaps loose heat transfer integrity, or loose insulation capability. Be patient - it may seem like the leads won't fit without a greater clearance between the lid and PCB, but they will. Ensure that the leads on the MOSFETs are straight and equally spaced - that will help things along. Once you get them inserted, it will have seemed so easy that you'll wonder why they didn't go in right away in the first place.


20. Install the Heat Sinks -
Next comes what may be the most frustrating part of building the SSMH PCB - at least it is for me, usually. Before the frustrating part, though, let's review the heat sink solution for the SSMH PCB/case and note how the heat sinks are aligned to the case:


Note that there are four mounting holes on each heat sink. We will only use two of them - the holes that are the closest to each other. However, note that the two holes perpendicular to those are offset - one is at a greater distance from the closer two holes than the other. Be sure that offset is to the outside on the SSMH case - as shown here. Otherwise, the heat sinks will not fit together on the case lid.

Once we've established that, our next task is to coat the bottom of the heat sinks with heat transfer goo. You see, the primary contact is between the MOSFETs, the Bergquist pad and the case lid. However, to enable the heat sinks to add their heat dissipation capability to the assembly, we need the best possible contact between the heat sinks and case lid. To do that, we need to use heat transfer goo between the heat sink surfaces and the case lid.

I should've taken some photos, but I guess I got too frustrated again. Anyway, you'll want to use a toothpick or similar to spread - very thinly some heat transfer goo on the bottom surface of the heat sinks. Once you do that, you'll place each one in position - one at a time - until you insert the screw assemblies.

In the heat sink kits that come with the SSMH kits, there's two longer screws (1/2") and two shorter screws (3/8"). Use the shorter screws on the second hole of the heat sink and use the long screws on the MOSFETs that use the first hole of the heat sinks. When inserting the screws, be sure you take the trouble to "seat" the shoulder washer into the MOSFET tab - it won't do it by itself. Essentially, we have a screw and washer on top of the heat sink and case lid, with a washer, lock washer and nut underneat. The MOSFETs are a bit different in that they present an additional thickness from the tab and also the shoulder washer - that's why the longer screws are used for the MOSFETs.

I'm sorry I skipped some needed photos, but here's the final assembly shown in detail:


Now, why do I say this was frustrating? Because - once you put the heat transfer goo on the bottom of the heat sinks, they'll slide like they're on ice. All the while, you're trying to thread a couple of small screws through. When they slide, the goo goes all over the parts of the case that will be visible to everyone once completed. So, it's kind of like they're out to get you. Be patient, use a good pair of needlnose pliers to insert the screw assemblies - and be sure to go extra light on that heat transfer goo. If all of this scares you, then don't use the goo, period.

One thing you should be careful of, though - be sure you don't torque the MOSFETs down so tight that the tabs cut through the Bergquist pads - that would ruin the insulating capability and cause a short. So, tight and secure - but don't torque.

Oh - by the way:
21. Solder the MOSFET Leads to the Pads on the PCB -
Piece of cake at this point, but don't forget to do it!!

We're almost finished!! Here's the case lid/PCB assembly completely finished and inserted into the case for a trial fit (and intermediate admiration of our work):


I used some super-duper heat transfer goo on this one - it's white.

Coming down the home stretch!!

We've finished it all except for the endplates. What's really nice - there's no work at all on the front plates. Once you slide the assemble into the case, that's it - the endplate is already drilled to match the volume pot shaft and the headphone jack.

The back plate is not as simple, but still not too bad. I get discouraged at this part, though, because to me, wiring is so tedious. What's nice and makes up for that, though, is that you don't have to drill the holes through the back plate and worry about dimensions, hole sizes, or whether it will all fit - it's already done!

So, given that, the only thing we have to worry about is the connectors on the back plate. These are the Power Input Jack, the Power Switch, and the RCA Input Jacks. These are pictured here in a blowup of our kit parts layout shown way back in the earlier posts:


22. Install the Power Switch -
The power switch, while rated for much higher voltage, is plastic. Thus, it will melt enough that the mechanism may be damaged if you use a soldering iron to connect wire leads to the tabs. Instead, use a couple of fast-on connectors as shown here. These are available in every hardware store. In fact, the ones shown here are for much larger tabs, but they work fine for the power switch, regardless.


Be sure you crimp them so that the wire is snug. Pull on it and work it back and forth to make sure you have a good connection. I have to crimp it in two places, but maybe that's because I use the cheap tool shown in the photo.

Before we install the power switch, we'll want to prepare the back plate for the connectors. As with the case lid center hole, we want to scrape the anodizing away from the holes so that the connectors' negative connections will make contact with the case. Negative = Ground in the SSMH, so again, our ground resource will be increased when we do this. Just an FYI, but the RCA jacks fit snuggly enough that the edges of the drilled hole may be sufficient to provide contact. Still, if you're scraping/filing anyway - might as well do them all (except for the power switch - that's all plastic, so it won't do any good).


Note - be sure you know which side is which! The outside of the endplates have counter-sunk mounting screw holes. That's the absolute indicator - do your filing/scraping on the other side. The counter-sunk part of the holes are the outside.

23. Install the Power Input Jack, the RCA Jacks -
Similarly, install the power input jack and the RCA jacks. Both require soldered connections, both ground and non-ground (or signal). The pic shows my usual workspace once I start wiring connectors - all h*ll breaks loose and the whole table turns into a mess.


In the photo, we can see the power input jack already wired and screwed into the back plate (more on that later). The power switch has already been installed on the back plate, and I'm in the process of finishing the wiring connections on the RCA jacks.

Here's a glamour shot of my soldering one of the ground leads on the RCA jacks. Some use a single ground wire and solder it to both tabs of both RCA jacks. However, I think two ground wires - one soldered to each tab separately works better.


The backplate finished with all connectors installed and the wire leads soldered. Note that when measuring the length of the wire leads, insure that you have enough slack to move the back plate up and over the main case body - this is the way that dis-assembly will be done. Also, note that the signal wires from the RCA jacks much be much longer to reach the input signal terminal block.


An outside view:

Note the insulators on the RCA jacks. Actually, the RCA jacks are best without insulators. As shown in the photo previous, there are no insulators on the inside - this is so the RCA jack grounds can make contact with the case. On the outside, the insulators are purely cosmetic. You'll find that it's almost impossible to plier the jacks down from the outside without scratching a circle into the backplate finish - the insulators will protect the finish and allow easier tightening.

With the power input jack, the hole is purposely sized larger than needed. This is because Radio Shack makes a similar power input jack that's larger in diameter. I left the hole big enough in case some want to use that jack. The jack in the kits will benefit from an additional finishing washer - simply use one of the washer/spacers that come with the headphone jack - not all of them are needed for the headphone jack.

24. Install Wiring and Back Plate -
Trim the wire leads to length if needed, but remember, there's a huge space behind the PCB - plenty of room to take up slack. The back plate must be able to move up and over the main case extrusion for convenient disassembly, so quite a bit of slack is needed.


Note also that the input signal terminal block is quite close to the sides of the case when assembled, so bend the wire leads at a 90 degree angle next to the terminal block and trim to fit. This makes it easy to obtain enough clearance for the input wiring. I like to braid mine in a Litz braid or similar, but I'm not sure it means anything over this distance.

25. Assemble the Amplifier -
Hey! We're done!

Be sure to use the endplate bezels. Don't worry - you can slide the bezel over an endplate even when the wiring is connected. For the front plate, use one spacer on the headphone jack behind the endplate - that should be sufficient for spacing.


Pictured here, I've assembled it without the screws. If everything works, I'll disassemble it, tap the case holes and use 6-32 machine screws. That's not really necessary, though, the supplied Hammond screws will work fine - but don't use them until you're certain the case and the amp all work fine.

Back view:


And we add the volume knob - the idea is to get it as close to the endplate without scraping anywhere in its travel. This may be sometimes more difficult than it sounds - it depends on how well you aligned the volume pot when you soldered it way back when.

Finished!!

All fired up and glowing - I used ocean-green LED's for this one.


Give your Starving Student time to burn in. I'm not an advocate of hundreds of hours like some claim for headphones, etc., but your Starving Student will definitely change tone in the first hour or two. When you first power it up, it will sound bassy, thick and "cloudy." Within an hour or two, the tone will have changed 100% - more detail, more transparency. Things will continue to improve over the next 12 hours, with subtle changes after that as more detail and transparency comes in.

The electrolytics and Wima caps take time to burn in - not hundreds of hours, but definitely over a day or two - that's a fact!

Very nice writeup, will this also be going onto diyforums?

Very cool.

Excellent work Tom.

That is truly outstanding, a very good guide indeed. Thanks.

Done.

Thank you Tom for beautiful tutorial. Very inspiring. Is it possible to order whole kit by one click on BEEZAR.COM?

Sorry, no. All the original run of kits were sold. Once the cases come in and I ship out the existing kits, I'll re-evaluate my tube stock and decide whether to offer more kits at that time.

Thanks, Smeggy!!