Prototypers wanted

[Nebby]

You forgot to jumper the primaries on the transformer

A to B and C to D

Didn't get that memo..... Thanks Kevin!

Tubes are now lit up! Sometimes it's the simplest things.

[kevin gilmore]

While you are at it, you have to jumper the wires on the side to the pot too...

[Pars]

Coupling caps: e-speakers is out of 4.7uf; Madisound carries them (Clarity Cap SA 4.7uf, 630V). 35 x 38mm. I know I saw a post or one of the emails discussed max physical size, but I assume the ones from madisound are fine?

[Nebby]

I used the 4.7uf SA's from Madisound, they're 45.6mm long so they just barely fit, though you won't be able to sit them flush with the board as the cap itself rests against the leads. You can see the size in my picture a couple of posts up.

Kevin, thanks, I got those after I noticed nothing was coming out from the jack. I'm just full of fail today.

It's playing music now and it sounds great

[mypasswordis]

Yay for a successful build! I want to hear it in a quiet environment (heard TomB's build at CJ) for a bit and we live in the same state, so if you're up for it....

[Smeggy]

Congrats Nebbs, nice job on keeping the smoke in!

[kevin gilmore]

these are actually great caps, available from mouser, and reasonable.

And they fit too.

598-936C4W4P7K-F

[kevin gilmore]

If you insulate the lm338 with a thermal washer and plastic mounting washer, it should be easy to secure the heatsink to the chassis.

the rest of the parts should be in today. And i got a bit sloppy with the machining as its very hard to hold stuff this thin down...

http://gilmore.chem.northwestern.edu/dsavitsk1.jpg

http://gilmore.chem.northwestern.edu/dsavitsk2.jpg

http://gilmore.chem.northwestern.edu/dsavitsk3.jpg

http://gilmore.chem.northwestern.edu/dsavitsk4.jpg

Now that i know the exact dimensions it should be easy to make new panels perfectly NC'd

out of .125 material that is thick enough for me to hold it in place.

[luvdunhill]

Tom:

A few more dimensions that might be nice to have on the drawing (though they can be gotten elsewhere easy enough)

- height of case

- height of IEC hole

- diameter of three screw holes on the rear

Kevin:

typically, the bezels on this Hammond series go between the end plate and the extrusion

[kevin gilmore]

Kevin:

typically, the bezels on this Hammond series go between the end plate and the extrusion

Yeah... About that... The board is not long enough, and the parts don't fit thru the panel right if

you put the plastic piece on first. !!!!

So if you assemble it correctly and push the board to the back end, then the front end parts are

.126 inches off.

Now for me its easy, just take .2 inches off the chassis. But i would have to do it at work

because i would take 1 swipe with the top on, and i need a 4 inch long end mill for that.

And a much bigger mill.

height of the case measures 2.0935 (back/front panel not including the plastic surround)

height of the center of the iec hole is 1.0595 from the bottom (center of ground pin)

all 3 screw holes should be #4-40 body drill size.

diameter of the hole for the rca jack to fit the plastic thru is .4055 inch

I will add 2 more holes to mount the iec jack to the back of the back panel

Edited July 2, 2010 by kevin gilmore

[luvdunhill]

So if you assemble it correctly and push the board to the back end, then the front end parts are

.126 inches off

interesting. So, does this extra room (if push all the way toward the back like you said) actually cause any issues? Seems that the pot would be fine if you add washer between the pot itself and the panel, same the TRS jack... the switch shouldn't need a washer at all...

[dsavitsk]

Yeah... About that... The board is not long enough, and the parts don't fit thru the panel right if

you put the plastic piece on first. !!!!

So if you assemble it correctly and push the board to the back end, then the front end parts are

.126 inches off.

Hammond made these (about) 13 inches long. The original two were too short. This is one of the things that will get worked out in the finals

[kevin gilmore]

The other trick is what to do about the top panel.

Some of the tube sticks up, but not much. So there would have to be

a fairly large diameter hole, otherwise there is no way to pull the tubes out.

Or make reasonable holes, and slit the cover in two, so you slide the cover out to

change the tubes. I'm kinda leaning towards that approach.

The final parts just showed up. Gotta go...

There are plastic ends available, which are one piece, and would fit perfect.

And be much easier to machine.

Overall, pretty good for a first round.

[kevin gilmore]

My unit is complete and works fine.

Very quiet for a tube amp.

Will swap to the inductor when it shows up.

Going to add 2 more holes in the back panel and add a grounding

safety wire there, and put tube holes in the top panel tomorrow.

[TomB]

interesting. So, does this extra room (if push all the way toward the back like you said) actually cause any issues? Seems that the pot would be fine if you add washer between the pot itself and the panel, same the TRS jack... the switch shouldn't need a washer at all...

Not sure what's going on here, but I agree with luvdunhill. Mine worked fine with the bezels, but would not without - at all (or with the backplates on the inside surface of the bezel). For instance, without the bezels, the pot sticks out far enough that you'd have to drill for the outside boss on the RK27. If you do that, there's nothing for the mounting nut to tighten down on except the pot itself (the endplate becomes superfluous). The only downside with the clearance that the bezels give you is that the locating pin on the RK27 sticks out enough that it rubs the inside diameter on my Partspipe knob, making it feel as if it's binding.

As for the headphone jack and the impedance switch, there are plenty of spacers to make things fit with the Neutrik and once you drill a hole big enough for the switch lever boss, the clearance is elemental. So, the only issue is with the pot. The extra clearance that the bezel gives is enough to allow you to clamp the endplate between the pot's boss and the shaft nut.

On the backplate - with the bezel, I actually had to add #4 washers as spacers behind the backplate for the IEC mounting screws. Other than that, it fit perfectly. (IOW, the RCA jack assembly should not be flush with the IEC - more like 1/32" behind the mounting surface of the IEC. All the mounting screws are 4-40's, but you have to tap the plastic mounting on the RCA jack assembly - no nut on the back of that 4-40.

[n_maher]

I got all the resistors installed in a short burst of free time this afternoon. Hopefully I'll get a bit more done later but I'm still waiting on the output coupling caps which should have been here by now but are not.

[kevin gilmore]

Not sure what's going on here, but I agree with luvdunhill. Mine worked fine with the bezels, but would not without - at all (or with the backplates on the inside surface of the bezel). For instance, without the bezels, the pot sticks out far enough that you'd have to drill for the outside boss on the RK27.

And that is in fact what i ended up doing. I tried it against the smaller boss on the pot, and that did not fit right either.

I'll try again tomorrow and add a very thin spacer to the pot to get the panel off the outside boss.

If there is a part number for extra aluminum front and back panels, i can certainly try again.

My chassis is definitely longer than the circuit board. Probably by at least .075

Its clear (at least i think) that the back panel has to be snug with the iec socket and the rca jacks.

The main part of the rca jacks. This is where at least .035 of the difference comes from.

If you do it the other way then the amount of ground available for the rca connectors shrinks, and

a number of the rca male connectors i tested don't fit in all the way and are loose.

The mounting hole for the rca jack was designed to be a self tapping screw for plastic.

Edited July 3, 2010 by kevin gilmore

[kevin gilmore]

I'm going to make another comment, and this is one of those philosophical things, some people do it one way

and others do it completely differently.

If you pay attention to underwriters laboratories, and the international electrical code, then for SAFETY

reasons, the 3rd wire of the iec connector goes to chassis ground. Pretty much everyone agrees with this.

Two wire power plugs are another thing entirely, and are real bad for audio as there is always a resistor

between neutral and chassis ground (or the whole thing is double insulated) Remember this is all about

safety, not good sounding audio.

But for minimum noise and ground loops, it is usually (but not always) better to completely float the

circuitry inside from chassis ground. The rca jacks certainly allow for this, and so does the neutrik

jack.

That is not possible given the current layout of the board.

For smaller systems with just a source and this amplifier, it is not going to make any difference.

Mix it up with a pile of other electronics, and it might cause trouble.

For example on my T2 there is a toggle switch inside the amp chassis that can disconnect circuit

ground from chassis ground.

[kevin gilmore]

So i'm definitely done sans knob and inductor.

I measured my chassis length as 13.035 with this

http://gilmore.chem.northwestern.edu/bigger2.jpg

(yep its an old picture)

Which kind of makes sense when you add .125 in addition with the

plastic bezels and things don't fit right. If you wanted to make it perfect

with the current circuit board, then a chassis length of 12.875 makes more

sense, then you notch the plastics for the board. Then everything fits flush.

http://gilmore.chem.northwestern.edu/dsavitsk5.jpg

you can see the grounding lug on the inside of the right screw.

I kind of like it better without the cheap plastics anyway.

I put in 2 x 30mm holes for the tubes.

http://gilmore.chem.northwestern.edu/dsavitsk6.jpg

Which gives enough room to get a tube puller in there on

the base of the tubes.

[dsavitsk]

The other trick is what to do about the top panel.

Some of the tube sticks up, but not much. So there would have to be

a fairly large diameter hole, otherwise there is no way to pull the tubes out.

I think we are going to switch to a split case design so that the top just lifts off (rather than slides as with the Hammond) to allow easier tube access.

I'm going to make another comment, and this is one of those philosophical things, some people do it one way

and others do it completely differently.

If you pay attention to underwriters laboratories, and the international electrical code, then for SAFETY

reasons, the 3rd wire of the iec connector goes to chassis ground. Pretty much everyone agrees with this.

* * *

For example on my T2 there is a toggle switch inside the amp chassis that can disconnect circuit

ground from chassis ground.

As you note, circuit ground and safety earth are connected together. I kind of like it that way for simplicity. But, we'll have to see if anyone has hum issues. I'd rather not add a toggle for both cost and space reasons if we can avoid it. And, since headphones are on people's heads, in a HV setup, I do feel better with everything connected to earth.

[jdkJake]

Looks to be a great new project. I am most interested in hearing a transformer-coupled design.

Let me know if you need more volunteers in the next round of prototypes.

My soldering iron and I are standby (along with my wallet) ;-)

jk

[Beefy]

I'd rather not add a toggle for both cost and space reasons if we can avoid it. And, since headphones are on people's heads, in a HV setup, I do feel better with everything connected to earth.

Is there room between the power and audio inputs for a ground loop breaker between earth and signal ground? You would also need to isolate the inputs and output from the chassis, but it might be an option that prevents hum issues across the board without compromising safety.

[kevin gilmore]

Actually you have it backwards. Because of the circuit lands on both sides of the board, chassis ground is pretty much connected to circuit ground anyway.

Using a cheater cord (same as cutting the earth ground to circuit ground) is definitely not a good idea.

[n_maher]

It occurred to me looking at my board this morning as I left for work that I may not have anything suitable for the small heatsinks that are required. I looked back through this thread and found one veiled reference to using tinfoil, something I'm not too excited about the prospect of, but I'm wondering what the actual part is that is required at these positions?

[luvdunhill]

that's my fault Nate. The two heat sinks are available at Digikey, I'm not sure about Mouser. Make sure you don't get that crappy version that TPA uses that has the three holes in in, one of which is conviently placed right in the middle of the device Anyways, the recommended parts are:

8 1 HS346-ND HEATSINK TO-220 W/PINS 1.5"TALL 0 1.49000 $1.49

9 2 HS216-ND HEATSINK TO-126 VERT MNT SLIP-ON 0 0.41000 $0.82