LA2A PCB ver 2.0 build thread

[Greg Dixon]

Were the tubes on the back or inside?

 

[chingon]

Inside along with the TB4. The PSU is also mounted on the outside. I haven't made a top cover yet. This is the first time I worked with metal and it really shows. Especially when I got brave with my pops arc welder and burned a couple of holes in the case. I also didn't plan out how I was going to route the wiring so its kind of all over the place. I didn't have any shielded cable so I got one of my mic cables made of Canare Quad and hacked away with what I needed. The mic cable is a little to thick and not very flexable but it works. The PCB standoffs I got from radio shack are way to long for a 2 space rack so for the meantime I used some 4-40 screws and nuts and used them as little legs/stilts to float in the case. this makes it height adjustable. THe painters tape is there for good measure . This set up is temporary until I figure out a way to mount the PCB. Maybe I'll get brave again with the welder and tack 2 nuts on top of each other and tack that to the case. I suppose I could cut the standoffs to a shorter lentgh and use them.
I found a funklogic 2 space cocobolo rack filler that I had stashed away in my closet for a few years so I plan on making a new faceplate out of steel again this time without bending the crap out of everything and line up the pots and switches in a straight line and use the cocobolo as a veneer.
I havent racked it up yet so i'm not sure if the thin faceplate will be able to hold the weight of the heavy box and don't even know if the rack holes line up correctly. lol....
It sounds pretty good though. I've never used an actual LA2A so I can't compare. I was just comparing it to the UAD LA2A and the damn plug sounds just like my unit. Not sure if thats a complement or not.

 

[wmb]

Bold. I used pretty much the same cable. It was a pain, especially the braided shield.

 

[Greg Dixon]

[quote author="chingon"]
Its a real tight squeeze and the box looks like ass because all I had to cut the metal with was a jig saw.[/quote]

I used a jigsaw for my meters too, but you'll notice mine (and the G1176 below it) are front mounted. They cover some very rough work. I would never attempt a rear mounted VU with my current skills and tools. It would look good though.

 

[idylldon]

[quote author="wmb"]Bold. I used pretty much the same cable. It was a pain, especially the braided shield.[/quote]

Mogami makes a nice wire for the inside of boxes because it's pretty flexible and small in diameter. They call it "console" wire, and I've used it in many projects and never had any issues. Check it out.

Part numbers (these might be Markertek numbers, though I think they're the same as Mogami numbers):

Mini Quad Console Wire: 2799
Console wire w/drain: 2944

Cheers,
--
Don

 

[Greg Dixon]

The second one sounds like the stuff I use. Canare L-2B2AT. I use it in my studio for everything except mic leads. I buy it in 200 metre rolls. Just ordered my 4th or 5th roll yesterday.

 

[codered]

Hi Folks,
Firstly my thanks to Drip for really dumbing down this project
I am trying to purchase an enclosure which is closest to the actual one.The bloo case seems to be the closest.Where can I get that?I've searched high and low and the closest seems to be a Hammond hinged case.I hope you guys understand what I'm talking about (the case with rack ears)

 

[chingon]

[quote author="Greg Dixon"]
I used a jigsaw for my meters too, but you'll notice mine (and the G1176 below it) are front mounted. They cover some very rough work. I would never attempt a rear mounted VU with my current skills and tools. It would look good though.[/quote]

Your metal work looks alot better than mine. I think a dremel would have worked out better and wouldn't have bent the metal up. How were you able to get your rack ear holes to look the way they do? I couldn't get close to that. I ended up with some mangled looking holes that don't line up with the rack rails. Go figure. I'm going to have another go at making another faceplate. The metal is only around $3 for the size i need so its no big deal.

 

[Greg Dixon]

[quote author="chingon"]How were you able to get your rack ear holes to look the way they do?
[/quote]

Easy, I didn't. I bought one of these.

http://www.electusdistribution.com.au/productResults.asp?form=KEYWORD

That's why all my stuff is the same colour. I have a wholesale account with that distributer, so I pay about $60 AUD for a 3 unit rack. Like I said, my metalworking skills aren't very good.

 

[idylldon]

[quote author="codered"]Hi Folks,
Firstly my thanks to Drip for really dumbing down this project
I am trying to purchase an enclosure which is closest to the actual one.The bloo case seems to be the closest.Where can I get that?I've searched high and low and the closest seems to be a Hammond hinged case.I hope you guys understand what I'm talking about (the case with rack ears)[/quote]

Make sure the new PCB will fit into the enclosure as I don't think the Bloo case is large enough. This is a BIG PCB. I used a Hammond chassis and a 3U front panel to kind of get the look of an LA2A while accommodating the ver. 2 PCB.

Cheers,
--
Don

 

[codered]

idylldon,

Thanks for the input..actually I hadnt thought about the size! The specs & availabilty of the Bloo case are nowhere to be found.
I have a question about the toobs on the PCB - all the original LA2As I've seen tend to become *really* hot especially if you fire them up early in the morning & run them for marathon sessions.So is this going to be an issue for longevity of the componentswith the tubes inside the enclosure.
Also is it Ok if I mount the tubes outside and route wires from the PCB- would that be a bait for any hum issues?

thx

 

[idylldon]

[quote author="codered"] I have a question about the toobs on the PCB - all the original LA2As I've seen tend to become *really* hot especially if you fire them up early in the morning & run them for marathon sessions.So is this going to be an issue for longevity of the components with the tubes inside the enclosure.[/quote]

IMHO, yes. Tube gear needs ventilation and that means air movement. If you want to have the tubes enclosed in a rack case, then just make sure you have some ventilation holes so cool air can be drawn in from the bottom or sides while the hot air escapes from the top. The ol' convection cooling process. I made my G9 tube pre this way and it works very well. Just look at the way old tube gear was ventilated and you'll get the picture.

Also is it Ok if I mount the tubes outside and route wires from the PCB- would that be a bait for any hum issues?

Depends on how the leads are run. It might make hum and maybe even oscillations more likely. If you pay attention to lead dress and keep the leads as short as possible, there's a good chance it'll work fine. If you notice the pic of my unit, you'll see that the tubes are out in the air and the PCB and other components are inside the chassis, and, therefore, they run pretty cool and I didn't have to use jumpers between the tube sockets and the PCB.

Cheers,
--
Don

 

[codered]

Don I just checked your build ..very clever enclosure planning!.So it appears that the 3u faceplate is holding the enclosure with just 2 screws is that OK?

 

[chingon]

I've been putting this project through the paces and noticed that i get quite a bit of hiss from it. Is this normal? Also when i turn it on i can hear the hiss volume slowly ramp up along with a low buzzlike sound and then it stays. Its actually a pretty noisy unit. The buzz sounds like its at the same rate as my cheap alesis monitor power amp so i'm guessing its picking up and amplifying this noise some how. During the build I installed the grids stoppers for safe measure even i'm not sure what its for or what ossilation is.
Another note: When I grounded the 4 pcb points i grounded them all in the same location instead of different areas as indicated in the manual. Could this be a problem?
Has anybody experienced this?

 

[wmb]

[quote author="chingon"]
Another note: When I grounded the 4 pcb points i grounded them all in the same location instead of different areas as indicated in the manual. Could this be a problem?
Has anybody experienced this?[/quote]

What you have done is called star grounding (all ground connections to a single point) and is not ideal for this project. I think the suggestion in the manual is to make the ground leads as short as possible. It's what I did and my units are pretty quiet.

When I was connecting them incorrectly through an unbalanced input there was hiss and a lack of bass.

Cheers, Wm.

 

[idylldon]

[quote author="codered"]Don I just checked your build ..very clever enclosure planning!.So it appears that the 3u faceplate is holding the enclosure with just 2 screws is that OK?[/quote]

Those are 1/4" titanium aircraft bolts with silver-plated nuts on back side. I don't think there is any danger of the chassis separating from the faceplate. :grin:

There isn't that much weight to worry about, so a couple of 1/4" bolts are more than up to the task, even if they aren't titanium.

Cheers,
--
Don

 

[wmb]

I'm really enjoying my new compressors but I've noticed that one of the units might be having some kind of spiking sound occasionally. I think I actually have a recording of it in a track. I've heard it several times in some sessions I'm doing lately. Nothing I'm using it for is critical right now as I'm using it on scratch parts.

There are only three channels I'm using at the moment. One is a mic'd gtr amp in another room the other two are a DI bass through an LA2A and a gp mic through and LA2A at the desk for scratch vocal/agt. Occasionally I will hear a quick pop but before I can look up at the meter bridge it's gone.

It could be something from the gtr amp but I'm not sure. I think I might have recorded the sound once on a drum track I was doing for a loop. I heard it and decided that I would use another section rather than investigate what might have caused it.

I have a feeling it might be one of he LA2A's but I don't know for sure. Has anyone else had a problem like this. Is there an obvious type of component that could cause this. I thought a tube might be responsible but I'm not sure.

Thanks, wm

 

[dripelectronics]

[quote author="codered"]
Thanks for the input..actually I hadnt thought about the size! The specs & availabilty of the Bloo case are nowhere to be found.
I have a question about the toobs on the PCB - all the original LA2As I've seen tend to become *really* hot especially if you fire them up early in the morning & run them for marathon sessions.So is this going to be an issue for longevity of the componentswith the tubes inside the enclosure.
Also is it Ok if I mount the tubes outside and route wires from the PCB- would that be a bait for any hum issues?

thx[/quote]

most components and parts are made to withstand much greater tempatures , now that wave soldering is the norm.

the pcb is thick FR4 and can tollerate temps up to 500 deg. or more.

the vented case should do just fine .

for the burn in tests i left one of the units operating for a month.
and performance seemed consistant.

g.

 

[dripelectronics]

[quote author="wmb"]I'm really enjoying my new compressors but I've noticed that one of the units might be having some kind of spiking sound occasionally. I think I actually have a recording of it in a track. I've heard it several times in some sessions I'm doing lately. Nothing I'm using it for is critical right now as I'm using it on scratch parts.
[/quote]

you might have to do some trouble shooting on that one unit.
this could be a poorly seated tube , to a loose ground etc.

youll have to simplify the chain , so you can make sure it's the
pcb or not.

 

[dripelectronics]

[quote author="chingon"]I've been putting this project through the paces and noticed that i get quite a bit of hiss from it. Is this normal? Also when i turn it on i can hear the hiss volume slowly ramp up along with a low buzzlike sound and then it stays. Its actually a pretty noisy unit. The buzz sounds like its at the same rate as my cheap alesis monitor power amp so i'm guessing its picking up and amplifying this noise some how. During the build I installed the grids stoppers for safe measure even i'm not sure what its for or what ossilation is.
Another note: When I grounded the 4 pcb points i grounded them all in the same location instead of different areas as indicated in the manual. Could this be a problem?
Has anybody experienced this?[/quote]

the original la2a ground scheme is how it is on the pcb.
the star ground method can work , but with this project
i have found by duplicating the original layout this works
best ,

otherwise i would have just used a solid ground plane on the pcb
to loose the multi ground set up.
i think many revisions ago in my designs and prototypes i did this
only to end up with an expensive noise machine.

you would be amazed at how much the xlr socket pin 1
can effect things.

either ground this to the case next to the socket , like in the manual ,
or ground it to GND#2 on the pcb ,
do not use the pcb pad marked xlr #1.

the 12bh7a seems to cause this ramping noise if its a bad tube or
seated poorly this can happen,

ive noticed this while the unit was on and connected to some speakers,
that pressing it in better ,stopped this .
(dont blow your speakers or fry your self)

if you have the gain dialed hi , it is normal you will have white noise.
try turning your source up higher , and the la2a lower.
this is often understated thing.

hope this helps,

g.