All things LA2a related

[Bluzzi]

Thanks again CJ. I was planning doing exactly as you say CJ, except the orientation of the T4B. I had not thought of that one! I guess its an esthetic thing though and will not affect the audio either way.

I'll be mounting components as per tradition. Why mess with decades of experience.

I'll be using non traditional VU meters though. I have some older Simpson meters (huge black bakelite ones and some more modern looking ones marked 3M. These are even bigger!).

I am not sure which (R24, R25,R26 or R27) resistor I will have to match. My guess is R24?

Jim

 

[khstudio]

The insert jacks on my console are unbalanced, tip & sleve. How do you guys hook up your transformer balanced gear to stuff like this?

My new LA-2A is my main concern. Trying to find the best way to deal with it in my (TRS) patch bay.

 

[CJ]

just get the phase right and you should be fine.
one secondary lead to ground, one to the tip.

now as far as chassis grounding is concerned, you might have to play with the A/B thing, an extra wire connecting board and compressor chassis' together, or no wire.

 

[khstudio]

CJ, your pic kills me every time you post.
:green:

It might be the best one yet.

Thanks for helpin man.



Hey, I'd like to post some pics of my LA-2A, How... & what's a good size?

 

[CJ]

go by the file size, as some of us are at the mercy of 56k modems.
25 kb per pic is friendly but hard to meet.
400 by 600.

i have a ton of space if you want me to throw them up.

mail to

[email protected]

or use the Lab photobucket whic I know nothing about.

 

[Coco]

I am about to order a Bloo kit and have read all the posts here. (Whew! Long read) I do have some questions. Some guys are asking about what pots and VU meter to use. I thought all the parts are included in the kit, or am I wrong to assume this? Is the T4B included as well or do I have to buy this too? This is my first DIY and am biting off a mouthful instead of a small piece but I figure you just have to **** your pants and dive right in. The only thing I have done before is change filter capacitors in my Hiwatt.

 

[Greg]

Originally Steve offered partial kits, but recently he's been offering complete kits. Hope this answers your question.

 

[Coco]

Yes, thanks. I was reading through the old posts on the thread and started to think (big mistake). I have never built or assembled a kit and I am "electronically challenged" so I want to cover my bases. I assume I have to buy wire and heat shrink or is that included too? Is there any type of drilling to the circuit boards? I read about drilling holes for tube sockets and the T4B?

 

[Greg]

Coco: I'm nearing the end of my Bloo LA-2A, and will admit it's not the easiest build out there. Being point-to-point, it's very easy to make mistakes. I've built many compressors and several preamps so I have some DIY under my belt, and this kit is by far the most challenging; however, it's definitely the most fun. If you have never built or assembled a kit, or even worked with tubes, I'd recommend you start with something else. However, Steve does provide detailed instructions, so if you are methodical and precise and make sure to follow them, I'm sure you can get the LA-2A up and running. Just wanted to throw that out there.

What type of lab material do you have? ...multimeter, scope, etc... ?

To answer your questions, Steve includes wire and some clear tubing, and I only had to drill holes to mount the Sowter transformers. I didn't have to drill any holes for the T4B.

 

[Coco]

Don't have many tools. Just the basics like a weller soldering iron, digital multi meter ect. No ocilliscope but a tech I know has one and he could check things out for me. Actually a friend has 2 he is not using so I should probably snag one. It is a big old beast and has a huge Lambda power supply that goes with it. I am patient and methodological and am confident I can do it, I will need a bit of help checking it over ect. but think I can do it over some time. I have decent soldering skills and have fixed some of my tube gear but that was simply connecting the dots like replacing parts that were alredy there and reconnecting the wire or replacing wire ect. Nothing too complicated. Maybe I like to punish myself since I always seem to go about things the hard way.

 

[Greg]

I was just worried that you hadn't ever really soldered or done anything with electronics. In that case I might say you're getting in over your head. But I will definitely suggest taking your time with this build. I haven't worked on this one for over 2 hours without taking at least an hour break, then coming back to re-check my work. As I go through I've also been following the schematic to get an understanding of how this thing works. Also, try and be as tidy as possible when wiring. If not you'll get a huge clusterfudge of wire in there.

But I'm almost complete... I just have to wire up the front panel, then I'll be ready for testing... I'll just give the it smoke test !!! (kidding)

 

[khstudio]

:!: Just a note to ALL builders who are unaware of the variable caps:

I've done tons of research on these: Listening, visually analyzing with a scope & RTA computer sweeps. I've also called UA & checked ALL the schematics trying to find out what?s going on. You will find MANY opinions about these caps & from my personal experience can have a dramatic effect on the sound & response of the unit. I will say if you build one right, all these variations can be cool for something.

C4 controls the frequency response of the entire unit (high end) & can cause a roll off that starts off slow from 2-3k to around 10k, then faster from approximately 10k up to 20k.
I've found that setting C4 to its highest point or slightly less yields little to no roll off on the high end, closest to flat. This seems to be in the 330pf ? 380pf range. When the cap was backed off, counter clockwise, the roll off could be down as much as 10 to 15db @ 20k. I was at about -12db with less than ½ turn counterclockwise from being full on. :shock: So be aware. Don?t think you can set it where you ?think? its right. These things are sensitive.

Now, UA told me they put a 1k test tone thru the unit and set the volume to 0, while checking on a scope or RTA (real time analyzer), then they send a 20k signal thru & set that to be as close to flat with the 1k tone as possible. I was very shocked when they told me this, especially after looking at some of the pics from the builders on this sight. Most of them sure don?t look flat to me. This, in my opinion isn?t bad. A ?little roll off on the high end is pleasant. It seems to be more HI-FI sounding when flat.
I will note that I?m using the Jensen transformers & their mods.

UA also told me that they DO NOT USE C14 on the reissue.
It wasn?t in the original LA2 units either, but was in one of the versions.
What does it do? I?ll tell you.
C14 is in the detector part of the circuit & causes the unit to react to the higher frequencies more. The sound to me is somewhat like a D-esser. The caps value affects the frequency itself. Nobody seems to know where it should be set stock so you?ll have to listen and see for yourself. Some guys don?t use it at all. Without the cap, the detector is un-weighted & reacts more evenly to all frequencies.

:idea: In my LA-2A, I?m going to try putting a multi switch on the front so I can dial in the D-essing function (C14) & the frequency of.

Something like ?
OFF, 100pf, 150pf, 220pf, 330pf

That should give some nice options.

BTW, I could use some help wiring the switch to the front panel for my D-esser control. My concerns are with the style of wire to use - shielded or unshieled. A very experienced tech told me today on the phone that all shielded cable has some capacitance. :shock:
Me not know that.
Anywho, would it be safe to run single wires from the output terminal strip,(where the cap belongs) acrossed the middle of the chassis to the front panel... maybe right under the meter? Would there be any problems with noise, crosstalk, oscillation, etc...?

I think I'm going to use a 3 position switch, center off.
Also, any idea what the best 2 cap sizes should be???
150pf & 330pf?

Or, could one of you brainiacs that know more than me help with the math & how to figure out the frequency affected by these caps in this part of the circuit???
That would be killer! :thumb:


*If there is any known or false information in this post please let me know so I can change it. I wish I had this info when starting my build. It took days of research & testing to find it.

Good luck with your builds. :wink:
Kevin
www.khstudio.net

 

[guavatone]

I'm thinking that it would be cool to have a C4 switch too. One for "vintage" sound and one for more "hi-fi"

maybe someone can comment about stray capacitance of wires 6" long or so. a relay would seem to be the best but sounds like too much work.

 

[khstudio]

Don't get confussed.

C4 = Hi freq roll off (or not if set flat)
C14 = Hi freq weighted compression/D-essing - located in the detector circuit. This is what I was reffering to about the switch. Thats not saying you can't try it with C4 too.

I'm also waiting for some inteligent replies concerning the wires: style & lenth.

 

[khstudio]

dude,
sorry, I just noticed you did say too. (as in also)
My bad.

O BTW, you asked me where I was from in you PM. I'm in South Jersey, Millville.
1 hour from Phily or AC.

 

[synthi]

Great idea!

I think having a switched cap for C4 and C14 would be nice!:

C4: 3 positions: flat (hi-fi), -6dB@20K, -6dB@16k
C14: choose your deesser freqs

Synthi

 

[CJ]

UA might have tweaked the output iron for better high end response. So folks using the original UA iron may not get the same milieage if tweaking cap for 20 k.

 

[synthi]

So what would be the better trafos for hi-end, UTCs? Sowters?

Thanks,

Synthi

 

[CJ]

I say whats the point of building vintage gear if it does not sound vintage?
Always go for as original as you can get on the first copy, listen to it, say "OK, I know what an early LA2 sounds like" (or close enuff), then build another one and "modernize" it if you want something different. (like more high end for guitar instead of a rolled off mellow vocal sound) Or mod the one you have. But if you do not have the original standard to go by, then whatever you build will leave you wondering "what it I had built the original."
Can you dig my trip, man?

If you want your girlfriend to sound like Billy Holiday, go for the original.

Too much coffee. Sorry!

 

[synthi]

:roll: Err.... What!? :grin:

Synthi