rainton's P2P LA2A chassis "original style" discussion thread

[Phrazemaster]

Closely related? On later revisions of the circuit's schematic, there is an identical (50-380 pf) variable cap with the designation C14. I'm assuming it has the same function as C4.
What would be the proper setting for this cap? Would I be better off just not going with a variable cap and replacing it with a 380pf to pass full frequencies?

Hi Xaxxon, It's a variable cap for a reason. You're supposed to check the unit for flat frequency response and adjust the cap to make it as flat as possible. So there is no answer for you other than "adjust it to suit your unit." No one can tell you the "right" value.

I also understand early units didn't have it at all, so complete bypass may be fine. I also hear folks saying the Arco adjustable cap sounds really awful, so once you determine the value for frequency response, to replace it with a silver mica cap with the value you discovered.

 

[rainton]

Closely related? On later revisions of the circuit's schematic, there is an identical (50-380 pf) variable cap with the designation C14. I'm assuming it has the same function as C4.
What would be the proper setting for this cap? Would I be better off just not going with a variable cap and replacing it with a 380pf to pass full frequencies?

Correct me if I'm wrong, but I think C14 and C4 don't have the same function.

C4 controls a Hi freq roll off for the gain circuit - so it changes the overall frequency response of the unit - no matter wether it compresses or not

C14 is located in the sidechain amplifier/detector circuit and it controls the  Hi freq weighted compression. Meaning you could adjust it compress hi-freq. content of the signal more than lower frequencies.
For example it could be adjusted to compress frequencies at 10Khz 2db more thant frequencies below 1Khz.

At least that's what my measurements told me

 

[xaxxon]

After looking at the schematic again, I can see that C4 does affect the whole circuit while C14 is localized.  Thanks for that. I know transistor circuitry well enough that I should have realized that.

I could swear that a few other people answered my thread, but now cannot find those posts.  It's too bad because one member posted a link to an interesting article on building an LA2A and another member had other interesting thoughts on these caps.

I didn't catch the member names but would appreciate it if they would repost!

 

[sr1200]

Has the next run been done yet?  I'd like to get in on it if possible.  I would need an adapter board for a  non pin cinemag style input transformer.  Out put transformer would need about the same.. its a 2 screw rectangle (similar to the power transformer but smaller).

 

[weiss]

If someone still has a neon lamp and caps for c4/14 left over, i would buy them from you.. 

 

[Phrazemaster]

If someone still has a neon lamp and caps for c4/14 left over, i would buy them from you.. 

You can get those caps from Nebraska Surplus. Don’t know about the neon lamp.

 

[rainton]

Has the next run been done yet?  I'd like to get in on it if possible.  I would need an adapter board for a  non pin cinemag style input transformer.  Out put transformer would need about the same.. its a 2 screw rectangle (similar to the power transformer but smaller).

The first run of the V2 LA2A style chassis is being manufactured at the moment.
It's a completely new revision that has 2 piece back chassis just like vintage units, plus a new custom made hinge made to the exact specs of the hinges used in vintage units.
sr1200 - I'll PM you - for everybody else interested just send me a mail - I have a preorder special going until Oct. 1st.

 

[kosi]

pm sent

If someone still has a neon lamp and caps for c4/14 left over, i would buy them from you.. 

 

[core13]

Also interested by new case

 

[damiangiannis]

I am very interested as well !

 

[rainton]

Since I received several requests for pics:

I can't post pics of the finished V2 chassis yet, since it's still being manufactured.
But here's some screenshot from the CAD that show where the main differences are:

The back panel is made of 2 pieces - the first one being an "L" shaped panel consisting of bottom & back:

As you can also see here I added a new cutout in the PSU section to allow for mounting a can cap as used in the vintage units if preferred. With every chassis comes a blind plate to cover that cutout and go with regular electrolytics.

This second screenshot show both back chassis pieces - bottom & back and top&sides mounted together:

Here's another screenshot highlights the top&sides part of the back chassis:

This allows for a super easy build process since it's possible to wire up the entire unit - even with front panel mounted, and closing the chassis at the end by mounting the top&sides piece.
It's actually the same design as used in the vintage units except my chassis has nuts punched into the metalwork to allow for easier mounting.

The difference on the front of my V2 chassis the stronger hinge custom designed to original specs, and the position of the little hole below the VU meter has been changed - in V1 it'S position didn't quite match the adjustment screw on the SIFAM meter - that is solved now

In addition to that I'll have the entire back chassis anodized...

 

[Phrazemaster]

Martin, you do the highest quality work. Out of all the guys that have tried to get things manufactured, you seem to have a gift for making it a reality. I'm still waiting on a certain M49 body that may end up being vaporware.

Thanks - looking fantastic!!

Mike

 

[weiss]

Again nice work, indeed!!! 

 

[sr1200]

That looks awesome!  I'm going to be transferring a working unit in a case that i frankenstein'd together to this... looks like its gonna be a breeze!  Anyone have any suggestions for aftermarket transformers that are close to the original?  I currently have Cinemags in it which sound great but they're a little hot going into the circuit (im getting a TON of GR when the knob is at around 10/20).

 

[Phrazemaster]

That looks awesome!  I'm going to be transferring a working unit in a case that i frankenstein'd together to this... looks like its gonna be a breeze!  Anyone have any suggestions for aftermarket transformers that are close to the original?  I currently have Cinemags in it which sound great but they're a little hot going into the circuit (im getting a TON of GR when the knob is at around 10/20).

Martin addressed another potential cause to this - the actual gain pot law. He found in another thread if he used Allen Bradley pots they ramped up slower. Do a search you'll find it.

And of course the transformer could be an issue too...

 

[sr1200]

Just saw the post about the logo.  Another guy that did cases left the area blank and provided a sticker with a popular brand name that accidentally fell in the box before shipping....

 

[damiangiannis]

Is the Facebook page still operational ? I m trying to get every info i can about parts ,planning to get raintons case and start my la2a ...Very nervous about it because of no electronic experience what so ever ...you guys on the other hand made me have hope !  ;D

 

[Phrazemaster]

Is the Facebook page still operational ? I m trying to get every info i can about parts ,planning to get raintons case and start my la2a ...Very nervous about it because of no electronic experience what so ever ...you guys on the other hand made me have hope !  ;D

I don’t want to disappoint you, but this is really not the best beginner project.

The most important reason is, it’s got dangerous high voltage tubes that could kill you if you’re not careful. The next most important reason is, until you know what you are doing you might ruin a lot of components and waste a lot of money.

It’s an exciting project - so why don’t you get the parts for it, and the case - and then set it aside for awhile and do other better projects for your first time.

I suggest some kits, like SoundSkulptor or Seventh Circle Audio microphone pres. or there’s other excellent kits.

The point is - get some soldering and building experience first. You need to crawl before you can run.

And above all please be careful! This hobby has taken a lot of people out.

 

[damiangiannis]

I don’t want to disappoint you, but this is really not the best beginner project.

The most important reason is, it’s got dangerous high voltage tubes that could kill you if you’re not careful. The next most important reason is, until you know what you are doing you might ruin a lot of components and waste a lot of money.

It’s an exciting project - so why don’t you get the parts for it, and the case - and then set it aside for awhile and do other better projects for your first time.

I suggest some kits, like SoundSkulptor or Seventh Circle Audio microphone pres. or there’s other excellent kits.

The point is - get some soldering and building experience first. You need to crawl before you can run.

And above all please be careful! This hobby has taken a lot of people out.

Thank you for the heads up !Not that i wasn't thinking of trying on my own but  I was thinking more about giving the project to an experience technician to assemble all the parts. I'm hoping that he will let me seat beside him and i'm thinking that i would feel more comfortable and sure if i  knew  some theory or experience details (i'm reading from you guys). Haven't decided yet but    i will probably follow the above scenario. Maybe in the future i 'll manage to make it on my own (starting from simpler projects that is) .So any help as referring to Facebook page and such would be valuable and very much appreciated .Thank you !

 

[Phrazemaster]

Thank you for the heads up !Not that i wasn't thinking of trying on my own but  I was thinking more about giving the project to an experience technician to assemble all the parts. I'm hoping that he will let me seat beside him and i'm thinking that i would feel more comfortable and sure if i  knew  some theory or experience details (i'm reading from you guys). Haven't decided yet but    i will probably follow the above scenario. Maybe in the future i 'll manage to make it on my own (starting from simpler projects that is) .So any help as referring to Facebook page and such would be valuable and very much appreciated .Thank you !

You have a good attitude! I wish you luck in whatever you decide to do. This is a great group of people so you can learn a lot from the forum here. Don't be shy about asking questions, but be sure to do some research first - a lot of folks get a little annoyed at answering questions that are overly easy and/or already covered in previous posts. Use the "Search" function!

Welcome, and good luck!

Mike