All things LA2a related

[khstudio]

Do you guys just use the schematic for a voltage reference chart?
I need to recheck mine -

The peak reduction on it seems to be happy around 1:00 / 60% while the gain never goes beyond 9:00 / 20%

... does the redution control seem too high :?

Where are your setting, mostly???
Please tell.

 

[Greg]

There are all the DC voltages on the schematic. I did a google search for LA-2A manual and it came up.

 

[thirtyips]

Quick question guys (or gals), I was wondering if it was possible to use 2 meters instead of one. One of the meters showing gain reduction and the other showing output and eliminate the switch between the 2 altogether. This isnt necessarily directed towards the la2a, but thats the project I am working on at the moment. Just a thought. Thanks

~Joe

P.S. Sorry if this issue has come up already, searched but could not find.

 

[CJ]

That would work.
Only issue I see is having the meter on the same winding as the output, which some folks around here say can degrade signal, depending on the meter used.

Once you set your output level, you can switch the meter to Gain Reduction, it is no longer across the output and you don't have to worry about negative effects.

If you want full time output metering, maybe a opamp buffer for the meter might be a good idea.

 

[thirtyips]

Thanks CJ, I might just try that

 

[dukasound]

Hi
I am confused about C4 because there are different opinion (value) from 100p to 390p.
I have three Silver Mica caps 47p, 100p and 220p and I can combine them. What are yours suggestions.
BTW I mean all Sifam users must drop R24 - 3,9K to 3,6K (Sifam suggestion)
Thanks
Duka

 

[keithcamilleri]

Hi guys maybe someone can help me,

I've been revising the circuitry but I cannot find any wiring problems till now, Voltage from A20 to ground is measuring 257V (shoudl be around(130V) and A19 is around 48V shiould be around 105V which is quite low... other voltages are within the limits and these are looking good, these numbers are with no T4B in...


hope someone can point me in the right direction...

thanks

 

[JerryPbury]

Keith this is what I posted before for the solution to my problem.

JerryPbury



Joined: 06 Jun 2004
Posts: 24

Posted: Sun May 15, 2005 11:56 pm Post subject: Success!

--------------------------------------------------------------------------------

Hey guys, I finally figured out what I did wrong on mine. R36 was a 470K instead of a 470 ohm. I don't know how many times I checked this area out but I decided to look at it one more time and it just jumped out at me.

Gain reduction works perfect. Output is great. I just tried it out with an SM57 into a Seventh Circle N72 into the LA2A. Wow!

 

[keithcamilleri]

Hi Jerry ,

thanks loads, I checked all the resistors and connection still nothing , the funny thing is the Screen Voltage ...why is it this low? cannot understand this I tried changing the 220K Res connectted with pin 6 of the 6aq5a I changed this from 220K to 180K and vokltages from 46V stepped up to 56V and pin2 (6aq5) instead of 2.7V now is ~3.6V ... 22K 2w resistor *a19) voltage still quite high 257V... any thoughts guys,


regards

 

[dukasound]

Guys!
All of us who make Bloo or other type of LA-2A, how you adjusted C4 cap :?
Thanks
Duka

 

[thedug]

Howdy,

I don't get this all the time but intermittently I am having a problem with my La2as, and they both do it, and it seems to only happen when I patch in certain chains, i.e. maybe an impedance/interfacing thing...

But the problem is a strange motorboating/glitchy noise thing that comes in bursts...

D-

 

[dripelectronics]

hi duka , heres what some curves look like using fixed capacitors.
(the frequency response cuts off at 15k or so (due to the trial version
or something?) 150 pf seems more like the real deal

 

[synthi]

no trial version for the rightmark audio analizer...
Also I`m pretty sure that the last vertical line is 20KHz, not 15Khz.

Synthi

 

[dukasound]

Hi
Am I right but 330p have a flatest curve?
Thanks
Duka

 

[Bluzzi]

Was there any consensus on putting a switch to select various pf values?

I was wondering if anyone had tried that and if they had gotten any "pops" or "clicks" in the output?

Maybe a shorting switch woudl be appropriate here?

Jim

 

[AnalogPackrat]

[quote author="thedug"]Howdy,

I don't get this all the time but intermittently I am having a problem with my La2as, and they both do it, and it seems to only happen when I patch in certain chains, i.e. maybe an impedance/interfacing thing...

But the problem is a strange motorboating/glitchy noise thing that comes in bursts...

D-[/quote]

Can you describe the patch up that causes it? What's immediately connected to the LA-2a (in and out)? What output transformer did you use? Those of us with Sowter outputs have installed 1k grid stoppers on the WCF to kill oscillation. I wonder if some load you're driving is causing a similar thing.

A P

 

[synthi]

I`m still collecting parts and building process is still a bit far away, but I`ve choose the expensive way and I`ve got 3 of the variable capacitors for each channel (I`ll be making a stereo unit). I`ll be switching between them and I can trim them for adjusting each to a response to match the other channel exacltly.

Besty Regards,

Synthi.

 

[thedug]

So it appears to be an acoustical/feedback thing. It seems to happen when cars or whatever go by.

I think it is a lowend thing.

Any ideas? Is the La2a just to slow ot compress low end like that?

I could post a sound file?

 

[thedug]

[quote author="AnalogPackrat"][quote author="thedug"]Howdy,

Can you describe the patch up that causes it? What's immediately connected to the LA-2a (in and out)? What output transformer did you use? Those of us with Sowter outputs have installed 1k grid stoppers on the WCF to kill oscillation. I wonder if some load you're driving is causing a similar thing.

A P[/quote]

See the post above... Also, I used the lundahls.

 

[erland]

The capacitors that came with my kit don't match up with the parts list.

Do I use...

20 µF 500 V instead of 10 µF 450 V

33 µF 450 V instead of 30 µF 450 V

47 µF 450 V instead of 40 µF 450 V ?


Can someone tell me what values the capacitors below have?

715P400V 223J 0505 - Small orange

715P400V 104J 0513 - Bigger orange

560G 100V - Small black

Thanks a lot,