mata_haze

ALL RIGHT now we'talking NEW La2A just born (twins)
« on: June 27, 2007, 06:27:24 PM »
here they are in all their beautifulness..
identical and amazing sounding La2A.
thank you Drip Electronic for PCB (very well done!!!)
thank you maeve61 for the original UREI T4B (they sound awesome)
and THANK YOU Brian Sowter for designing the INPUT and OUTPUT transformers for us. they sound as we expected: brilliant!

thank you everybody at Prodigy as this would not have seen the light without you all!!!
DIY FOREVER!









ROCK AND ROLL!!!!


capnspoony

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #1 on: June 27, 2007, 07:15:48 PM »
I just got a pair of drip's pcbs... I can't wait to get started... NICE WORK!  :green:
defender of the ancients

mata_haze

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #2 on: June 27, 2007, 07:51:56 PM »
Quote from: "capnspoony"
I can't wait to get started...


with this board putting an La2A together it's a Breeze...really.

Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #3 on: June 27, 2007, 08:52:24 PM »
How does your Sifam meter respond? Correct or way off?
Regards as always, Purusha

SSLtech

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #4 on: June 27, 2007, 10:06:52 PM »
Did you calibrate it?

Define 'way off'. Do you mean in GR mode or in signal mode?

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

drpat

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #5 on: June 28, 2007, 12:03:38 AM »
Who looks at the meters on an LA2A anyways??? I keep mine covered to avoid ass chewings by meter maids. Let's face it, these things aren't precision instruments.

Just put your left hand on the GAIN knob, right hand on the REDUCTION knob, close your eyes and ride it like a Harley!!! Vroooom Vrooooom!!!
I use the LA2a on very hot signals like lead vocal.

jensenmann

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #6 on: June 28, 2007, 03:24:18 AM »
congrats, very nice one!

And a nice collection of Neumann, Filtek and Siemens modules you have :thumb:
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #7 on: June 28, 2007, 03:36:39 AM »
Quote from: "SSLtech"
Did you calibrate it?

Define 'way off'. Do you mean in GR mode or in signal mode?

Keith


It's in GR mode. I need yet to solve this with my Sifam LA29 meters and LA-2A.
It looks like it needs some additional circuit to respond to the scale.
Mine shows -20db on GR meter scale when it's actually doing only 7-8db of GR.
Regards as always, Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #8 on: June 28, 2007, 08:11:05 AM »
Quote from: "drpat"
Just put your left hand on the GAIN knob, right hand on the REDUCTION knob, close your eyes and ride it like a Harley!!! Vroooom Vrooooom!!!


Maaaaahvellous stuff.. :thumb:
http://www.lazpro.com
I reserve the right to not sell to idiots

SSLtech

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #9 on: June 28, 2007, 10:57:05 AM »
You adjust R25 until it matches. Without calibrating R25, they don't track accuratley on ANY LA-2a.

Replace R25 with a trimpot of about 1.5 or 2 times the stated value of R25 then start it halfway and NEVER take it all the way to either extreme...

Somewhere in there will be a setting which makes the meter agree when switching between GR and +4, after setting a tone to 0VU output in +4 mode with no GR present. Increase the GR and set it so that it matches at around -5dB (5dB gain reduction). It will be maybe a little off at -3dB, maybe a little off at -8dB... a little off all over the scale, but I find that matching the meter at-5dB is usually an excellent compromise.

The only way to get them to track correctly is to MATCH the optos in your T4b. Then you re-adjust R25 and try again.

Read the comments by David Kulka and myself in the T4B threads, and you should be able to find out a lot. T4B matching and behaviour research is something that I've done a LOT of...

If you buy a NOS T4B from David and plug that in, you should find that there is a better match between optos, since they DID select and match the optos. Setting R25 will then give you about the closest match that you can get.

However, if you've not adjusted and set the value of R25, you'll NEVER getting them to track would be like winning the lottery, and if you put a different T4 in there, it wouldn't track again, until you adjusted R25 again.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.


Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #10 on: June 28, 2007, 01:12:17 PM »
Thanks Keith, this is just the info I was looking for  :thumb:

If you were in my neighborhood I would buy you a  :guinness:  
...ups can't do, alcohol is sinful so I guess it would have to be a
strawberry juice with a weep cream on top :sam:

 :green: :green:  :green:
Regards as always, Purusha

SSLtech

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #11 on: June 28, 2007, 01:36:39 PM »
I actually just did this on a re-T4'd UA LA-2a this morning. I used a 50kΩ variable resistor. The value in the end turned out to be 24.2kΩ, so I put a 22k resistor and a 2.2k resistor in series for R25. Tracks within about .025dB, but that's with a genuine UA T4b... random optos in a T4 will probably be within a dB or so.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #12 on: June 28, 2007, 01:43:31 PM »
Will try it and report back how it went. I have original T4B in this unit...
Regards as always, Purusha

CJ

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #13 on: June 28, 2007, 03:47:33 PM »
Crooked T4, nah nah nah..nah nah.....nah..!
 :grin:
Just kiddin.
Seriously though, all you crooked T4 people out there, simply unscrew the cover and rotate the base. There is a tensioner in the form of a warped snap ring, but it can be persuaded.
We do have our techniques, 007.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #14 on: June 28, 2007, 04:07:14 PM »
I just wonder, do you solder 600R resistors also to the LA-2A output?
Regards as always, Purusha

Purusha

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #15 on: July 31, 2007, 03:46:58 PM »
Quote from: "SSLtech"
You adjust R25 until it matches. Without calibrating R25, they don't track accuratley on ANY LA-2a.

Replace R25 with a trimpot of about 1.5 or 2 times the stated value of R25 then start it halfway and NEVER take it all the way to either extreme...

Somewhere in there will be a setting which makes the meter agree when switching between GR and +4, after setting a tone to 0VU output in +4 mode with no GR present. Increase the GR and set it so that it matches at around -5dB (5dB gain reduction). It will be maybe a little off at -3dB, maybe a little off at -8dB... a little off all over the scale, but I find that matching the meter at-5dB is usually an excellent compromise.

The only way to get them to track correctly is to MATCH the optos in your T4b. Then you re-adjust R25 and try again.

Read the comments by David Kulka and myself in the T4B threads, and you should be able to find out a lot. T4B matching and behaviour research is something that I've done a LOT of...

If you buy a NOS T4B from David and plug that in, you should find that there is a better match between optos, since they DID select and match the optos. Setting R25 will then give you about the closest match that you can get.

However, if you've not adjusted and set the value of R25, you'll NEVER getting them to track would be like winning the lottery, and if you put a different T4 in there, it wouldn't track again, until you adjusted R25 again.

Keith


Thanks Keith. It works like a charm  :thumb:  

BTW, is there any special reason why to change the trimpot with the fixed resistor after the calibration?
Regards as always, Purusha

Kid Squid

ALL RIGHT now we'talking NEW La2A just born (twins)
« Reply #16 on: August 02, 2007, 06:54:11 AM »
Very nice indeed Matta  :thumb:
It is not the same as 4+12, nor is it the same as 4+8, but 4+12 IS the same as 4+8+12....

http://www.facebook.com/LazyLizardLabs


 

Related Topics

  Subject / Started by Replies Last post
18 Replies
2659 Views
Last post January 28, 2009, 08:42:40 PM
by deuce42
9 Replies
1584 Views
Last post May 15, 2009, 07:35:35 AM
by radiance
3 Replies
854 Views
Last post January 11, 2011, 02:42:59 PM
by thefastvinny
26 Replies
6943 Views
Last post September 30, 2013, 04:38:55 PM
by tv