All things LA2a related

[college101]

OK GUYS...

I figured out my grounding problem!!  Got that fixed...But I am stumped on my next problem..

I cant get signal to pass while in GR mode...I can actually set the zero Adjust to Zero NOW!!! wEEEEE

which is great, but I cant get it to show the reduction! Please advise!!!

 

[Sredna]

Dont have the T4 in yet...

Could be the problem... 

 

[college101]

OH man..OK...I totally forgot...Going to drop that in and repeat test!!

 

[college101]

For the burn in period...Do I need to have signal going threw the 2A or just have the unit ON?

 

[Biasrocks]

Congrats on a working build, let's see some photos.

Burn-in?

Don't buy into the audiophoolery hype.

Tube gear tends to settle in after about 30-60 minutes, but other than that, turn it on and start
using it.

Mark

 

[lassoharp]

turn it on and start
using it.

+1

 

[college101]

SO>...audio passes, but it doesnt register on the vu meter...Im going to re-do the input wiring again...

 

[Sredna]

Why the input wiring?

 

[college101]

Well it has to be...I would think since the needle is not functioning...

 

[college101]

I re-checked my wiring, and blue is on two and red on three...so I am lost...cant figure it out

Well...Honestly...I am so confused...the signal does not register on the vu meter...  The needle does move when I have it on +4, but its at the Negative 20 instead of at the Red Zero...When I switch from GR to +4, the needle jumps to -20....

Please advise!!

 

[college101]

I have also inserted the t4b, no change in needle movement...

 

[college101]

Ive been doing some thinking...Trying to come up with the next thing to check for..

So far Ive come up with

1) positive wire off of 1 and 3 and negative wires off of 1 and 3 from sw#2 have to be backwards...
( when I switch to +4 mode, the needle jumps to negative 20 zero refernece, instead of the positve Red zero) does this make sense?

2) High Frequency Osc? Possible, but I did a much better job wiring this time...
  The only thing that bothers me is the wires from SW#2 travel right by the 33 and 40 big capacitors, and then travel above the IEC receptacle...

PICS later tonight...

I took measurements of every part before putting it into the circuit...

I dont understand what is wrong...and Im starting to get lost again...I feel much closer to it working though... The zero adjust works fine for calibrating the needle to the Red zero( in the correct place-last time I could not control it-now after the re-wire, it is working properly)

Audio passes from the input to the output into my guitar amp, just does not register in +4 mode

Let me know what you guys think

 

[Sredna]

1) positive wire off of 1 and 3 and negative wires off of 1 and 3 from sw#2 have to be backwards...
( when I switch to +4 mode, the needle jumps to negative 20 zero refernece, instead of the positve Red zero) does this make sense?
Audio passes from the input to the output into my guitar amp, just does not register in +4 mode

Try to connect the VU directly to the output, with the 3,9K resistor of course...

 

[college101]

So basically, take the two POLE wires off and connect them to tb#1-via- negative wire  inline with the 3.9k resis to #8 and the Positive wire to #10

 

[Sredna]

Yep!

If it still not working, try reverse the VU...

 

[lassoharp]

Well...Honestly...I am so confused...the signal does not register on the vu meter...  The needle does move when I have it on +4, but its at the Negative 20 instead of at the Red Zero...When I switch from GR to +4, the needle jumps to -20....

??
Hopefully you do know that when the meter is set to +4 you are monitoring output and the needle should be starting at -20.  When set to GR the needle should hover around zero.

when I switch to +4 mode, the needle jumps to negative 20 zero refernece, instead of the positve Red zero) does this make sense?

Yes.  To repeat again, that is where it's supposed to be.  Think about why that is for a moment.

 

[college101]

OK lassoharp...Im going to think for a bit...Be right back

+4 is supposed to be -20 ?  HUH...im lost

While in GR mode.. the needle sets to zero, and then does not move...

While in +4, the needle is bouncing( but very little movement-but there is movement ), but seems to be moving on its own affair- no movement control by peak reduction or gain pots being turned...

I also checked the pots on the back, no change...

Once I get home tonight, I will try what sredna has suggested, to take the SW#2 out of it

 

[emrr]

Burn-in?

Don't buy into the audiophoolery hype.

Tube gear tends to settle in after about 30-60 minutes, but other than that, turn it on and start
using it.

Mark

Burn in is an industrial/electrical process, a time after which one may inspect for problems and make alignments.   New tubes are more likely to fail in the first 48 hours, than at a later time.    Are you meant to live?  Do you need corrective surgery.  

Every vintage design tube vari-mu limiter I've ever worked with requires anywhere from 2-5 hours before one can align the meters and walk away, expecting zero to be at the same point upon return.   That's about the amount of time required for temperature to stabilize.  

There's nothing audiophoolery about it.   Likewise, none of this should prevent you from working immediately either.  

 

[Sredna]

OK lassoharp...Im going to think for a bit...Be right back

+4 is supposed to be -20 ?  HUH...im lost

While in GR mode.. the needle sets to zero, and then does not move...

While in +4, the needle is bouncing( but very little movement-but there is movement ), but seems to be moving on its own affair- no movement control by peak reduction or gain pots being turned...

I also checked the pots on the back, no change...

Once I get home tonight, I will try what sredna has suggested, to take the SW#2 out of it

No, do what Lassoharp suggested!
You need to read up on basic function of a VU meter.

The +4 position means that the VU meter show the output signal and the 0 position is related to a certain signal level. The  +10 position is the same but the 0 level is 6 dB louder. (simplified explanation)

In the +4 and +10 positions the needle should sit at -20 dB and when you have a signal going through,
the needle should move according to the signal.

In the GR mode the needle should sit at 0dB and when a signal is applied and with use of the gain reduction pot the needle should go left (negative).

I strongly suggest you to read the LA2A manual.

 

[lassoharp]

+4 is supposed to be -20 ?  HUH...im lost

+4 will read +4 when there's that much signal passing through . . . . when there is no signal passing, it should read something else . . .