All things LA2a related

[AnalogPackrat]

Paul,

These were with your signal generator (tuner tone)? Can you directly measure its output level with your meter so we have an idea what was going into the unit?

Analog Packrat

 

[Paul B]

I dont have a way of doing that. Or I just do not know how to do that. My lack of knowledge is not making this very productive. :?

 

[Paul B]

I have some other things to try. I will reposition C5 because it might be slightly interfering with the mini turret board when the box is closed. Also need to hard-wire around the rotary switch.

 

[AnalogPackrat]

Paul,

Hang in there. You'll get this thing working. I assumed that you used your signal generator to make those measurements, right? If so, just connect your meter directly to the signal generator output and measure VAC so we can see what's going into the LA-2A.

I wish I could measure my Bloo and compare to yours, but my stuff is all packed up while I finish up some work on my house. More DIY :?

 

[Paul B]

Ok, I have some results. The input signal on the above test was measured at .2VAC.

I cranked the signal up to .7v and got the following results. I?d also mention that the above measurement was done before the signal went into a passive direct box. I got no measurable voltage after the signal passed thru the direct box. The signal into the box was strong enough to get the following results at the output

.7 v input signal, With +4 setting for the VU:
T4B out T4B In

PR at 0: PR at 0: PR at 50 PRat100
Gain VAC VU VAC VU VAC VU VAC VU
10 0 -20 0 -20 0 -20 0 -20
20 .2 -9 .2 -9 .2 -9 .1 -15
30 .4 -5 .4 -5 .4 -5 .2 -9
40 .6 -2 .6 -2 .6 -2.5 .2 -7
50 .8 -.5 .8 -.5 .8 +.5 .4 -5
60 1.1 +1.2 1.0 +1 1.0 +1 .5 -3.3
70 2.3 peg 2.2 peg 2.4 peg 1.1 +1.5
80 4.8 peg 5.0 peg 4.8 peg 2.5 peg
90 8.0 peg 7.2 peg 7.2 peg 4.2 peg
100 8.8 peg 8.4 peg 8.4 peg 4.6 peg

I know the chart didnt space correctly, I hope you can sort thru it.
it appears that it wants to squash but somewhere along the line I?m losing signal.

The Gain coming out of this thing, soundwise, is off the charts. I cant imagine having to turn the thing past 30-40 when the thing works!

Thanks for hanging in there with me

Paul[/url]

 

[AnalogPackrat]

Paul,

Yeah, the LA-2A is no slacker when it comes to gain. It sounds to me like at least most of your main audio path is fine since you are getting reasonable output (yeah, you probably won't be going past 40 on the gain knob very often). Your meter also appears to work when monitoring the output, but may be a bit off. It's hard to say unless we know for sure that your signal generator is outputting a sine.

That leaves the part of the meter switch that relates to gain reduction, the T4B, and the sidechain amp. Lets check the T4B first. Pull your T4B and measure resistance between pins 7 and 8 with the cover still on. Then measure resistance between pins 4 and 5. Now take the cover off and make these measurements again holding the T4B under a bright light. What happens to the resistance?

Analog Packrat

 

[Paul B]

OK, I know what to do now :grin: :evil:

I have some weak connections on the circuit board and the pins. All the pushing in and pulling out of the T4B has weakened some points that measured just fine last time I checked them.

Ill report back tomorrow
thanks again

Paul

 

[AnalogPackrat]

I just thought of something. Gain is applied after compression, so its possible that you aren't hitting the input with enough level to really get far up the compression knee. Can you increase the ouptut of your generator any further? Set the PR pretty high (50 or more) and the gain to something that doesn't peg the meter at +4 (say 30 or so). Now meter the GR and vary the output of your generator. Does the meter register? Try switching to limit mode and check again.

I've got to turn in for tonight. Sorry this is taking so long, but it ain't easy debugging a circuit by email...

Analog Packrat

 

[Paul B]

Thanks Analog,

Ive done that already with varying results. the shorts in the t4b would help explain that, I would think.

 

[Paul B]

I fixed the connections in the t4b. Analog, per the test you suggested I got the following:

xxxxxxxxxcover onxxxxxxxcover off w/ bright light
resistance
pin 7&8xxx468kohmsxxxxxxxxxx286 ohms

pin 5&6xxxxinfinityxxxxxxxxxxxx262 ohms

you did mean pins 5&6 and not 4&5, right? I got infinity when I measured 4&5 cover on and off. 5&6 and 7&8 are the ones that go to either side of the opto resistors.

the results have not improved with the fixing of the t4b. so its obviously a component failure and not me. :wink:

seriously tho, I did also hard-wire around the rotary switch, and that didnt change anything. let me know what you think.

Paul

 

[AnalogPackrat]

Paul,

Yeah, I meant for you to measure across each opto. They both seem to work, though the infinity looks suspicious. The thing is, the "light on" condition is when compression should be happening. Try looking over the V3 & V4 wiring as that is the sidechain amp for the EL panel. Maybe it's not getting enough drive. Also, on the 8-pin T4B socket, the crossed wires are soldered to each other, right? I'm getting ready to leave the house for the day. I hope Scenaria or Keith can help you out some.

Cheers,
Analog Packrat

 

[Paul B]

Just me being stupid again. Its not infinity, its a resistance beyond 2000k, which is the capacity of my cheap DMM

so cover off they measure about the same about 280 ohms.

cover on, pin 7-8 resistance slowly climbs to about 468k ohms
resistance 5-6 goes beyond 2000k ohms.

I obviously have a huge difference in the resistance.

 

[SSLtech]

Don't worry, that all looks good. The circuit has tracking adjustment built in to compensate for differences in opto resistance. (R25)

Keith

 

[Scenaria]

ok so your LDR's are showing that they work when light is applied...

but if you take the cover off the T4b when in the octal socket.. and shine a light on the LDR's the VU meter does not show deflection in GR?

This still suggests to me that something is wrong between the Octal socket, rotary switch or the meter turret board..

 

[Paul B]

Ok good,

the needle deflects back and with a bright light I can get it to peg to the left.

Audiowise, I put the cap back on the t4b and it takes a ridiculously strong input signal to make the meter deflect in GR mode and to get a meter reading on +4

I rechecked V3 and V4 per Analog's suggestion and it looks good. Yes, the T4 cross is soldered at the 'X'.

Hope this gives a better clue where to look next. I appreciate all the help.

Paul

 

[Scenaria]

did you solder the cross on the octal socket to ground?

I thought you mentioned the other day that the EL panel flickered?

im a little confuse as if the EL is lighting and the LDR's are working there should be some decent compression...

 

[Paul B]

Not as confused as I am :?

The output has gain for days, but to get the VU meters to register anything (GR and +4) it needs an input signal so strong it is unusable, and turn both the Gain and PR to at least 60-100. The cross on the octal socket is grounded.

 

[AnalogPackrat]

OK, I'm back home. This is very confusing. Maybe there are two problems--on affecting the metering and something else messing up the compression. Are you sure that R24 is correct? Can you tell us how the meter reacts in the +10 setting? Maybe you got the +4 and +10 wired backwards. The only thing I can think of with the lack of compression is that your EL drive amp stuff isn't driving the EL panel hard enough. Does the EL panel still flicker with the input level? I've never looked at mine to see how bright it is. Scenaria or Keith may have a hint for you there...

:?:
Analog Packrat

 

[Paul B]

It doesnt get particularly bright - about as much as a glow in the dark toy at its brightest.

R24 is correct. +10 meters about 6db behind +4. The +4 setting bypasses R23 and +10 sends the signal thru R23.
any advice on troubleshooting the EL drive amp stuff?

 

[AnalogPackrat]

[quote author="Paul B"]
R24 is correct. +10 meters about 6db behind +4. The +4 setting bypasses R23 and +10 sends the signal thru R23.
any advice on troubleshooting the EL drive amp stuff?[/quote]

Right, just making sure we didn't miss something obvious. Did you set the back panel trim pots per the instructions (I can't rememebr which way they're supposed to go)? Make sure they aren't wired backwards--swapping the outer two connections (everyone wires pots backwards occasionally). Other than that, recheck all of your voltages on V3 and V4 and compare to the schemo at the back of the Bloo manual.

<checking your old post with voltages>

Looks like V4 may be the problem. What are your DC voltages there?

Analog Packrat