All things LA2a related

[Paul B]

Hi everyone,

I just finished a rebuild of my Bloo and arrived at the exact same situation that I had before I ripped it apart and re-did it.

Passes audio, has plenty of gain. Meter zeroes fine in gain reduction mode. Absolutely no compression or needle deflection no matter how high I turn up the Peak Reduction.

In +4 and +10 modes, I can barely get the VU to register and that?s only if I turn the gain to 10.

Using Sowters, grid stoppers in. Using the 1k, 22k 4.7k config.

Voltages were a little hot, nothing too far out:

A24-25 6.5VAC
B21 367VDC
B20 290
A20 105 (a little weak)
A14 238
A17 94
A19 139

V1: pin 1 121
Pin 3 1.1
Pin 6 130
Pin 8 1.16
V2: pin 1 109
Pin 3 4.2
Pin 6 236
Pin 7 82
Pin 8 114
V3 Pin 1 93
Pin 3 .88
Pin 6 92
Pin 8 .88
V4 pin 2 92
Pin 5 105
Pin 6 139

I have tried taking the cover off the T4B and shining a light on the panel. There was no delfection on the meter (in gain reduction mode) when I tried this.

I have checked and re-checked everything 50,000 times, checked for grounding, continuity, blah blah blah. Any help in where to look for the problem is greatly appreciated,

Thanks,

Paul

 

[CJ]

Does the EL panel flicker with the music?

 

[Paul B]

Hi CJ,

The flickering barely becomes visible with peak reduction at 10 o'clock. when turned up full the flickering is as about as bright as a strong glow in the dark toy. Still no needle deflection on the VU.

At +4 I have to turn the gain all the way up and then the VU only jumps to a max of about -1db. at +10, I can only get it up to about -7db.

Any tips on how to, er, get it up?

thanks for your help

Paul

 

[CJ]

Sounds like the EL panel is doing it's thing. Is there a volume reduction when you crank the GR up to 11?

And what does the meter do when it's reading level, not GR?

 

[Paul B]

Even with GR cranked to 11, ZERO volume reduction, no VU deflection. When measuring level, have to turn gain ALL the way up to get any register in the meter, only goes up to peak level of -1db. With the T4B taken out, I get a stronger signal thru the meter

 

[Scenaria]

four things to tripple check

octal socket wiring

T4b assembly

the rotary switch wiring

and meter turret assembly

when looking at these things its easy to *assume* something its wired correct without tripple checking it.

just look those things over carefully. if your meter isnt really showing any deflection at all then I suspect its in the rotary switch area


can you hear the audio getting louder (when turning up the gain) and compressing when turning up the input?

in other words do you think the compressor is working and the meter isnt showing it?

 

[SSLtech]

Using a resistance meter, with the LA-2 powered off, the T4B plugged in with the screws removed to allow you to slip the cover on & off the T4, and the front panel open:

Sounds like the unit might actually be compressing... that might explain the low signal level... We'll get back to it.

In a not-too brightly-lit room, do a resistance measurement between R27 (the end that connects off to the octal socket... the other end should connect to meter trim pot on the front panel) and ground. Once you have a steady reading, take the cover off the T4 and shine a flashlight on the optocells.) you have the glowing side of the El panel facing the optos, -right?) and see if the reading changes significantly.

 

[Paul B]

Scenaria,

I will re-check those areas. I will also try hard-wiring aroung the rotary switch. To answer the question, I dont think it is compressing OR registering on the meter.

SSLtech,
I will try that later this afternoon when I get home.

thanks guys for your help

Paul

 

[Paul B]

OK I did the test that SSLtech recommended. I got a change from 48k to 2.1k when I shined a bright light on the opto resistors. The EL panel is facing towards the optos.

 

[Paul B]

I forgot to mention that I have the sowter input tranny mounted on the inside of the box - let me know if that is a bad idea

 

[AnalogPackrat]

Paul,

Sowter input tranny on the inside is fine. That's how I built mine--no problems. Keep checking the other places Scenaria and Keith mentioned. I had one incorrect wire on the rotary switch when I first built mine. It's easy to screw up there. I'd especially re-check R24 (3.9k). That resistor affects all meter settings. Are you sure the T4B is wired correctly? I would take a fresh look at the internals and make sure nothing is shorting to the can when you close it up.

Good luck,
Analog Packrat

 

[AnalogPackrat]

Paul,

One other thing...have you tried running it with the T4B out? What do the +4 and +10 meter readings look like now? Is the output level higher?

Analog Packrat

 

[Paul B]

Hi Analog,

Thanks for responding. I did try it earlier with the T4B out and yes the levels are quite a bit higher, still seems on the weak side. Still need to crank the gain all the way up to get a response.

Let me ask you this; I put my DMM to the end of the pink and the gray wires of the output tranny, and the resistance was almost zero - does this sound right?

paul

 

[AnalogPackrat]

Paul,

When you say that with the T4B out the levels were higher, do you mean the meter readings or actual measurements at the output jack? Do you have an signal generator that can output a sine wave? If so, set it up to output about a 1Vp-p sine and inject that into the input of your Bloo with the T4B removed. Turn peak reduction to 0 and measure the output using the AC V setting on your meter (or look at it on an o-scope if you have one). Vary the gain and write down the range of outputs you see. Power off and put the T4B back in. Repeat the above (leaving peak reduction at 0). Try again with peak reduction set at 50 and again at 100. Write down you settings and the output voltages.

What I'm trying to do is determine whether your signal path is behaving and if it is affected by the T4B as it should be. If that all looks OK, then we'll look at the meter stuff. Divide and conquer.

BTW, when you zeroed your meter in GR mode, you set it at "0" on the meter scale, right? Because the meter moves to the left to indicate gain reduction. Just making sure...

Analog Packrat

p.s. About the output tranny DCR reading...I'm no expert on tranny stuff, but looking at the Sowter specs it should be about 15 ohms. If you get less than that, you may have a wiring error on the meter switch that's shorting the output leads.

 

[Paul B]

Analog and others,

I meant the meter readings.

I have something that will generate a sine wave, but Im limited to either 440 A or 1k - let me know which one would be better. Im sure by now that no one would mistake me for an electrical engineer, and I have no idea what a 1Vp-p sine is. I'll just try using what I have. Off to the rehearsal studio to go grab it. Oh, and I did set the meter at zero in GR mode.

I appreciate the help,

Paul

 

[Scenaria]

have you actually listened to the output?

the thing is...

everything might be working as expected but your meter might be wired in wrong via the rotary switch

I wouldnt depend on the meter to tell you if its compressing or if theres gain..

toss signal into it (even from a cd player is fine)

and listen to the output... is it distorted? is there alot of gain? can you hear the music being squished?

if yes. then we can narrow things down.. if no then we need to look elsewhere

1khz would work fine

 

[SSLtech]

...so would 440.

What's your signal aource anyhow? Let me see if an SM57 is enough...

Keith

 

[SSLtech]

I'm back...

Yes an SM57 plugged in direct through no mic preamp is all it takes to drive the VU meter to the endstop with only moderate effort close to the capsule.

Remember that you need to connect a line signal to pin 2 (hi) and pin 3 (low) and not pins 1 and 2 or 1 and 3... likewise for the output.

Then it's what Scenaria said... what's it sound like?

Keith

 

[Paul B]

I've listened to it many times. Ive used an SM58 and a tele straight in and with a FMR preamp. The output sounds strong and starts to distort at higher levels. There is absolutely no squash soundwise and no needle deflection in GR no matter what the peak reduction setting.

I dont know what high or low is, regarding the pins on the in and outputs. I have it wired per the schematic on the Sowter site: input, green to 2 and brown to 3. output pint to 2 and grey to 3.

I will run the tests shortly

Paul

 

[Paul B]

OK, here's the results I got. They were virtually identical at all settings:

t4b out and t4b in with Peak reduction set at 0, 50 and 100

no register until 40
GAIN
40: .1VAC
50 .2
60 .2
70 .6
80 1.5 -1.3 as the PR is turned up
90 2.4 - 2.2
100 2.7-2.5

the input signal was strong and the VU meter did peg from about 75 and up.