All things LA2a related

[sysexguy]

Hi AP, you da man!!!!! All my voltages are as per the Bloo manual

thanks :thumb:

Andy

 

[AnalogPackrat]

Glad to help, Andy. Hope you get the rest of it together with no trouble.

:guinness:
A P

 

[sysexguy]

:thumb: oh yeah!!!!!! :grin: thanks for the kind assistance :sam:

Andy

 

[emx]

Anyone here have a link to turret and T4 pin voltages for the LA-2a. I did a search but could only find a dead link to Cayocostas earthlink one wich isnt' online anymore.

 

[sysexguy]

pm sent

 

[HogFish]

Hi.Hope I can get some help, this is driving me quite mad.Ive built a Bloo La 2a, but wired the layout according to cayocostas diagram.This includes a 10k 2w instead of the 22k 2w,470 ohm instead of the 1000 ohm, Sowter Iron on input and output. Unit passes audio and sounds fine,the T4 cell is compressing properly,lights up and responds to input properly, all the voltages are within the realm of OKness,(245V on B+, 117-120V on V4 pin 5, 108 to 110 on V4 pin 6,55-56v on the neon lamp)but I cannot for the life of me get the ******* meter to work at all. It is wired properly according to cayocostas diagram. There is no voltage difference between the + and - side of the meter voltage wise. There is about 5.8 to 6 volts on each terminal.When I close the front panel, the + meter Terminal rubs against the case of R37, and the needle jumps up to around 0VU, but when it clears the resistor case,it goes dead again.Also, if I hold the front panel in place at the point it touches the R37 case,the switch works OK when I switch to +10 and +4 modes of operation.I have been trying to work the problem for about three weeks now and have had no success at all. If you can help, by all means dont be shy. Im about to give up on this thing........

 

[sysexguy]

My meter "-" was touching the output XLR jack's case. I just covered the terminal with heat shrink.

Andy

 

[AnalogPackrat]

Hogfish,

There's not a lot of circuitry involved with the meter, so you should be able to work out what's wrong. First, identify all the stuff that affects the meter and understand what the switch is doing. In GR mode, the meter is looking at the sidechain signal (via R27 and one of the CdS cells in the T4b) plus a DC offset provided by the neon (via R4 and R25). In output monitoring mode it's just looking at the secondary side of the output transformer through R23 or nothing. R24 is always in the meter circuit. Of course, the meter switch is there.

If I were you, I would go through the Bloo manual and read all the sections about wiring the meter switch, the little board attached to the meter, and the wiring for R4. It almost seems like you are missing the link from R24 to the minus terminal. If you don't tie the free end of R24 to the little bits that screw the small turret board onto the meter, you have not made a connection from R24 to the negative terminal.

You should also do something to prevent your meter terminals from shorting to anything when the unit is closed. You may need to trim a mm or two from the problem terminal (being careful not to bugger up the threads).

Keep at it,
A P

 

[HogFish]

Well, I finally got working.This was my second time building the unit, The first build didnt work, and there were so many problems,I decided to tear it down and rebuild it. On the 2nd build, I had to replace the small turret board,because I broke one of the turrets removing parts. I bought a new turret board,but it isnt the same size.Its slightly bigger,and it dosent have those metal terminals on the end so I had to drill a hole thru the TB to make it fit over the - terminal. I did link the - side via wire from turret #5 to the terminal tho.How I got the thing working is weird. I put a small wire link between the + pole on the switch the the 3rd contact (the one that is supposed to be open) and the meter sprung to life. Why this works is beyond me, maybe someone here can explain, anyways thanks for your help AP.........

 

[rubric]

Hello all!

I'm hoping to solicit some troubleshooting help with my Bloo LA2A. I followed the Bloo manual for the wiring, and I'm using Sowter iron.

I've got two problems. Whether they're related or not, I'm not sure:

1. The unit passes audio just fine. However, as I move the gain knob to the midpoint (50 or so on the display) the audio instantly turns into white noise. The output jumps to the extreme right on the meter as well. I've never something like that before!

2. The compression doesn't work as I would expect. It does start attenuating volume as I move the peak reduction up, but once I get past a certain point (around 20 on the display) it stops compressing entirely. It also compresses very heavily when it is working...more than I would expect anyway.

I put grid stoppers on V2, and I went back through the manual and double-checked all my wiring, and it all looks good to me. Sadly, I don't own a scope for signal tracing. I'm out of ideas as to what may have gone wrong. All the DC voltages were fine before I started running audio through it.

If anyone reading this has any suggestions on what to try, I would be very grateful for your help!!

Thanks.

 

[CJ]

that's the amp breaking into oscillation.
get the white noise going, then move wires around carefully.
someone fixed it by moving the big output cap around.
you can adjust feedback resistor or pop in a 12AY7/6072.

 

[rubric]

Thanks for your reply CJ!

I moved the output cap around, and I was able to get more gain out of the unit. It was still breaking to oscillation at high gain settings, but then I put the T4B back in and I can crank the gain all the way with no problems!! Awesome! I'll try substituting V1 for a 12AY7 as soon as I can get my hands on one.

Now on to the compression. I took the can off the T4B and turned off the lights. The ELP lights up as I apply Peak Reduction, but then it shuts off as I turn past 30:00 or so. I've also got a low-frequency oscillation happening when the ELP lights up. I'm guessing this is what people call "motorboating". I had this problem before, and when I put the grid stoppers in it went away. Now it's back. Any ideas??

Thanks so much for your help thus far, I can't tell you how much I appreciate it!

:thumb:

 

[CJ]

the shut down thing is a weird one.
check for an un-soldered wire.
or try the wire moving thing again, only confine this to the sidechais to stop the motorboating.
check grounds for clean low ohms surface contact, no paint.
check lid to chassis ground, don't bank on the piano hinge for a ground.

 

[rubric]

thanks again CJ.

i spent as much time on it as i could last night. i managed to buy a 12AY7, so I popped that in. it works great. the amp oscillation problem i was having was really finicky based on wherever i put the output cap. with the 12AY7 there's no problem at all.

still no improvements on the compression side. i made sure the front panel is grounded to the chassis (i had to scrape off some paint around the piano hinge). i'll continue checking grounds and solder points tonight after work. i need to spend some time with the schematic as well to hopefully identify the "sidechain"... although i must admit that i don't really have a clue what i'm doing.

 

[CJ]

check your power supply caps, the ones that feed the side chain.
you using audio taper pots?
jus curious, what kind of 12ax7 did you use?

if you really have "motorboating" in the side chain, try bridging the filter caps that feed the side chain with another one of equal or greater uf and volts rating.

 

[rubric]

yep, definitely using audio taper pots. the 12ax7 is an electro-harmonix.

i'm afraid i may be out of my league here. i don't know how to check the power supply caps, or any cap for that matter (my DMM doesn't have a capacitor test). i don't know how to locate the filter caps that feed the side chain, nor how to bridge them with another cap.

can you dumb it down a few shades? i apologize for my ignorance.

thanks!

 

[CJ]

ok, skip the cap test.
measure your dc volts on tubes v3 and v4.

 

[rubric]

alright! that i can do.

V3
1 - 92.5
2 - 0 (??)
3 - 0.8
4/5/9 - 0
6 - 92
7 - 0 (??)
8 - 0.8

Should 2 & 7 be zero?? Those are the grids, right?

V4
Center - 116.5
1 - 0
2 - 8.7
3/4 - 0
5 - 71.5
6 - 115.7
7 - 0

See any problems??

 

[CJ]

what is center?

correct on zero volts, v3 grids are 2 and 7

 

[rubric]

V3 center is zero as well