All things LA2a related

[CJ]

The low volts on V4 plate might just be the screen circuit.

If you use a different circuit, that voltage could move around, but even 86 volts is semi normal, so there is nothing major wrong, just maybe a circuit difference and a tube that has drifted a bit.

 

[Bluzzi]

Hey guys! I finally got my LA2A to sound good! I plugged in a 12AY7 as per CJ's original advise and reminded again by AnalogPackrat! That makes it happen!

So far I only listened with a headphone but I went from a AT4047 into a John Hardy M1 right into the LA2A. My gain at about 10 oclock seems good enough and reduction at about 12 and 1 oclock moves needle enough and voice remains nice and present without loss of highs. Silky smooth so far. Real sweeeeeet....Pushing reduction all the way really sucks the juice out and I didn't try increasing gain to see what would happen.

I'm just so damn happy this thing works. All it was was a wire I moved! For now I am not touching it. I'll start on my second one in august. Love it!

I took a picture of it. Not pretty without paint but she just had to pose so proud is she!

http://i22.photobucket.com/albums/b304/Bluzzi/LA2A.jpg

Again thanks to CJ, AnalogPackrat. Also to Duka who probably doesn't remember me but gave me words of encouragement a while back.

A huge thanks to Ron (Cayocosta) for all his help and encouragement as well as making the layout available to us mere mortals like me.

Man, I'm bitten by DIY and there is no cure!

jim

 

[AnalogPackrat]

Nice job, Jim! Glad you tamed it with CJ's 12AY7 swap. Man, I need to try that on mine. I think your build looks fine, but you are going to have to show us the inside! What's next on your build list? :grin:

A P

 

[Bluzzi]

Thanks A P. It was your mention of the 12AY7 that made me put one on. I had bought them just in case as I had read that some were finding the gain a bit extreme.

I may even try your resistors swap later if need arises for more attenuation. I do still have to try it in real recording situation. But already it was a major improvement in the tests I performed so for me its the right direction. Whatever works.

I'll post more picts after I get back from vacation and give it a real world test. I will be painting the front panel as well. And then you'll see the wiring too! The naked truth! I promise!

I have another LA2A ready to be done and after that I have 2 GSSLs with sidechain to do. After that I am planning a Supro s6424 build.

But I would also like to do 2 Pultecs and then a bunch of preamps.

But I really need to get back to my music as well.

What about you? Anything in the works?

jim

 

[AnalogPackrat]

Jim,
Hey, those 100k plate resistors with the 12AY7 were all CJ's idea! I see you've definitely got the DIY bug. I've got a pile of stuff to work on, too. I'm currently stuffing some of Fabio's 1272 boards and some Neve Outs, too. I've got a dual What compressor (Fabio style with DOAs and iron) ready to build, V72, NYDave passive EQs, passive mixer, CJ one bottle, NYDave one bottle, Firefly guitar amp, Vox AC-4 amp, another pair of 1272s using Marinair iron, lots of analog synth stuff...it's a disease! If I ever build a second LA-2a thing it will be CJ's all octal version.

Looking forward to more pics of your build. Enjoy your vacation!

A P

 

[imo]

AP and Jim,
First, congrats on getting everything going Jim! It is a beautiful sounding compressor. I have mine up and running, paired with an Elux 251, and the combination is pretty phenomenal. I was wondering if you guys had any info on the tube sub (the 12Ay7 for the 12Ax7) I couldn't find it, and i vaguely remember reading about it when i originally scoured the thread. Where are the 100k resitors in the circuit? I would love to have a bit more headroom with the compressor.
Thanks
Ian

 

[emx]

Just Curious about something. I picked out an output transformer for my unit with 50%High nickel and 50% Iron as the other option was all high nickel and I had read somewhere that the bass response in iron heavy cores was better. Is nickel known for being more high end heavy? I write bass heavy music so I thought the 50/50 would be better even though it was cheaper. Just wanted to get more opinoins on this matter.

 

[Bluzzi]

[quote author="imo"]AP and Jim,
First, congrats on getting everything going Jim! It is a beautiful sounding compressor. I have mine up and running, paired with an Elux 251, and the combination is pretty phenomenal. I was wondering if you guys had any info on the tube sub (the 12Ay7 for the 12Ax7) I couldn't find it, and i vaguely remember reading about it when i originally scoured the thread. Where are the 100k resitors in the circuit? I would love to have a bit more headroom with the compressor.
Thanks
Ian[/quote]

Thanks Ian,

The resistors to replace are R9 and R13. I haven't tried it yet and may do so in future.

I have another LA2A to do with A10 and A24 but if I had any suggestions for others it would be to use an input transformer with less gain. Even I may just sell my UTC iron and buy Jensen or Sowter.

OK, I found the thread with the tube talk. Go to page 4 of ...

http://www.groupdiy.com/index.php?topic=231&postdays=0&postorder=asc&highlight=12ay7&start=0

jim

 

[imo]

Thanks Jim. I found the thread. I have put in the 12Ay7 and the 2 100k plate resistors. Will report back on sound soon. The AY7 does seem to be getting really hot, though all of the DC voltages look to be pretty close to CJ's from his schematic.
Also I have noticed no roll of on my unit up until past 25k. I am using the variable cap for C4. The best results i had was running the variable, turned to its lowest value in series with a 150p with the + leg floating. Then i was able to get a mild (1/2 db) drop around 16k.

Anyone have any ideas on this?
Ian

 

[API]

Hello,

I am having a number of problems with my Bloo LA2A!
I have completed my build and double checked all my connections, tubes light up and all voltages seems to be right.
But, there is almost no volume on the output, what ever i put in i get maybe a tenth of it on the output with full gain.
Also, there is no meter movement (the adjust works though) from the audio.
There is a large hum from the +4 and +10 settings, and also the switch pops when i turn it to these positions.
What else, only one half of the neon is lighting up, is that normal??
It tried it with the T4B out and then there is no signal at all on the output.

Another thing i noticed from Coyastas layout was that i do not have C6, C14 or R30 in my circuit!
Do i need these??
They were not mentioned in the Bloo manual.

Does any of these symptoms ring a bell with anyone???
Any help appriciated!!!

For the record i use original UTC A-10 and A-24 iron, and a original UREI T4B.

Regards,
Dennis

 

[AnalogPackrat]

API,

As far as the missing components go--those are all related to the stereo link stuff, so you don't really need them unless you plan to run a linked pair. If you do want that option, you'll need to add them per the schematic.

On your other problems, it is hard to say, but since you say you get no output at all without the T4b, something is definitely wired incorrectly. The T4b operates as a variable resistor (actually two--one for metering and one to actually modulate the signal) that shunts some of your input signal to ground. The amount of shunting is controlled by the sidechain amp (V3 and V4). With no T4b unit in, you should be able to control the output level with the gain pot and view the output level on the meter (+4 or +10).

Also, since your metering switch changes the output (the hum and pops which should not be there), you should carefully recheck the wiring there. I messed mine up the first time (lots of people have).

Have you tried messing with R3 and R37? It's easy to get those wired backwards and then have them turned all the way the wrong way.

Can you post your DC voltages on V1 and V2 with no input signal and no T4b present? Can you also describe the connections you've made on the A-10 including the way it connects to R5 and R6?

Cheers,
A P

 

[API]

Hi again.

Update:
I was wrong on the level thing, i had connected the signal in the wrong way (out of phase!) so now i have stronger signal coming out of the input transformer than what i put in.
Also, have checked the output transformer and its also working.

I was also wrong about not having any output without the T4B, i have the same output level with or without it.
The output pot works, but i dont get any meter reading.
Also, the switch still pops when i change from GR to +4 to +10.

Where should R3 and R37 be set??
Is there a standard position??
The wiring of these are correct as well.

Checked the wiring of he switch and i cant find any faults.

Here are my DC readings for V1 and V2.

V1:
1: 119v
2: 0v
3: 1.23v
4: 6.3 heater
5: 6.3 heater
6: 230v
7: 0v
8: 3.86v
9: 6.3 heater

V2:
1: 103v
2: 0v
3: 3.9v
4: 6.3 heater
5: 6.3 heater
6: 230v
7: 79v
8: 109v
9: 6.3 heater

Does this make any sense to you??

Also again, it looks like only "half" of my neon lamp lights up.
Is that normal???

Thanks,
Dennis

 

[AnalogPackrat]

API,

Glad you got the A-10 wiring sorted...now on to the other issues...

[quote author="API"]
The output pot works, but i dont get any meter reading.
Also, the switch still pops when i change from GR to +4 to +10.
[/quote]

What output pot? You mean gain? You don't get meter reading for +4 or +10?

Where should R3 and R37 be set??
Is there a standard position??
The wiring of these are correct as well.

RTFM. Somewhere in there it tells you which way to turn them before you start testing it. I want to say its all the way CCW, but there's a 50% chance I'm wrong. Don't have the manual with me at work.

Here are my DC readings for V1 and V2.

V1:
1: 119v
2: 0v
3: 1.23v
4: 6.3 heater
5: 6.3 heater
6: 230v
7: 0v
8: 3.86v
9: 6.3 heater

V2:
1: 103v
2: 0v
3: 3.9v
4: 6.3 heater
5: 6.3 heater
6: 230v
7: 79v
8: 109v
9: 6.3 heater

Does this make any sense to you??

Are you sure your reading on V1 pin 6 is 230V? That's about double what you should see. Check that R13 and C2 are wired correctly and that R13 is really 220k. Pin 8 is too high, too, but it's probably because of the pin 6 problem. Just for fun check R14, too. V2 looks OK.

Also again, it looks like only "half" of my neon lamp lights up.
Is that normal???

Mine acted funny because I had wired R4 backwards. Which way does the needle move relative to R4 when the meter is in GR mode? What's your voltage on the neon (between the neon and R28)? Does the brightness of the neon change when you sweep R4 around?

A P

 

[API]

Hi again.

Yes, i am glad i sorted out the A-10!!

API wrote:

The output pot works, but i dont get any meter reading.
Also, the switch still pops when i change from GR to +4 to +10.


What output pot? You mean gain? You don't get meter reading for +4 or +10?

Yes, sorry, i am talking about the gain pot, R1.
When i turn it the output level changes, but ther meter just sits still at the far left with no mevement, bith on +4 and +10.

Quote:

Where should R3 and R37 be set??
Is there a standard position??
The wiring of these are correct as well.


RTFM. Somewhere in there it tells you which way to turn them before you start testing it. I want to say its all the way CCW, but there's a 50% chance I'm wrong. Don't have the manual with me at work.

RTMF=Read The Fu***ng Manual ??
That was a new one for me!
I found nothing in my Bloo manual about these to, not even what they were used for!
Does anyone know which way to turn for basic testing??

Are you sure your reading on V1 pin 6 is 230V? That's about double what you should see. Check that R13 and C2 are wired correctly and that R13 is really 220k. Pin 8 is too high, too, but it's probably because of the pin 6 problem. Just for fun check R14, too. V2 looks OK.

Yes, i got a 230v reading here, bad i guess?
Will check the wiring and value of R13 tomorrow and let you know.
Will check R14 to.

Mine acted funny because I had wired R4 backwards. Which way does the needle move relative to R4 when the meter is in GR mode? What's your voltage on the neon (between the neon and R28)? Does the brightness of the neon change when you sweep R4 around?

From memory the meter moves in the same direction as i turn R4 in GR mode.
Is that right??
The voltage between the neon and R28 is about 60 volts, which i think is correct.
The neon shuts down when i am at either end of R4 (at least when its fully CCW), will double check tomorrow as well.
And again, only of the "wires" in the neon lights up at all.

Regards,
Dennis

 

[AnalogPackrat]

[quote author="API"]
Yes, sorry, i am talking about the gain pot, R1.
When i turn it the output level changes, but ther meter just sits still at the far left with no mevement, bith on +4 and +10.
[/quote]

So you can hear gain reduction happening but it's not showing on the meter?

RTMF=Read The Fu***ng Manual ??
That was a new one for me!
I found nothing in my Bloo manual about these to, not even what they were used for!
Does anyone know which way to turn for basic testing??

See, I was wrong, twice! It's full CW and it's not in the manual! I think it's somewhere in the first 50 pages of this thread...sorry.

Yes, i got a 230v reading here, bad i guess?
Will check the wiring and value of R13 tomorrow and let you know.
Will check R14 to.

Yeah, something is definitely wrong around there. Hope you can find it.

From memory the meter moves in the same direction as i turn R4 in GR mode.
Is that right??
The voltage between the neon and R28 is about 60 volts, which i think is correct.
The neon shuts down when i am at either end of R4 (at least when its fully CCW), will double check tomorrow as well.
And again, only of the "wires" in the neon lights up at all.

Sounds like your neon is fine. They aren't bright. If you've got 60V and can adjust the GR offset, you're fine. I think you may have something wired wrong on your switch, though. Or maybe you have a shorting switch and it's putting that DC offset on your output :shock: . Did the switch come with your kit?

I think you're close. Just get that V1 thing fixed and check the meter switch again.

A P

 

[API]

Hi again.

So you can hear gain reduction happening but it's not showing on the meter?

NO, there is no gain reduction.
What I can do is adjust the volume from zero to full (which is not much) with the gain pot.

See, I was wrong, twice! It's full CW and it's not in the manual! I think it's somewhere in the first 50 pages of this thread...sorry.

He, he!
No problem, have found the Bloo manual quite dull, lots of missing info.
I guess its full CW when you look from the back??

Yeah, something is definitely wrong around there. Hope you can find it.

Will check it out later today.

Sounds like your neon is fine. They aren't bright. If you've got 60V and can adjust the GR offset, you're fine. I think you may have something wired wrong on your switch, though. Or maybe you have a shorting switch and it's putting that DC offset on your output Shocked . Did the switch come with your kit?

Ok, actually my neon is quite bright (because only half of it is working??).
Yes, the switch came with the kit.
Will double check that it´s switching as it should.

Is there any known wiring faults in the Bloo manual that i could have done??

Later,
Dennis

 

[API]

Hi again.

I am on tour for a few days so i wont be able to check things out.
But i do found something wrong.
The position of R12 and R14 are switched!
This fault is in the Bloo manual, and i had not double checked this to the schematic (which was right of course!).
Will chenge the position of these when i get back home and report what i find out.
Hopefully i will get some better voltages.

Thanks,
Dennis

 

[AnalogPackrat]

Dennis,

That would be a problem! If you fix the resistor swap I bet you will have normal operation of the audio path (V1 & V2). You may still have something wrong that is preventing compression from occurring, but at least it should pass audio.

So, if you can get normal operation of gain, but without compression, try this next. Hook up a signal to the input, pop the cover off of the T4b, turn off the lights and watch the EL panel. Does it pulse with the input signal?

Keep working on it, you'll get there soon. I will check my Bloo manual again tonight because I vaguely recall that I found an error in it when I was building mine--I think one step referred to the wrong capacitor. I'll post what I find

A P

 

[AnalogPackrat]

Dennis,

I checked my manual when I got home. I had marked the R12/R14 corrections, so either I noticed it or someone posted on this thread about it. The cap error I remember is on page 13, last sentence. It refers to C3 isntead of C5, but it's pretty obvious since it specifies the 10uF cap. I don't see any other corrections marked in my manual...

Cheers,
A P

 

[API]

Hello again.

Now i am back home at the tech desk!!!
So, i switched R12 and R14 and that helped alot!!
I now have the correct voltages on V1.

But there are still problems.
The Gain pot now works better, but when i turn it up everything works good up to 70 (on the Bloo), about 10 past, then it all gets muffled and every time i go past the 10 past mark there is a small pop.
Also, the meter follows the gain pot, even if i do not have a signal applied.
And when i go past the 10 past mark the meter hits the full mark.

Another thing, when i am in +4 and +10 mode, if i tap the meter switch the meter jumps back and forth!
Also, the same thing happens when move the cable that goes from the switch to the output xlr.
Do i have a grounding problem???
Or???

Another thing that was left out in the Bloo manual was the linking between A11 and A14.
This helped the gain pot issue a bit but it still pops at 10 past and gets muffled, but opens up a bit again at 15 past but dies again at full on.

One strange thing is that when i set the gain reduction pot at full CW it also effects the gain pot.

I still have no meter reading in GR, and meter does not show the output volume, it just goes up according to where the gain pot is set.

Maybe i have to low input volume??
I read something about this in the early pages of this thread.

Any ideas????

Regards,
Dennis