LA-4 Help Thread!

[dirtyhanfri]

...

 

[dirtyhanfri]

The meter switch

 

[gary o]

Pic a little fuzzy.....tour gonna need to hunt for shorts or mistakes round the IC 2 area .....&  ratio switch too even when you think its all ok keepimg looking its usually the simplist thing that you checked over & over...if you have a few ICs you could put one of the ones that got hot in the IC 1 position to test the IC to hear if it passes audio or  if something is killing them.....I had a hot IC 1 it was dead I must have shorted it somehow ......

 

[dirtyhanfri]

Hi

I followed your advice and started checking simplest things, starting by resistors values, I´ve found some of them with strange values.

In the area around Ic2 and points 17, 18 etc.

Also near Ic3, the 4k99 1% and the 10k were bad too.

I´m almost sure I´ve checked the values before soldering... Could something damage them? This build has been in many issues, bad transistor orientations, burned 15R resistors, bad powering... So I think it wouldn´t be so strange.

It´ s time to sleep a bit, got work tomorrow soon, and then I´ ll get some 074's, change the bad resistors, close my fingers and hopefully start enjoying the calibration process....

Thanks

 

[tzman]

Hi

I followed your advice and started checking simplest things, starting by resistors values, I´ve found some of them with strange values.

In the area around Ic2 and points 17, 18 etc.

Also near Ic3, the 4k99 1% and the 10k were bad too.

I´m almost sure I´ve checked the values before soldering... Could something damage them? This build has been in many issues, bad transistor orientations, burned 15R resistors, bad powering... So I think it wouldn´t be so strange.

It´ s time to sleep a bit, got work tomorrow soon, and then I´ ll get some 074's, change the bad resistors, close my fingers and hopefully start enjoying the calibration process....

Thanks

Always make sure to check resistors values out of circuit. The other components on the PCB will influence the resistance of your reading (because there are other component in series or parallel with the resistor). So if you would like to check the values of the resistors, try to unsolder one leg, take that leg out of the PCB and then check the value...

 

[dirtyhanfri]

Ok, I thought that without power, and measuring just in the legs (on the component side) would be ok...

I´ ll check with one leg out tomorrow, thanks for the tip.

 

[dustbro]

I'm experimenting with an old meter I got off of ebay for my next LA-4. It's an old Simpson model 745, and I cant find any info on it.
Metering +4 and +8 work fine. I can get the meter to zero when set to GR, but any signal that crosses the threshold will send it into full deflection.
Does this mean that I need to add a rectifier to the meter? or is there a tweak I can do to the circuit to make this meter respond properly?

 

[pedroplanet]

And finally my unit is done!

Used vactrols and Api style output transformers

 

[pedroplanet]

messy wiring

 

[kepeb]

'treshold' oops.
looks nice

how did you do the white on red print?

 

[pedroplanet]

'treshold' oops.

ahahahah!! I haven't noticed this!

nevermind, it sounds great!

I painted it with some paint left from my red car

 

[dirtyhanfri]

Looks so nice, I love that colour, congrats.

I´ ll back in the work with mine today, after sucessfully building a SSL9k Mic Pre.

 

[dirtyhanfri]

Still stucked on this...

I`ve replaced the Ic´s, put back the Vactrol, soldered according to the pdf, and using a 15K resistor instead of 82K and 10K trimmer instead 500R. Somewhere in the first pages of this thread I`ve read something about 2K5 trimmer, would be correct?

Right now I have compression on 12 & 20:1 ratios, lower ratios acts strange, also I keep with no output on the meter...

Any ideas? I´m almost sure there´s no shorts or bad solderings....

Actually I can hear compression in higher ratios, Maybe I´ll try to adjust the trimmers...

 

[dirtyhanfri]

Well, this is going on!!!

I can calibrate the needle to stay in 0, I can hear the compression, niiiiiiiiiice.

But, the sound us so ugly, Low end loose up to 1Khz, crispy sound.

Also, back in the meter, in +4 and +8 it moves a little, around -20, but I think I got to install the Germanium Diodes, when I play a drum track in it, the needle oscillate so fast with cymbals and hihats (high freqs) you get me guys? Got to look deeply into that, and look for a schematic of the germanium diodes connection.

Metering doesn´t care me too much, I could live with just GR Metering, but, the sound is quite ugly, and I got to solve it, I had similar issues with mi SSL9k Pre, (I was using tantalums instead electrolytics in some caps and that was the cause) Maybe the 6.8uF electrolitycs in the audio path?
I remember they are 50V and no 63 as the BOM says. Swapping IC´s didn´t change anything....

I was reading the whole thread looking for someone with similar issues with no luck... I´m thinking (intuition) that this is because a bad cap, but I´m not sure. I´ve cheked my tranny wiring and it looks ok...

I´m almost there, finally, surely this is because a silly mistake by me. Right now I´ll go to the studio and look deeply into that, I´m gonna recording some tracks the next week and I´d like to use this comp.

Thanks guys!

 

[MikeClev]

But, the sound us so ugly, Low end loose up to 1Khz, crispy sound.

I had this problem when I first tested mine. It turned out to be a problem with how I had wired up the transformer and output meter. Double check your connections!

Mine is calibrated perfectly now, sounds really great with no or minimal compression, but I get distortion when compressing, gets worse as you increase the compression. I am using two VTL5C3s...  Anybody got any ideas?

I couldn't find any accounts of anybody using VTL5C3 in the LA-4, so perhaps it just isn't suitable?

 

[gary o]

Dirtyhanfri I think yr right I would forget about the meter for now.....I would guess something else is wrong elswhere causing bad sound & strange compression.....the diodes can be added to meter later....I wouldnt say different cap types may make it sound ugly usually the difference in caps is very small & comes down to personal taste....It seems like yr ICs are ok then you have swapped them all around so that is good...

Im not a real tech maybe some one else can help you better..........but I would first make sure PSU is supplying the right + & - voltage ......get the thing to pass audio nicely with no compression......once happy with audio I would look at the compression side chain in this case I wouldnt trust the meter (for now)......I also would trust the vactrtol I would wire an LED the correct polarity onto the side chain circuit this way you can see the LED light when you play say a cd thru the la4 if compression is on & threshold low enough......you should then see more light if you turn the CD sound up or threshold further down & so & you will probably see the difference with the ratios too.......at this point of coarse you wont get any compression so now you can connect a LDR (forget meter one for now) any old one for now really just to test.....when connected the daylight will cause output to fall as if compressing, put thumb over LDR output level back to normal......hey presto it works ,I hope, for rough test put led in match box with LDR & you should get audio compression......then look at the meter circuit once working

As I said Im NO tech this is just some of the things I would try... so please clever chaps reading Im sure you have some great advise for us....

As I post I read you have a reply so some of this may not apply....


thanks all the best

 

[dirtyhanfri]

Ok, I wired the tranny again and now it sounds good on my humble test rig (ipod and sh*tty speakers), low and high freqs, compression and the meter working apparently ok in the GR Mode, (+4 and +8 still bad) sounds fine.

Time to start trying it in the studio, thanks!

 

[dirtyhanfri]

Well, I´ ve been recording some voices with it right now (after a ssl9k pre) and looks to work ok, couldn´t calibrate it, but the sound was ok. Compressing nice with no ugly distorsion.

Thanks to every people sharing info to make this project possible, this is a great build!

 

[MikeClev]

Okay.. I switched R13 for a 150k and trimmer R34 for a 10k trimmer. It wouldn't calibrate close enough for my liking, and while I was poking around I busted the two vactrols (2x VTL5C3). Bummer.

I had a couple of VTL5C3/2s around so I decided to try one of those (they are the dual ones)

Bingo! A little tricky to calibrate, but now its working just great.

 

[Rybow]

It's good to see you have made some progress dirtyhanfri! Sorry I haven't been around to help out. Been going through a move at the moment.

The metering issue. Even though your meters are rectified (should be according to the data sheet), it is not a true VU response. Joe Malone had a good article on it somewhere. That's why the needle jumps all over the place. If you want to slow it down to be closer to a true VU response, throw a 470uF/50V capacitor across the meter terminals.

Just wondering why you installed a 15k in place of the 82k? I know Luny posted a bit back about a mod for timing, but I think that was a 150k resistor. I tried it, but I couldn't get it to calibrate. Went back to 82k.

You guys are making me want to use my LA 4's so freakin bad! Unfortunately, they are stuck on a ship[, and I won't see them for 3 more months.