D-LA2A Support Thread

I took a quick pic of mine that I finished a few months back.  I built it to be more of a buss comp but I have found it works just as well as my other LA 2A for tracking.  I really like this compressor.  Great sound and great build.

I did stepped gain switches, and a few other nice little mods.  The center switches are a stereo attenuator (0, -2, -4) and the other two toggles are 3 positions with different output load resistors.  Thanks everyone for your help!

jplebre said:

Desol, so you find yourself popping the hood all the time for the 1M?

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It depends on where the unit is located. Like the other guys said, if you put it in a rack and you calibrate it after a while, that's where it'll end up every time....unless you move it and change the relative temp (ie: inside/outside of rack) ...then it'll be somewhere else. I don't worry about it too much.

OK, almost finished my D-LA2A. Had to wait a bit for the optos, but got them recently and time to finish this project off. Still have a small problem with the right meter. It worked fine for a while, but I suspect that while adjusting R25, went to far and fried it. Confirmed this by bridging the signal to the left meter and all works as it should. The zero position adjust is not linear, but a parabola, where the lowest meter adjustment is in the middle, and going either direction from there will increase the needle's position.



Quite a few mods thrown into this project. I had scoured through the posts and decided these where what I wanted.

12AY7 tubes for the first stage of the amp with corresponding 100K plate resistors for less gain. The picture of the front panel is showing the unit at unity gain receiving a 1.23v input signal. There is a slight 1db difference between input and output in bypass. Whatever.

Added Kingston's mod of shorting the 68K resistor after the input transformer in addition to the 2K7 comp/limit resistor to give it about 6-8db more gain when using it strictly as a tube amp. Was worried about sending the signal up to the front panel and back right after it comes off the input transformer, but it works great. This is the added "Preamp" selection along on the Comp/Limit switch.

Drive control reduces negative feedback. Replaced R11 with a 50K resistor in series with a 500KA pot. Also works well as a fine gain control between the gain steps when testing and adjusting the meters.

SC HPF on front panel.

T4B Optos are from Kenetek

Stepped Gain and Peak pots.


Have to say it all went together fairly easy. Had connected one output transformer backwards making it a step up instead of step down transformer. oops.  And one of the resistors in the gain pot were shorting causing full gain at only the second position. Yikes. Pretty easy fixes all in all. All voltages seemed a bit lower than expected, but pretty consistent.

Finally fired it up and throw an instrumental mix as well as a drum mix at it. Very nice indeed. Not too heavy and very smooth. Didn't measure the noise, but I had to crank about 3/4 of the gain before I was hearing anything.


Thanks for the boards Volker, and all the effort.

Front panel was done at Prodigy Laser. Great service. Chae noticed a small missing text as I had to redo the file into a Correll format and missed it on the redo. Very fast turn around too. Way cool.

It sure is great how everyone puts a little something into a project like this. May thanks to ALL the contributions.

Great build - you must be very proud

Hi,

Ive just finished building my unit. All seems to be working fine. The only problem im having is the power for the LED VU Meters and the Bulb. I am currently taking the power from the 5V section on the power supply on the far top right of the board but i am finding that the VU's Flicker and drop in and out. Is there a better place to take the 5V tap from? I put some resistors on the VU Meters LED's and it's better but still not constantly on. I am using the Hairball Audio VU Meter and normal fender Bulb.

Jon

question on heather and AWG.
The 12AX7 pull 300mA, the 12BH7 600mA and the 6AQ45 pulls 450mA if I'm not mistaken?

Since the 2 channels are separate, would 24AWG wire be ok?

And, back with another question. After enquiring on the T4B, I've noticed the original schem has a 2.2M resistor (R8) across pin 3 and pin 1/4 of the opto.
This resistor is not on the board and from the looks of it (old T4B pictures) is quite massive - probably 2w or more.

Should I install this resistor inside the T4B ? if so, in which cases?

I'm building a T4B replica with EL panel, not vactrols.

Thanks

Bump on the wire gauge for heaters.
According to farnell, my cable is rated 600v/10A

Should be fine for the heaters, no?
http://uk.farnell.com/alpha-wire/3071-bk001/wire-ul1015-22awg-black-305m/dp/1199054

Should be fine

Has anyone got any thoughts on my VU Meters? I am still having the same problem.....

Sounds like you may have an intermittent connection somewhere on the 5v supply.
What voltage are the led's rated at, that you used>?

Just keeping asking yourself questions and searching and measuring, etc...it's something minor and i'm sure you'll find it.
Just be very careful with this circuit. I've felt the power behind it.

The VU Meters are rated at 3.6v-5.2v 20mA (Hairball Audio Meter). I also get the relays ticking over of there own free will when i have the VU meters LED connected and i have been working the compressors for a while.

have other people taken the 5v for their VU Meter LED's from the 5v supply on the board that is meant for the relays?

jonathanmorbin said:

have other people taken the 5v for their VU Meter LED's from the 5v supply on the board that is meant for the relays?

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yes, I do - with no problems (and I have light bulbs in the meters, your 20mA LEDs shouldn't be any problem)
do you have a proper heatsink on the 5V regulator?

Hi Just finishing my build and I am in the troubleshooting stage!!!

I have a couple of questions/queries the answers to which will hopefully help me to solve the issues I am having.

1. The BYPASS/IN switch - When in the BYPASS mode how should the unit behave.?  I understand the unit should pass audio but does this just bypass the compression stage? Should the VU meter still show the input level and the gain pot still effect input level in the BYPASS mode?

Currently when in BYPASS the unit passes sound and the Gian POT works for input level. The VU meter shows input level BUT the Gain Reduction does nothing.

When I switch to IN I get silence.Nothing works and nothing is shown on the VU meter.

I know people have reported problems with relays being incorrect and I know the fix for this BUT does this sound like this is the problem or does this sound like something else ( possibly wiring ).

I purchased the board fully populated and therefore am unsure exactly what relays were fitted and I don't want to go about desoldering them if the problem lies elsewhere.

Any help geatly appreciated.

Ian 

Ian, is the unit passing sound when not powered up?

While SSLtech does not believe in bypass, the D-LA2A has a "true bypass".
with no power (or not switched to "In") the relays are passing the input XLR to the output XLR,
no signal to the circuit, nothing shown in the meter (neither output/VU nor gain reduction)

Hi,

Thanks for the fast response - no audio passes through the unit when power is turned off. Does this therefore mean the relay is of the incorrect orientation?

Regards

Ian

Yes, there is something wrong.
Could you post a foto of the relays?

Yes I will take one later and post it. many thanks - I was pretty sure this was the cause of my problems.  I read earlier in the thread that they simply reversed the power traces to the relay switches and removed the diode and this corrected the problem. Maybe I should try this.

Attached is a pic of the whole board showing the relays (if this helps) i will take a close up later and post also. From memory they are GS5,s


Ian

g9builder said:

... I read earlier in the thread that they simply reversed the power traces to the relay switches and removed the diode and this corrected the problem. Maybe I should try this.

Attached is a pic of the whole board showing the relays (if this helps) i will take a close up later and post also. From memory they are GS5,s

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G5V2 would be right. If it is G6 (polarized) removing the diode and reversing the power traces will work - however: without any power the footprint is the same = unit must pass audio!

wrong XLR wiring?
regards
Bernd