D-LA2A Support Thread

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I am still experiencing that hum in channel 2. If the gain knob is turned up past 8 the audio cuts out and the meter pegs. i took another looks at R229 and R234 and although they both read good on a meter I am still suspicious. Would a compromised resistor due to a short in 6AQ5A in these locations potentially cause the problem? Since these are pretty beefy resistors I wonder if another component is blown.

Will have to probe around with my meter. I have a scope but have never really used it. Are there points in the circuit I should check first for the noise? Thanks, guys.
 
Update: I replaced R229 and R234 and am still getting the signal cutting out and meter pegging at 8/5 on the gain knob for channel 2. Looking at the back of the board i'm pretty sure the heater short was on the side of C206 that connects to R234. Reading the chain a bit more it seems that my issue may be a result of high frequency feedback? Wondering if RV237 may be compromised. Have read other posts where wiring issues were at fault...things seems fairly in order there. Will have to keep poking around.
 
bernbrue said:
the plastic washer between regulator and heatsink is VERY important!!! If you look closer you will see that the metal screw is also isolated from the heatsink (ground).

IMG_20131223_193224_721.jpg


regards
Bernd
Click to expand...

thanks!
this totally solved my issue. i have one last question regarding this project. i have the original utc transformers installed. and im wondering if i should mount them isolated in order to not get any ground loop. is this correct thinking? or will it not matter?
 
bernbrue said:
the plastic washer between regulator and heatsink is VERY important!!! If you look closer you will see that the metal screw is also isolated from the heatsink (ground).

IMG_20131223_193224_721.jpg


regards
Bernd
Click to expand...


I go as far as using nylon nuts and bolts as well. They tighten nicely, and make it pretty impossible for their every to be electrical contact to the heatsink.
It might be overkill, but it give me piece of mind particularly with gear that travels!

http://www.jaycar.com.au/productView.asp?ID=HP0160
 
What is the mouser part # for this?  Anyone know?

 

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Also will this work for the ICI?

I'll just install in on it the chip and leave it in a vertical position so it doesn't touch anything.

 

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In the Drip boards he calls for C8A to be .01uf and C8B to be .022uf both at 400volts.  What should we use?  .032uf?

I know the pdf says 0.1uf wima but is this correct?

Thanks.

edit: I have an extra one of these from another project will it work since its after the diodes and should only be in a 5volts area?  Its rated for 50volts.

http://www.mouser.com/ProductDetail/TDK/FK26C0G1H104J/?qs=%2fha2pyFadugcXy8xf4igHin1m%2fc0OvUEBPD1Rk13R4USHU6Mw11W9w%3d%3d



 
Ok Guys,

My D-LA2A is up and running no smoke or flames, hahahahah.

I have not calibrated yet and I still have to wire up the jewel Lamp and Meter lamps. 

I have a couple of questions that I notice just from running a quick drum loop through it

!.  First is the Right side gain pot since it is so close to the power switch has a buzz and I can change the sound when I move the AC wires, how do you guys deal with this.  The wires running to my pots are all shielded but I think the interference / buzz is coming from the solder connection areas cause when i touch it it changes again.  Should I twist the AC power wires?

2.  The left channel seems hotter (Gain wise) that the right.  I did do the 25k pot 75k resistor.  Didn't check if the resistors are matched would that matter?

3.  My ne2's that are on the pcb next to the t4b's are flickering the left side more than the right.  Is that normal?

4.  the output meter works on the left side however the GR meter doesn't move, I have swapped the two molex's on the pcb but still the GR meter doesn't work.  I do hear the compression but it just doesn't show on the meter.  Where can I look to fix that?  Right side work great for both output and GR.

I am so excited about this project.  I will have pictures coming very soon.

Also like to thank Josh aka (California Road) for selling me his 85% built kit.  Wait to you guys see this faceplate.  Killin!!!!


-Scott







 
can someone help me.

The unit passes audio just fine.

bypass works great however with the peak knobs unplugged from the pcb and no t4bs installed i have an issue.

The left pot seems hotter than the right one.

To get zero on the meter with a test tone the left pot is at 20 on the front panel and the right channel has to be at 35.

I have not calibrated the unit yet as I though it would be important for the gains to be equal first.

I measured the pots for ohm and they don't get the same reading in the same spots, i did off, 1/4, 1/2 and 3/4 turns i could see if they were a little off but they are not close.

Should / can I get "MATCHED" pots?

I have the ones that are in the bom for the 25k and 75k resistor mod.


errrrr. Thanks in advance.

-Scott



 
Hi,
I suggest to finish the unit completely before spotting any errors. Then you should calibrate the compressor. There are lots of information about how to do that.

http://groupdiy.com/index.php?topic=32677.msg553490#msg553490

Since we do not know which case and frontpanel you use, we can´t comment on your buzzuing issue. AC wires must be twisted.
regards
Bernd
 
Thanks for the info Bernd.  I have reread those posts and anything dealing with calibration. I have included a video of my issues.  I am getting closer but would like to get even closer and put the lid on this thing

Still having issues trying to calibrate this thing.

I don't think it should be this hard.

Everything seems to be working just not reading correctly on the meters.  Check out the video I think it explains a lot.

https://www.youtube.com/watch?v=VHM9MeaYZl0&feature=youtu.be
 
Ok So I have found a few things out that I must do.

I have to add a 3.6k resistor to my hairball meters.  This will hopefully adjust the 0vu in the meter so that when I get zero on the meter the incoming signal will be the same as the out in my DAW.

I will also add a 100k trimmer set to 33k for the RX25 resistors I guess the real 33k resistor are causing it not to track right so i need to either go higher or lower on these.

I have tested my pots with nothing connected to them.

Here are my results

Gain Pots set to      Left          Right      Difference
0                        24.63k        25.7k        1.07k
20                      24.25k      25.34k      1.09k
50                      21.94k      23.07k      1.13k
80                        7.01k        8.28k      1.27k
100                        30R          4.5R      25.5R


PR Pots set to        Left        Right        Difference
0                        103.8k      87.7k        16.1k
20                        98.7k      82.9k        15.8k
50                        88.8k      73.3k        15.5k
80                      23.86k    15.84k        8.02k
100                        1.8R        1.7R          .1R


Could the difference in gain pots be why my gain knobs have to be at different spots when sending a 1k tone through the la2a.

I ordered new bourn pots. 

http://www.mouser.com/Search/ProductDetail.aspx?R=PDA241-SRT02-253A2virtualkey65210000virtualkey652-PDA241SRT02253A2
 
The 3,6k Resistor is needed, for every VU Meter (not Hairballs fault).
This will help for sure.

For the Pots: they do have tolerance, especially log versions.
The new ones you ordered are specced to 15%.

So - all looks fine right now, don't worry.
 
Ok Boys and Girls I am real close I can smell it now.

I have installed the 3.6k resistors on the positive side of the meters and now when my meters read zero my daw reads the same input reading as the output.  DONE

I made the adjustment at RX04 for the GR to Zero Out on the meters.  DONE

I have installed new gain pots and I am still having and issues with one pot needing to be turned higher than the other to get equal gains returns in my daw and on the meters.

The left channel is almost at halfway up about 47 on the faceplate scale for the meter to read zero.
The right channel only needs to be turned up a quarter of the way to 25 on the faceplate scale in order for the meter to read zero.

I have installed new 25k pot with the 75k resistors.  Why are these not closer?  Is something happening on the left side that is cause a gain drop?  Could a tube be bad. 
How can i get these gains to track closer together?

:-*OK BOTH POTS are now tracking the same both are about a quarter of the way up for the meter to read ZERO.  The problem was the resistor of the left must have became a cold solder from installing the new pot.  So now onto finishing the calibration.

Thanks
-Scott






 
OK, Its all done, HAHAHAHAHAH

Fully built and Calibrated.  The Pots and the wiring on them were the biggest issue I guess.

I suggest anyone building this to install  trimmers at RX25.

Everything works great. 

Gains settings are just a hair off from equal on both sides.
I am getting an accurate 5db of gain reduction on both sides and when I link them they are both perfectly equal.  But even without the link they are less than .25 of a db aways from each other.
Pretty cool.

One little issue remains and that is a hum in the right channel once I raise the gain above 65.  I have all the power wires twisted but I think it has to do with the pot being so close to the Light and power switch in the middle of the faceplate.
After I fix that all that is left to do if decide if I want to put in the zeners instead of the neon lamps
Find a setting for the limit response.
THEN PUT THE LID ON AND INSTALL IN THE RACK,hahahahha.

Thanks for a great project!!!!!!!!!
 
So I am going to leave the limiter response set to open (factory set)

The hum on the right channel is from the Limit/Comp switch so I will have to remake that with shielded wire.  I have move the wire out of the way of the power switch and all is quite now so I might just leave it but for those building I would use shielded wire for the limit/comp switch.

Now where did I put my lid?
 
just ordered a bunch of parts for my new la2a..

does anyone have some of the 3watt 4.7K resistors going spare? don't find it in any of the stores here in germany, even mouser backordered them..

i still didn't get the whole "zener diode" thing. what do i actually need? led's? only my meters?

thanks for your help!
weiss
 
Sorry I don't have any resistors.

You can replace the neon lamps with a 62v 5watt zener diode.  They are a bit quieter and will last far longer than the neons.  I have the neons in and will seed how long they last.  The neons are mounted on the PCB and tell you that the pcb is getting juice.  Nothing to do with the meters, they have led's in them.

-Scott



 

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