D-LA2A Support Thread

[weiss]

Hi,
would be nice to have bigger pictures of your built. The picture you posted cannot be found (Error 414). I had a look at the video. A few things to consider (maybe too obvious, but we have to start somewhere):

< No audio is being processed at all (compression, limiting etc)>
Maybe a silly remark, but did you do the heater wiring underneath the pcb?
Try to make your left channel work properly. Then compare it to the right channel

- Left meter does not output vu signal
3K6 resistor installed? Toggle switch wired correctly? Molex connector plugged into the right place?

I bet there are some very simple things gone wrong! Read the wiring & calibration guide attached.
Bernd

thanks, i fixed the pictures. Yes i read that guide and i soldered all heater wires as the manual says. Voltages are okay.
What 3,6k resistor do you mean? Wiring is correct and molex as well.

 

[bernbrue]

So lets do some basic tests:

- Turn all pots to 0.  Switch bypass off.  Set meters in VU mode.  Sent a signal through the unit. You should hear nothing at first, then turn up 
  the gain pots. You should hear the signal on both channels, the VU meters should twist up.
- Set the unit/meters in GR mode. The meters should stick to 0dB. Turn up the gain reduction pot. The unit should start to compress, the 
  meters should go down.

The video is quite confusing, since you hear music all the time and it doesn´t get louder when you turn the gain pot.

General things to check:
- Are the relays the correct ones? Do they click when switched on/off?
- what about the grounding? In the picture I can see, that not all ground wires go to the same star ground
- did you connect ground of the 5V psu to main ground (jumper)?
- the vu meters need an additional 3K6 resistor on their negative side.
- check direction of the diodes, that replace the neon lamp.
- check the input/output transformer wiring, especially the molex connector on the pcb.
Bernd

 

[weiss]

Hey thanks for your reply Bernd!

- Turn all pots to 0.  Switch bypass off.  Set meters in VU mode.  Sent a signal through the unit. You should hear nothing at first, then turn up the gain pots. You should hear the signal on both channels, the VU meters should twist up.

I hear the same signal in bypass mode and non-bypass mode. Vu displays -20db all the time on both channels. Gain pots do nothing when turned up.

- Set the unit/meters in GR mode. The meters should stick to 0dB. Turn up the gain reduction pot. The unit should start to compress, the meters should go down.

Meters stick to 0dB but when i want to compress via the peak reduction pot, the signal stays the same and meters don't move.

- Are the relays the correct ones? Do they click when switched on/off?

Yes, they click when turning on and off. Type: Omron G5V-2 (5V)

- what about the grounding? In the picture I can see, that not all ground wires go to the same star ground

They do.

- did you connect ground of the 5V psu to main ground (jumper)?

Yes.

- the vu meters need an additional 3K6 resistor on their negative side.

Thanks for this. But everything else should work even if i missed this resistor!?

- check direction of the diodes, that replace the neon lamp.

I did. the round mark on the diode points to north to the top of the pcb.

- check the input/output transformer wiring, especially the molex connector on the pcb.

I did so as well, using this information:

WSM600/15K: 1--Brown / 4--Green / 5--Blue / 8--Grey
WSM15K/600: 1--Yellow / 4--Green / 5--Grey / 8--Pink

 

[bernbrue]

Very strange!
Are your voltages correct? Did you measure? You should have something like 120V after R113 (220K) and 220V after R117 (10K).
If the unit doesn´t pass audio and the gain pot does not influence the audio level, there must be something wrong either
- with the tubes (V101/102)
- gain pot
- B+ voltage
- bad soldering
- broken input or output transformer

I attached the original schematic for you to check the preamp (upper part of the schematic)
Bernd

 

[weiss]

Very strange!
Are your voltages correct? Did you measure? You should have something like 120V after R113 (220K) and 220V after R117 (10K).

- I think so, R113 has 118V and R117 about 215V
- V101 is JJECC83S tube and V102 Electro Harmonix 12BH7AEH
- For pots i used 100k log b by omeg
- my soldering was never bad during my last projects, everything worked from the first start
- transfomers are all new

how can i measure the heater voltage?

 

[bernbrue]

I saw in your video that the VU meter of the right channel starts to move when you turn up the gain pot. Thus the signal passes at least the circuit up to output transformer. I myself make sometimes very obvious mistakes, so there is no accuse meant in my assistance. I suggest to double check the right channel first:

- check xlr input/output wiring
- verify that both relays of each channel are working (I suppose here is something wrong)
- check the molex connector of the input transformer
- check the heater voltage at each tube (pins 4&5, 6AQ5 pins 3&4)
- check your test setup (I saw the RME meters of your input channels moving)
- even brand new transformers can be broken, especially the Edcors you are using

Bernd

 

[weiss]

how can i test the relay? i think as well that there has to be the issue, i really didn't find any wrong wiring until now.
All my heater voltages are around 3,25-3,28V. Is that correct? And i can say for sure that my setup works!

 

[audiophreak]

Hello All,
                    After having my D-LA2A up and running for a while now (  and sounding absolutely Fantastic  ;D  )  the 6AQ5A's get very hot and extremely close to C171/172 and C271/272 - so I found a couple of 7-pin test sockets ( as I used a 3u case  ) and those caps are much cooler now , ( how ever  C171 still is hot to the touch compared to the others )  I may have to replace that one.  She still sounds awesome , so I don't think this has affected operation in any way , heres a pic

 

[brewbacca]

I tried the test where I opened one of my t4b's up and ran the unit in a dark room. I didn't see any light coming from the illuminated panel, but the meter dipped a bit when on gain reduction mode. That was probably getting light from the meters or the neon lamps.

I'm wondering if there's a problem with my t4b's. Does anybody have any suggestions for testing the t4b or the socket for the t4b? Like, what voltages should be on what pins?

Edit: I'm getting around 3.5V on pin three of the t4b socket. Is this high or low? Also, should pin 1 and pin 2 both be connected to ground? I get continuity between pins 1 and 2 on both the socket and the t4b's I have.

This is the pin order I found earlier in the thread:
1  NC
2  GND
3  EL panel input
4  GND
5  VU meter LDR
6  GND
7  Signal LDR
8  GND

Thanks guys! I'm so close I can taste the happiness

Yet another edit: After some searches it seems that yes, pins 1 and 2 do connect.

 

[offthewallstudio]

Hi everybody. I want to build this unit. I need a mouser cart for this. I can buy the PCB for a Dual LA 2A.
and the  PSU transformer from Volker.

I can buy the metal box template from Dan. I NEED everything else! lol...

Much help would be appreciated!!!!! I am new to this website and not sure how it works so feel free to email me
[email protected]

This is for the DUAL LA 2A not a single, thank you!!!!!

 

[brewbacca]

There's a link to the BOM and other super useful on the first page of this thread. You can use that to make a mouser cart. The BOM is missing a few items and I think(?) has some extra items, so I recommend reading through the pdf and checking parts in the BOM against the PCB before ordering. Also, definitely go for the 25K pot in series with a 75K resistor for the Gain pot. The search at the top of the page is also super helpful for looking things up in the thread.

Also, don't do this late at night! Aside from the dangerous voltages, it's easy to make dumb mistakes. I just finally noticed that I wired my heaters incorrectly for the 6A5QA after about a month of scratching my head trying figure out why the compression wasn't working!

Good luck!

 

[brewbacca]

Hell YES! Got this thing working finally!  ;D ;D ;D

Sounds pretty good so far. I'm not hearing a ton of noise too so I must have done some things right the first time

Full disclosure: I wired the heaters incorrectly for the 6AQ5A sockets and thus ruined some tubes. Got some new tubes and fixed the heaters.  Now I feel much more confident about tracing voltages and reading schematics

 

[offthewallstudio]

Hello everyone! I am getting ready to build a D-LA2A. I have one built 2 of the 500 series mic pres with very minor problems. Any tips or pointers would be most appreciated! Is there a list in order on how to build this? 

 

[darkus]

I just wired up my d-la2a but now i feel ive been getting mixed information.

Bernbrue said the meters need the 3.6k resistor on their negative side. In the wiring guide that i found from the compiled pdf i saw it was on the positive side. Which way is it?

Also the gain pot mod, is the resistor in series with the first pin or parallel between the two (im excluding the shield pin)

Someone said parallel earlier in this thread and on this page i read its in series, which way is it? 

Im still waiting my matched Kenetek T4B's but ive powered it up, all voltages look good, tubes are glowing etc. im so happy.

 

[jipsu]

I just wired up my d-la2a but now i feel ive been getting mixed information.

Bernbrue said the meters need the 3.6k resistor on their negative side. In the wiring guide that i found from the compiled pdf i saw it was on the positive side. Which way is it?

Morjensta

Taken from the La2a schematic, looks like the negative side.

 

[saxmonster]

I used the positive side

 

[darkus]

This is exactly what i mean. Wtf?!  ;D

The wiring guide said + so i have it there. Havent tested yet if it works.

What about the potmod wiring? Confused here....

 

[softshoe]

I'm wondering if anyone can help me. I've got audio being passed when the gain pot is at zero. (seems to be high passed audio). In trying to find the problem I began breaking connections to see if I could isolate the problem. I ended up with most molex connections removed and only 1 single 12bh7 tube and I was still getting audio.

General info:
* Both channels act identical and will pass audio with just 1 12bh7 and the input/output transformers connected.
* The channels otherwise function as expected. The gain and peak  knobs work as expected. T4bs light and will compress the audio.
* The peak reduction knob will effect the audio when gain is zero.
* input transformers are utc a-10

Things I've tried
* I tried connecting audio to the adjacent  channel to see if there was some type of short getting audio in the ground. no audio was passed
* I tried different 12bh7 tubes. (5-6) all same
* tried both channels. they act identically

I'm stumped at this point. Anyone have any ideas?

Also, should all 8 tubes be too hot to touch?

 

[dmp]

Bernbrue said the meters need the 3.6k resistor on their negative side. In the wiring guide that i found from the compiled pdf i saw it was on the positive side. Which way is it?

I don't think it matters. The vu meter is measuring current, and needs a 3.9k in series like other vu meters. It doesn't matter if the resistor is on the + or - side.

 

[saxmonster]

Hi Guys,
Having an issue with my D-LA2A now.  The left channel seems to have this high pass filter that comes on when no signal is going through the channel.  I have included an audio file of it.  Sorry for the TV in the background and the clicking clock, the wife was home hahahah.  What should I start looking at to get rid of this issue.  It doesn't seem to do it when I first turn on the unit.

I am running a elam251 clone into a 1073 clone which work just fine.  I have narrowed the signal channel issue down to the left channel on my la2a.  the right channel seems ok for now.  Thanks so much.

http://www.ehornstudios.com/media/LA2A.aif

anyone?  I got a visual on all the caps and everything looks great.