D-LA2A Support Thread

[benlindell]

Ben, if you get nothing it could be something with the relays (one switching, one doesn't).

Do you have a scope to trace where the signal disappears?

I tested the relays for continuity both In and Out and they test fine, this was my first guess as well.

I don't have a scope but an audio probe. I'm gonna follow the schematic and see how far the signal gets. I'm excited to be done with these, they sound great when working.

Any hints on the Gain problem on the working channel?

 

[benlindell]

So I'm getting signal in most places that are supposed to have signal, it's just all very low, this is all with tubes and t4B that work perfectly in the other channel, even the output transformer is getting signal as well as in and out of the relay, albeit all low level.

I think the tell of the problem is that the Gain reduction meter isn't moving from 0 at all and I hear/measure no difference when moving the threshold pot, so I'm guessing my problem is in the sidechain right? The Gain pot does have a little effect, it goes from no signal to weak signal with noise.

Where in the side chain should I be able to measure signal? I must be dealing with a defective part, I've now triple checked the resistors and caps, looked for shorts, tested continuity, used all known good removable parts...

 

[benlindell]

I went through the whole schematic testing for continuity and the darn thing is all good. Anyone have an idea for where to keep looking? I'm running out of things to test.

 

[[silent:arts]]

Ben, first make sure the audio patch is working properly.
take the T4Bs in both channels out.
do both react the same now?

 

[benlindell]

Ben, first make sure the audio patch is working properly.
take the T4Bs in both channels out.
do both react the same now?

They both get no sound now (with and without t4bs) I'm starting to feel like throwing this thing out the window, it works once then stops working again! I'm trying different transformers, different tubes, nothing works.

Edit: It's gotta be the molex on the input transformer, even though all 3 of my sowters I've tried, the 3rd one was touchy, it'd work sometime and then if i moved the wires it'd stop. I'm using the pushdown type molexs not the solder type, so now I'm gonna solder it instead and report back. Also when I injected signal into the gain pot it worked fine, lots of gain.

 

[benlindell]

AND YES it seems to have been all the molexs for the input transformers weren't making a good connection, I tested with one being soldered instead and it works, both channels! Now if I can figure out how to control the gain on this bad boy. when I'm at unity gain my gain pot measures 96kOhms (removed from the circuit). Should I try different tubes instead of 12ax7s or maybe go get a 90k res with 10k pot? Maybe it's cause I'm using a linear pot, that's probably what's doing it right?

 

[MicDaddy]

Hi Ben, I've been quietly following along the issues you've been having and am thrilled to hear you've got her worked out! 

For anyone that has stuck the 'limiter response 1M' to the front panel, are you using it and in what regard?  I'm not quite sure if I want to populate it on the pcb or stick it on the panel......    :

 

[benlindell]

Hi Ben, I've been quietly following along the issues you've been having and am thrilled to hear you've got her worked out! 

For anyone that has stuck the 'limiter response 1M' to the front panel, are you using it and in what regard?  I'm not quite sure if I want to populate it on the pcb or stick it on the panel......    :

Thanks man!

I always like what it does, to me it just makes it less sensitive to the "body" of the sound which I like to have control over when setting it up, it's almost another threshold control.

 

[desol]

I'm starting to feel like throwing this thing out the window, it works once then stops working again!

It a basic rule of DIY, that when you reach this point, if give up, your not cut out for DIY...but if you keep going...you WILL find the answer soon. Seems to be a test of some sort.

Nice to hear you got it worked out...thus far. Those molex's can be tricky. Both properly crimping and soldering and pushing them in the hole. I didn't get my proper stride till about the thirtieth one. Pretty much all of my problems with this build were wiring.

 

[benlindell]

Hi Ben, I've been quietly following along the issues you've been having and am thrilled to hear you've got her worked out! 

For anyone that has stuck the 'limiter response 1M' to the front panel, are you using it and in what regard?  I'm not quite sure if I want to populate it on the pcb or stick it on the panel......    :

Thanks man!

I always like what it does, to me it just makes it less sensitive to the "body" of the sound which I like to have control over when setting it up, it's almost another threshold control.

Here's sweeps of my unit to show the effect of the response control.

The blue line is with the response set to high and the green line is response set to low, the other two are intermediate steps to show how the response changes.

This shows exactly what I hear, the unit doesn't compress until it detects signal at higher frequencies, useful right?.

One observation, on my unit I used linear pots for the response adjustment, in the future I'd probably want them to be log as there was no change from high down to about 30%, 50% was the exact same as 100%

 

[MicDaddy]

Oh awesome!  Thanks for that graphic Ben, I'll be sure to put this on the front panel.

I did see a member used a Lorlin rotary of 120K increments, I think I may go that route. 

Is there a better or worse trimmer for R25?  Am I ok sticking any old 100K pot I have laying around in there?

Edit:  Looking back, it was Briomusic who used an 8 step Lorlin, perhaps he can help with a part number and any feedback if he intends on changing or is happy with the performance. 

 

[MicDaddy]

Hey Briomusic, can you also share with us the stepped attenuator calculations you used for your input gain switches?  I think I'm gonna leave pots for peak reduction, but I want switches on the gain.

Thanks, it's much appreciated!!  ;D

 

[benlindell]

What is a safe case temp for these? I'm definitely going to leave a space above this guy cause it's running about 137°F/57°C

 

[MicDaddy]

What is a safe case temp for these? I'm definitely going to leave a space above this guy cause it's running about 137°F/57°C

;D might get double use as a foot heater over the winter, perhaps warm the coffee also.. kidding of course.  That is one hot mama

 

[audiophreak]

Hi All,
      need a little front panel labeling help .... I'm doing the graphics for a front panel for my D-LA2A and I'm using a 6 pos. switch for the SC HP Response . Currently have the positions labels as (  0R , 200K , 400k , 600K , 800K , 1M )  as those are the resistor values used , but not sure I like that description/labeling . 

  any thoughts as to another way to label these position  ? 

 

[benlindell]

Hi All,
      need a little front panel labeling help .... I'm doing the graphics for a front panel for my D-LA2A and I'm using a 6 pos. switch for the SC HP Response . Currently have the positions labels as (  0R , 200K , 400k , 600K , 800K , 1M )  as those are the resistor values used , but not sure I like that description/labeling . 

  any thoughts as to another way to label these position  ?

I would probably suggest just doing a simple 0-10 scale maybe as it isn't a very linear nor definable control. Also I'm going to switch my linear pot to a log (audio) taper pot because from halfway to fully clockwise it really didn't change much at all.

 

[audiophreak]

Thanks Ben,
                    I wan t to stick with switch positions for recall ability but panel real estate is tight, so 6 position is it. Just obsessing over how to label the positions " A,B,C" , " 1,2,3 " ,  in Hz ?  " 30, 60, 90, 120, 180, 220 "  , "  Flat , Mid, Open  "  ???? 
 
  I was also thinking of using a Pot to select the increments then measure the resistance of the pot, then insert the corresponding resistor in the switch position.

  ..... or am I WAYYYyyyy over thinking this  ....  ;D

 

[MicDaddy]

 
  I was also thinking of using a Pot to select the increments then measure the resistance of the pot, then insert the corresponding resistor in the switch position.

  ..... or am I WAYYYyyyy over thinking this  ....  ;D

I would appreciate your efforts in this please post your results. 

For my own clarification, 1M gives the most 'flat' response, whereas 0 would be less sensitive to the low end?  Or is it vice versa?

 

[audiophreak]

I would appreciate your efforts in this please post your results. 

For my own clarification, 1M gives the most 'flat' response, whereas 0 would be less sensitive to the low end?  Or is it vice versa?

  ... Not sure on that myself  :-[  was hoping someone with more knowledge of the circuit would chime in. 
  I will definitely post whatever I find out , I have the PCB, PT, heater wiring, all mounted in the case, front panel is at Prodigy Engineering for Laser engraving- just agonizing over the naming convention of this control , then spend the $ on the Sowters and T4Bs

EDIT : spelling

 

[tmuikku]

I would appreciate your efforts in this please post your results. 

For my own clarification, 1M gives the most 'flat' response, whereas 0 would be less sensitive to the low end?  Or is it vice versa?

  ... Not sure on that myself  :-[  was hoping someone with more knowledge of the circuit would chime in. 
  I will definitely post whatever I find out , I have the PCB, PT, heater wiring, all mounted in the case, front panel is at Prodigy Engineering for Laser engraving- just agonizing over the naming convention of this control , then spend the $ on the Sowters and T4Bs

EDIT : spelling

Hi! I haven't looked the schematics but it is most propably just an RC filter with variable R so it is time for learning for you fellows Do a Google search with "rc high pass filter". If you are lazy and don't want to do the math (just look the equations and you'll know how R affects the filter) try some of those online calculators and see how changing the R affects.