D-LA2A Support Thread

[desol]

desol: first remove the power switch from the middle of the case.
running 115V / 230V next to the potentiometer / switch wires is a very bad idea in this build.

Hi Volker,

Ok. So i removed p switch and no real change, but i will watch for that anyway. But i did find that the pots weren't grounded properly...so i changed and i think they are wired and grounded right now....and buzz is better but still there. I also found that on channel two, with just GR switch is engaged and input all the way up...output pot causes meter to swing up(+2) then down again to zero? Channel one doesn't do this...needle stays steady when you move channel two (output) pot. And then, engaging channel two meter....now moves channel one meter a little too?? I looked for a little while at the schematic trying to see what is causing this, ...still trying tho. I can't see what switches are which...to see what channel two pot is connected to, to see where to look. Looks like voltage is bleeding into channel 1 from channel 2 meter circuit somewhere. Will keep looking..


I also did some voltage checks at a few capacitors, i'm pretty sure they're normal:

c105, 205 - 92v and 89v
c102,203,202,203 - 89v,69v and 208v    89v,67v and 202v
c101, c201 - 80v and 82v
c115,c215 - 57v and 57.5 volts

Hmm. Back to work..

 

[audiophreak]

Hi All,
      Need a little help here ... would like to get the Rondo PT for this project, used the link posted in this thread, but cant figure out how to switch to English ( I'm in the U.S. and non German speaking / writing  )  , I messed around just clicking on stuff and found an email contact info , and sent an email about a week ago with no response, ( possible they don't speak / read English ).

  Would really like to use this PT , any help / suggestions would greatly be appreciated.

  Thanks,
            Chip

 

[briomusic]

[silent:arts] sells them in the WM:http://www.groupdiy.com/index.php?topic=39570.0
(english spoken  )

 

[audiophreak]

Thanks briomusic !!

                            not sure how I missed that  :-[   

                                                                              but email sent 

 

[[silent:arts]]

Hi Chip,

Rondo-Mueller is based in the east part of germany, not many people there learned english (but most speak fluently russia).
Mr. Mueller doesn't like to do the same "one-off" winding job every day, I finally agreed with him to stock the transformers for my DIY projects.
(even it is no fun for me receiving +100kg parcels at my home)

 

[audiophreak]

Thanks Volker 

 

[Audioman]

Hi All,
For the distortion problem solved (wiring problem on ch 1)
but on both unit the hum is still present (on first unit on ch1 on second unit on ch2)
i have measure on first unit 55° degrees on the electrolytic c171 is it normal ??
Any idea ??

desol: first remove the power switch from the middle of the case.
running 115V / 230V next to the potentiometer / switch wires is a very bad idea in this build.

Audioman, nice build with unique front panels

1- in my unit is some hum on the second channel when i switch on the channel (with the in/bypass switch)
2- the first channel of my unit works fine but if i bypass the channel in the audio a boom appears (maybe the switch is not good..)

the switch only triggers the relay. any DC at the output?

3- in the second unit a strange distortion appears if i push the input and ouuput stage

try swapping the tubes from unit 1 & 2. any changes?

Cyrill: congrats!
interesting 1178 front panel layout.
COOL  8) 8) 8)

 

[desol]

Yes!!...it's working!  

Very nice sounding...different than my other compressor's. There is a tiny amount of buzz(-50) still; it's the limit/comp wire, which will be quickly changed over to shielded wire.

All of my problems were wiring and adjustment. If you have distortion it's almost guaranteed a wiring problem. The stereo tracking is a little off as well. It may be T4b's or 6AQ5's(different brands)...either way..a small issue and will fix later.

Right now i'm just so happy with the sound of this thing!! Thank you Volker, i'm really happy i got one up and running. My first tube project...and yes i felt a shock...so i was careful after that!





edit: Oh yes...and i did the modification for 12ay7's in V1...which worked out nicely.

 

[electrisizer]

All of my problems were wiring and adjustment. If you have distortion it's almost guaranteed a wiring problem.

what was the mistake in your wiring that causes distortion?

i still have distortion at some frequencies. its not caused by transformers as assumed pages before...

first time i hear them in circuit is at cathode on the v103/203

 

[desol]

Actually maybe that's not entirely true. I had distortion a couple times throughout troubleshooting...both instances were wiring.

I had the wires out of polarity once on GR/Meter circuit (which caused all kinds of weird things..meter bouncing with pots when channel bypassed) and then again on limit comp switch...which caused distortion. Plus i wired the link switch incorrectly..which caused no compression and distortion when engaged.  

I haven't checked it with a scope or anything, just my ears.

 

[desol]

EDIT: Resolved #3 http://www.groupdiy.com/index.php?topic=32677.msg540317#msg540317

 

[Audioman]

Hi Desol,
So you calibrate you unit turning right the response limiter trimmer and left the stereo adjust trimmer ??
Can you tell me if in your unit the electrolytics warming a bit ?? ( i notice in my unit 55° degrees on the electrolytic c171 )
Let me know
Thank you
Fabio

Hi Volker! (...or anyone)

I've finished my d-la2a and everything seems working good. It's quiet, gain and peak reduction are working well on both channels, switches and related functions are working ok...and it sounds nice.

When calibrating the freq resp and stereo adjust controls(freq response is on the backpanel), i noticed they were backwards? ie: they needed to be turned all the way to the 'left' for the signal to be full, lots of compression/needles to move, etc. So i reversed the wipers on the freq response potentiometers...and now they are like normal...turn all the way to the right for good response. But this didn't reverse the stereo response trimmers...they still need to be turned all the way to the left. If i turn them all the way to the right...the signal gets distorted and not too good. When i adjust both of them to the left, they move together (linked) and the signal sounds nice again.

How could i have reversed this?  ???

Now i have freq resp's all the way to the right....and stereo adjust's all the way to the left? ...and it's ok...

Thx,
Darrick

 

[desol]

Hi Fabio..

Yes. Limiter response pots all the way to the right...and stereo adjust trimmers all the way to the left.

I tested my electrolytic c171 and it's ok at 55C(131F). If i turn stereo adjust all the way to the right...i get distortion...no meter movement(linked).

 

[Audioman]

Hi Desol,
Waiting for some info from Volker .
I'm asking you about the Electrolytics because i have an hum on one channel of both unit and i don't know why !!!
I hope to discover the problem .....
today i try your trimmer setting and i let you know the response
thank you for the info !!!
Fabio

Hi Fabio..

Yes. Limiter response pots all the way to the right...and stereo adjust trimmers all the way to the left.

I tested my electrolytic c171 and it's ok at 55C(131F). If i turn stereo adjust all the way to the right...i get distortion...no meter movement(linked). All the way to the left...everything's ok.  ?

I know it should be to the right...but it's not for some reason.

 

[desol]

So you calibrate you unit turning right the response limiter trimmer and left the stereo adjust trimmer ??

Yes.

 

[Audioman]

Where you find the calibration procedure ???
I can't find it in the forum ....

So you calibrate you unit turning right the response limiter trimmer and left the stereo adjust trimmer ??

This is just my unit.

Normal calibration is turning both freq resp and stereo adjust to the right.

 

[desol]

I can't remember, it's in this thread...you just have to search a bit....and search google too. Bits and pieces everywhere...

Hi Desol,
Waiting for some info from Volker .
I'm asking you about the Electrolytics because i have an hum on one channel of both unit and i don't know why !!!
I hope to discover the problem .....
today i try your trimmer setting and i let you know the response
thank you for the info !!!
Fabio

How bad is the hum? Did you shield/check all wiring? Check input/output wiring? Wire positioning? Wire polarity?

(In the end) ...I carefully went through my unit gently(carefully) touching wires to see which caused hum, and then shielded those.
At first i had alot of hum...because i wired the inputs/outputs incorrecty..  
I ended up shielding pretty much all wiring except for meter wiring...

Now my unit is very quiet.

 

[[silent:arts]]

taken from the UA Teletronix® LA-2A Manual:

Limiter Response Calibration (RV137/RV237):
The LA-2A was designed for use in broadcast applications.  The audio signal in FM
broadcasting undergoes pre-emphasis and results in a 17 dB boost at 15 KHz.  Due to this
increase in signal level, transmitters are subject to over-modulation.  The LA-2A provides a
control (R37) which controls the amount of high-frequency compression.
This potentiometer is factory set for a “flat” side-chain response (clockwise).  Increasing
the resistance of this potentiometer by turning it counter clockwise will result in
compression which is increasingly more sensitive to the higher frequencies.

 

[[silent:arts]]

taken from the UA Teletronix® LA-2A Manual:

Stereo Balance Adjust (RV103/RV203):
...
The interconnecting wire should be less than 2 feet in length and should be shielded.
...
To calibrate the units for stereo operation:
- Connect the units together as described previously.
- Turn the Peak Reduction knob counterclockwise (no compression).
- Set R3 on each unit to a clockwise position.
- Set each meter to read Gain Reduction.
- Adjust the Peak Reduction control on the left channel until approximately 5dB of gain reduction is achieved.
- Adjust R3 on the unit that shows the greatest amount of gain reduction until the gain reduction indications are equal.
- When operating, set the Peak Reduction controls to the same setting on both channels.

 

[Audioman]

Thank you Man !!!

taken from the UA Teletronix® LA-2A Manual:

Stereo Balance Adjust (RV103/RV203):
...
The interconnecting wire should be less than 2 feet in length and should be shielded.
...
To calibrate the units for stereo operation:
- Connect the units together as described previously.
- Turn the Peak Reduction knob counterclockwise (no compression).
- Set R3 on each unit to a clockwise position.
- Set each meter to read Gain Reduction.
- Adjust the Peak Reduction control on the left channel until approximately 5dB of gain reduction is achieved.
- Adjust R3 on the unit that shows the greatest amount of gain reduction until the gain reduction indications are equal.
- When operating, set the Peak Reduction controls to the same setting on both channels.