Author Topic: 1vac on output

April 22, 2022, 06:57:34 PM
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Danchinho

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OK, having setup issues.
I'm worried I'm misunderstanding some basic stuff.

First, the potentiometers never stop turning. No matter how many times i turn they can always turn some more. P3 & P4 click after a while but never stop turning. P5 doesn't click and can be turned continuously.

Test point 0V and V+ 15.75v
Test point 0V and V- -16v


input transformer 
1&5 = 2.21ohm
6&10 = 1.81ohm

output transformer 
1&3 = 4.8ohm
6&8 = 5.4ohm
9&12 = 11.5ohm
13&16 = 11.5ohm



I've got Logic as a DAW and a Cranborne R8 as a rack and interface. Worried I'm doing something wrong so if there's anyone else with a similar set up please feel free to advise me!
I've put the extender in slot 1. There are some other units in but I presume that's ok as I'm using the extender.
I've put a sine wave on a Logic channel and set the I/O to 1 on input and output.
The sine can be heard through the speakers. I then connect an XLR lead to the module output on the back on the R8
and tried to get an AC measure against pins 2&3. In fact any pins. Nothing. Then I thought maybe the speaker lead so I disconnected that and measured it. Nothing. Get a reading with one pin but nothing with two.

April 23, 2022, 09:57:35 AM
Reply #1

JPK

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You need to separate the issues.
First, without connecting the LA502 yet, setup a sine source on one output XLR of your rack. Check that you can measure it with your AC voltmeter.
When done, you can plug the LA502 in (with the extender) and connect the working source to the analog input of the compressor.
JPK

April 26, 2022, 06:35:20 PM
Reply #2

Danchinho

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OK.
For all the other noobs this may prove useful.
My basic assumptions were wrong. A friend and made up some XLR cables for me. He put the live, shield, etc on different pins to what is normally used. He was consistent in the leads themselves but not what is standard. Realised when I took the male and females off. 
Using a standard cable I was able to get a VAC reading.
Made the necessary adjustment (volume not frequency iirc..) to obtain 1VAC on the output.
Then follow the set up instructions as written by JPK.
The potentiometers don't stop turning but don't worry. Just do the 20 turns JPK says and treat that as 0.
I'm writing this in case it helps anyone as basic in their knowledge as me.

June 07, 2022, 03:44:44 AM
Reply #3

Nate08

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You need to separate the issues.
First, without connecting the LA502 yet, setup a sine source on one output XLR of your rack. Check that you can measure it with your AC voltmeter.
When done, you can plug the LA502 in (with the extender) and connect the working source to the analog input of the compressor.
Pin 2&3 of my xlr source read 1.0vac, & .98vac when running through the LA502. Gain fully clockwise reads 26vac, and when set to 15vac the peak knob will not reduce down to less than 1vac. It will only reduce the voltage down to 2.3vac with the peak knob fully clockwise. I tried to calibrate the led’s anyway (revision 1.4) and no -3db light after gain @ 15vac and peak set to 10.6 vac. Could this be because of the peak setting being unable to reduce the current to less than 1vac & if so, where do I start?

June 07, 2022, 02:20:46 PM
Reply #4

Nate08

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Update: I had my led’s backwards. After reversing, able to dial in the -3db led, but due to not being able to reduce the voltage down to 1vac or less, the -20db led cannot be calibrated. 

June 08, 2022, 04:07:21 PM
Reply #5

JPK

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and when set to 15vac the peak knob will not reduce down to less than 1vac.
How low can you drop the output voltage?

For the setup of the -20dB LED, the output voltage must be adjusted to 1.5VAC.
JPK

June 08, 2022, 04:12:39 PM
Reply #6

Nate08

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The output voltage will only go down to 2.3vac with the peak knob all the way up.

June 08, 2022, 05:01:07 PM
Reply #7

JPK

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Did you turn P3 20 turns CCW?
With 1VAC input, switches 1 & 2 to the left and switches 3 & 4 in center, GAIN at 0, U6 removed :
- What AC voltage do you get on TP2 against 0V when turning PEAK from min to max: 0VAC to 14VAC.
With U6 inserted:
- What AC voltage do you get on TP2 against 0V when turning PEAK from min to max? 0VAC to 1.9VAC.
- What DC voltage do you get on TP3 against 0V? 0 to 1.2VDC.
JPK

June 09, 2022, 04:12:18 AM
Reply #8

Nate08

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P3, P4 & P5 CCW 20 turns: yes.

U6 removed AC voltage 0v to tp2:
0~10.93vac

U6 inserted AC voltage 0v to tp2:
0~1.79vac

DC voltage 0v to tp3: 0~1.13v

June 09, 2022, 03:02:31 PM
Reply #9

JPK

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U6 removed AC voltage 0v to tp2:
0~10.93vac

This is a bit low.
Check your resistors values from the colour code. In particular R19 to R25.
Check you didn't swap the pots.
JPK

June 10, 2022, 01:46:02 AM
Reply #10

Nate08

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I did in fact swap the pots. Good to go now. Thank you.