In this video we will calibrate the meter of an Urei LA4A – or the PCB Grinder Hand of Light Unit for accurate tracking.

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Gain Reduction meter adjustment (MTR0 on HOL – Hand OF Light)

  • Startup Unit (it is better to wait a few minutes afster startup)
  • Put meter in GR 
  • With no signal applied it should read 0 VU
  • If not Adjust MTR0 potmeter

Tracking Meter Adjustment (MTRT on HOL)

  • Apply a sinewave 1000 Hz between 0.1 and 1.4 V – I used 1V
  • Put meter in OUTPUT
  • Adjust output until meter reads 0 Vu
  • Adjust Treshold until meter reads -5Vu
  • Set meter in gain reduction
  • This should read also -5 VU
  • Adjust MTRT until meter reads -5 VU


Video Transcription

today we’re gonna calibrate this hand of light unit by PCB grinder it’s a LA4A

copy it’s a fairly easy build took me
about 40 minutes so the only thing you

have to do is to adjust some potentiometers inside the unit and we’re ready

to go so let’s turn it down and the only
thing you need to adjust this is a

little screwdriver let’s open up the
units be careful with the power supply

and stuff so you don’t get any electric
shocks but normally if you just stay out

of this zone over here it will be all be
good. If we turn on the unit and we are

in gain reduction mode it should say
zero and it isn’t so adjust it until it

is zero more or less it is. Now we will add
one kilohertz sine wave with voltage of

1V so let’s add it you can do it with
your audio interface as well. If it’s between

100 millivolts and 1.4 volts it
will be ok. Just there is some singal. We

will turn the unit in output mode we
will add output so its signal will be on

zero volts. Here we are and now we will
subtract 5V from the meter

so with the threshold we’ll go, my
ratio is on 8:1, until minus five

If we go to gain reduction mode
normally it should say also minus five

here we go. But it’s minus one so we will
adjust meter tracking, that’s this one

Here we are. Your unit is ready and

One thing I will advise
you guys it’s not to case two of them in

one unit I think I will recase mine
I made this units I think a few years

ago it’s one of my first builds I did so
that’s why it’s a little bit more

messy as my newer bills but we all have
to learn about it.

Thank you for watching

and see you soon