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Drawmer 1968 ME Calibration Method! Dynamics Processors (HW)
Old 22nd December 2014
  #1
Lives for gear
 

Drawmer 1968 ME Calibration Method!

Ok.....So you've had your Drawmer 1968 (ME/MKII) Compressor for quite some time, I mean they are getting on a touch, and possibly you want to swap out the Tubes in the Gain stage and generally clean things up so the gain on the Drawmer 1968 is maybe not so woolly and woofy as they can sound when in need of a tune up! So you go and grab a set of nice NOS valves and then what? Fear not....Below you will find the Drawmer 1968 ME/MKII Calibration. Should you have need to change parts etc, you might want to tighten up and adjust the Compressor afterwards, unfortunately it's not as simple as an 1176 type scenario, though not as fiddle ridden as building a Rocket. For all Drawmer 1968 owners, here are the calibration details. You can easily find all the details below by the circuit board and/or ask a Tech to do this procedure for you! Sorry I have no Schematics at the moment, though it worked for me.

Regards
TheLastByte
--------------------------------------:

From Drawmer UK:

Drawmer 1968 Audio Calibration:

AUDIO CALIBRATION

The audio calibration of the 1968 should normally not need any adjustment. However if component changes have been made, it may be necessary to adjust one or more of the pre-set potentiometers. To adjust the presets you will require an adjustable level, balanced test signal of 1KHz sine wave, initially set to a line level of +4dBu (1.23V RMS. You will also require an accurate VU measuring meter (with adjustable gain), an oscilloscope and a sweep scope.

The front panel of the unit must be initially adjusted for both channels, as follows:-

*** Threshold rotated Counter Clockwise to 'OFF'.
*** BIG switch to the 'Off' position. (Up).
*** Attack set to position ‘1'.
*** Release set to position ‘1'.
*** Gain rotated fully Counter Clockwise to '?20dB'.
*** Bypass / Normal / Side Chain initially set to 'Bypass'. (Right).
*** Stereo Link switch in the 'Off' position. (Up),
*** Meter set to VU position. (Middle).

The following series of tests will ensure all the features of the 1968 are operating correctly. In most cases, the conditions for each test should be continued into the following test. Consequently, it is suggested that all test should be carried out in the numbered sequence.


1:*** Turn the ?3 VCA Presets R46 and R78 fully counter-clockwise.


3.*** Insert a sine wave signal of 1KHz into both 'LINE' input XLRs at a level of 0dB (ref +4dB) and allow the unit to warm up for about 15 minutes.


5:*** SET VU METER.
*** With the unit in Bypass adjust preset R14 (channel 1) and R190 (channel 2) until the meters indicate 0dB on the VU meter.

6:*** V.C.A. CALIBRATION

*** 6.1*** Connect an audio level meter to the output of channel 1.
*** 6.2*** Switch the unit into ‘Norm’.
*** 6.3*** Rotate the Output Gain pot to 0dB on front panel graticule.
*** 6.4*** Adjust presets R172(CH1) and R173(CH2) until the output level is set to +3dBu for each channel..
*** 6.5*** Adjust preset R46 on Channel 1 to give a gain reduction of 3dB. The VU meter should now read 0dB.
*** 6.6*** Repeat for Channel 2 (Preset R78).
*** 6.7*** Rotate the THRESHOLD control on Channel 1 fully clockwise to apply 20dBs of gain reduction to the unit.
*** 6.8*** Adjust preset R37 to give a gain reduction of 20dB. The external test meter should also read 20dB gain reduction.
*** 6.9*** Repeat for Channel 2 (Preset R69).
*** 6.10*** Switch the Stereo Link switch ON. Check that Channel 1 and Channel 2 track within 0.5dB of each across the full Threshold range.
*** *** Switch the Stereo link OFF.
****

7:*** G.R. METER CALIBRATION

*** 7.1*** Switch the meters to G.R.
*** 7.2*** Using Preset R50 set the GR meter to give a reading of +3dBu.
*** 7.3*** Repeat for Channel 2 (Preset R82).
*** 7.4*** Adjust preset R48 on Channel 1 to set the GR meter to read 0dB.
*** 7.5*** Repeat for Channel 2 (Preset R80).
*** 7.4*** Rotate the THRESHOLD control on Channel 1 clockwise to show 10dBs of gain reduction on the VU meter of the unit.
*** 7.5*** Switch the unit back to GR and adjust preset R36 to give a gain reduction of 10dB.
*** 7.6*** Repeat for Channel 2 (Preset R86).
*** 7.7*** Remove the Gain Reduction. Repeat above steps until no further adjustment is necessary.
*** 7.8*** Switch between VU and GR and check that the meters are identical. Adjust as necessary.

Now .....Enjoy that Drawmer 1968 Compression on Multiple sources from Master Bus to Drum's, Vocals, Guitars, Bass, and literally anything else! Good luck!

TLB.
Old 22nd December 2014
  #2
Lives for gear
 

TLB

Are any similar mods possible with the 1969 ME.

Cheers

and merry xmas and a happy new year from another Sydneyite.
Old 22nd December 2014
  #3
Lives for gear
 

Nicknack,
Sorry Man.....this one's for the 1968, not sure how it would apply to the 1969, maybe see if there is a 2nd Preamp Board and a Compressor board, if so, I imagine they might be close, possibly a question for Dave Hill or Fletcher and/or Drawmer if you can squeeze info out of them! They are indeed tight with info and keep tech stuff close to their chests thus the 1968 recalibration I'm sure will be appreciated! Merry Xmas to you Brother!

Regards
TheLastByte
Old 15th July 2017
  #4
Gear Maniac
 
Samuelito's Avatar
Hi,

I'm trying to calibrate a 1968 ME but I'm having problems when linking the channels.
I'm being really precise. I'm using a HOFA digital meter in the DAW and still I'm getting different results every time I finish calibrating.
I swapped the tubes, just in case that was the issue, but nothing changed.
When the channel link is not engaged, all is good.
BTW, what are they for R2 & R178? I only once got in 0.5 difference when linked after calibration after playing with them.
Thanks,

M
Old 15th July 2017
  #5
Gear Maniac
 
Samuelito's Avatar
Ok,

I finally go it right. By accident, but right.
After several attempts, I accidentally left the stereo link switch on. (don't know if from the beginning or somewhere in between) and I realized at the end. To my surprise the 1968 is now perfectly calibrated in mono as well as in stereo with a 0.1db range.
BTW, I think R2 & R178 are small trims for the input signal. Do know if I'm right, but they do affect the input.
Best,

M
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