STU.915.301.500

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The STU.915.301.500 is our VPR compatible version of the Studer 1.915.301 microphone amplifier circuit from 1978.
We changed the gain range from 12dB to 87dB to a more useful range of 0dB to 75dB. Other than that we staid as close as possible to the original schematic. The input transformer is either the Haufe ST8456 or Lundahl LL1538, the output transformer is a NOS Haufe RK173.

[ original schematic | original data-sheet ]

Documents:

STU.915.301.500 Schematic
STU.915.301.500 PCB
STU.915.301.500 Parts List
#STU915301500 on Instagram

Full Kits are available in the White Market

 

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Calibration

Important: before powering up your STU.915.301.500 set the trim potentiometer R26 (30Hz ADJ) counterclockwise to the left stop

Gain Calibration
Set the controls to the following positions:
- GAIN switch to 0dB
- VAR, GAIN to 0dB
Set your signal generator to 0 dBu at 1kHz
Adjust GAIN CAL R21 to measure 0 dBu output

Distortion adjustment
Increase the output level of your STU.915.301.500 to +21 dBu
Set your signal generator to 30Hz (make sure the Bass Cut switch on the STU.915.301.500 is off)
Measure the distortion and adjust 30Hz ADJ R26 for minimum deflection

 

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If you can't measure distortion, but have an Oscilloscope:

R26 too low (counterclockwise to the left stop):

R26 adjusted:

R26 set too high:

 

[[silent:arts]]

Looks like the orientation of some components is not clear to everybody:

 

[egroys]

These look gorgeous! I can’t find much about them online. Would anyone happen to have some samples? Curious what the vibe is and what folks like to use them on…

 

[Phantasm]

Just built one of these and went with Lundahl input transformer as Volker recommended that one over the Haufe option as I'm using mainly for line level. It's superb on initial tests - albeit on instruments not voices. Doing some very nice things on drums.

Thanks Volker for the help and advice on choice of transformer. Can see this living on drums!

 

[egroys]

Just built one of these and went with Lundahl input transformer as Volker recommended that one over the Haufe option as I'm using mainly for line level. It's superb on initial tests - albeit on instruments not voices. Doing some very nice things on drums.

Thanks Volker for the help and advice on choice of transformer. Can see this living on drums!

When you say mainly at line level, do you mean you're running your drum bus through them to color?

 

[Phantasm]

When you say mainly at line level, do you mean you're running your drum bus through them to color?

Yes - well not the drum bus as such but individual tracks from my sampler. My console doesn't really allow me to set up a bus annoyingly. It's very clean which is fine but no character so feeding it with a colourful pre works great when driving the transformer a little. Also, using nice outboard gets the sound I'm looking that can't be done from the on board dynamics and EQ. I do occasionally record things via a mic so it will have a little use there but will be 95% of it's time on samples. The difference is very noticeable when compared to the same sounds on another track and switching between the 2. Somehow I found that it can be 2db quieter than a clean track but sound louder. It's incredible!

 

[egroys]

That's beautiful! I'd love to hear anything you're willing to share before/after the STU!

 

[Phantasm]

That's beautiful! I'd love to hear anything you're willing to share before/after the STU!

PM me your email and i'll do a a sample file when I get a minute to do one

 

[DOCTEUR]

Hi Volker,

I'd like 2 please of Mic preamp STU.915.301.500 Shipping to France.

Have a nice day.
Eric