T1     Calrad 45-700  audio transformer  (Ocean Electronic)
T2     Bogen T724  4 watt  P/A transformer  (Grainger)
R1     250k ohm variable resistor
SW1  12 position single pole rotary switch  (Radio Shack)
C1     .1 uf capacitor
C2     Value of C2 depends on the set up of the headsets.
          (all non polar)
          1) one 600 ohm impedance element = 1 uf
          2) two 600 ohm imped. elements wired in parallel = 2.2uf
          3) two 600 ohm impedance elements wired in series = .5 uf
          4) 10k Hi "Z" headphones = .068uf to .05uf
          5) two low "Z" elements  in series like Stromberg
              Carlsons can be run on 2.2 uf, but 4.7uf might be
              a better match up.

Notes:
1)    1 uF is a good fixed compromise value for C2 if several different impedance headsets
        will be frequently used.
2)    The range of C1 can be from .05uf to .22uf. It is not that critical.
3)    Only ten of the twelve positions  are used on SW1
4)    White lead on T1 goes to the rotary switch SW1 with yellow
5)    Experimentation is the key to getting the right values on this unit.
       What is right for you and your set up is what counts.
6)    See photo below for proper phase ID of the two "pink" wires on the Bogen 725
       transformer.

---

My version of Steve's S-T-M  Calrad/Bogen

 
 

 

The S-T-M is excellent for comparison of headphones. It works very well for one or two sets of phones as well. It will run a range of headphones, from magnetic to sound powered.
More S-T-M circuits using different transformers are in the works to be placed here on this page in the near future.

T1     Stanley audio transformer Part Number 227-E-1-3-98
         Pri 100 ohm  Sec. 100M (100k) ohm
         (Fair Radio Sales number T3/AM-20)
T2     Bogen T724  4 watt  P/A transformer  (Grainger)
R1     250k ohm variable resistor
SW1  12 position single pole rotary switch  (Radio Shack)
SW2  6 position single pole rotary switch (Radio Shack)
SW3  SPDT toggle switch (Radio Shack)
C1     .1 uf capacitor (Radio Shack)
C2     4.7 uf capicitor non polar (Radio Shack)
C3     2.2 uf  capicitor non polar (Radio Shack)
C4     1.0 uf  capicitor non polar (Radio Shack)
C5     .5 uf capicitor non polar (Radio Shack)
C6     .05 uf capicitor non polar - not shown in circuit can be
          put in for 10k Hi "Z" headphones (Radio Shack)

Notes:
1)    The range of C1 can be from .05uf to .22uf. It is not that critical.
2)    Only ten of the twelve positions  are used on SW1
4)    #1 lead on T1 goes to SW3. It is split and one lead goes to brown on SW1 and  the
       other goes to red on SW1. This allows you to shifts the ratio range a full
       step for better use of the Stromberg Carlson elements.
5)    Experimentation is the key to getting the right values on this unit.
       What is right for you and your set up is what counts.
6)    See photo below for proper phase ID of the two "pink" wires on the Bogen 725
       transformer.

---

My version of Steve's S-T-M  Stanley/Bogen

 
 

T1    Calrad 45-700  audio transformer (Ocean Electronic)
R1    Choice of R1 depends on radio set up, but 100k is a good choice
         for diodes that measure around 96k ohms. See Ben Tongue's web
         site for more information on this choice.
       http://uweb.superlink.net/bhtongue/index.html.
C1    .1uf capacitor
C2    .47uf capacitor

Notes:
1)    The colors (green and white) on the transformer on the low
        impedance side are interchangable. Polarity is not important
        on this side of the transformer, but it is critical on the hi
        impedance side (green and red).