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Beyer Dynamic PCB Transformers.



Although out of production for many years, these transformers are quite popular and I have had several questions about their specifications.


Audio transformers are not designed for and should never be used as mains-insulation transformers.
Even a transformer with an insulation rating of 6.5 kV do not have sufficient insulation distances for use as mains-insulation transformers.

Beyer Dynamics PCB transformers.

Part-number: TR/BV 310 abb ccc
310 means a studio grade dual-in-line PCB transformer.

a is winding configuration, where:
0 has a single primary.
1 has a center tapped primary.
2 has split bi-filary primary.
3 has split bi-filary primary connected in the middle ( single winding brought out ).

Beyer Dynamics series 310 pin-out.
Fig.1: Beyer Dynamics series 310 pin-out.
The dot marks the start ( inner-most end ) of the winding.
Pin 8 is static shield and core.
Pins 7, 8 and 9 goes to GND for best CMRR.

bb is turns ratio, where turns ratio is 1:bb.
00 means a special turns ratio ( probably a custom manufactured type ).

ccc is an type number for the particular transformer:
001 to 020: standard transformer, Rgen = 200 Ω.
021 to 030: special transformer, Rgen = 200 Ω.
031 to 050: standard transformer, Rgen = 600 Ω.
051 to 060: special transformer, Rgen = 600 Ω.
061 to 080: standard transformer, Rgen = 1200 Ω.
081 to 100: special transformer.
101 to 120: special transformer, turns ratio ≤ 1.
251 to 275: standard transformer, Rgen = 200 Ω
276 to 299: standard transformer, Rgen = 500 Ω

Table 1: Some standard types for 200 Ω source impedance.
TR/BV310Rgen = 200 Ω
at Rgen
(open secondary)
30 Hz - 15 kHz ±1 dB
Maximum input level
( THD ≤ 1%, f ≥ 30 Hz )
300 mV
Primary open circuit inductancetyp. 6 H @ 50 Hz
Primary open circuit impedancetyp. 1.885 kΩ @ 50 Hz
Turns ratio1:11:31:51:71:101:151:20
Transformed impedance200 Ω2 kΩ5 kΩ10 kΩ20 kΩ45 kΩ80 kΩ
Primary DC resistance50 Ω50 Ω50 Ω50 Ω85 Ω85 Ω115 Ω
Secondary DC resistance75 Ω580 Ω1.45 kΩ3.45 kΩ4.75 kΩ10.4 kΩ13.5 kΩ
Code number ( bbccc )01001030020500307004100051500620007

Table 2: Some standard types for 600 Ω source impedance.
TR/BV310Rgen = 600 Ω
at Rgen
(open secondary)
30 Hz - 15 kHz ±1 dB
Maximum input level
( THD ≤ 1%, f ≥ 30 Hz )
300 mV
Primary open circuit inductancetyp. 16 H @ 50 Hz
Primary open circuit impedancetyp. 5 kΩ @ 50 Hz
Turns ratio1:11:21:31:51:71:10
Transformed impedance600 Ω2.4 kΩ6 kΩ15 kΩ30 kΩ60 kΩ
Primary DC resistance140 Ω140 Ω140 Ω140 Ω190 Ω190 Ω
Secondary DC resistance190 Ω575 Ω1.45 kΩ3.9 kΩ7.05 kΩ11 kΩ
Code number ( bbccc )010310203203033050340703510036

Table 3: Some standard types for 1200 Ω source impedance.
TR/BV310Rgen = 1200 Ω
at Rgen
(open secondary)
30 Hz - 15 kHz ±1 dB
Maximum input level
( THD ≤ 1%, f ≥ 30 Hz )
300 mV
Primary open circuit inductancetyp. 30 H @ 50 Hz
Primary open circuit impedancetyp. 10 kΩ @ 50 Hz
Turns ratio1:11:21:31:5
Transformed impedance1.2 kΩ5 kΩ12 kΩ30 kΩ
Primary DC resistance310 Ω310 Ω310 Ω475 Ω
Secondary DC resistance430 Ω1.4 kΩ3.75 kΩ8.45 kΩ
Code number ( bbccc )01061020620306305064

These transformers do not like DC.
I tried with a TR/BV 310 001 001 coupled as a voltage transformer with 40 Ω source impedance and 100 kΩ load.
Initial THD+N at 70 mV, 100 Hz was 0.022%, mainly 2. harmonic ( there has obviously been DC on this one ).
After applying 100 µA from an ohmmeter for a few seconds, THD+N increased to 0.028% still mainly 2. harmonic.
After demagnetizing the transformer, THD+N fell to 0.017%, but this time only 3. harmonic.
Demagnetizing was done by increasing the input level until the transformer went into saturation ( ca. 25% THD+N ), leaving it there for some seconds and then reducing the level to 0 over 20..30 seconds.

Leakage inductance is not specified for these transformers.
I measured 2 transformers with pins 1, 5, 7, 8, 9 connected to GND.
This was done by putting a 1 µF capacitor in series with the primary and measuring the resonance frequency.
TR/BV 310 001 001 is 2.1 mH and TR/BV 310 001 031 is 4.4 mH

Mechanically these transformers seems very rugged, but internal wiring is down to 25 µm for some types, so handle with care.
Pins 1..8 are gold-plated and are very easy to solder.
Pin 9 is raw my-metal and can be difficult to solder. The trick is to take a scalpel and scrape it until it shines just before you solder it.
Some general precautions for handling signal-transformers are listed in [1], page 28.


IA19A: Transformer balanced line input amplifier.
Description of a current mode input amplifier using Beyer Dynamic transformers.
This is an archived article since I do not make the PCBs anymore. Unpack the zip file in a separate directory ( links will not work ).


[1] Audio Transformers by Bill Whitlock.

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