The Synton 203 Phaser is an effect unit based on the technology of the famous Synton 903 Phaser. The 203 basically follows the concept of the 903 but offers a larger phase shift (2000 degrees) and an extended control system. It offers the advantages of an analog phasing system with respect to headroom and signal-to.noise ratio, both specifications being superior compared to digital or bucket brigade phasing and flanging devices. The unit use selected philips LDR (light-dependent resistor)





brochure 203 front

brochure 203 back
















203 parts

The Synton 203 uses the HA4741 and LM324 as quad opamp (The HA 4741can be replaced by the LM348, the TL074 needs to many current).

The powersupply regulator is a XR4195 dual 15 volt.

Potmeter are Piher potmeters with 4 mm metal shaft.

The 12 LDR are special philips LDR which are not availlable anymore.

The 203 can internal be switch from 220 to 110 volt.  If you must do that, i suggest remove the switch and wire the the transformer.  Do not forget the pcb board under the transformer!!

Known  problems:

  1. Broken quad opamps:  If an quad opamp is broken most of the time the output ( pin1, 7,8 and 14) is almost the same as the power supply. In some case that is fine, fi comparator.
    You can check this with a meter by measuring the output voltages of the opamp. Normaly you will measure zero or a small dc signal or a audio or lf signal. If you find an with + or – 15 volt ( in the case that the PSU is 15 volt) the opamp is bad.
    You can check this by connecting the output pin with the next pin ( = – input, fi connect pin 1 with 2, connect pin 7 with 6). If the output voltage doesn’t go to zero this opamp is bad.
  2. Broken tatalium caps. These caps at could give serious problems. They are used for decoupling caps in the powersupply lines. If they are broken  most of the time they short the power supply.  You will measure allmost zero volt at one or both (+/-) powersupply lines. They are hard to find. If you cannot locate these my advice cut them out and check or the power supply is ok. ( fi + or – 15 volt)
    If only one power line is shorted and the fuse is to big, the rectifier could also be broken. Check this also. The Syntovox 221 has a lot of tatalium caps!! You can replace them by other tantalium caps or by normal other caps. !! Pay attention to the polarity!!
  3. Brokenor bad LDR.  The synton phaser uses 12 special Philips LDR.  If these are broken you must find an other LDR. I have used as replacement the VT935G ) these fits in the blackbox.  The philips version is better (larger range) but not availlable anymore.


    Controls oscillation frequency of the LFO between approximately 0.05 Hz and 10 Hz.

    This control knob is for applying the output contro1 voltage of the envelope follower (ENV) to the control input of the low frequency oscillator (LFO). This facility is useful for decreasing the LFO modulation speed in accordance with the audio input level. Application: changing vibrato speed on decaying tones of a musical instrument.

    This control is for setting the range of modulation by the LFO or the ENV. For a maximum phase shift the knob should be turned fully clockwise to HF. If the modulation effect has to be applied to audio program with lower-frequencies, it can be useful to alter the control range by turning the knob more in the LF direction.

    This controls the output voltage of the LFO. The amount of phase shift by the LFO is dependent on the setting of this knob.

    The phase shift caused by the output of the envelope follower can be adjusted between zero and maximum withthis control knob. The LED in the MODsection is monitoring the speed and depth of the LFO and ENV control effects.

  • INPUT 1/0
    Input attenuator. Only to be used when the input signal should exceed + 6dBmor when the FEEDBACKcontrol is used.

  • FEEDBACK.1/0
    With this knob feedback isadded to the phaser system for making typical band filter effects. It can be used on both phasing or vibrato effects. Turning up this control will cause higher gain within the pass band of the system, which might also cause distortion. In that case it is necessary to reduce the input signal by turning the INPUT knob down.

  • MIX 1/0
    This knob is for adjusting the optimal effect. Here the direct signal is mixed with the delayed signal, for making the typical phasing effect, which should occur with the knob about halfway can be useful for simulating doppler
    or vibrato effects.

  • STATUS 1/0
    This switch provides click free switching on the effects of the 203. The SWITCH Jack input can be useful for connecting a foot
    switch to the unit. (See note). The STATUSswitch also resets the LFO, so that when switched on, the effects always will start at the same point.

    XLR on back panel. Accepts normal signal levels (0 dBm). See technical data.

  • OUTPUT 1
    XLR on back panel. Phasing output.for all effects.

    XLR on back panel. This output only gives the band filter effect when the FEEDBACK control is used.
    It can be very useful to simulate stereo effects when it is used together with input 1.

    Power requirements are 220 VAC normally Other mains voltages on request.