The opamp used in the syntovox vocoder are quad opamps (LM324, Harris HA4741 /LM348 and TL074). The microphone amplifier use the NE/.SA/SE5534bor TDA1034 opamp. The HA4747 can be replaced bij LM348. Reason of using these opamps is the power consumption. The TL074 need 2 times the current as the HA 4747. (!!! You cannot replace the HA4741 by a 741. The 741 is a single opamp)
Syntovox 202, 222 and 221 uses Piher potmeters with 4 mm metal shaft.
Replacing parts always cut pin of the parts and remove the pins and use desoldering braid clean the holes.
Known parts problems:
- Broken quad opamps: If an quad opamp is broken, most of the time the output ( pin1, 7,8 and 14) of the opamp is almost the same as the power supply. In a few cases that is fine, fi comparator, but if this is used as an opamp this is bad.
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. If you find an high DC voltage ( in the case that the PSU is 15 volt) the opamp is probably bad.
If you connect the output pin with the next pin ( = – input, fi connect pin 1 with 2, connect pin 7 with 6) the output voltage should change. If the output voltage doesn’t go to zero this opamp measure the + input ( 3, 5, 10 or 12). The output must be the same ( if the output is connected with the – input) with the + input.
- 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, cut them out and check or the power supply is ok. ( fi + or – 15 volt)
Check also the rectifier it could also be broken. 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!!
- Leds. If you replace these by a new one, change them all or accept the big difference in light!
- Oscillating filters, If one of the filtercaps is broken the filter can start to oscillate. If you check the output of the filters ( pin1,7,8 and 14) with a scoop you can easely find the bad filter. ( Note the noise will be feed to the higher filters)
Models: The first 221 has a internal (ringcore) tranformer and no switch for voice/unvoice. The difference in later model is the place of the power transformer. The later models has a rincore mounted at the backpanel outside the unit and the last model has a separate PSU.
The power supply of the 221 has a number of different regulators:
A 7812 volt regulator is used for the led power supply. The two big boards ( analyser an synthesizer) has a 7815 and 7915 regulator (the earlier models uses the TO3 regulators).
The smaller boards has its one xr-4195 regulators for providing +/- 15 volt. The board with the microphone amplifier has two 4195 regulators.
All opamps has a +/- 15 volt supply except the first row LM324 at the synthesizer board. They have lower negative voltage instead -15volt.
The syntovox has a lot of trimpots.
The trimpots at the synthesizer board are for trimming the feedthru. You can calibrate this by feeding a LFO ( positive) signal of about 50 Hz and 5 volt. ( or a rectified ac voltage) to the cv input at the backpanel ( remove the matrix pins!!!) Listen to the output and adjust the trimpots for min feedthru.
The board with the microphone input has two trimpots for adjusting the sensitivity of the voice/unvoiced section. (check the elector vocoder, the voice/unvoice sectie of this vocoder is based at the 221. There are also two trimpot for trimming the feedthru of the VCA’s which are controlled by the voice/unvoice circuit. At this board there is also a trimpot for adjusting the frequency of the internal oscillator.
Almost all power supplies of the 221 can be set at 110 volt /220 volt by setting the primairy windings in series (220V) or parallel (110V). Double check the transformer because it could be different transformers be used.
The 222 has a standard +/- 15 volt power supply. The noise source of the 222 is MM5837 ic.
The unit has 1 trimpot. With this trimpot you can adjust the VCA’s at min. audio leakage from the synthesizer (carrier) section.
The 222 can 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!!
The 202 has a standard +/- 15 volt power supply.
In the 202 there is an extra small board. This board is the extra channel.
The 202 can 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!!
Syntovox SPX 216
The 202 has a standard +/- 12 volt power supply.
The SPX-216 has 3 boards. A frontpanel board and a main board and a board with the backpanel connector. The board with the backpanel connector is the switch board for the formant swiching.
The Spx216 has two trimpots for setting the speech compressor and 1 trimpot for the noise level.
The transformer can be set at 115 and 230 volt. This transformer has 3 taps ( wires) 0 volt, 115 volt and 230 volt. You must always use the 0 volt tap and or the 115 v or 230 volt tap. The not used wire should be isolated.