Optimus STA-300

[Ramussons]

Hello,

I have a Optimus STA-300 Tuner Amplifier passed on to me. It was purchased from Radio Shack in the US.

The FM / AM band is set to select frequency band in US and not to that in India. Since it uses a PLL Frequency Synthesizer, it should be possible to change the Frequency selection settings.

Besides, I'd like to alter the power supply for a 220 V input.

Can one of you please help me with a schematic?

Thanks,
Ramesh

 

[rumpfy]

Ram,
It appears to me that the unit is a US based design and the power transformer is made for 120 volt only.
Inspection of the unit will show if the transformer primary winding is made up of two, 120 volt windings; windings in parallel for 120 volt and windings in series for 240 volt. My guess is that it is 120 volt only. If you need a schematic to do the conversion then you need help. Best bet is to just examine the terminal strip on the mains transformer to see what is what.
There are references on the web to the unit and there is a parts list. BUT it is very brief. To use this thing I suggest a 240 to 120 volt transformer is what you need. There is a specification on the web too, and this says the FM band is 87.5 to 107.9 MHz. This is the international FM band. If you want to change this you will have trouble. I think there is a japanese frequency band for FM of 75 to 95 MHz but I'm not sure. What is different about India?
hope this helps.

 

[Ramussons]

Thank you rumphy.

The power transformer is a single winding, 120 Volts. Replacing it with a 220 Volt one is not the issue.
But, on the board that contains the fuse and the power switch, I find there are some wires from the Primary side of this Transformer going to the main mother board. What does it do?

As far as the tuner is concerned, the AM band has stepping frequencies that are in agreement with the broadcast frequencies.

But on the FM side, the frequency steps thru' ODD number decimals - like 90.1, 90.3, 90.5 and so on. But in India, the FM frequencies are European and can have both ODD and EVEN like 90.0, 90.1, 90.2, 90.3 and so on.
The IC data states that it's very simple to configure the chip for the European band. I need the schematic, if available, for this.

Thanks once again.

Ramesh

 

[rumpfy]

The 'international' FM band is 88 to 108 MHz. So that no radiation goes outside this band, the lowest and Highest frequency is 0.1 MHz inside the band limits. This means that the lowest station frequency is 88.1 MHz, and the highest is 107.9 MHz. The spacing of station carrier frequencies is at 0.2 MHz intervals so each station has a carrier frequency which is at an ODD frequency.
On the AM side, the usual spacing of station carrier frequency was 10 KHz; However, in Europe, the spacing was reduced to 9 kHz. So there is an arrangement that for the US, the stations are selected on a 10KHz spacing for AM and 0.1 MHz for FM. With Europe, the station spacings are 9 KHz for AM and 0.05 MHz for FM. This is a function of the frequency selection process in the receiver. My guess is that the Optimus, being for the US market, is NOT SELECTABLE, but I may be wrong.
You ask about the wires from the primary side going to the electronic board and I dont know. Is it possible there is a panel lamp (on/off indicator lamp)? It is also possible that the mains lead goes to the radio receiver and is an 'internal aerial' for AM and FM.
It may also be possible that the leads go to another power outlet to be used for an attached turntable or tape deck perhaps. When the mains switch on the OPtimus is OFF, then there is no power to the turntable.
Thats all I can suggest.