I found another 555 variant but it says it is suitable for currents less than 20mA. I am looking for a similar solution with at least 50mA output.http://sound.westhost.com/project95.htm
...a simple little project will provide you with positive and negative supplies, allowing a true chassis ground connection, and will be suitable for preamps, equalisers, etc., provided the current is below about 20mA or so.
The circuit is very simple, and is easily made on Veroboard or similar. Construction is not critical, and the schematic is shown in Figure 1 below.
Rectifier diodes should be ultrafast (UF4004 or similar), or you can use 1N4148 signal diodes. Losses will be slightly higher if you use signal diodes, or lower if you wanted to go to the trouble of using Schottky diodes - the latter are not warranted in such a simple circuit (IMO). The zener diode is to protect the circuit against transient overvoltage, and is optional (but recommended).
Figure 1 - The Negative Voltage Converter
Using only a standard NE555 timer and a few other parts, this circuit should be up an running in about an hour. The 555 is configured as a minimum parts count astable (i.e. no stable states) multivibrator, and runs at around 17kHz with the values shown. The zener diode (D3) should be a 16V/ 1W type. Resistors are 1/2W carbon film, and small caps may be polyester or mylar (63V types are quite Ok in this circuit).
Use a standard (bipolar) NE555 timer - not a CMOS type. CMOS timers do not have the switching abilities of the bipolar types, and output voltage will be lower.
The circuit itself is a simple voltage doubler. You may well ask why the output is not -24V if the circuit is a doubler. Look at the circuit, and you will see that the output of the timer is AC coupled with C4, so it is actually only 6V RMS with a 12V supply. For an input of 13.8V (standard car voltage), the doubler action gives an output of -12.5V with no load. There is a small loss due to the diode losses, and additional losses in the 555's transistor switched output.