Phoenix Gold MPS-2240

[garais05]

Can anyone help with Phoenix Gold MPS-2240 schematic diagram?I want to rebuild that old amp!

[Perry Babin]

Onemoreamp is the PG guy but if you can define what you mean by 'rebuild', it may help him to better answer your question.

[garais05]

Want to change smps trafo,replace sg2525a with tl494 to increase supply voltage and output power.And if needed replace other elements to fit higher voltage.And there are three pieces of optocoupler 4n35,so its very difficult without schematic diagram to understand what else should i change for my needs.So if anybody have schematic diagram,please help!Thanks in advance!

[1moreamp]

Thank You Perry

The opto-couplers provide isolated voltage sensing feedback to the supply so it can control the rail supply, and they also trigger muting and over power shutdown functions . This explains all three opto's inside the power supply circuit. To be exact see below:

OP1 is the DC output detection and feedback isolation opto and it turns on the overload led when the amp is over driven and produces DC output above a given level.

OP2 has its LED side across the 15 volt rails and when these rails are on and equal his signals the Sg2525 at pin 1 that all is OK and the supply operates normally. Without this the amp faults offline.

OP3 is a isolated turn on from the turn on lead that operates turn on muting functions of the amp so you don't get THUMP when it is turned on.

Most all of these functions are very necessary for the amp to operate properly and as designed. And are all hallmarks if a quality noise free feedback design used by most all high end amp makers. So nothing special here and without these devices in circuit and working you now lack noise immunity from the 12 volt power supply side and lower the overall quality and SQ of the amp to that of a flea market amp.

Changing to a 494 will not increase amp output unless you tear out the whole supply and start over from scratch. < this is not a pretty thought since these amps work so well as built and the circuit board will not accommodate such a major circuitry change without completely destroying its gold plated beauty. I Strongly advise against such a maneuver

If you simply want to change the output rails supply then you must understand that this The toroid windings are something special and they must be added to to raise output power and voltage above a small level of increase. I have done a 2220 to 2240 upgrade before and I played with taking it to a 275 level. And I succeeded but it was a huge time sink and just a pet project I did for fun.

So unless you want to rewind the toroid with custom windings your not going to be able to raise the supply rails much and the limits I am aware of are about +&-37 volts to each main large cap. And this is different for each models toroid as they all use a different set of windings. A simple low level < +&- 5 volt rise can be had by simply changing a single zener diode. But this will only unlimit the original toroid, and once this is done you will see the voltage drop off under load fairly quickly.


Might I ask you what you actually intend to try and achieve for a output increase ?

This amp has its limits and those limits are mostly set by the sink weight and surface area design. This is why PG stop this amp design at 75 watts per channel at 4 ohms. And 250 watts Mono at 4 ohms, or 2 ohm stereo. The heatsink is part of the design limitation of this amp model, and 125 watts per output pair are also the SOA limits of the Toshiba output devices.


PS you might also notice that the output transistors are using +&-21 volts and the whole amp before them are at +&-29 volts typical no load. The outputs are on a lower rail then the rest of the amp. Its design\ed to work this way, like many other amps on the market.

I am gonna let you chew on this for a while and get back to me.....