The modification of MPC1000 No.2

Last time, maybe,about 4 months ago, I changed the internal power supply of my MPC1000 to external transformer one.

It is good change in the sound of MPC,but it was not convenient to bring , and I felt it was not easy to play it.

Also,thinking about gig tour, I want to make the machine smaller and lighter.

And external power supply was heavy....

But that modification succeeded to make the sound better than old type, so I tried to think the new modification of making an internal power supply.

I got to know a toroidal core transformer , it has core like a ring of donuts , winding copper wire around the core.

The core cancels magnetic flux and good at suppressing noise.

Also it is small,light,high efficiency...I doubt the description of transformer.... but I tried it.

(It costs 2or 3 times higher than usual one, so I had some hope...)

Adding that, I used to make a microphone preamp using that transformer ever ,so I had some experience and expectations about that transformer.

The blue boxes are transformers.

The MPC1000 needs +-12v,+5v power supply.

+12v line needs about 300mA

-12v 90mA

+5V 400mA

I measured the real board.

Adding the information about internal power supply(old one)

+12v1.5A

-12v 0.3A

+5V 2A

It is small but has so enough power to supply the board.

This time I used 2 transformers.

115v 15v x 2 15VAC(500mA /each)

115v 9v x 2 7VAC(350mA/each)

I could not get 100v version of them, so I had to think the voltage value ,because it gets less 15% in use 100v.

And about the capacity of a current ,I wanted the transformer more enough capacity,but they are big and I could not install them into MPC.

If it does not work well,I have to change another transformer,that has more current but less voltage.

The power supply circuit is quite normal, nothing special.

But we never know what happens after make and try it.

This time I found points below:

・Transformers get hot well(around 40℃ 5v is hotter than 15v)

・Regulators also get hot well (around40-50℃）

When I built external one, I never care the temperature of trans,

(15v about 37℃、5v33℃ 15v 0.5A 5V 1A）

But these transformers get hot, I checked the datasheet,and found it normal.

High quantity of current flow and a transformer is sealed with plastic resin, so it tends to get hot.

Regulators are also get hot as same as external one, so these are normal, they generate the heat of 1w or 2w, but I felt it much more.

But I compared this power supply with tube amps, this PS is not hot at all, it is warm.

First I bought small capacity of 5v transformer, had to buy another one.

This is test circuit.

There was a trouble , when I finished making the board and did some test, it was OK , and then, tried to install it into the case, but I failed it .

Because the size of the board was a little bit big ,so had to cut the board.

I usually start to do some modification ,watching my tool box , and do not do in a planned way,so often have to change plans.

And this summer , it was terribly hot , I could not think deeply ,then did some works, and I met some problems.

Then test.

I found the heat problem was serious, attached heat sinks.

These heat sinks( black fins on side panel of the machine) are tentative, small size, then I changed large one.

Next test was sound checking.

According to the experience of last modification, I can not find the differences in simple music, so I record complexed music files playing MPC.

And I tested 3 patterns : old power supply, external, internal.

As a result, I could not find the differences between internal,external type, but the old style, the sound got lighter than others, and for me ,it gets small image of sound.

These are kind of favor thing, but especially about low frequency,I like the sound of new power supply.

Usually I do try and error many times.also in this time I did.

This modification seems simple,not gorgeous one,but I often do same type of modification.

It needs lots of working and patience ,but I feet that they are essential works for making sounds better and clear.

So please enjoy our sound imagining those works.