Line 6 DL4 Power Supply Mod questions

[samgraysound]

Hi,

I picked up a broken Line 6 DL4 that wouldn't turn on. The problem turned out to be the power input jack switched connection was broken, so nothing was grounding to the power supply. Pretty simple.

But I spent a lot of time looking at this power supply and I think its kinda...dumb?

It calls for a 9vAC 1200ma power supply. But that is just rectified through a zener diode down to 6v. And the amp draw on that 6V is only 200ma (I checked). Plus the 6v goes into a MAX887 Voltage regulator which is can handle up to 11v input according to the datasheet.

Is there any reason I shouldn't just bypass the rectifier circuit and just run this off a normal 9vDC supply with appropriate mA rating?

I've attached the schematic of the power supply.

 

[samgraysound]

and here's the datasheet for the MAX887

 

[PRR]

For AC input, it is a half-wave rectifier so the transformer AC current rating must be much more than the final DC. 6:1 seems excessive; likely they had a crate of 1200mA warts.

Quite a few "9V DC" supplies will rise over 11V when lightly loaded. I would not go that way without pre-regulation.

 

[samgraysound]

For AC input, it is a half-wave rectifier so the transformer AC current rating must be much more than the final DC. 6:1 seems excessive; likely they had a crate of 1200mA warts.

Quite a few "9V DC" supplies will rise over 11V when lightly loaded. I would not go that way without pre-regulation.

Interesting. Would a 9v (or 6v) zener do the trick, or do I need a full voltage regulator IC?

 

[abbey road d enfer]

Interesting. Would a 9v (or 6v) zener do the trick, or do I need a full voltage regulator IC?

Depends on your power supply. Switching ps are quite stable; it's the old non-regulated linear ps that can be hazardous. You would then need a pre-regulator.
You need to experiment. With a regulated 9V ps, the MAX887 would see a little less than 5V at its input, which is well within the 3.5-11 range, so shouldn't be an issue.
While you are at modding the DL4, you could well bypass the zener, which would result in less heat dissipation.

P.S: whatever you do, don't leave the batteries in; this part of the design is seriously debatable.