Regulated Split Rail Supply Sagging

[Puffin]

I have built a regulated split rail supply 24+ Ov 24- to power an old Exposure Pre Amp. This is dual mono with a board for both channels. The boards are marked DC input 24vdc for a split rail supply. The boards also have an LM317 and 337 after the DC input.

The pos rail of the PS is drooping to around 10v and the negative rail to around 2 volts. I did make a supply for this years ago and from memory it was an unregulated supply and it worked fine. Any ideas anyone?

 

[leadbelly]

Schematic? Transformer description and rating?

 

[jan.didden]

I have built a regulated split rail supply 24+ Ov 24- to power an old Exposure Pre Amp. This is dual mono with a board for both channels. The boards are marked DC input 24vdc for a split rail supply. The boards also have an LM317 and 337 after the DC input.

The pos rail of the PS is drooping to around 10v and the negative rail to around 2 volts. I did make a supply for this years ago and from memory it was an unregulated supply and it worked fine. Any ideas anyone?

One immediate thing you can check is whether the input to those regulators also sag. Diagnose.

Jan

 

[Puffin]

I will put info up later.

 

[richie00boy]

If the negative rail is going down that low I wonder if the layout is wrong or fake parts. The pinout of the 337 is different to the 317.

 

[Osvaldo de Banfield]

Perhaps 'litycs has gone out and need to be replaced.

 

[Puffin]

Ok, some pics and a part schematic. This is all there is on the sellers page. This was an ebay buy at not much money. I tested everything after I had built it with a DBTester and it was good. When I put the full fat mains through it it blew one of the rectification IN4007 diodes. I replaced the diode, but it didn't want to work, so I bypassed the on-board regulation with a bridge rectifier (seen in the pic) it tested all ok at +/- 24v.

This is a pic of one of the pre-amp boards.

 

[Osvaldo de Banfield]

The PSU is a LM317 wired as current source plus a shunt regulator. Unnecessary in my opinion. A simple LM317 as series regulator will be better.

 

[Puffin]

The PSU is a LM317 wired as current source plus a shunt regulator. Unnecessary in my opinion. A simple LM317 as series regulator will be better.

Yes, I made one of these recently for a Diamante (Twisted Pear) Pre-Amp and it works well. I should trust in my own DIY skills!

 

[Osvaldo de Banfield]

I didn't doubt in your skills nor that the circuit will not work, I only say that simple things usually do its job better than complex solutions.

 

[Puffin]

I didn't doubt in your skills nor that the circuit will not work, I only say that simple things usually do its job better than complex solutions.

No, I didn't read it that way. I should not look at the parts count on the stuff on ebay and think it is good value for what the parts would cost me to make it myself.

 

[leadbelly]

Well, the transformer looks decent sized, so the most likely reason is the preamp draws more than the 125 mA the current limiter is set to. As Jan says, measure at different points in the circuit.

 

[Puffin]

I am thinking of ditching the current limiting and modifying the board. In the past I have had success with adding a power transistor to the circuit to boost the current as in the link below.

https://www.eeweb.com/extreme-circuits/ampere-or-current-booster-circuit

 

[Puffin]

UPDATE: Whilst checking the current draw at different points on the board I seem to have killed something! Oh well, I should have made it myself anyway.....which is what I will do now

 

[Osvaldo de Banfield]

It happens frequently. When searching with the DMM test leads in an IC, for example, and move the vision to DMM's display, the points move itself or by an error in hand movements, and pufff: the thing makes smoke by it 4 sides.