Why did it fry?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I’m sure I’m missing something obvious, but I’m quite new to this...

I’m building an Elliott Sound Products P05 mini power supply for the ESP riaa pre-amp . I think I might have hooked it up to the transformer wrong. It showed a good voltage when it had no load, but as soon as I tried to hook it to the pre-amp, resistors 1 & 2 started getting overheated. I’ve replaced R1 and R2.

Transformer outputs 2x15VAC @25VA - see pictures
8D543FEB-1DE5-45AE-B9D0-37248FC3BBD9.png

I hooked black and orange to AC1, yellow and red to AC2, and gnd to chassis ground.
91A31174-5071-4C50-B5C9-401DEFD9B53E.jpg
2C262325-956F-4785-93EF-A283AB91C8DB.jpg

Questions I have:
1a. How should I hook it up to the transformer?
1b. Should I use a 15-0-15 transformer instead?
2. Should I replace other components, too?
3. Could it have something to do with the phono preamp circuit?

Thanks in advance.
 
You have a dual secondary transformer. The schematic shows a wiring diagram to cover both a single supply and a centre tapped transformer. You can make your transformer a centre tapped by joining the Red+Org wires, then use the Blk+ Yel for the 2 feeds AC1 + AC2 and the joined wires for Grd.
 
Administrator
Joined 2007
Paid Member
I would wire the transformer as Puffin suggests and then recheck the output voltages off load as you did before.

A phono preamp should draw minimal current and so at this point it does sound like there could be an error somewhere as you connected it all up.

You can use a bulb tester even on such a small supply as this, try a very low wattage one like a fridge lamp. That should prevent major damage and overheating.
 
Similarly, check you have wired the primary correctly.
for US 115v supply, Violet & Brown connect together & go to live: Blue & Grey connect together & go to neutral.
for Europe 230v supply, Brown goes to live; Violet & Grey connect together but not to anything else; Blue goes to neutral.
 
Similarly, check you have wired the primary correctly.
for US 115v supply, Violet & Brown connect together & go to live: Blue & Grey connect together & go to neutral.
for Europe 230v supply, Brown goes to live; Violet & Grey connect together but not to anything else; Blue goes to neutral.

You sure? This doesn’t seem right to me. I have Blu + Vio together and Gry + Brn for 115v

Still troubleshooting... had to walk away yesterday :mad: I’ll give it another try today.
Thanks everyone!
 
Last edited:
You have what appears to be a 2 pole DC socket a barrel (Grd) and a centre pin Usually (Pos) The DC voltage out requires a 3 pole socket. What is the PS powering? and how does it connect to the component?

EDIT: I see it is to power an RIAA preamp. Please post some photos of this.
 
Here’s a picture of the preamp.
When I connect the power supply to ground, the resistors start to heat up.
You’re saying I have the wrong type of connector? As I understand your comment it seems to me that V+ and V- need to remain isolated from ground. That makes sense to me, now. Duh! Can you recommend a connector style so I know what to look for at Digi-Key?
View attachment 776642

Also: can I safely hook up a dual secondary output transformer in parallel in this schematic? Does ground on the board simply go to chassis ground? The two circuit board grounds are the same (trace connects both)
 
Last edited:
Hi, can you add any pics to your post and not as an attachment as I cannot open it. The 3 phase DC needs to be connected to the Preamp. The Preamp should show where DC +/- and Grd are connected. The transformer you have is fine for a 3 pole DC supply.

Before you connect it to the preamp have you checked the DC voltage coming from the PS? You should get full DC voltage between + & - and half that DC voltage from either of the leads + or - and Grd.
 
You have what is known as a symetrical power supply.
Very common in audio: -15v/0/+15v.
As Puffin states - you require a 3 pin connector.
3 pin low power connectors are less common than the 2 pin barrel type.
You could hard-wire the power supply to the phono pre-amp or use XLR connectors.
Do not use 3 pin XLR for danger of mixing with signal wires.
See Five-pin – DMX512 and DC Power for Audio Systems -
XLR connector - Wikipedia
 
No, it’s currently connected via black and white (grn is chassis ground) from the cable in (on the other end of the board). R,W,&G are RCA inputs. I think I know how to fix hook it all up now.
DF497D67-C97C-4644-BE83-CCE086928AB0.jpg
I’ll do so and post a pic.
Then I’ll do something like a 5pin XLR later...
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.