Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Pitchfork]

Can anyone suggest a company that can repair a mains transformer?
It's from an brand new amplifier & the primary winding is open circuit.
The output windings are 27-0-27 & 17-0-17 but I cannot find a suitable replacement anywhere with dual secondaries.
BTW its a conventional chassis type type not torroidal.

[STMO123]

My sons transformers just turn back into trucks and repair themselves

[Plomien]

My sons transformers just turn back into trucks and repair themselves

I was about to say ask Optimus Prime....

[vauxfan2k]

transfrormers... robots in disguise  

[Marks DTM Calib]

Unlikely to be repeirable at all as mass produced units have welded E/I sections.

Whats it off?

[Turk]

If the amp is Brand New then surely it will be under warranty ?

[Bumbazor]

I had a transformer fail in a mixer. Like yours it had dual secondaries. Problem was there was no markings on it so I had to so it the hard way of counting the windings. But eventually I worked out the voltages.
The main problem I had was finding a replacement. I ended up having to use two separate transformers to provide each of the outputs the original dual secondaries provided. One was toroidal, the other chassis.

In the end I got it working.

For a like for like replacement you might have to go to a dedicated audio spares place, but like previously said check the warranty first.

[Pitchfork]

It was bought as B grade therefore no warranty
An 'own brand' made in china for the retailer, no idea of who the actual manufacturer was & the retailer will not tell me
Looks like I'll need to put 2 separate transformers in to overcome the dual secondaries problem
I may try to dismantle in case the open circuit primary fault is near the beginning of the winding. Shortening the length a little would not make a difference to the performance.

[Kevin Wood]

Problem is, the primary will invariably be the innermost of the windings making access difficult.

Depends how neat a job it needs to be. First thoughts would be to replace with 2 transformers, as you say. The likelihood is that most of the power will come from one of the windings, meaning the second set of voltages can be provided by a very small transformer (likely feeding preamp or driver stages).

If you need to do a much neater job two thoughts come to mind:

1) There are companies who will wind one-off transformers to your specifications for not too much money, but obviously more than an off-the-shelf one.

2) Someone (RS?) used to sell bare transformers with just a primary winding so you could wind a secondary to your specifications.

I just bought a couple of toroidals from Rapid electronics for a Hi-Fi DAC I've just built and they have a very wide range, reasonable prices and they look to be nice quality transformers.

Kevin

[Pitchfork]

Correct the 27-0-27 is rated at 1.4A for the power amp
The 17-0-17 for the preamp @100mA so would be a lot smaller  if I go for the 2 transformer solution (which is most probable)
I could even simply drop the higher rails down once DC  with some wire-wound resistors & bypass the preamp rectifiers (That's what every other manufacturer does anyway e.g. Marshall, Carlsbro even my beloved Sessions!)
BTW never mention RS in front of me! I work for Premier Farnell

[Kevin Wood]

BTW never mention RS in front of me! I work for Premier Farnell

LOL

Kevin

[Marks DTM Calib]

Correct the 27-0-27 is rated at 1.4A for the power amp
The 17-0-17 for the preamp @100mA so would be a lot smaller  if I go for the 2 transformer solution (which is most probable)
I could even simply drop the higher rails down once DC  with some wire-wound resistors & bypass the preamp rectifiers (That's what every other manufacturer does anyway e.g. Marshall, Carlsbro even my beloved Sessions!)
BTW never mention RS in front of me! I work for Premier Farnell

Ok, so we are talking about a 100VA ish transfomer.....so wind your own!

I would not drop the rails using resistors and particularly not wire wounds!

Marshall, Carlsbro  and all other session amps are, to be quite frank, piss poor hifi type setups......

[Pitchfork]

Correct the 27-0-27 is rated at 1.4A for the power amp
The 17-0-17 for the preamp @100mA so would be a lot smaller  if I go for the 2 transformer solution (which is most probable)
I could even simply drop the higher rails down once DC  with some wire-wound resistors & bypass the preamp rectifiers (That's what every other manufacturer does anyway e.g. Marshall, Carlsbro even my beloved Sessions!)
BTW never mention RS in front of me! I work for Premier Farnell

Ok, so we are talking about a 100VA ish transfomer.....so wind your own!

I would not drop the rails using resistors and particularly not wire wounds!

Marshall, Carlsbro  and all other session amps are, to be quite frank, piss poor hifi type setups......

Who said anything about Hi-Fi?
I'm a musician with a 5K PA Rig!
Guitar & PA amp manufactureres all use ceramic WW resistors to lower the voltages for pre-amp stages as they all use BiFet op amps somewhere in the circuits that run at +- 15v

[Marks DTM Calib]

Yes, which means two things

1) The opamp supply rails will follow and be affected by the music transients.

2) The opamp supply rails now have significant inductance (due to the use of wire wounds) which will affect the dynamics!

It just highlights how cheap the setups are in relaity (and mega over priced to you and me!)

[Pitchfork]

Yes, which means two things

1) The opamp supply rails will follow and be affected by the music transients.

2) The opamp supply rails now have significant inductance (due to the use of wire wounds) which will affect the dynamics!

It just highlights how cheap the setups are in relaity (and mega over priced to you and me!)

Therefore the original design (which I admit is good, as is the build quality- apart from the transformer obviously) with 2 secondaries is the way to go.
Would the inductance of the transformer secondary also have a detrimental effect?