Tweakers' Asylum

Danger!

71.141.242.3

Al Sekela

In Reply to: RE: Please help: what is this connector called? posted by Chrome on November 08, 2007 at 20:13:53

Your proposed experiment may result in amplifier oscillations and complete destruction.

The added inductance of the extended power supply leads can allow some mutual inductive coupling and create an unwanted, positive feed-back path.

Follow Ups:

RE: Danger! - Chrome 13:57:02 11/12/07 (3)
I didn't see your post 'til after I'd done the mod.
No problems so far (and I've had it cranked up pretty loud at times).

The power supply jumper is about 2 feet in length, made of zip cord.
Ultimately, I plan to put both transformers in an enclosure separate from the power amp; then I'll have two jumpers.
I strongly suspect this is what Linn did to make its Spark external PS for the LK280. I remember that the "Spark option" involved removing the transformer from the LK280 chassis; I think what they did was to transplant it into a box with another PS, and added some receptacles on the back.

What would be some signs of the potential problem you mentioned?

thanks

dmc
- A loud squeal. Smoke. Flames. - Al Sekela 15:45:01 11/12/07 (2)
  As long as the amp has sufficient local filter capacitance to ensure that the umbilical cable inductance does not permit oscillation, you should be fine. However, this is a dangerous thing to do.
  - RE: A loud squeal. Smoke. Flames. - Chrome 16:00:51 11/12/07 (1)
    How do you think the manufacturer did it?
    I don't think any changes are made to an LK280 to use the external PS with it, except that its transformer is removed. (I.e., the manufacturer's Spark external PS used an umbilical (two, in fact).)
    
    Is there a way (within reason) to construct the umbilical so that its inductance is small enough as to be negligible?
    
    Do you know of anyplace I can read up on this kind of thing (such a concern hadn't even crossed my mind; I'd best get educated).
    
    thanks again
    
    dmc
    - Not sure there is a simple text. - Al Sekela 16:57:03 11/13/07 (0)
      I would use shielded, twisted-pair wire for the umbilical, and provide plenty of filter capacitance as close to the load as possible. What you don't want to do is place the big filter capacitors at the far end of the umbilical cable!

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