Insulating WOPL 400 transformer bolts

[laatsch55]

And there is no cure for that...

 

[Gepetto]

And there is no cure for that...

Yup, take the transformer end bell off one side and die cast cradle off the other side of the transformer and epoxy the cardboard bobbin inner sleeve to the transformer steel core.

 

[Gepetto]

The very slight hum you hear from AC transformers that you cannot fix is the magnetostriction noise. That is the steel lams expanding and contracting very microscopically due to the 60 Hz flipping of the magnetic dipoles within the steel itself. That is within the physics of the steel itself and you cannot remedy that.

 

[George S.]

Magnetostriction. I like that word. You know as I walk the dog around the block tonight and evermore that words going to be on my mind as I pass those transformers.
Thinking next time I have the transformers off the amps I'll most probably add non-conductive epoxy as a precaution. I have some small syringes for injecting DeOxit into switches and pots. I'll look for some large ones capable of handling epoxy. Be nice to put it where it counts.
I'm off to walk the dog and listen to magnetostriction. Later.

 

[Gepetto]

Magnetostriction. I like that word. You know as I walk the dog around the block tonight and evermore that words going to be on my mind as I pass those transformers.
Thinking next time I have the transformers off the amps I'll most probably add non-conductive epoxy as a precaution. I have some small syringes for injecting DeOxit into switches and pots. I'll look for some large ones capable of handling epoxy. Be nice to put it where it counts.
I'm off to walk the dog and listen to magnetostriction. Later.

It is a good word to know George...

 

[laatsch55]

Slides right off the ol tongue...

 

[George S.]

Keystone 3058, perfect! You'll need to shorten the bolts a little to keep them from hitting the storage caps.

 

[laatsch55]

COOLNESS!!!

 

[George S.]

Note these step washers are for the replacement bolts for the 400 transformer that I referenced at the beginning of the thread, with the two layers of heat shrink cut off. One layer of heat shrink on the bolt will not pass into the stepped washer, the fit is that good! Additionally, the stepped washer fits the chassis hole and transformer cradle also perfectly.
These won't work on a 700, way too small. Haven't tried them on a 400 4 fin without the cast aluminium cradle, but thinking they should work.
Watch the bolt length, add some nylon spacers under the bolt head or carefully shorten the bolts , maybe a 1/4" looks correct. Don't damage your storage caps.

 

[wattsabundant]

Having worked with ferroresonant transformers for nearly 40 years, I've heard a lot of them where the steel worked loose and they were painfully loud. If a linear transformer, such as one in an amplifier was rattling, it could be redipped and baked. A replacement, if available would likley cost less.

 

[CrazyIvan]

Keystone 3058, perfect! You'll need to shorten the bolts a little to keep them from hitting the storage caps.

Will you be selling a kit?

 

[George S.]

Don't think so, too damn busy doing other things. If Joe wants to offer them that's cool with me.
A 400 and 700 insulated bolt kit would be a good addition to his offerings.

 

[grapplesaw]

Don't think so, too damn busy doing other things. If Joe wants to offer them that's cool with me.
A 400 and 700 insulated bolt kit would be a good addition to his offerings.

Joe should bundle a little add on kit for the 400 with these, bridge rectifier board Capacitor mounts and terminal strip. All costly to buy one off from mouser

 

[mlucitt]

Has anyone done any testing to document the benefits of the insulated transformer bolts. A test before and a test after using the same amplifier would be necessary. In my experience, some amps can be improved this way and some amps don't seem to need it.

 

[George S.]

I just know that every piece of test equipment I've opened and looked at have them. I remember Joe saying it was a industry standard to use them. Honestly, I know no more about them then that.

 

[Gepetto]

It is all about that noise floor, eking out 109dB SNR instead of settling for 107dB. Same with wire routing and dress.

 

[grapplesaw]

You bet even on a 500

 

[Loggitie]

Silly question : here in Europe the metallic parts (chassis) have to be connected to earth. If I understand correctly the transformer assembly described here, it will be isolated from the chassis, and so not connected to earth. Am I wrong ?

 

[George S.]

I built three WOPLs.
I completely isolated the transformers from chassis ground using the stepped washers on the bolts and nylon washers between the the transformer and chassis.
The amps chassis do not have a earth ground connection through the power cord.
All components are grounded to each other through the interconnect cables shields.
I take care to separate stacked chassis with rubber feet to prevent ground loops.
I do have a earth ground on the preamps power cord, this is the systems earth ground (right or wrong).
The system is dead silent with no hum.
Build it the way you want, which may also be building it to local regulations.
It's good to have choices.

 

[mlucitt]

Silly question : here in Europe the metallic parts (chassis) have to be connected to earth. If I understand correctly the transformer assembly described here, it will be isolated from the chassis, and so not connected to earth. Am I wrong ?

Not a silly question at all. Here in the USA, all metallic electrical equipment is required to have a solid Earth Ground.
The Phase Linear amplifiers were designed and built before these regulations were put in place. In effect, they are "grandfathered". If the Phase Linear amplifiers were being built today, they would have a 3-conductor power cord and the chassis would be connected to Earth back at the electrical panel to prevent electric shock.