Headphone trick not used here?

[rutledj]

I'm just curious about transformer coupled hum caused by the placement or the xfrmrs too close or in the wrong orientation. I don't see it mentioned here much or the trick of powering up the pt and clipping headphones to the ot and moving it around until you hear the least amount of hum.

Is that just not a problem with these amps?

Rut

[heisthl]

I thought I knew all the "old timer" tricks but I've never done that one. What's the procedure? My guess is you would just connect your headphones to the OT secondary with the primary side not connected and then fire up the already mounted power transformer and move the OT in and out of the noise fields til you find a quiet spot?

[Bob-I]

I've never found that it makes a difference if you go with tried and proven placement. I typically place the xformers based on well built amps.

[Ed de Jager]

i actually did the headphonetrick in my Dlite found it very useful as space was tight in my chassis.

Ed

[rutledj]

I thought I knew all the "old timer" tricks but I've never done that one. What's the procedure? My guess is you would just connect your headphones to the OT secondary with the primary side not connected and then fire up the already mounted power transformer and move the OT in and out of the noise fields til you find a quiet spot?

That's pretty much it although the PT doesn't necessarily have to be mounted. You could just apply power to the primary (with all other wires taped up of course) and proceed as you outlined. You really can hear the hum increase and decrease but I'm not sure if that hum makes a difference in a finished amp. You would think so if you can hear it but I'm not sure.

Rut

[paulster]

I thought I knew all the "old timer" tricks but I've never done that one. What's the procedure? My guess is you would just connect your headphones to the OT secondary with the primary side not connected and then fire up the already mounted power transformer and move the OT in and out of the noise fields til you find a quiet spot?

Exactly. You can also do the same, substituting the OT for the choke to find a quiet spot for that too.

I've never found that it makes a difference if you go with tried and proven placement. I typically place the xformers based on well built amps.

True, but for new layouts on undrilled chassis', especially with tight confinements, it can be a benefit as there are some surprisingly quiet (and noisy) placings that can be found even by small relative movements.

[fabiomayo]

Very nice tip, thanks. I have one concern though. What is a more important
issue, a little hum due to transformer placement or the OT secondaries lead
dress? Perhaps the best place to put the transformers wouldn't end up as
the best lead dress of the secondaries... Any thoughts?

[LeftyStrat]

Very nice tip, thanks. I have one concern though. What is a more important
issue, a little hum due to transformer placement or the OT secondaries lead
dress? Perhaps the best place to put the transformers wouldn't end up as
the best lead dress of the secondaries... Any thoughts?

What you'll find is that very minute movement of the transformer can result in significant reduction of noise. Distance on the order of millimeters or especially an angular change of a degree or so (You see a lot of chokes angled this way in some old amps).

Even if you don't use the technique on every amp you build, it is a worthwhile experiment to see how placement affects noise.

I actually do it by soldering in a phone jack on the secondaries and running a cable to a bench amp. This amplifies the hum to the point that you'll always have a little, but you will definitely hear the change from really bad hum to very little.

[fabiomayo]

Very nice tip, thanks. I have one concern though. What is a more important
issue, a little hum due to transformer placement or the OT secondaries lead
dress? Perhaps the best place to put the transformers wouldn't end up as
the best lead dress of the secondaries... Any thoughts?

What you'll find is that very minute movement of the transformer can result in significant reduction of noise. Distance on the order of millimeters or especially an angular change of a degree or so (You see a lot of chokes angled this way in some old amps).

Even if you don't use the technique on every amp you build, it is a worthwhile experiment to see how placement affects noise.

I actually do it by soldering in a phone jack on the secondaries and running a cable to a bench amp. This amplifies the hum to the point that you'll always have a little, but you will definitely hear the change from really bad hum to very little.

Thank you so much. I'm about to start my build (for almost a year now )
and I'll certainly take that advice, especially since my layout differs a little bit.

[rutledj]

I just tried this on a build and got the most hum with the OT positioned close to the PT as in most you the builds posted here.

I get almost none if the OT is moved to the opposite side, however, this puts then OT wires running near the preamp circuitry.

Would this cause a problem?

Rut

[heisthl]

I've made this mistake more than once , If you want them spread run the wires on the outside of the chassis and bring them back through like it was mounted close.

[LeftyStrat]

I don't think it would be a good idea. If you used my method of amplifying the hum with the phone jack into an amp, you're going to have a lot more hum than normal.

All you want to do is find that point where there is a noticeable drop. If you put the transformers right up next to each other with the laminate aligned, it will be really loud. When you rotate the OT it will drop. You can move it a few millimeters in and out and find a point where there is a large drop off.

With my amplified method, you are not trying to eliminate hum, just find that spot where there is a drastic increase/decrease, and move just slightly beyond that.

If you just use the headphone method, it will drop to inaudible at this sweet spot.