Heyboer & Pacifc - Transformer Vibration & Hum in a

[RJ Guitars]

There have been several behind the scenes efforts at resolving transformer vibration recently in Wreck layouts using Heyboer and Pacific transformer sets. While to your ears vibration and hum might sound very similar, it's important to recognize that these are two distinctly different issues and the cause and/or cure for them is not the same.

Transformer vibration is the actual physical vibration of a transformer on the chassis. It can potentially be either the power transformer or the output transformer, but the cause is typically due to magnetic coupling from the fields in the power transformer. The over simplified explanation is that something is loose and rattling in a transformer. The indicators of this problem is that the hum is coming from the amp as soon as you power it up and it is not something you hear in the speaker. The amp itself is actually vibrating. I have seen this with both Pacific and Heyboer transformers far too often in recent times with a slightly higher incidence in the Export versions. It's easy to identify by placing your hand on the transformer(s) or chassis and feeling for the vibration. If the sound continues when you unplug the speaker (caution this is not a healthy practice for your OT), then it's a physical vibration.

Transformer hum is different in that it is not a vibration that you hear coming from the amplifier chassis or transformer itself. It is something you hear in the speakers. I am not talking about signal hum that get's amplified through your circuit. I am talking about the output transformer directly coupling to the power transformer and producing hum that is heard in the speaker system. The Wreck layout can be prone to do this because of that close proximity of the two transformers. You can use the same test as defined above to test, but there are iterations that will help you learn more about the problem. If the hum goes away when you unplug the speaker (caution this is not a healthy practice for your OT), it's definitely hum. If it occurs as soon as you power up the amp before the tubes have a chance to heat up, it's transformer coupling. If the hum doesn't show up until after your tubes warm up - that is a different problem.

Transformer orientation matters. I have found that subtle location differences can make a big difference. In studying a Wreck layout using Edcor transformers the PT and OT transformer lamination's not only have to be at 90 degrees to each other, but the center lines for them have to be closely aligned... if you start at the back of the chassis and draw a line toward the front going straight through the center of the OT, that line also needs to go precisely through the center of the PT. This is how the Chassis drawings for a Wreck are indicated here on the TAG specification sheets. I have not studied this using the variety of transformers that are available for these builds but I would recommend using the headphone trick to establish the zone of least hum and mount your trannies accordingly.

I have stated this in an oversimplified fashion and the complexities and variations of hum and vibration problems can be extremely complex. However, this is a problem that I am hoping we can help some of these folks find a solution around and all of us learn something. Vibration is most likely an indicator of a transformer flaw and when that happens the vendors ultimately need to tighten up QC and own this problem. However, it's seldom cut and dried as to which transformer is causing the vibration - could be either or even some other loose item on your chassis. So resolving this will probably take our effort as well as the vendors. For my part I have been in contact with the transformer companies and many other individuals have done the same. The transformer companies are aware of the problem and I think they can be persuaded to work with us to resolve this.

Transformer coupling hum and hum in general is a problem that we can learn form the wisdom of the gurus should they care to share that knowledge with us... the TAG crowd is typically strong in this type of servcie and I have confidence we'll see some cool stuff come out of this before it's all said and done.

Helpful comments and perspective that guides us to understand and solve the issues is requested.

thanks,

rj

[M Fowler]

Good write-up rj thanks.

[Jana]

I suspect I will probably catch a lot of flak for what I am about to say but here goes. I think the transformer layout of the wreck amps is one of the worst possible layouts I have ever seen. There, I said it. I shudder every time I see pictures of wrecks and the orientation of the PT in relation to the OT and the close proximity. It goes against everything I have learned with my experience building amps. I could say more but I am probably already on my way to getting the "won't be down for breakfast" notice.

[diagrammatiks]

are you talking about unloaded or loaded transformer hum/vibration?

flux leakage decreases with load.

[RJ Guitars]

All my work was on unloaded systems so I am missing those data points. I suppose it's a weak consolation that the amp is not humming when you are in the middle of a raging solo and it's only noisy when you stop playing... but your technology has merit.

That does provide one interesting experiment that could be done though. Adding a resistive load onto the secondary without any signal could give you audible data points of what happens to the hum as you load the tranny down.

Good point!

[M Fowler]

I hear you Jana.

After you back the PT away from the front valence for clearance that doesn't give you much "playing with the headphone trick" wiggle room.

We could add a drip rail to the back of the chassis and stagger that OT over the side some.

Mark

[Cliff Schecht]

I suspect I will probably catch a lot of flak for what I am about to say but here goes. I think the transformer layout of the wreck amps is one of the worst possible layouts I have ever seen. There, I said it. I shudder every time I see pictures of wrecks and the orientation of the PT in relation to the OT and the close proximity. It goes against everything I have learned with my experience building amps. I could say more but I am probably already on my way to getting the "won't be down for breakfast" notice.

This isn't heresy, it's the darned truth. I've read and heard the same thing a hundred times. With that said, we are building audio circuits that by nature defy the laws of standard circuit design (in some aspects at least) and push the active devices out of their intended operating regions. Trainwrecks are no exception. Ken used 300V wire to carry 400V+, recommends putting 420V on a pair of 6V6's and did all sorts of little tricks in the name of good tone.

Ken did what he found to work. Maybe to some it's part of the mystique but to me it just shows what some know how and a bit of ingenuity can do. Trainwreck circuits are all about the final product being greater than the sum of its parts. They're simple circuits which extract a lot of gain from very few stages. This by nature will make parts selection and placement more crucial, even small changes are more likely to be noticed.

I hate to practice voodoo electronics but maybe there is a tonal reason why Ken positioned the transformers the way he does. This seems pretty unlikely FWIW but who knows with KF!

Certainly there is merit in the notion that Ken wanted to meet a certain aesthetic with his amps and maybe this dictated his transformer positioning as well.

With all of this said, I have built at least ten amps with the transformers positioned as Ken does it and none of these amps have noise problems in the least. This includes Trainwrecks, Fenders (my 5F6A is built with close transformers and is dead quiet even cranked) and whatever frankenbuilds I have cobbled together. I don't think it's the best way to mount a pair of transformers but I have found that it works just fine in practice if you line everything up orthogonally.

[geetarpicker]

Believe it or not the wire in original TWs was rated at much higher voltages than what was actually in the amp. It just looks like 300v wire at least compared to most stuff you see these days.

I know Ken talked about how the transformer orientation in old Marshall plexi 100s was part of the tone, and is one reason why the sound changed around '69 when they shifted the OT in those amps by 90 degress and went to a stand up PT. That said, he might have prefered the shorter wiring distances available with the way he placed things, and perhaps sacrificed a little hum in the process. Still, I find it amazing how little original wrecks hum though some clones following similar layouts do have such issues.

[Cliff Schecht]

Thanks for the info Glen!

Like I said, I use the TW style transformer mounting often even in non-Trainwreck builds. I find that the 90 degree orientation is much more crucial than aligning the center of the cores FWIW..

[Bob S]

Using the headphone trick on one build with the standard TW layout I found that if I skewed the OT slightly, the hum almost disappeared completely.
Only 2 - 3 degrees made a big difference.
Doesn't make sense, but hey it worked for that amp.

[surfsup]

Bob, I can relate. The first time I did the headphone trick, it was on this amp, so I remember it well. If I slid the OT over a few millimeters FURTHER from the PT, the hum significantly increased for a couple inches, then died out again around the choke location or further. But there was this spot right where it is that was dead silent, and close to the PT, which was perfect. Go figure. The headphone trick is a great trick though. Without it I would have heard humming that I would have assume to be from bad grounding.

[Structo]

I have a Magnetic Components PT in my ODS clone that seems to have that mechanical or inductive hum.
I didn't try tightening the screws on it because I was afraid it might make it worse.
The only time I really hear it is when I'm heating the tubes up in standby.

But yes, it does sort of bug me.

[xtian]

Thanks, RJ. I'll put this knowledge to use in my upcoming build.

[2tone]

420 v on 6v6's isn't out of the ordinary..Lots of manufacturers didi tat. Plus it's more like 400 v in the Express. That's not pushing it. Other things Ken did were for sound, not for convenience. Like the 80uf load on the rectifier tube in the Rocket..Not recommended but it does work. maybe shortens the life from 15 years to 10 years..who knows. I haven't had problems with it...

[LarryLarry]

I used a huge lay down style Foster PT for my express but it was to big to lay down so I adapted it to stand up. I had to mess with my OT after it was mounted to get rid of the hum. I too found that just a couple of degrees made all the difference. Here are a couple photos of the end (albeit ugly) result. This amp is now dead quiet!