Choosing transformers: is mercury magnetics a snake oil scheme?

[Mike K]

Mains transformers designed in the days when valve rectification was common, or (competently) designed for use with valve rectifiers more recently, should get hot in use. It’s not a flaw, the opposite really, it shows that the HT winding incorporates a degree of resistance, which is required by a valve rectifier. If it wasn’t designed in, external resistors would need to be added, to comply with peak anode current limits drawn in the reservoir cap charging cycle.

If you guys really wanted to geek out I could pull up the specs for the two I'm talking about. I always measure the resistance of all the windings (it's the best practical way to calculate loaded voltage) and I think these two PTs were very similar. The MM had a much larger core and claimed to have a much higher heater current rating. In terms of cost, I'd have to look up the numbers but I think the MM was $60, and the Hammond, at the time was $50ish. That's of course much different now.

In terms of actual circuit practicality, with an adequate PSU design, both performed perfectly well. I've never done an actual an actual A/B test where I literally swap or switch like an OT, but I've built similar circuits with both, and in terms of measured voltages they both perform the same.

What I'll equate this to is Hammond's ruthless corporate efficiency. Let's compare a Hammond enclosure to that which one would get from say Mojotone, or another custom maker on Reverb or the like. They are 0.04 or 0.05" thick, which I'll say, I've used for a lot of small amps with light transformers. They are pretty light duty though and are easy to bend. They are the BARE minimum (maybe less if you're using a heavy transformer set of building something for gigging). The steel chassis' are a little better, but still not as stout as what I use these days. At any rate, that is my impression of how Hammond sizes cores. There's no extra.

I mentioned it before, but in terms of using transformers for a specific amp, MM PTs were spot on for the voltages I expected. I had no hum or buzz issues due to core coupling, etc. I have had this issue with Hammonds though. Again, I'm not sure there's anything to write home about with the MM PTs except they have a 10 year warranty (some people seem to have issue with actually claiming it, I've never had a warranty issue), they seem to have a more robust heater supply which is nice if you want to add extra valves over a stock design i.e. you can use an existing PT design and add reverb or tube trem without much issue, and for the rated primary current, they seem to have a bigger core. This is not applicable to vintage designs where they are constrained to a specific package. They do use their own proprietary steel - I don't know that it could be much better than M6, but it isn't because they say which designs use that over standard. I tend to think, based on OT efficiency, that it is better than what other manufactures use because of the increase in headroom and dynamic volume characteristics I've noted in comps. That could be something to do with winding pattern as well as other optimizations. What I was told is they tune each build for maximum inductance, so that may include a number of tweaks, and I'm not sure how they control that in the production process, but they claim to be able to control it.



In terms of PT designs for guitar amps that actual comply with specs for inrush current, you'd be surprised how few do. In some instances, this has become an issue and destroys diodes, particularly when standby switches are used, but I really don't use them that much anymore, and avoid them in the traditional sense with tube rectos. A mute switch is much more practical.

[catalin gramada]

You touch an important point. The coupling noise is related by leaks and minimal leaks belongs to very well designed transformers. Of course very important for certain designs. For sure a "quiet" transformer it worth a difference. (just Partridges comes in my mind)

[Mike K]

You touch an important point. The coupling noise is related by leaks and minimal leaks belongs to very well designed transformers. Of course very important for certain designs. For sure a "quiet" transformers it worth a difference. (just Partridges comes in my mind)

It certainly is, but I don't have nearly enough data to say whether it's coincidence or not.

I don't have much experience with Heyboer PTs either, and they may be just as good in this regard. Some small experience I've had with Edcor they've been quiet too. I think the only ones I've had coupling issues with are Hammonds.

[Mike K]

Often times I mix and match - here I used Hammonds for PT and RT and a MM for OT. I think the customer didn't really care, so I gave this a shot. In retrospect, I wish I had used a different PT. This one came out low on the voltage tolerance and I was already spec'ing on the low end. I had some minor coupling issues, but that I mostly attribute to this being a head unit with reverb. I think perhaps a z-mount would have been a better option. Overall the tone was really good and the customer was pleased.

[The Dude]

I know this is an old thread but I came upon it looking for something else and couldn't resist putting in my 0.02 (joined this forum just to do so).

First comment: This entire thread reeks of inexperience. Don't take that personal, but with all these threads I see nobody comment that has any actual experience in testing A/B in real life. In some threads I've seen this reported, but honestly can't figure out how they came to the conclusions they did. But hey, we all have different ears.

Years ago I first started trying MM - and yeah I was skeptical of hype and secrecy, but I was also curious AF, so I wanted to try. I paid full price for my first one, and TBH, I wasn't in love with it. My observations at the time compared to Hammond and Heyboers I was using: It WAS LOUD - on the same amp way more efficient. It WAS bright - like almost too bright to the point it would sound washed out when cranked. It was built perfectly and much better than a Hammond, and far better than Heyboer (who use wood shims in their transformers - still can't wrap my head around that - think I'm lying, I have some I can take pics of now).

So for a while I really likedHeyboer, and they were doing it for me. Until I made some clips one day and someone pointed something out to me that I had never noticed. A terrible low frequency resonance - a BRRRRR sound, that followed the transformer on whatever circuit I would put it on. That was an "AHA" moment for me, and when I really started to understand what made transformers "sound" different. I knew they did, but I couldn't always explain what it was. I can say with a great deal of certainty that EVERY Mercury has a resonance tone that sounds more like a hard K sound - like KAHHH or KRRR (vs say lower modes like BRRRR or GRRRRR). That may not be for everything, but once you get that, you can really work with it. And you may prefer that kind of resonance over another. I can't say you're wrong if you like the lower modes of Heyboers, but for me, they aren't it. They sound flubby and muddy, and this is somewhat irrespective of circuit. You can tune some of it out, but it will always be there to some degree - just like a speaker has a characteristic voice that will follow with it no matter the amp, so will an OT.

As far the secrecy, I can totally understand that. Put it bluntly, guitar players are idiots. And a lot of times amp builders know even less (trust me, I've been there). MM doesn't want to dink around arguing with you about specs that they worked hard to develop that create some subjective experience and then for you to take those specs to another supplier so they can try to copy at a lower price. Try it. If you don't like it, return it. If you are designing amps and have a repertoire with them, they will give you the relevant info. For PTs they are a little more difficult to work with, but I have to say, the published specs on other PTs are just as bad in determining the actual voltages you'll get. The best are actually Hammond, who give you the necessary info to properly calculate loaded voltages. But they have the biggest tolerance too... As far as MM PTs that were designed for a specific amp - they were damn near perfect. Perfect loaded voltages. As far as price, with the "good guy pricing" i.e. once you've bought a couple, the PTs cost about the same when you factor in shipping (if you're buying a Merc OT, it's cheaper to get their PT than to pay shipping from another supplier). Their OTs are more expensive, but to me, they sound better than anything else. They have far more clarity and punch and no weird harmonics i.e. low modes or FIZZ (I found every Classic Tone I used had horrible fizz driven).

As far as my preconceived and incorrect notions, mostly coming from the internet, I can say MM has proved me wrong in a few instances. One was PT loading, the other was OT loading. In both cases they were correct and I was not, so I can see why they don't want to argue with internet know-it-alls about transformer designs. I will say also that a Mercury OT sounds like a Mercury OT at 5k with a giant core or 12k with a medium core. There are some minor differences, but they sound more like each other than they do other brands. That was always a big surprise to me and I've tested multiple MM against other OTs both at the same and different impedances and core sizes. Honestly a tiny MM always kicked the $hit out even a big fat cheap OT.

Back in the day when I was learning all this I did some blind tests too - I put them on a popular amp building forum and even had a couple Mercury's in there to throw things off. I did not post the results, but only emailed them back to people once they had emailed me their guess, so as to keep forum chatter from biasing things. A Mercury (Axiom) won, hands down, but a Mercury Tone Clone (which was the proper OT for that amp design lost). The tone clone sounded great IMO, but was a vastly smaller core than any of the competitors (as is sometimes the case in stock OTs) and people definitely prefer the sound of larger cores, IME.

Right now I'm playing a little VOX AC15 type amp that I built with a Gibson MM OT - it's tiny, only 10W running 10k with two EL84s to about 10W in true Class A PP. I compared it to an off-the-shelf Vox AC15 and it doesn't sound as good clean (it doesn't have the volume or headroom) but driven it kicks the snot out of the Vox. If I were going for headroom AND sweet driven tone I would have used higher voltages, biased up toward 15-18W and used a large Radiospares MM OT. But I was going for a less headroom and a bit less volume. Not sure it's something that would be commercially successful, but I like it. There's lots of different ways to build amps and lots of different ways they are going to sound good or poor. Generally though, you do get what you pay for.

PS I have MM Radiospares 18W clone and Heyboer 18W OT from Mojo that I want to compare. I'll tell you right now, they are totally different other than physical size. The laminations are much different on the Heyboer and the bobbins are different (although, in theory, that in no way should affect tone, but I can tell you which one is cheaply made). I've worked with the MM Radiospares clones before and they were phenomenal, so this Heyboer really has to knock it out of the park to have a chance. It might, I have no bias, and it might just sound better with certain speakers and preamps. The price was quite different, even with my healthy discount from buying lots of Mercs, I think the MM was still 50% more in cost. But if I'm going to skimp somewhere in an amp, it's not going to be the iron... just my philosophy.

Wow. First post and you're calling out members here as "reeking of inexperience". You made a lot of bold claims in your diatribe backed up by nothing more than your own subjective hearing- no scope shots, no frequency spectrum analysis, no distortion measurements, etc. - just your ears, which we are to, for some reason, trust more than anyone else's. Sure, others in this thread have voiced opinions without data, the difference being that they haven't called out the rest of the forum members. As for myself, I've never said MM doesn't make a great product. I've said that they are overpriced, but that's just my opinion. You are free to justify the cost if you like. If you are going to try to pass yourself off as the final authority on MM transformers, you may want to provide some testing documentation. Otherwise, your opinion is no different than anyone else's.

[Mike K]

LOL - put down your pipe and read on, Dude.

I'm no authority on anything and it's all subjective. I'm only calling out criticism with no personal experience. Scope traces are worthless for this type of thing.

[g1]

Scope traces are worthless for this type of thing.

This is more of a technical type forum. We value data and scope traces a bit higher than 'BRRRRR vs KAHHH'.
If it's real, it can be measured.

[Mike K]

This is more of a technical type forum. We value data and scope traces a bit higher than 'BRRRRR vs KAHHH'.
If it's real, it can be measured.

Do you measure your speakers and select them based on the frequency plots, because I sure don't.


I'm sure if I had a spectrum analyzer I could measure some differences. If you can't hear the difference between resonances with your ears, then perhaps have your hearing tested. Your ear is quite good at doing a FFT as fast as any computer can.

Do pickup winders put out measurements for their pickup resonances? Yet you don't don't doubt that they exist, and they can be measured.

And if one could show a difference between resonances, how would that prove one is better than the other. I just stated its there. If you don't hear it, fine, it's not there for you. If other people have a preference one way or another they are going to prefer one vs the other.

You're trying to make a subjective experience objective, and it's simply a waste of time. I think you just want an excuse to trash something you never tried and justify it. Same as every other post before on this thread. I'm calling it out. Sorry some ad campaign made you butthurt - did you quit drinking Bud Light because of Dylan Mulvaney?

[Mike K]

Mr. Dude and Mr. G1 - both seem to have very thin skin about how the music industry operates and how someone starts a thread. You're attacking me for stating something that seems fairly obvious to most people who have cared to try... why would I waste my time and money trying to convince you? I have clips that clearly show differences - I won't post them, there were some previously in this thread. There's been all sorts. Those things can be produced to go whatever way.

You're clearly going out of your way to "educate" others on something you honestly have no idea about or "shut me down" in some way (you literally called me a shill). You have zero experience and all opinions. I can only claim my opinions which are based on actual experience, you haven't even attempted to back any of yours up. If you want to continue to flex and try to bully me out based on weak arguments, go for it. If you want to muscle up, I suggest you try it yourself if you don't take my word.

[SoulFetish]

Troll

[nosaj]

why would I waste my time and money trying to convince you?

Yet here you are spending your time doing just that. Agree to disagree and move on to another subject.
Remember your the NEW guy to the bar, read the room an try not to step on toes.
nosaj

[tedmich]

Yet here you are spending your time doing just that. Agree to disagree and move on to another subject.
Remember your the NEW guy to the bar, read the room an try not to step on toes.
nosaj

Respectfully I think that ship might have already sailed!

[Chuck H]

Hey Mike... Read the room!!! The things we measure aren't arbitrary. It's more like "Why did this work but that didn't." Or even "Why did this SOUND GOOD and that didn't." What other reasons could there be to measure something??? Now...

Throughout the vintage amp era there have been A LOT of amps that used even questionable transformers and still find themselves at the top of the heap for tonal quality. The OT is only ONE PART of a design. And, in fact, a design can be made to work with a selected transformer. But that knowledge can somewhat depend on vast experience and measurements. As someone who designs amps I understand this. And, in fact, in most cases there's nothing to be gained by any modern "upgrade" transformer installed in a coveted vintage design for these reasons. This said...

There is A LOT to be learned here for someone that's actually interested in improving their chops as an amp designer. I speak from personal experience. The ideal that the ears tell all with regard to any electronics circuit is just the blathering of offense and inexperience. This river runs deep. Sometimes fast. Can you swim?

[nosaj]

Just opened a SWR Workingmans 15 with some old sanken transistors Mercury Magnetics transformer Looks original
nosaj

[catalin gramada]

You lucky bastard !