OT A/B test

[Tonegeek]

I Use Mercury Mag transformers in some of my builds and while the amps do sound the way I want them to, I have never fully bought into the hype that they are any better than some other popular transformers out there. So, I decided to check it out for myself using a simple A/B test rig. The reason for the rig is so you can instantly switch between trannys. It is near impossible to A/B parts if it takes 30-40 minutes to swap them out. By then you will not remember what the part sounded like and since the differences in one part of the same value over another is usually very subtle - well you get the idea.

Contestants:
Mercury Magnetics O50JM
Primary impedance- 3.2k
Retail Price $210

Magnetic Components P-Tm-O50
Primary impedance 3.4k
Retail Price $54

Test amp:
50W Bluesmaster based amp, MC Marshall PT, El-34 outputs, no choke pushing 2X G12H65 Celestions in a THD style pine cab

I bought a knife switch off Ebay for $8 to switch the primaries and scrounged a DPDT switch from my parts bin to switch the secondaries and in my case the neg feedback. The image is self explanatory and the whole thing took maybe an hour to rig up. (See schematic for how it is wired up). In my case the MC tranny was already mounted in the amp and the MM tranny as you can see is sitting outside the amp.

WARNING: THIS RIG EXPOSES THE HIGHEST VOLTAGES IN THE AMP. YOU HAVE BEEN WARNED!

Initial evaluation:
I played around with the setup for about 30 minutes switching back and forth and listening. The differences between the trannys are subtle. The MC tranny appears to have slightly more high end. This could be seen as the MM tranny having a more even response. The lows on both were strong and solid but the MM seems to have slightly more girth or definition.

I am going to be doing more evaluation this weekend. My ears are shot today from too much high volume guitar wankage. My opinion may change once I have a couple of more dedicated test sessions.

I thought about recording the tests, but don't feel like the recording would pick up the differences. I only have a Shure sm58 and a computer with the built in sound card, so not the greatest gear for recording.

[roknroll]

imho once the drummer, bass, and keys come in, does it matter? If one has to struggle to hear a difference in an intimate setting then I would go with the less expensive one. If a difference doesn't hit me right out front and immediate, then the subtlties are not worth the extra money even if they are in a positive direction, again imho. I have built amps for some great guitar players whose ear I totally respect. The amp leaves the shop with the MC which I regularly use. A month or two goes by and they come back asking if I could swap in an MM equiv because of some internet chatter they read. One week goes by and they are back for the original MC. Not saying the MM isn't a quality product which it most certainly is, just can't justify the cost difference. You could claim the ear doesn't have a long memory which I agree with, however the way a tranny amp combination feels creates a stronger more lasting memory YMMV

[xtian]

Tonegeek, awesome experiment! Also interested in low volume impressions.

[amplifiednation]

Very cool experiment! I would love to rig one of these up and test some old iron vs new iron!!

[dreric]

Great experiment! I've struggled with the MM hype / price tag so it's cool to see an evaluation.

Taking the time factor out of equation is great. Is there any way that you could make it a blind test? ID the transformers as "A" and "B" play them and record your impressions, then reveal the identity of the transformer. Trying to get some subjectivity out of the equation. I have three amps with MC iron, I'm cheap, so I'd want that to sound better than the MM stuff.


Years ago Audio Research used to ship their Hifi tube amps with felt gloves. You were supposed to use the gloves when ever you touched a tube. They even claimed that their, very expensive, tubes had never been touched by an un-gloved hand. The reason was that fingers, no matter how clean, left an oily residue on the glass which would cause "electron eddies" and "alteration of electron flow" degrading the sound of the amp............ we have it easy with trannies and coax.

Eric

[Aaron]

Very cool experiment! I would love to rig one of these up and test some old iron vs new iron!!

Don't do it!!!

I spent years collecting old parts for my ODS build and just finished gutting an old Marshall for my next. I'd be heart broken if there wasn't much difference in sound

I'd like to hear a blind test though.

Aaron

[martin manning]

The amp leaves the shop with the MC which I regularly use. A month or two goes by and they come back asking if I could swap in an MM equiv because of some internet chatter they read. One week goes by and they are back for the original MM.

Typo there? I presume the last "MM" should have been "MC"?

Great experiment Tonegeek, and thanks for posting your observations. It's rare to get such a clear A/B comparison.

I'm not convinced that MM's prices are worth any benefit that might exist. In general this could be a slippery slope though- dismissing a lot of small differences could add up to a big difference overall. Given that the transformers are such a large fraction of the cost of an amp makes this particular decision easy for me.

[Bob S]

This is a question that has been bugging lots of us for ages.
We all want the best components available.
For taking the time & effort to do this - and posting the results -
Thank You Tonegeek!

[rogb]

This is very interesting, well done for sharing.

I was planning on ordering a MM OT sometime soon

[bluesfendermanblues]

Great test tonegeek.

I have a bluesmaster with an MM OT (FTBO-MM), that I originally bought in order to upgrade a Fender 59 Bassman RI, I couldnt really hear any difference and sold the Fender with the original OT installed (got tired of fighting that amp to get good vintages blues tones). And the MC OT now resides in my Bluesmaster clone. Its fine, but nothing particular.

Since building my four Dumble clones and D-lators, I have build three tweed clones; a 5F1 Champ, 5E3 Deluxe and a 5F4 Super. In these three amps, I have used Hammond standard OT's and IMO they sound just fine. Not better, Not worse, but the cost of Hammonds is 1/3-1/4 of the MM.

I don't want to bash MM, but in my amps it hasen't proved superior to Hammond.

Your testing is a welcome contribution. If MM is not better why pay extra in order to support MM marketing budget.

[roknroll]

Thanks for catching the typo!!

[Tonegeek]

@roknroll
I have the same thought. My son plays drums and the kit is in the same room I do my builds/repairs in. There is a world of difference in playing by yourself and having the drums (and bass on occasion) mixed in. I expect that tiny extra high end the MC has will be missed when I go against the drums.

@dreric,
I will be doing a blind test at some point. You can't underestimate the affect avertizing and the fact that you paid an arm and a leg for something might have on your perception. I just spoke to my wife about risking her life for the cause. She would be the one to pull the switch while I play!

@martin
Good point on the additive effect of "small differences" This is a very important point that I have seen mentioned periodically on this forum for years, and should never be forgotten. "It's a system." However the implementation is where the magic happens as even after you figure out that part A might sound better than part B, who's to say you can't make part B sound better by changing some other part of the circuit? In that case how do you really know which part is "better". With amp building there are a lot of ways to skin a cat. I guess the bottom line on this transformer issue is to figure out if the transformer is the only way to get the response you want or can you alter some other less expensive part to do the same thing.

BTW, I threw the schematic together for this presentation. If there are errors, or you have questions, please give me a heads up.

More testing to come...

[Structo]

Not sure if it was mentioned but I would use a rotary make before break type switch.

That would keep a load on the OT.

I know this was a "build it with parts you have" type build but just thought I would mention it.

However, I always liked those old knife switches.
Reminds me of the old Frankenstein movies.

[martin manning]

Even if you used a shorting switch for the primary side, you'd want to keep a speaker load on if the HT is on. I think I'd just switch the standby off, wait a few seconds for the DC to bleed down, switch the transformer primarys and secondaries, then turn the standby back on. I think you could use a common 125VAC 6A DPDT toggle switch for the primaries.

[Tonegeek]

the knife switch is basically doing the same thing as standby, just from the outer legs of the primary instead of on the center tap. What I do when selecting a transformer is flip the knife to the middle, then switch the secondary/feedback toggle to the other side, then close the knife switch. You want your guitar volume down during the transition. There is a slight pop, mostly when the knife disengages. A normal DPDT switch probably would work here but I was concerned about arcing.