My output tranny shootout

[hesamadman]

I havent had much amp time lately but I wanted to share my experimentation with 2 completely different output transformers. I built a 30 watt amp using an AC30 style power amp, solid state rectifier, a custom preamp consisting of a pre gain, full tone stack, and PPIMV. In this amp I used a hammond 1750T (ac 30 reissue) and a genuine marshall jtm30.


This is definite "to each their own" kind of scenario. The ac30 reissue was a much cleaner OT. With it, the amp produced a nice clean rock and roll distortion. The amp allowed for a beautiful clean tone with my Fender Tele and my Les Paul Deluxe.


The jtm30 (designed for 6l6 style tubes) was super gnarly as well. It made the amp a whole other beast. It was a great tone for and punk rock/metal or anything on the heavier side. It had a very thick sounding gain. Very bass heavy....in which I had to do a little component swapping to reduce the bass, but the end result was a perfect amp for the above mentioned genres. So this OT seemed to (at least with the el84's) have a much thicker gain and a more dominant low end. Almost no clean tone at all ha ha. A good lead sound. But it was a fun shootout.

[Champ_49]

That's really interesting.

So is it the 1750N the one that produced the high gain and bottom end?

What are your thoughts in general about Hammond?

[hesamadman]

That's really interesting.

So is it the 1750N the one that produced the high gain and bottom end?

What are your thoughts in general about Hammond?

The high gain and bottom end came from the genuine marshall jtm30. Which is odd to me because it's such a small tranny in size and a general rule of thumb with these is the bigger and more iron = more bass. But I love hammond. That's about all I use. In reality they aren't much more in price than some of the others.

The hammond equivalent is a 1750na

[Champ_49]

I have never used hammond before but I saw a clip of a jcm800 2204 and the guy said he used a hammond. It sounded really good and gainy.  I have a jcm800 2204 and I'm sure there us something wrong with one of the trannys Because I rewired the whole amp and didn't change anything but the trannys.  I currently have magnetic components trannys.

I'm thinking of swapping them all out for Hammonds as they supply them locally here.

Is there a particular reason you use Hammonds? Like how would say it sounds.

[jojokeo]

For those that have gone to the effort and expense to make their own amp type breadboard like Brad, SG, Dummyload, & others - this to me is one of the really great benefits of having one. To me changing trannies in an amp without a lot of room (as most are like this) really can be a major chore. Hence, I rarely do this because of it but am very interested in the idea of sampling various OTs. And if someone has sampled various OTs in numerous designs is there an overall preferred manufacturer that makes better trannies for clean amps vs overdriven and vice versa?

[Fresh_Start]

I built two virtually identical Princeton Reverbs, one with Mercury Magnetics iron and the other with Hoffman's. There wasn't a huge difference, but I did have a chance to play both amps side by side. I was surprised to find that Hoffman's OT sounded a bit better to my ears.  Slightly more upper mids, less sharp high end, a little cleaner bottom end.

I did swap tubes too to try to keep things equal, but this wasn't a "blind taste test."  Still the results were not what I expected.

I've also had 3 different output transformers in a Tweed Princeton. The original small, cheapest one actually sounds and feels best. The "Upgrade" from Allen has too much bass and doesn't break up as early. Of course that might be perfect for someone else's ears.

We can debate capacitor choice, carbon comp vs. metal film resistors, etc. until the cows come home, but IME the output transformer, tubes and especially speaker/cab choices make bigger differences.

Cheers,

Chip

[John]

I remember reading somewhere (probably here) that one of the many reasons for that "vintage Fender" tone was the OT was just barely big enough for the job, so it introduced a little sag along with everything else.


I have found that Webcor transformer sets out of the old reel to reels sound pretty good too. For around $75 shipped, you get the trannies, a nice choke (usually) and a really cool looking cabinet for stuffing it in. Plus 20 pounds of scrap metal.    I got one that is so nice I'm seriously thinking of refurbishing it; it seems a shame to just gut it. 60/70 years ago they really had a sense of style, and the inner craftmaship with all those levers and springs and stuff is just amazing.


Ooops, sorry, drifted a bit.

[VMS]

I wonder how much the difference on the primary impedance (JTM30 6k and 1750T 4k) affects the way they sound, or is the marshall OT just wound so that it has better low frequency responce.   

 

[jojokeo]

We can debate capacitor choice, carbon comp vs. metal film resistors, etc. until the cows come home, but IME the output transformer, tubes and especially speaker/cab choices make bigger differences.

Good info Chip & also agree completely the statement above.

I remember reading somewhere (probably here) that one of the many reasons for that "vintage Fender" tone was the OT was just barely big enough for the job, so it introduced a little sag along with everything else.

Ooops, sorry, drifted a bit.

Hmm, I think of sag being caused by more of a voltage drop on the power supply rail from loading affects and slowly returning again. But, I have to admit to feeling it a bit even on a few settings w/ some of my effects pedal designs also. And it's okay to "Drift Away" in my book too. ;) "oh, give me the beat boy and free my soul, I wanna get lost in your rock n roll and drift away..." great lyrics & great song.

I wonder how much the difference on the primary impedance (JTM30 6k and 1750T 4k) affects the way they sound, or is the marshall OT just wound so that it has better low frequency responce.   

It's definitely got to be thought of as the main difference & reason between their sound & response (aside from a minor difference in a little iron mass and/or wire size & length).

Thanks for the input boys!