Toroidal transformer question

[rfgordon]

To the collective wisdom I ask: Why do no guitar amp makers use toroidal transformers? Is it because they're too linear and transparent?

The reason I ask is that I have an offer from a company to wind me some guitar amp transformers (4k primary/4/8ohm secondary @ 50 watts) that use grain oriented M6 steel for a good price. However, they be toroidal trannies.

So, is it tradition that we in guitardom discriminate agains electromagnetic donuts, or is there a sound (toneful) reason?
Thanks,

[doctord02]

my understanding is cost, generally speaking. There are a few manufacturers that do use toroids; my Laney combo uses a toroid power transformer, fwiw...

[rfgordon]

Well, I decided to give one a try. The deadline was tonite. The guy let me order just one, with a money back guarantee. I'll have it sometime in the latter half of July, then I'll try it in my amp and see what it sounds like.

The engineer told me that one amp manufacturer (he wouldn't say whom) used toroidal OTs due to space concerns--had to be 1 1/2 inches tall. Sounds like a rack-mounted unit to me.

Anyway, when I get it I'll give a report to the group, post a recording.

Cheers

[BobW]

Carvin, and Gallien Kreuger (sp?) are two among a few who use toroids. Toroids typically are more expensive to build but careful layout of an E type core can yield the same quiet results as a toroid. Plitron makes toroids specifically for audio amps.
http://www.plitron.com/
BobW

[MarkB]

Here's a toroid build I bookmarked a while ago:


http://myweb.absa.co.za/johnhowell/1U.htm


Definitely good for rack builds.

[908ssp]

Maven Peal is another user of toroidal power transformer. They apparently are quieter as you often see them in regulated power supplies. They are supposed to be lighter but since they are round they take as much or more room. The magnetic field is supposed to be smaller so they can be placed closer to sensitive stuff.

[Darkbluemurder]

I believe Mark Stephenson does as well.

[MarkB]

I just remembered the Hoffman tube pedal with toroid PT:

http://hoffmanamps.com/projects/tube_box_3.htm

[rfgordon]

Well, folks, the verdict is in.

I got my toroid OT in the mail this past weekend (4k pri. 4/8 ohm taps 50 watts). I swapped it into my amp and was quite impressed. At first I was worried because the parts layout dictated that the only place to stick it was right next to the PT, which is laydown mounted. This meant that the laminates of both trannies were both close and co-planar. Potential recipe for big time buzzzzz.

Howsomever, I was pleasantly surprised to find that, even mounted there, the amp is not only quiet, but quieter than before.

OK, so how's the tone? Very nice. Note separation in overdrive is dramatically improved. This tranny (compared to the 1961 Harmon Kardon OT it replaced) passes a bit more upper mids, so the grind has a wee bit more crunch and "kerrang" a la Marshall. The bass is tighter and clearer. I dimed the amp and got the floor really shaking! I'm sold on it.

I think this tranny's frequency spectrum really compliments that of the Tone Tubby I use.

When Boris gets back from vacation next month I'm gonna order a few more, and also get a quote/order some PTs from him. This thing is less than two inches tall, so it could even be mounted inside a chassis. Putting the trannies inside would make for a very clean chassis exterior.

Anyway, if you want to try one for yourself, contact Boris Sasic at sales@engineeringvista.com. I think he plans another wind in Sept/Oct timeframe. BTW, this one cost me $54 including shipping.

Cheers

[David Root]

That is one hell of a good price. Plitron would be a lot more! Your experience is everything I have been told to expect, so I think I'll be trying some too. Does this guy do PTs as well?

[rfgordon]

I've emailed Boris for a quote on a PT, but he hasn't gotten back to me. When he does, I'll certainly pass it on.

[tictac]

I've read toriodal OT's need to have the DC curents balanced to keep from having noise problems. Some HiFi manufactures that use them actually use servo controlled -bias to keep each tube at the same operating current. Maybe that's why you dont see many toriodals in guitar amps.

TT

[Tdale]

I have thought about having one made too. I'm not very good on spec's so I wouldn't really know what to order.

Is 4K a normal primary value for an OT in a Hybrid-A style amp?

Tommy

[rfgordon]

I can't speak about toroids needing balanced DC, but the OT I have works nicely. Boris will have one made with whatever impedances you want. 4K just happens to be common for 2 x 6L6 (sometimes EL34) or 4 x EL84 or 4 x 6V6. Boris' toroids come with UL taps no extra charge. I don't use them, but some folks do. The one I have is dead quiet, quieter than the vintage Harmon Kardon OT I started the buld with and the new Heyboer that I put in this week.

[David Root]

Just got my PT/OT quotes back from Boris. The company is a huge operation in Serbia.

This is for a 4 -- KT66 cathode biased 50W @ ~1% THD, 65W @ ~10%.

OT -- 60W (40-20KHz bandwidth); 4K primary. Sec. 4, 8 & 16 ohm taps. Potted & shielded.

$129.00

PT -- Primary 120 VAC /60Hz. (Their standard is 115 VAC which is no good any more in the US/Canada). This probably cost extra.

Power 350 VA, "wound on 400VA core".

Sec. 1: 350-0-350 @ 400 mA.

Sec. 2: 5V @ 4A (for 2 -- 5AR4 in parallel)

Sec. 3: 6.3V CT @ 8A

$118.00

Quote only good for 10 days from today.