DCR and Impedance - modern audio transformers

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Sc

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ruffrecords said:
I am confused. On the one hand we were discussing a Sowter output transformer and next you are talking about the differences in input transformers and the effect they have on the sound of ribbon mics.

Let us be clear. I am not disputing there are differences between modern and vintage output transformers. I agree dcr and inductance are related but the relationship is complicated by the AL of the core and the thickness of the wire used but other than that there is no advantage per se in high dcr.
I'm glad you experts see this as a complex matter too  ::) - but thanks Ian - you brought me to a much simpler solution in my example. Alltough the -20dB input pad is not the problem (this is original TAB - design and certainly wanted) - the problem was a messed up pcb connection to the 600T-Attenuator pot.

BTW - any experience with the Sescom line (think 80ties, but not much info found)? Got a large pack of these mic and line trannies for about nothing - so if it's crap no problem. 
 

rackmonkey

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Sescom has been around since at least the late 60s or early 70s. They originally went by the name Scientific and Electronic Systems Co., but dropped the long name early on and went with the just the acronym. (You still see some transformers out there with the original name now and then, though.) They aren’t as well known as the Jensens or Cinemags or Sowters of the world, but they’ve sold a lot of transformers as evidenced by the used market.

They made all sorts of audio related equipment over the years, from PA and pro audio focused preamps and EQs to rack cases and cabling, etc. But transformers have been a major focus all along. They were well known back in the day for making lower cost substitutes for plug-in transformers and preamps for Altec PA equipment, Ampex recorders and the like. But they’ve had a wide variety of transformer types on offer at different times in their existence.

Their transformers can be quite good, and i’ve used them in a number of projects over the years. Just depends on the intended original use. Some folks have a less positive perception of them. But I think that’s less due to the quality of their actual transformers as it is to the crappy quality of the rack cases they used to make. But my experience with the transformers has been largely positive (I’ve tested many of their older models thoroughly). Some aren’t worthy of serious projects because they were designed for some less critical use. But some are indeed very good and I wouldn’t hesitate to use them.

But we’re talking here mostly about their older transformers. These days they seem to have gotten away from making transformers for PA and pro audio gear, focusing more on in-line impedance matching and bridging and DI use cases.

There’s a catalog in the Technical docs section, in case you haven’t seen that.

Which model is it you have?
 

Sc

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Thank's for the info - good to hear it's not just crap. Got the stuff NOS/NIB from an audio business closing down - I compared the stock to a catalog, but quite a few are not listed (probably earlier stuff). Impedances are shown on the package - the tolerated dB levels only in catalog (a rough estimate by size is easy though). It's a bunch of about 80 total in MI-1, MI-2, MI-5, MI-6, MI-12, MI-14, MI-17, MI-23, MI-24, MI-30, MI-33, MI-35, MI-37, MI-39, MI-41, MI-42, MI-43, MI-44, MI-47, MI-51, MI-59, MI-62, MI-65, MI-67, MI-80, MI-83, MI-87, MI-88, MI-89, MI-94 - a lot of these are small signal ones. Then another bunch of XLR implemented ground lifters and matching trannies IL-17, TR-128, TR-129, TR-120, TR-133, IL-2, IL-1. And a handful rather exotic fixed modules with it MIC-4, PA-2, TC-2, SA-2, C-2. So maybe tmpfl  :D.
But just if anybody should have an older catalog ..... 
 

rackmonkey

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Sc said:
But just if anybody should have an older catalog .....

I have a paper catalog from the early 90s around here somewhere. I’ll take pictures of the transformer data pages and post them. Probably this evening (central US time).

These are all model numbers that fall into the “useful” category. There are some very good ones in there.
 

AusTex64

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I like Sowter transformers so I’m not bagging on them. But I ran into problems using their model 9330 interstage transformer in my Pultec EQP-1A builds. It made the Vintage Windings and Carnhill inductors ring. Impedances are 2.5K/10K, 360 ohms primary DCR. I replaced it with a UTC A-18, no more ringing. Brian Sowter and I corresponded around this issue. He said they made the 9330 as a low cost option. They sent me a sample of their 1475 interstage, 10K/40K, 1600 ohms primary DCR. Solved the inductor ringing and also sounded great.

I have a Crimson CT-A10 and an original UTC A-10 here to test. Curious to see how close they are. I’ll bring my LCR meter home tomorrow night.
 

soapfoot

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I'm curious about those Crimson A-10s, as well. I'm optimistic--they seem to be made by a person with a passion for the originals, and that always helps.
 

rackmonkey

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soapfoot said:
I'm curious about those Crimson A-10s, as well. I'm optimistic--they seem to be made by a person with a passion for the originals, and that always helps.

There’s a couple of threads about them in the Magnetics section, including sound files. I think someone measured one up, too.
 

CJ

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the Fairchild 670 signal output made by Chicago Transformer had some stability issues.  why? well there is a feedback winding, and you know what can happen with those.
So Brian Sowter worked hard to get rid of the stability issues, resulting in an improvement over the original CTC xfmr.

i had no ringing problem with the Pultec innerstage from Sowter, but i used hand wound DIY inductors, using more than one to get better bandwidth.

there were a ton of different lam alloys available back in the golden age of audio, now your choices are very limited, especially with Mag Metals no longer stamping nickel, and other M6 companies going belly up, so your B-H curves are going to be different from the past on a lot of transformers. South Korea is making some good stuff now, you can get a few shapes on evilbay to experiment with, and you might be able to get them to stamp a custom lam if you sent them enough money. i sure would like to wind some WE 618 inputs on that weird lam,

i put up a couple of manly prints for the very mu, i believe they use the same geometry as the Peerless S-217-D (pultec output) if you want to wind and build an eqp or very mu, they are in the Magnetics section. i was surprised more people did not jump on those prints!

i believe the Triad output DCR readings are correct, back then i had access to one of those 1500 dollar fluke bench meters with all the decimal places,

Hammond makes so many transformers, i suspect some are in house, and the less expensive stuff sourced overseas. so it is hard to generalize about a company that has a substantial catalog.

Lundahl really likes the twin coil stuff, which is what UTC used a lot.

Jensen likes E-I lams and hi octane lams so they can use less turns,
their 4:1 output is probably the best xfmr i have measured and it is only $125. great for LA2a,

the best way to test a transformer is to install it into the circuit and listen to it, some are good for that rolled of sound of the 50's, some are good for the straight wire approach of the 21st century,

nobody uses the old wax used for impregnating coils anymore, and nobody uses foldback winding on their inputs like UTC anymore. but fortunately there is still stuff popping up on evilbay for all you retro freaks!  :D

look at this beaut, ever seen one of these before?
 

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