Best replacement UTC o-12 1176 input transformer?

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Well-known member
Jun 9, 2004
I know there will be a few opinions on this, but what currently manufactured input transformer would be the closest match (sonically and specs) to the original 1176 Rev <F, considering availability and price?

I've read some of dissections of the UTC P-12/O-12 and it looked fairly reproducable, has anyone tried to make reproductions? I still want to preserve the original 500:200 ohms for a drop in replacement to an 1176 with a T attenuator. There is something about the sound through the old iron on the originals that is missing on the reproductions/clones...

I'm puzzled...

You have a pre-F that is missing the input iron? -They can still be found if you need the original part.

-OR you want to try different iron and change something, but preserving the impedances?

I'm building another project that I want the exact front end of an 1176LN Rev <F... but if I want to build more than 1 of them, I don't want to be stuck trying to hit EBay to buy more vintage input transformers...

if you want the "exact" same thing, your choices are to either find used/NOS UTC O-12s on eBay, or go to magnetika and get them to pull out the UTC O-12 blueprint and make you some. be prepared to pay something like $50 apiece in quantity.

none of the usual suspects make the same thing, because honestly, the O-12 doesn't spec out as a "good" quality transformer. but that's why you want it, because it doesn't sound "good," it sounds like an O-12.

some options:

contact cinemag. maybe by using their cmmi-2c "backwards" you could get something close to what you want. or maybe they have something small and cheap that they sell as an oem product that would come close. explain that you don't want good, you want small and cheap, like an O-12, and maybe they can help you.

try one of the "ground loop isolation" transformers from radio shack or parts express. they're cheap and small.

try the oep A262A2E in 2:1 mode using only one of the windings on each side (leave the other two windings unhooked). add each of the unhooked windings back one at a time and listen. some combination may get you close.

wind your own.


have you listened to 1176 circuits with different input transformers? If you havent you might spend some time doing so before you drive yourself nuts looking for an ouncer. That transformer totally shortchanges what the circuit can do IMO.

is there something wrong with 27 pieces of 24-25 EE with a bi-filar primary consisting of 516 turns of 37 gauge, and a split secondary consisting of 2500 turns each of spider web 50 gauge?

I admitingly have not heard this transformer, but just from looking at the sheet, I would have to say that something else is to blame, not the 12.

straighten me out. what does not sound good?
phase? distortion? headroom? soundstage? bottom? top? in between? all of the above?
[quote author="soundguy"]kdawg-

have you listened to 1176 circuits with different input transformers? If you havent you might spend some time doing so before you drive yourself nuts looking for an ouncer. That transformer totally shortchanges what the circuit can do IMO.


Then ther was the later one with the 5532.

Sometimes I actually miss the smoother sound of the Silver Faced ones I had.

I've got earlier Black Face, and Blue Trim ones now, and I do love 'em. Funny though, I think my LA-3As with their shitty little Beyer xfrmrs sound cleaner than the old O-12/1176s.

I've thought of trying a UTC A-20 instead of the 0-12. I've got several lying around (they're still cheap). I think I'll do that this week.
I'm definitely after something that sounds more like an o-12 than a newer, cleaner transformer. Whether or not is sounds "good" or not is open to opinion I guess, but it's something that I'm trying to replicate.

I know nothing of winding transformers, is it expensive to get into? I made an electromagnet with a nail and some copper wire once :grin:

CJ - On the o-12, they are not using any of the center taps for the input circuit. In the construction of a transformer, if I had no use for those center taps, would it be easier to wind it for just this use - and would that change the sound?
More labor than money. But if your into it....

You can save some hassle by not bringing out the C.T., but the winding structure won't change, it is still

1/2 Sec
Bi Filar wound Pri
1/2 Sec

Not bringing out the lead should not change the sound, but you never know with transformers.
Some of those early breakouts used by Peerless and Triad are pretty spooky,
if you look at the lead plate patterns. Balance between the core and case capacitance might have an effect on the high end, but we are splitting hairs here.

You can dial in a null on a transformer, and then move the leads with chopsticks, and watch the needle dance around, and thats at 1000 cps, so.......
[quote author="CJ"]
straighten me out. what does not sound good?
phase? distortion? headroom? soundstage? bottom? top? in between? all of the above?[/quote]

I would say all of the above but mainly soundstage, my main thing with it is that it sounds like a small transformer. There is absolutely nothing "wrong" sounding with that transformer by any stretch of the imagination but it has an intense character to it. I find it to definitely be bandwith limited, its just a small sounding transformer, but it has a cool midrange quality to it. I built a rev D and screwed around alot with input transformers, if you put a beefier transformer on the input, the output of the box gets several times larger, allowing more low end content into the circuit causes to my ear (no idea what the scope would say) more distortion which for me is a good thing as I use an 1176 as a distortion box more than anything else in the first place. I dont know the history of the design, but it isnt hard to imagine that the ouncer was selected not for its physical size or price (there's plenty of room to mount any transformer in there you'd want), but to limit the low end so the circuit would have a little cleaner sound to it. I imagine that less distortion was probably a priority more than more distortion in a box that already had off the chart distortion compared to some of its peers of the time. I always want my stuff to sound BIG, the circuit can definitely handle BIG but the biggest the big gets is intensely influenced by what the input transformer is allowing to pass into the circuit. Thats the best I can figure after plugging in lots of input transformers and comparing recordings. The ouncer has a very "light" quality to it, its forward sounding but I think that forward quality comes out from the lack of real tight bottom.

using an A20 over an 012 is a huge difference, a20's were among the ones I tried. Plug it in and you'll see. The 012 is a fine enough way to go, especially if you dont have an 1176 with one but if you are building a few you might consider listening to some other stuff before going nuts searching out piles of 012's, I think given the choice in todays climate more folks would go with a beefier sounding input transformer, the circuit can definitely handle getting whacked with a little more authority than an ouncer can deliver.

Hi, I have an old 1176 blue stripe serial #331 and recently had it recapped. When I checked it out after getting it back I noticed the input xformer is a Microtran M-90 magnetic, not the UTC 0-12 that is supposed to be in there. I didn't look closely at the insides before I sent if off so I don't know if a switch was made a long time ago (has LN mod) but in any case i am wondering if I am losing out on a better sound with this input trans, anybody know anything about this one? Also I guess I will be looking for a stock UTC for this thing just so I can hear it the way it is supposed to be. It sounds good but looses a fair amount of top end when compressing hard, don't know how much is normal. So... looking for a UTC ouncer and any info on the Microtran M-90 magnetic that I have in there. Also Soundguy, you mentioned trying other input trans options, what do you recemmend, I guess if I was going to go in any direction other than stock I would make it a bit cleaner. thanks for any info, Sean
Bryson, let me know how you like the A-20 in an older 1176, if you read my earlier post I am in the same situation; might like to make my blue stripe a bit cleaner, maybe. So also might be interested in a single A-20 if you think it is cool and want to sell me one...? regards, Sean
turn the attack knob to the left until it clicks.

now the limiter is off.

thats the sound of the transformers and the line amplifier.

If you "lose a lot of top end when compressing hard" it is the limiter circuit that is doing that, not the input transformer assuming you are using it under "normal" conditions and not saturating the input with level in order to get it to compress alot.

If you want clean, try a lundahl. You can also try different caps on the output to the output transformer, on the D boards its the film cap closest to the transformer on the left side. Changing that output cap can open things up a bit as well.

I suggest you plug whatever you can get in there and judge for yourself, thats all I did. Any pratical experience you can gain listening to this stuff is worth way more than any crap you can read that I post up here, I have specific tastes and build boxes to solve specific problems and what I think is "good" is hardly good for everyone or most or many.

My original comment was not to get people ripping ouncers out of 1176's more than to suggest that it was likely installed to get a certain type of performance out of the circuit and that the circuit is capable of handling much more bottom end before crapping out. If you put a different transformer in there, any kind of transformer, its gonna sound different.

Maybe if your 1176 sounds good you should just worry about it sounding good instead of what it is "supposed" to sound like, there are soooo many variables in there I dont know what "supposed" really should be and I have heard piles of 1176's over the years. Replace components when you have a specific problem to address that way your component selection will have some authority to it. All that said, that transformer could very well be stock, some of those 1176's with the LN mod are OLD. I wonder how many of them were made before incorporating the LN mod into the circuit, anyone know?

chose whats good for you.

Can anyone tell me, are these old UTC H8 transformers suitable for 1176 DIY build?
I thought it may work OK for the input? 

Also freq is indicated as flat from 50 hz to 10k hz. 
Not sure if that would normally be considered OK, but I get the feeling these may actually have an OK frequency response outside of that range.

Keen to hear from others with more experience, or insight into this.


(Hard to get pic to show up at reasonable resolution between too small and too large, sorry!)

Note:  I just checked the UTC 1955 catalogue info on this range of transformers & it says: "The frequency response ratings are based on military requirements.  Actually, most of the units that do not carry DC are appreciably better in response than the range shown."

Hmm, I'll just respond to myself then..    (~;

+8dB seemed to me initially like not much handling capability (on the UTC H-8 transformer) but I just cross-checked and it seems that is the same as what the O-12 was rated at anyway.  So I suspect in practice that these will actually have quite a similar characteristic to the O-12's, going by the limited info available..  Have to suck it and see, hey!

Speaking of which..

I'm gonna be building four 1176 style comp's in the coming months, using the MNATS Rev J boards, and trying out various input and output transformers to try to end up with a nice range of flavours across the 4 units.  So I can report back on the results from my own experiments, along the lines of what Dave 'SoundGuy' described, just trying out some different combinations and seeing what works.

Being the MNATS "Rev J" boards, what I'll end up with will be along the lines of the original Urei "Rev F" (with T-Pad & transformer input) and maybe one "Rev G" (same but with the IC input rather than input transformer).  I don't think I'll use the Rev J on-board transformer options on any of them (OEP & Lundahl options available), but rather I'll initially install the Hairball O-12 style input & B-11148 output transformers as a starting point on the first unit, and then audition others in comparison from there.

I have one of each of those Hairball "Rev F" transformers, plus several other transformers that I think should be suitable to audition for the following input & output options:

Hairball UTC O-12 style
UTC H-8 (similar to ouncer size format)
Big old (Aussie) Trimax MS-896 (mixing / matching) 150+150 : 150+150  +10dB

Hairball EA-11148
Jensen 123-S
70's (Aussie) ARLEC Telephone Line matching 600:600 transformers  (like Jensen 123 size)
Big old (Aussie) Trimax TA-763  mixing / matching  150+150:150+150  +18dB
PTC B-1360 (from Magnatech pre-amp)

A question on alternative 1176 input transformer options:
Will a larger mixing / matching transformer (such as those much larger units which were presumably originally built for using with valve gear?) still perform well in this application (ie. input of an 1176 circuit)?
Or is there a point where a larger input transformer needs to be driven with significantly more signal (or other different properties) to work properly?

Any insights into this question would be much appreciated.
Hummm that's a very old topic but i am curious how this 1176 clone ended and what combination of transformers you choosed finally. I'm currently building mine around the UTC H8 for the input in place of the hard to find O12 .
The H8 is kind of a lowly part I think. Looks like it's only flat up to 10kHz. Then again, the O-12 isn't exactly the best possible part either. It's pretty low power so at high levels you might get low frequency distortion. There are probably a lot of transformers that would work fine or better. The only reason to use the O-12 is just for authenticity or maybe you want the character when driven hard. Personally I wouldn't be too picky. For example, you can find Jensen mic splitter transformers for $30 USD on Ebay. If you wire two windings in parallel you have 600/150 which gives you a little more step down but that's ok and the power handling is probably about the same (+4dBu for Jensen vs +8dBm for O-12 but my brain has trouble trying to convert and account for differences in toleraces so I could be horribly wrong about this). Or maybe a JT-16A in reverse (600/150) which would handle way more signal. OEP almost certainly make a part that would work fine with the 1176 (probably don't need the shield anyway cause the signal is hot). There's also Cinemag CM-3303 that is often referenced as a good replacement.

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