what to do with all these transformers?

[enginefire]

Happy New year Geekslutz!
been away for a while, so i hope everyone is good.

I have been collecting trannys for a while, always thinking that I would get around to doing something with them, and I think now is getting to be about that time.

here is what I got:
4 x UTC A-20 (pri 50 - 500, same on the sec)
2 x Hammond 804 (150/600 both sides)
4 x Altec 15095 (150/600 primary, 15k secondary)

any ideas? I was thinking of some kind of balancing box, or maybe using some of them as input transformers on a mic preamp...

[radeng]

I have a 12 channel balancing box loaded with A-20's. They do work well for this. The Hammond 804's are big broadcast grade units right? Like UTC LS series? How about building a M/S box out of them? I just did that with a pair of Peerless E204D's. The Altecs are good to have laying around for general purpose use.

[enginefire]

how did you wire the a20's for unbalanced to balanced and vise versa?

[MrMegaEli]

I might be interested in the A-20s

[enginefire]

let me guess... for cheap?
not really interested in selling them, I would like to put them do use (my own use).

[radeng]

Originally Posted by enginefire

how did you wire the a20's for unbalanced to balanced and vise versa?

Balanced input is terminals 1 and 6, with 3/4 strapped to the shield Unbalanced output is terminal 8 and ground.
My box already came set up as bal to unbal. This is an interesting piece, I believe this may be an actual UTC factory item. It has space for up to 24 transformers and is loaded with 12. Has curious DC +15 bias input with an adjustment pot and 2 large caps.

I added the Mogami harness, but it is otherwise "stock".

It sounds great doing what it is set up to do, but I have not tried going backwards through it.

[radeng]

Originally Posted by enginefire

2 x Hammond 804 (150/600 both sides)

I just looked these up. They are for "Isolating, Matching, Hybrid" and good to +15 dbm. Perfect for M/S use. Use the Jensen line level circuit, it has ground lifts.

[MrMegaEli]

Originally Posted by enginefire

let me guess... for cheap?
not really interested in selling them, I would like to put them do use (my own use).

ok thanks, and of course not cheap, they aren’t cheap transformers, the prices however are cheaper than what it would cost to make a reproduction. Price depends on condition of course . A used one would be around 60 bucks, new maybe a little more?

[enginefire]

MrMegaEli, that is a pretty fair price... but i am more interested in building a balancing/unbalancing unit for yours truly at this time

radeng, thanks for the pics of your unit, it looks fantastic. I think the a20s should be able to do the inverse just by connecting the straps backwards between the primary and secondary, if that makes any sense. both sides have the same impedance options, so if its 500 on the primary and 50 on the secondary to balance, to unbalance it should be as easy as 50 on the primary and 500 on the secondary.

Can you elaborate more on this m/s preamp you are describing?

[MrMegaEli]

Sorry, I forgot to tell you that recently I used an A-20 as an input transformer for a DIY pultec, 500ohm input is close enough to 600ohm. Strapped 500:500.

The Altecs could be cool for output transformers.

[radeng]

Originally Posted by enginefire

Can you elaborate more on this m/s preamp you are describing?

It's a M/S decoder, rather than a preamp.

Those Hammond transformers are beefy enough that you can use them at line level as inserts (though they will work fine for mic level too):

******//www.jensen-transformers.com/as/as065.pdf

Works great with my RCA 44BX and 77D as a M/S pair.

[enginefire]

raden, i found this site with a real nice MS description a little more than half way down: PZM Modification kit, Phantom Powering, Attenuator Pads, All Things Audio
I think those 2 hammonds now have a purpose!
Mr mega eli,how do the a20s sound?

[radeng]

Originally Posted by enginefire

raden, i found this site

Uneeda Audio is a great site. I have built a couple of projects off there. I combined the T-faders from the classic Neumann schematic with the ground lifts from the Jensen application note to make my M/S box.

[enginefire]

what is the purpose of the t faders? Do they adjust the impedance or are they for volume?

do you think it would be easy to add a 3rd output for the phase reverse decoder track?

[enginefire]

when you look at the jensen schematic, what do you make of the resistor values? they are labeled "51" and "301" does this actually mean 51 ohm and 301 ohm, or am i missing something? they seem like very specific values. would 1/4 watt 1% be the right choice?

[radeng]

The t-faders are for level, you set the Mid control and then crank in the Side to taste.

Not sure why you would need a phase reverse output. Couldn't you just use the polarity switch on your console input?

I was able to go through my resistor stash and find some that measured spot on. I don't know how critical the values are. Bill at Jensen could answer that.

[enginefire]

my console does not have phase reverse for some reason. I will be recording directly to the computer anyhow, so i can just duplicate the track and flip it in the box... i was just trying to figure out a way to record all three channels at once just for the sake of it.

[radeng]

Originally Posted by enginefire

my console does not have phase reverse for some reason. I will be recording directly to the computer anyhow, so i can just duplicate the track and flip it in the box... i was just trying to figure out a way to record all three channels at once just for the sake of it.

You can use 2 channels to record the raw M and S mics. The M/S box can be used in post on inserts to decode the L/R, and vary the stereo width on the fly. If you use it at the time of the original recording, the ratio settings of the t-faders is your permanent choice.

You only need to do the three fader trick on your console if you don't have a M/S box. It's a poor man's solution. You will be among the lucky few with a real transformer matrix, these unusual hybrid repeat coils don't exactly grow on trees. To buy new Jensens is very expensive.

[enginefire]

yeah i got lucky on ebay... 2 mccurdy VU meters with some amp electronics and the two hammond 804's for $20... it was from the next town over so there was no duty and shipping was cheap!

If i understand you correctly, because the 804's are completely reversible thanks to their design, it is possible to use this MS encoder you are suggesting as a decoder as well? That would be fantastic.

I see if i can get it together this weekend and post some pictures
thanks for your help radeng!

[lassoharp]

let me guess... for cheap?

let me guess . . . you bought them on ebay for $$$? Collecting is an expensive pastime these days.

For something interesting you could use them as 2 X 1 or 4 X 1 mixing coils. Or mic splitters.

and of course not cheap, they aren’t cheap transformers,

Not when you have hordes of people chasing and routinely paying super inflated prices. I bought 8 of them at a hamfest for 7$ each years ago and a radio ham guy I was with remarked that they were getting expensive. Perception and agreement pretty much seals the price.