I Need To Get OFF the Vintage IT Grid...

[schmidlin]

Looking to gear up with some tube compressor builds and have been using old iron for the input transformers and need to switch to new.  I had no love with Edcors: I need some proper old-school shielding, not too expensive and has full spectrum.  So any suggestions?  American would be nice.

I'm considering Cinemag, but their stuff all seems to 150 ohm in.  Isn't 600 the way to go?

Thanks in advance!

 

[lassoharp]

With 150 to Hi-Z ratio you'll likely be using a U-pad which of course you can optimize to bridge any impedance so you should be fine there. If your source is a 600r line then use a 150ish shunt resistor in the pad.

My understanding has been that a 15% loading mismatch is acceptable for most transformers to maintain rated response.

I've played around a bit with using the 600r vs 150r winding on input iron using a standard '150r' mic pad in front. On some iron you can hear a audible difference and on others it's hardly noticeable. In the case of using the 600r winding(with unterminated sec) being fed by a 150r or less source, it's supposed to drop the +/-(whatever the iron says, usually 1 or 2 db) roll off point to a fraction( 150/600) of the rated value.  I've never plotted any points to confirm this. I mainly listen for the more irritating distortions that can sometimes happen with mismatches.

Any of the interstage types, A-18, A-16 would seem a good choice because of the lower step gain. Seems all those limiters with high ratio iron are always in need of big padding.  You'll also have the more friendly 10Kish input impedance.

 

[emrr]

isn't all the cinemag 150 input stuff only rated for mic level?

 

[lassoharp]

Another thought - If you don't require the isolation - go straight into a dual pot.

I'm getting ready to build up a couple of the simpler circuits myself - 436 and the Federal and have planned on giving this a try. It worked reasonably well with a parallel mixing circuit I was experimenting with and would take care of the vol control issue. Definitely cheaper than a Daven + iron.

 

[schmidlin]

Good heads up, emrr, those max at -3db input.  Heck, I just fried a UTC A-11 in a Federal and that IT goes to +3 input: don't want to go that direction again.

Lassoharp, your direction is very interesting, I hope you'll post your findings of your successes.  But I would be leery of that side chain voltage getting back to your source, but I'm no expert by any stretch.  Blocking caps?

So what are people using today for new builds?

 

[Kingston]

I just went through this, trying to find alternatives for edcors and other cheapos like OEP for vari-mu projects. I even set a target that they must be able to handle mid-side conversion at the input and output of the amp.

I couldn't find anything cheap but flexible. I did eventually find an ideal solution, very flexible, but depending on where you come from, it might get a bit expensive. (Kand audio seems quite a good deal for these stateside)

LL1676 http://www.lundahl.se/pdfs/datash/1676.pdf

LL1674 http://www.lundahl.se/pdfs/datash/1674.pdf

depending on the step down or step up of your task they have cheaper and almost as flexible alternatives. These might work quite well: LL1544A LL1545A.

There's of course the very expensive LL7902 and LL7903 for some ridiculous levels and ratio tricks.

I really wanted to, but I simply could not find this kind of shielding, flexibility and choice from any other manufacturer. I really would have liked something from Cinemag as well...

 

[lassoharp]

Good heads up, emrr, those max at -3db input.  Heck, I just fried a UTC A-11 in a Federal and that IT goes to +3 input: don't want to go that direction again.

Lassoharp, your direction is very interesting, I hope you'll post your findings of your successes.  But I would be leery of that side chain voltage getting back to your source, but I'm no expert by any stretch.  Blocking caps?

So what are people using today for new builds?

I would be very interested to know how you fried an A-11.  Opened the winding under normal use?

 

[schmidlin]

Good question: it was under loan to a local studio for testing.  From what I hear, *good* studio equipment runs at +4, and the A-11 is rated for +3 input so...who knows, but one side of the primary opened up.  I *reinvested* the casing (nice double shielding btw!) with another IT and it is chugging along nicely so far.

Thanks Kingston for the Lundahl info.  Can't find the input max from the spec sheets. Still wonder who is making the Retro ITs, et al.

 

[Kingston]

Can't find the input max from the spec sheets.

They don't give it because they don't know what configuration you will be using it in.

For example,

we know that LL1676 connected as 600/10k (1:4 ratio) will see 50 Hz: 0.2% distortion at 22V rms (+29 dBU) measured at secondary.

That was 5.5V rms (+17 dBU) before the 1:4 step up at the primary.

Loud.

Used in 1:2 configuration even louder of course.

 

[lassoharp]

Might have a look at these - looks like PP feeds ~20K. 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110561706457&ssPageName=STRK:MEWAX:IT#ht_500wt_692

Be silent. . .