A12 Transformer alternatives

[Old Troll]

Being somewhat familiar with the product lines from Cinemag, Jensen and Lundahl, I've been wondering about substituting the output transformer on an A12 from the apparently steel core CMOQ-2S to a Hi - Nickel core CMOQ-2H. The photos in the assembly manual also show the alternate pad pattern for the Lundahl 1578XL input transformer shown as an alternative on the schematic. I'd think that swapping to the Lundahl input and a hi-nickel output transformer could really smooth out the sound of this usually rather "colorful" preamp, if that's what someone wants.

Now I see that there are "A12 Transformer Upgrades" on the order page which simply list a "Low Nickel" and a "High Nickel" choice. My question is, are these just for the output transformer? If so, which model/brand of transformer are they? I'd also like to verify that the present rev of the PCB for these A12 modules still has the pattern to take a Lundhal input transformer.

I like transformer coupled preamps, because I'm often doing live event recording of things like church choral music that requires I have long mic lines. Yes the A12 wouldn't be a first reach for that kind of thing, but the thought of modding something to be able to use it for something different intrigues me. The A12 is a really minimalist mic amp which I also like, so if I could tailor a few of these for use on stuff requiring smooth, clean sound, it'd be interesting.

[cAPSLOCK]

I am interested inthe actual responce to your question...

But in the meantime, have you thought about using the J99 in this circumstance? To fancy a circuit?

[tpryan]

Now I see that there are "A12 Transformer Upgrades" on the order page which simply list a "Low Nickel" and a "High Nickel" choice. My question is, are these just for the output transformer? If so, which model/brand of transformer are they?

From this topic: http://seventhcirclestudios.com/SCA/php ... php?t=1772

We're now stocking CMOQ-2L low-nickel and CMOQ-2H high-nickel output transformers for the A12. These parts give lower distortion and less "color" than the standard steel transformers for more variations in tone.

I'd also like to verify that the present rev of the PCB for these A12 modules still has the pattern to take a Lundhal input transformer.

It does, along with pads to mount a single DC servo as well.

[Old Troll]

Thanks for the response Tim. The CMOQ-2H was exactly what I was hoping the "high nickel" transformer was. The stock Cinemag input transformer may also be a high nickel core transformer, but this isn't clearly specified in their data. I take it the stock steel core transformer would still come with the kit, or is the upgrade charge just the difference in cost between this and what you'd get with the -2L or -2H upgrades?

To cAPSLOCK: My dream would be to have a rack full of John Hardy Twin Servo preamps to do everything with. especially the two channel jobs he designed for Sony Classical that had 2 dB/step gain switches. But the financial reality at present would likely dictate using C84s for a lot of my work, in spite of the quadrupled parts count. All that cross-coupling does do what it advertises.

The J99 is an excellent variation on the Deane Jensen circuit, though curiously not using Jensen transformers. Tim could probably verify, but I suspect the Lundahl and Cinemag transformers fit on the SCA card real estate better than the Jensens would have, especially since there needed to be real estate reserved for two 990C opamp modules.

It might turn out that trying to clean up an A12 with a Lundahl input transformer and a high nickel output transformer would end up costing close to what a J99 would. I haven't tried pricing the 1578XL on a direct order from Lundahl, but wouldn't be surprised if it cost upwards of a $100.

One of the other reasons I'm considering the A12 module is that it provides a secondary output from an unused winding on the output transformer. This is actually brought out to a pin header on the board, so it would be simple to wire a second XLR3M output jack in an empty adjacent module slot to provide a FoH or monitor feed from a given module. Since the primary output uses two windings in series, this single auxiliary winding will be -6dB down from that, which for monitoring would be just fine.