mdc wrote: Sun Mar 10, 2024 10:02 am

I put on a couple NBA games and finished up 4-channels of Helios mic pres last night. Still need to get the front panels made, but at least they all seem to work when I checked them out at home. They're based on two '2128' amp cards in a row with a gain in the first stage, a trim control in the middle, and a discrete buffer on the output (helios apparently never used balanced outputs on anything, so there's only a transformer on the input).

As far as DIY pres go, these are pretty affordable - not a lot of parts, only one transformer, pots instead of stepped gain switches. Probably about $150CAD in materials per channel (plus whatever the panels end up costing I guess...).

twelvepoint wrote: Sun Mar 10, 2024 3:15 pm

mdc wrote: Sun Mar 10, 2024 10:02 am

I put on a couple NBA games and finished up 4-channels of Helios mic pres last night. Still need to get the front panels made, but at least they all seem to work when I checked them out at home. They're based on two '2128' amp cards in a row with a gain in the first stage, a trim control in the middle, and a discrete buffer on the output (helios apparently never used balanced outputs on anything, so there's only a transformer on the input).

As far as DIY pres go, these are pretty affordable - not a lot of parts, only one transformer, pots instead of stepped gain switches. Probably about $150CAD in materials per channel (plus whatever the panels end up costing I guess...).

These look so great

mdc wrote: Mon Mar 11, 2024 1:13 pm Thanks! And yep - they're for 500-series, they just don't have front panels yet. Matt from Iron Age Audio released schematics and gerber files for a Helios pre/eq DIY project a few years ago and he was kind enough to modify the PCB layout so it's just the preamp.

I used hammond transformers as I'm in Canada so they're the easiest/least expensive option to source. I have boards for a few more channels so I'm curious to try a different transformer option and see if it actually makes any practical difference versus the hammonds.

TylerDeadPine wrote: Mon Mar 11, 2024 8:03 pm

what's the specs on the transformer? Might have something for you for the low/high cost of shipping

mdc wrote: Mon Mar 11, 2024 9:24 pm

TylerDeadPine wrote: Mon Mar 11, 2024 8:03 pm

what's the specs on the transformer? Might have something for you for the low/high cost of shipping

I’m intrigued!
It’s a 1:10

https://www.hammfg.com/part/1140-MN-A

TylerDeadPine wrote: Tue Mar 12, 2024 5:41 pm

mdc wrote: Mon Mar 11, 2024 9:24 pm

TylerDeadPine wrote: Mon Mar 11, 2024 8:03 pm

what's the specs on the transformer? Might have something for you for the low/high cost of shipping

I’m intrigued!
It’s a 1:10

https://www.hammfg.com/part/1140-MN-A

Cool - i'm waiting for a reply from Carhill but I have some nice transformers I kept from and old preamp project that R. Neve designed, and I have zero info on them. if what they give me works out I'll send one too you and if you give thumbs up then I'll build my own too!