The Optimal Helios

I can definitely hear an improvement in detail and depth of the sound with the new knobs...

Thank you Rocinante, i'm still wondering what knob scheme use in the aphelios, and also what colour for the panel, i'd like to paint it black as Jagger suggests, but i'm waiting for the new pcb to arrive. 
Btw, i absolutely love the neve, i must save some money for new modules so i can fill the other buckets

PCBs arrived today!
 
transformer fits ok, i've already found an error: no phase switch!!! fixing this error will be easy, just a dpdt switch wired point to point to the trnsformer primary. let's hope it is the only mistake...

Thank you Rocinante!!

I'm planning to stuff the board during the weekend i'll let you know if it turns out well..

They'd be easy enough to rack but im not sure how many people have 500 racks on top of one another. I need another rack hmm....

Beautiful. Just simply beautiful.

Don't think it's been asked, what's the little 6 pin port in between the two 500 series slots?

Thank you guys, whenever i read post like these i feeling like a boy that just scored his first goal.

about the 6 pins connettor the story goes like this:
when i first conceived the double500 module i was looking for a way to fit two 500 series modules like the api550a vertically and still be able to have both the +-16v and +-24v like in the 51X connector without the need to remove the metal chassis or drill it to have leeway for the longer 51X connector. The space between two such modules vertically inserted in the slot was really small but i found that an 6 pin connector would fit. 
In fact in the next backplane revision i will put a 10 pin connector in place of the 6 pin connector in ore der to have more voltages to use, e.g. 30 and 44 volts or high voltage and filament voltage for valve modules. The system is very open and can be configured easily. 
Now for example i have the 1073 at +24 volts and the helios at +24 for the transistors and +-16v for That1646

That is just super resourceful and clever.

I'm very happy with the new helios pcb, so I decided to go  little further and create a rack for the double500 serie modules:

i've not decided what to do with the space on the right yet... plenty of options there

Paolo

Hi Rocinante,
the case is a custom built using different parts available at a store near where i live, i'm thinking about creating a kit. the psu would be the 51x psu with +-16 and +-24 but with a beefier main transformer. 

I have a pair of Igor's he69 pcb's. While I really like the front panel layout his pcb's allow, the relay system he used just does not seem to work. I've tried every possible combination of relays, voltages, etc... gleaned from forums, then some A-hole stole a package from digikey off my front porch which was the last semi-recommended relays to try (where the hell you think your gonna resell that, thieving bastard?!) I decided the hell with it. I'll make my own pcb's that work.

The physical layout of Igor's pcb in 500 series is great, so I'm borrowing it. I already have 2 of the he69 switch/cap pcb's built, and I really don't want to try and desolder the grayhills, so backwards compatible it is.

Igor's pcb offered a ton of options, but I don't need em. Over complicates things. I'm going to replace the relay system with a pair of CAPI plug in relays. Simple, space saving, and less that can go wrong when shipping on a proto batch of pcb's from China is $50.

Simple THAT 1246 input stage, helios eq, DOA gain makeup with a trimmer, and options for the originally spec'd ll1524/1517 (I already have a pair) as well as 2503/cmoq-2 1:2. I put in a couple jumpers to give the option of running a 2503 1:3 as well. I have plenty of gar2520's and 1731's to try, and also have some APP 992 and 14ge opamp kits on the way.

Basically what I'm going for is a simple front end > helios passive eq > "gainstage playground."

I'm taking a break right now from notating the schematic, I'll post it up when I'm done. Just wanted to get some thoughts on the idea.

Thanks Roc, I appreciate the ideas.

I was pretty keen on keeping this an "isolated experimentation" project to mess around with different opamps and tranformers on the output, but I'm totally down with adding a transformer input if it's a simple replacement for a THAT 1240 series front end. Igor's input transformer design required a seperate DOA in some sort of mixed feedback with I think a ll7101 (there's documents on lundahls site explaining it, I just dont understand them).  I don't have the line in transformer competence to know what would work... Any suggestions?

As far as gain stage, from my understanding both helios and neve gain stages run on 24v. I'm looking to stick with +/- 16v 500 series as that's what I'm working with. I think it will be interesting to play around with different DOA and transformer combos. I'm really excited to get the APP DOA's. I'm also keen to play around with inductors. I've used carnhills for the 10H low inductor but wound my own rm8 inductors for the mid on n48 400 cores. I might take a stab at trying to wind some 10H on rm10 n48 630, but it's 4k+ of turns with 40 gauge magnet wire... Should be easily feasible on rm10 if my calculations are correct, but I'm not going to hand wind that. A coil winding machine might be in my future...

Anyways, input transformers. Thoughts?