helios preamp pcb's [boards now available]

[mus1k_freak]

Since there seems to be some interest in pcbs, ide like to get a list going of people who want some since there aren't all that many in the first run, ill update the first post in the thread with who's interested, itll be $10 for a pcb plus $3 shipping in the usa and $7 outside the US. if your interested shoot me a pm and ill add you to the list until all boards are accounted for then once you send payment ill mark as paid, this way I can get them shipped out ASAP once they come in.

I will provide a mouser cart link for all parts needed, a BOM and a build guide. so it should be a pretty straight forward build, now for the fine print, this is the first revision of these, so there may be a few bugs that need to be worked out.

 

[mitsos]

well, you know I'm interested, but like I said, I'm in south America, by the time they get to me you'll be on the 2nd (maybe even 3rd) revision! But I'll stick around for the commentary while I wait for the 500 series pre/eq!  ;D

 

[mus1k_freak]

Already started laying out a 500 version with the Helios 69 eq high pass filter and some other bells and whistles, just waiting on feedback from Rev 1

well, you know I'm interested, but like I said, I'm in south America, by the time they get to me you'll be on the 2nd (maybe even 3rd) revision! But I'll stick around for the commentary while I wait for the 500 series pre/eq!  ;D

 

[mus1k_freak]

I've sent stuff to South America before only took about 10 days if your interested I'll send some to you

On a slightly unrelated question if I I want to run a 500 module at 32 volts would I use +16 and - 16 as the ground?

 

[mitsos]

well, we can try! This is Brasil of course, the post office express service is on strike atm, just in time for carnaval... Maybe they wanted some extra days off?  I'll PM you later.

As for 32V, yes, this can work on transformer isolated circuits. It's been brought up a few times here before, look around for some discussion. Basically you don't want to connect the -16V to the normal VPR ground.  The Helios runs on 24V, you can grab the 32V and then regulate it to 24, or use a zener, or whatever. The 500 series Helios does this, do a search on google images, there are a couple of gut shots.  Just don't use a DC-DC converter, it's a lot of money for little benefit, and opens a can of worms as far as development.  Famous KISS principle.

 

[mus1k_freak]

That's what I thought,  regulate it back down to 24 and use the - 16 as ground,  if I use opamps for balancing the output I'll use  the regular ground with the two power rails, just gotta get my grounding all straightened out

well, we can try! This is Brasil of course, the post office express service is on strike atm, just in time for carnaval... Maybe they wanted some extra days off?  I'll PM you later.

As for 32V, yes, this can work on transformer isolated circuits. It's been brought up a few times here before, look around for some discussion. Basically you don't want to connect the -16V to the normal VPR ground.  The Helios runs on 24V, you can grab the 32V and then regulate it to 24, or use a zener, or whatever. The 500 series Helios does this, do a search on google images, there are a couple of gut shots.  Just don't use a DC-DC converter, it's a lot of money for little benefit, and opens a can of worms as far as development.  Famous KISS principle.

 

[mitsos]

Not sure if you can mix them like that. Do a search here, it's been gone over but I can't find the threads now, but the consensus was that it would work on a trafo isolated circuit.  Take a look at the soundskulptor neve stuff, he does some type of ground floating, and if I'm not mistaken, the AML neves are also like that. 

IMHO, you are better off with an output transformer, it might "look" like it costs more, but if you count the time you'll spend designing a proper balancing circuit and troubleshooting it later, the transformer wins hand down. Just wire it up and it works, every time.

 

[mus1k_freak]

Very true,  and I do enjoy some good transformer mojo I have a sowter 5069f I'll be trying on the first run for a output tranny

 

[Dylan W]

Off the top of my head, a lot of the 500 series Neve stuff uses a 7908 to bring the -16 to -8. As mitsos said, it's been covered in a few threads.

 

[mus1k_freak]

just checked out the don classics nv73 preamp schematic, he uses a http://www.digikey.com/product-detail/en/CC6-2412DF-E/445-2492-ND/920452 to get to 24v, little pricey but looks simple enough, i wonder if thats any better then just regulating the 16 rails down

Off the top of my head, a lot of the 500 series Neve stuff uses a 7908 to bring the -16 to -8. As mitsos said, it's been covered in a few threads.

 

[Dylan W]

Here's the thread. http://groupdiy.com/index.php?topic=54891.0

 

[mitsos]

nice searching.. couldn't find it myself. 

Also, here is the thread that made me decide not to use those things.  not many people here have complained about noise, but then, I don't know of anyone else who put 16 channels worth of pres/eqs/etc together, all with dc/dc converters.

http://groupdiy.com/index.php?topic=43315.msg547670#msg547670

 

[mus1k_freak]

ah yes i do remember seeing that thread now, using a regulator to bring the -16 down to -8 definitely seems like the most efficient way to get 24v. the whole virtual ground, 500 ground, and -8 ground have me a little confused but i think once i start drawing it out itll all come together. cant wait to get the first run of boards in!

 

[ruffrecords]

ah yes i do remember seeing that thread now, using a regulator to bring the -16 down to -8 definitely seems like the most efficient way to get 24v. the whole virtual ground, 500 ground, and -8 ground have me a little confused but i think once i start drawing it out itll all come together. cant wait to get the first run of boards in!

How close is your board layout to the original? Do you plan to use the same finger connector?

Cheers

Ian

 

[mus1k_freak]

The board layout is pretty different from the original, it follows more the flow of the schematic then the orginal layout, ill double check the dimensions, but i believe its much smaller about 4"x3" ill see if i can post a picture from the gerber files. I didnt have any fingers on it, just solder pads for the in, out and power connections, i figured it would be mounted in a 1u case or retro fitted in a 500 frame. im looking forward to using one for gain make up to your helios eq boards

 

[ruffrecords]

I got a reply from my ex-Helios gu. He says the 1:1 tap was used mainly to save cost but he pointed out that nobody used primary side pads in those days. The few console builders that did use pads always had then on the secondary side of the transformer (including Neve). He also gave some details about the original Lustraphone M10 input transformer:

"The Lustraphone M10 had three taps

Violet    H
Red      IN Lo

Black    Out Lo  Grnd
Blue    -20  i.e.  Ref O/P
Grey    -10dB    Re. O/P
Green    O/P

The -10db output  was only used in the Olympic Studio one desk
which  did not have a pad switch , also the mic  gain went up to 80dB"


On the topic of mixing he said:

"the MMC1 card was a Mic Mix Card the feedback was taken from the emitter of the
output 2N4058 via a 15K in series with 64uF cap to the base of the input transistor 2N3707
the bias values  for this transistor was also changed, if you look on the original cards you will find theses
components missing ( if used as a mic /line card }"

so the Helios mixers definitely used virtual earth mixing with 15K bus feed resistors.

Cheers

Ian

 

[mitsos]

That's awesome! Thank you for checking all that!

Well, API used input pads in their circuits in the 1970's, maybe it's an American thing?

So the Olympic console used a 1:5 trafo with no pad whatsoever? Interesting... EDIT: I was looking at that wrong, if it's -10dB it's about a 1/3 tap, right?

I admit I got a bit lost on how the mic circuit was used for summing, I'll re-read it later with the schematic in front of me. 

cheers!

 

[ruffrecords]

The taps seem to be 1:1, 1:3 and 1:10 giving 0dB, 10dB and 20dB gain.

Cheers

Ian

 

[Joechris]

Here you have a Helios input without the transformer tap for line. As you can see this module is powered by 36V
so it has the line amp Ian posted for EQ makeup, and a resistor and a zener to bring the voltage down to 24V for the 3 transistor pre stage.

 

[ruffrecords]

Very interesting. I have seen other references to the 'Arctic' in the EQ for instance. Was this one specific console and can you date it?

Cheers

Ian