Rocinante
Well-known member
Have we gotten anywhere with the Mic/line issue? I've been recreating the gerbers in eagle to try to fix the issue to no avail.
stay at home type 69 project
- Thread starter dogears
- Start date
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ruffrecords
Well-known member
Rocinante said:
Distortion in transformers depends on signal voltage. Using the tap on the secondary means the voltage across the primary will 20dB greater than if you used a 20dB pad at the input. Maybe this additional colouration is part of the sound of the Helios. If you want to get as close to the original as possible then use the tap. The choice is yours.
Cheers
Ian
I think it's fine the way it is with the understanding that there can potentially be 48V present on the inputs at any time.
One alternative would be to reconfigure the input to have a three position toggle drive some relays to be able to isolate the phantom power.
Or omit phantom power and use an external supply.
Or make the line input a front jack.
It's just one of the difficulties with 500 series, it's not really made for two inputs.
One alternative would be to reconfigure the input to have a three position toggle drive some relays to be able to isolate the phantom power.
Or omit phantom power and use an external supply.
Or make the line input a front jack.
It's just one of the difficulties with 500 series, it's not really made for two inputs.
Rocinante
Well-known member
I'm going to rack it as I want to use 24v keeping more like the original plus hopefully higher headroom.
Ian, didn't Neve wire a switch in some of their preamps to the 10468 so it could be also used in reverse for the line input? Could we do that with say an EA10468?
I was going to do that with my Neve-ish summing mixer but just got Carnhills instead.
IIRC the lustraphone transformers had a seperate tap for line right?
Ian, didn't Neve wire a switch in some of their preamps to the 10468 so it could be also used in reverse for the line input? Could we do that with say an EA10468?
I was going to do that with my Neve-ish summing mixer but just got Carnhills instead.
IIRC the lustraphone transformers had a seperate tap for line right?
The lustraphones didn’t have a line level - at least not the schematic. Just straight in after the transformer. The rack mount version has two separate input points on the board for this reason though, and is set up for single supple (24V or whatever makes you happy).
ruffrecords
Well-known member
Yes they did but they also put a pad in front of it as well otherwise it would saturate on line levels. Also, as best I can rememeber, this was only done on switching modules. Nominal output was -8dBu for a _4dBu inputRocinante said:
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The Carnhill is the equivalent of the 31267 which was the standard Neve line input transformer usually wired 10K:600
The tap was to replace a 20dB input pad on the mic. Helios line inputs were generally unbalanced and switched in at the secondary of the transformer.
Cheers
Ian
dogears said:
Sorry mate,
I completely Disagree.
It's a receipt for disaster, there should never , ever be Phantom Power on a Line Input, ever.
Thanks for your work Dogears, I don't want to diminish your work in any way, but it's my honest opinion from 20 years of Engineering.
Whoops said:
Add my 25+ years to that as well. It bears repeating for future generations:
"There should never, ever be Phantom Power on a Line Input, ever."
I don’t disagree. The problem is with a 500 series there’s not much way around it. Even if you defeat phantom from line mode, there’s still a common jack. There is no way to prevent a user from plugging something in when phantom is hot.
Alright, added three relays for the input and changed the selector to a SP3T. Now in line, phantom is no longer connected to the input. However, you can still fry gear if you try.
Files are updated (H9) in the same dropbox folder - new gerber, bom, and card outline.
Files are updated (H9) in the same dropbox folder - new gerber, bom, and card outline.
TwentyTrees
Well-known member
I've ordered a set of the "M" boards (with output buffer) from Elecrow, should be here in the next couple of weeks. It'll take me a while to build them up, but I'll let you know how I get on!
Rocinante
Well-known member
Dogears, thanks for the modification man. Naturally I had just added the relays in Eagle and then saw your post.
I think this will be my 4th version of the Helios. I am fairly certain I am going to use the 22113 again like in the version 3 that Whoops so gracefully shared. That way I have the option of adding a xfmr.
I think this will be my 4th version of the Helios. I am fairly certain I am going to use the 22113 again like in the version 3 that Whoops so gracefully shared. That way I have the option of adding a xfmr.
Rocinante said:
Hi Rocinante you can use the Dave Amels buffer used on the Kravitz console to drive a transformer, it's simpler than the 22113,
you have the schematic and details here:
https://groupdiy.com/index.php?topic=1222.260
dogears said:
Thank you so much Dogears
Rocinante
Well-known member
Whoops to the rescue. PM me your address Whoops, so when I get PCB's done I can send you one, albeit it'll be awhile. Slightly off topic but what do we know about the 22117? I saw a dual 22113 card on one of the helios sites and I'm also trying to figure out where that went.
Rocinante
Well-known member
Here is a pic of it.
