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Post by rocinante on Mar 21, 2016 23:30:44 GMT -6
So I grabbed a couple of Martin's line level ezln72 part 1290 pcbs (ba183) and I am planning on building a summing mixer. I have seen the insides of many of the pro factory made offerings and well.... they seem to leave a lot to be desired. Like where the hell are the 3055s, and the carnhills, and all the other stuff.
First I am gonna see if there is a possibility for switching out the master section of my Soundcraft Ghost and if its any good following the stereo out into the DAW.
As far as a summing mixer it will be 16 to 2. It will have 8 insert sends and returns with two aux and 3 stereo monitor outs. Worse comes to worse I will have a bad ass neve fronted summing mixer if I ever decide to go console-less.
Don't get me wrong I like the Ghost. I've used Neve's, Trident, amek, mackie, a&h, soundtracs etc... and despite some gs members opinions I think its a fine desk. No its no monster console but it aint bad. It definitely doesnt suck. I guess I want the option to use a summing mixer should I want to. But if im gonna get one I want it to be like the nicerizer or similar. Id like to make it adaptable to 500 series gear I suppose.
At any rate anyone try this?
Got any ideas?
Thoughts?
I debated making it a Neve/Helios amp switchable box but I think that might be too much.
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Post by svart on Mar 24, 2016 8:33:05 GMT -6
I'm not quite sure what you're saying.. Are you saying you want to replace the summing network in your mixer with the neve-based one? If so, you HAVE to be aware of the impedances of the channels, the bus and the inputs to the neve modules or you'll be in for a rough time with noise. Making the series bus resistors too high and you'll have resistor noise and poor crosstalk. Making them too low and you'll waste current and heat the opamps un-necessarily, and have current noise. This is if you choose to replace the internal summing bus itself. I don't know if the Ghost has discrete line outs for each channel, but if it does, you could build a summing device to plug into those instead and see where that takes you. Scale your series bus resistors for the output impedance of those outputs and you should be good. Also, summing mixers are always passive, with active gain, so it'll technically be a neve-ended summing device, rather than a neve-fronted one..  As for me, I replaced the summing bus on my mixer with one cloned from the SSL9000 console. I scaled my bus resistors to 5.6K (good median impedance for BJT opamps to drive) and then matched the summing amp impedance to 5K-ish. Seemed to work pretty well as I get noise floor around -100dB (terminated I/O, unity gain). |
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Post by rocinante on Mar 24, 2016 9:01:33 GMT -6
Yes. Yes. And thank you. I've been hoping you'd chime in Svart. I am having a hard time (and have been for a bit now) looking at the schematics and manual to determine the impedances. I kind of minimally threw it out there in GDIY land but alas no response.
And so yes I plan on seeing if I can replace the internal summing bus with the neve's.
"As for me, I replaced the summing bus on my mixer with one cloned from the SSL9000 console. I scaled my bus resistors to 5.6K (good median impedance for BJT opamps to drive) and then matched the summing amp impedance to 5K-ish. Seemed to work pretty well as I get noise floor around -100dB (terminated I/O, unity gain)."
I could fucking hug you for this. Okay how do I figure out how to match the bus resistors and therefore the summing amp?
"I don't know if the Ghost has discrete line outs for each channel, but if it does, you could build a summing device to plug into those instead and see where that takes you. Scale your series bus resistors for the output impedance of those outputs and you should be good."
So you're saying either way id have to keep the ghosts output impedance in mind be it the direct outs or the internal summing network?
I know they are two different outs but they wouldn't be the same?
Yes a third plan was to run all the ghost direct outs to the "Neve BACK ended summing mixer" that way I could utilize the inserts and auxes amongst other things.
So worse comes to worse I'll have a decent summing box that I can add too and possibly make switchable from the ghost (I have no idea how yet but I'm working on it)
Oh and Svart...
Thank you comrade.
Dylan
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Post by svart on Mar 24, 2016 10:43:30 GMT -6
Yes. Yes. And thank you. I've been hoping you'd chime in Svart. I am having a hard time (and have been for a bit now) looking at the schematics and manual to determine the impedances. I kind of minimally threw it out there in GDIY land but alas no response. And so yes I plan on seeing if I can replace the internal summing bus with the neve's. "As for me, I replaced the summing bus on my mixer with one cloned from the SSL9000 console. I scaled my bus resistors to 5.6K (good median impedance for BJT opamps to drive) and then matched the summing amp impedance to 5K-ish. Seemed to work pretty well as I get noise floor around -100dB (terminated I/O, unity gain)." I could fucking hug you for this. Okay how do I figure out how to match the bus resistors and therefore the summing amp? The easiest way is to get a schematic and see what the series bus resistors are for the channels into the summing bus. You'll probably see an opamp(or more) driving a series resistor in the 2k-10K range going to the summing busses. That's likely what Soundcraft designed their bus impedance as, and unless you want to change it, you should stick to. The neve style transformers in the 1290/1073 reflect an impedance of 600-1200 ohms, which is a little on the low side for strictly matching.. It might not make *that* big a difference though, but you could make a small resistive pad to use before the transformer so that the summing network only sees the pad impedance.. "I don't know if the Ghost has discrete line outs for each channel, but if it does, you could build a summing device to plug into those instead and see where that takes you. Scale your series bus resistors for the output impedance of those outputs and you should be good." So you're saying either way id have to keep the ghosts output impedance in mind be it the direct outs or the internal summing network? The outputs will most likely be LINE level outputs, so their output impedance will dictate an optimal load impedance of 5K-50K (10k and 47K are popular values used, but there is NO standard for line level impedances..). This will likely be found in the user manual somewhere. In this case, just find a passive summing network in the 10k-47k range and call it a day. The neve amps will be isolated from the line outs by the network so you shouldn't need to do anything else. This option is likely the best option although it involves making a lot of connectors and stuff.I know they are two different outs but they wouldn't be the same? Not likely. They are usually buffered separately.. Usually.. I don't know how they do it in the Ghost though.Yes a third plan was to run all the ghost direct outs to the "Neve BACK ended summing mixer" that way I could utilize the inserts and auxes amongst other things. In most in-line mixers, the direct/line out and the summing busses are taken from further down the chain, so your inserts and stuff should still be usable.So worse comes to worse I'll have a decent summing box that I can add too and possibly make switchable from the ghost (I have no idea how yet but I'm working on it) Oh and Svart... Thank you comrade. Dylan See my replies in pink, above! |
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Post by rocinante on Mar 24, 2016 12:46:43 GMT -6
Svart, you gave me a ton to work with. Thank you and thank you.
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Post by svart on Mar 24, 2016 13:51:54 GMT -6
One other thing to mention..
There are two types of summing network.. The "passive summing with gain" and the "virtual ground" network.
These have some very distinct differences..
Passing summing bussing will change overall impedance as channels are added or subtracted to the network. because of this, the amount of signal loss will change as channels are added or subtracted. The more channels you add to the network, the more loss you have and more gain you'll need to use (the the more noise you are amplifying). You also need to use higher value resistors to get better channel isolation.. But this will increase the amount of makeup gain you need too..
With the virtual ground network, the series resistors are part of the feedback network so adding and removing channels will automatically change impedance and gain. Because one input of the amp is grounded, it will also amplify noise by the amount of gain the amp is set to. Your grounds need to be very clean.. This type of amp also needs to source and sink ALL the current on the buss and needs to be a fast and powerful opamp to handle it unless the bus resistors are higher values...
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Post by jimwilliams on Mar 24, 2016 18:18:41 GMT -6
Another difference, virtual ground into an inverting opamp is 180 degrees out of phase. The Neve card is not.
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Post by svart on Mar 25, 2016 13:08:31 GMT -6
Another difference, virtual ground into an inverting opamp is 180 degrees out of phase. The Neve card is not. Yes, true, but it's as easy as swapping the + and - output pins to fix that. |
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Post by rocinante on Mar 25, 2016 16:59:43 GMT -6
I am still researching and am still "designing" everything. Thanks to the both of you. I had been fairly certain I was going to go with using the direct outs (albeit from the patchbay) but iirc they are not balanced. Which sucks.
So maybe a summing mixer that can accept a stereo in that'll have 4 inserts?
A seperate summing mixer on its own is probably the best call.
I havent bitten more than I can chew yet (I built a friggin helios) but its gonna be more work than I anticipated (and I anticipated a lot)
I also want to make it so its adaptable.
Okay so my next question;
Can someone point me in the direction of how best to do the inserts?
And of course;
Thank you.
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Post by rocinante on Mar 25, 2016 23:01:19 GMT -6
Shit, you know what just dawned on me? Neve boards operate at +24v. The Ghost operates at +,-17v. I suppose one could run a seperate psu inside the console and just tap the mains but it certainly would take work. Not to mention probably introduce noise. Not very polished or pro at any rate. And so thats why they use api style summing in many of the Ghost mods; because they can tap the ghost's 17v and 0v.
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Post by rocinante on Mar 30, 2016 1:32:17 GMT -6
So I have made some progress and put together a few designs of what I am thinking of doing while talking to various people and researching a bunch. I believe that it is important in DIY to only build stuff you want. Something that if it was in the classifieds or at vintage gear or what not, I would think: "I must have." I am also realistic and don't have a ton of money to spend on experimenting. That said I have some choices to make here and I could use some help. For now Fuhgedabout the Ghost. That doesn't mean I am tossing it it just means that my original plan wont work and if I am gonna build someing in place of the Ghost, it better be better. I think it will. Focusing on a Nevish summing mixer has now become the plan. Incorporating some features I would like on a summing mixer while keeping it simple (and one of the main reasons I am building a summing mixer) is also another priority. I am also leaving the option for usb and 500 series format connectivity available. You know, might as well keep the options open. Okay so my ADDA right now is a MOTU HD192 and 2408 mk3. I plan on buying some nice 2 channel ADDA in the very near future. I found out that it is actually somewhat important to know what converters you use when building a summing mixer and the impedance's involved. Who knew. As you all know the output is going to be two EZLN72 boards each going to either VTB 1148 or LO1168 or Ed Anderson 11148 or Dan Deurloo neve outputs, etc... Something nevish. So here are the options I am considering for the inputs. Option 1: -the most expensive- 8 x vtb 9046 > the ezln72 > vtb 1148 > stereo out. Option 2: -nearly as expensive as the first- 8 x cinemag cmmi-10c > helios 2128 line amp > ezln72 > vtb 1148 > stereo out Option 3: -the way the fucker cheaper option- 16 x ic inputs > ezln72 > vtb 1148 > stereo out Option 4: -probably the same price as 3 but I am still not if it is possible- 16 channels into 2 x vtb 9046 > ezln72 > vtb 1148 > stereo out Option 5: -the most economical- 16 x passive channels > bus resistors > ezln72 > vtb 1148 > stereo out Below is a very rough draft of the lay out. Nothing is to size or where it is going to be. It is just for a vague idea and perspective. Please let me know your thoughts.  |
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Post by svart on Mar 30, 2016 10:37:27 GMT -6
So I have made some progress and put together a few designs of what I am thinking of doing while talking to various people and researching a bunch. I believe that it is important in DIY to only build stuff you want. Something that if it was in the classifieds or at vintage gear or what not, I would think: "I must have." I am also realistic and don't have a ton of money to spend on experimenting. That said I have some choices to make here and I could use some help. For now Fuhgedabout the Ghost. That doesn't mean I am tossing it it just means that my original plan wont work and if I am gonna build someing in place of the Ghost, it better be better. I think it will. Focusing on a Nevish summing mixer has now become the plan. Incorporating some features I would like on a summing mixer while keeping it simple (and one of the main reasons I am building a summing mixer) is also another priority. I am also leaving the option for usb and 500 series format connectivity available. You know, might as well keep the options open. Okay so my ADDA right now is a MOTU HD192 and 2408 mk3. I plan on buying some nice 2 channel ADDA in the very near future. I found out that it is actually somewhat important to know what converters you use when building a summing mixer and the impedance's involved. Who knew. As you all know the output is going to be two EZLN72 boards each going to either VTB 1148 or LO1168 or Ed Anderson 11148 or Dan Deurloo neve outputs, etc... Something nevish. So here are the options I am considering for the inputs. Option 1: -the most expensive- 8 x vtb 9046 > the ezln72 > vtb 1148 > stereo out. Option 2: -nearly as expensive as the first- 8 x cinemag cmmi-10c > helios 2128 line amp > ezln72 > vtb 1148 > stereo out Option 3: -the way the fucker cheaper option- 16 x ic inputs > ezln72 > vtb 1148 > stereo out Option 4: -probably the same price as 3 but I am still not if it is possible- 16 channels into 2 x vtb 9046 > ezln72 > vtb 1148 > stereo out Option 5: -the most economical- 16 x passive channels > bus resistors > ezln72 > vtb 1148 > stereo out Below is a very rough draft of the lay out. Nothing is to size or where it is going to be. It is just for a vague idea and perspective. Please let me know your thoughts. Honestly I don't see a benefit to doing anything but the bus resistors into the summing network, and then the amp cards (with their associated input/output transformers (option 5). Pretty much every device being plugged in will have an output buffer, so no input buffer is needed to the summing network unless you just really want to. |
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Post by rocinante on Mar 30, 2016 11:53:11 GMT -6
Thanks so much for replying Svart. So like this?  |
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Post by svart on Mar 30, 2016 12:21:27 GMT -6
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Post by rocinante on Mar 30, 2016 13:21:06 GMT -6
Thanks so much Svart.
Yeah I downloaded Forsell's dissertation on the subject which gave me a decent enough grasp.
It certainly is one of the more affordable of the options.
So as I understand it, I'll need two 5k resitors; one each for pins 2 and 3 with the pin 1 ground going to a bus bar and that bus bar is connected to the ezln72 0v? Then the stereo L and R pin 1's also get connected to the bus bar?
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Post by krcwell on Mar 31, 2016 20:18:10 GMT -6
Passive summing into transformers... Very cool.
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Post by rocinante on Apr 12, 2016 10:06:14 GMT -6
Alright, an update. And some decisions.
Well it turns out I am of one of about a million who have decided to take on the Neve-ish summing mixer. I knew there had to be a few but like it's actually ridiculous. Here's what is even more interesting; nearly every single post goes nowhere. A few show a finished product in the end somewhere usually a good deal of time later but most people it seems change direction. Or they just ended up buying a Dangerous 2Bus or 8816.
So here's what i have come up with after a little experimenting during some sessions lately.
I sometimes like using the groups in my mixer. I am not opposed to them. All in all even though I have 16 channels that are direct out (which on the ghost are also the selectable busses) from mixer to AD converters plus 2 for mixdown I could make by just using the groups. In the DAW I have made all my projects and sessions into 8 busses. It is a fine workflow and I am totally okay with the results (as a matter of fact very little has changed) So in all reality I have very little issue with having a 10 channel summing mixer. Maybe 2 stereo in and 6 mono in ?
So 10 channels.
Each with a switchable insert.
Each with mute, pan, and level.
Each with switchable direct out via hardwire bypass.
Two sets of stereo out with one for monitors or monitor controller.
Two inserts on the stereo master bus via majestic-12's stereo master insert switch pcbs.
Do I need an aux or two on several channels. Maybe 4 channels with 2 auxes? I know i do not need auxes on all 10.
Let me know your thoughts guys.
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