HEY JOEL - revisiting headroom on soundcraft ghost console..

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Post by Jim Williams » Fri Sep 11, 2009 7:28 pm

The reason is the available open loop gain of the opamp in the audio band. Many common devices may have well over 100 db open loop gain at low frequencies like 100 hz. At 10k hz 072 types have 40 db OLG. 5534/2 and other common audio opamps have 60 db OLG at 10k hz. That National part has 85 db or so. With large numbers of inputs, a summing amp will run out of loop gain at some point. Drop the distortion 25 db and the mix will open up.
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Post by joninc » Tue Sep 15, 2009 12:55 pm

bump for joel - paging joel...

also Jim - are these opamps residing in the master section or are you talking in each channel?
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Post by centurymantra » Wed Sep 16, 2009 6:57 am

I'm thinking Jim Williams is pretty on target here. I have a Soundcraft Delta with a master section that has been modded by Jim and I can run it REAL hot with it still sounding pretty great. There is, of course, a point where it craps out, but I can run it well above zero and get it pretty darn near the top of the meters with good results.
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Post by Jim Williams » Wed Sep 16, 2009 9:01 am

joninc wrote:bump for joel - paging joel...

also Jim - are these opamps residing in the master section or are you talking in each channel?
It's been since 1995 since I've been inside one. As I recall, the 5532's were used for the stereo mix as well as balanced outputs. The inputs were mostly 072's with a couple of 5532's used for faders. All of them should go but that requires some housecleaning.
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Post by joninc » Thu Sep 09, 2010 12:01 pm

again finding myself in the place where things aren't as open as i would like so i revisit this thread and reminds me of the question i asked joel but never got answered:

joel hamilton -

are you saying to ride the master fader down to keep the overall level in the mix buss at the right place (ie: around zero)? even with faders on individual channels hitting the red etc?
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Post by The Scum » Thu Sep 09, 2010 4:07 pm

are you saying to ride the master fader down to keep the overall level in the mix buss at the right place (ie: around zero)? even with faders on individual channels hitting the red etc?
The architecture flows like this:

channel output -> mix buss -> summing amp -> master fader -> fader amp -> output amp

(There's an insert point in there somewhere, but we'll assume that nothing's inserted, so it's moot for now)

You can see that the master fader is after the summing amp. So if you clobber the summing amp, all the fader does is turn down the already clobbered sugnal.

If you're concerned about running out of mix buss headroom, you'll need to pull down the channel faders.

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Post by joninc » Thu Sep 09, 2010 4:12 pm

that was my assumption too - but joel's post is a little unclear as he talks about slamming certain channels - maybe they are all going to busses that are turned low?
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Post by The Scum » Thu Sep 09, 2010 4:41 pm

I think that's what me means by
just up off the pegs on a lot of those channels
Scorching the bus/subgroup, but barely opening the fader that brings it back into the mix.

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Post by Sean Sullivan » Thu Sep 09, 2010 5:20 pm

Are you comfortable modify equipment? I completely re-did the master section of the Soundcraft Ghost at the studio and it's like a new console, it opened right up.

I believe I have a print out somewhere of everything I did. Send me a PM, and I'll give you some pointers. It's a combination of things I compiled from Jim Williams, Creation Audio Labs, and other sources.
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Post by joel hamilton » Thu Sep 09, 2010 8:42 pm

joninc wrote:again finding myself in the place where things aren't as open as i would like so i revisit this thread and reminds me of the question i asked joel but never got answered:

joel hamilton -

are you saying to ride the master fader down to keep the overall level in the mix buss at the right place (ie: around zero)? even with faders on individual channels hitting the red etc?
In the middle of a mix... didnt see this..
I am saying that I leave the master fader all the way up and keep the individual faders WAY lower than you would think. Like seriously barely turning things up at the channel in some cases, because they are multed and routed to like 4 places in parallel so they take up a lot of "space" at the mix bus even with the basic channel itself barely turned up.
Just pick an arbitrary spot that you think sounds good, and shoot for that on the main outs. Like WAY below "0". shot for something like -20, and then gain that UP a bit with a 2mix device of some sort, whatever you have. if you have a snazzy 2 channel EQ, use that. If you have a snazzy 2 channel compressor use the snazzy 2 channel compressor. Whatever. Just use some other amplifier to get your gain structure to sit in the right place at the main outs of that console.
I have even printed off of the main insert send instead of the main outs on that console.

Try anything.
I have even thought of the idea of borrowing a summing box with 8 channels and taking the group insert sends out to a passive summing box like the fulcrom (folcrom?) and using that to sum, and then returning the whole thing to the main insert return point after some sort of decent 2mix comp, if I was using one.
The bottleneck seems to be right at the main summing amps in the main L-R outputs. Every other point out of that console sounds a little better to me, and running the master section very, very low level seems to help with that.
Like i said, gain up your print levels a bit with a decent outboard device on the main outs, not in the insert. You can insert a 2mix comp and trim your levels down a little with something that doesnt fall apart when attenuating... maybe even just a pair of passive attenuaters (read "resistors") would work?!? You know, maybe like a pair of detented pots that you could insert at the mix insert point, and just click it down 3 db at a time and gain up the main outs an equal (ish) amount with something outboard and see if you can trick the whole system into a better overall output sound.
The main outs on that desk are really the achilles heel, aside from the CRM volume pot...
Maybe Jim would know how a custom, discrete summing amp could be made to take the place of the internal main outs.. maybe even something IC based, but with higher headroom, and xformers on the output? it would be a brilliant mid for the ghost, because the channels themselves sound really good, good eq, good overall tone... but they load up the outs so much that the cardboard tube of a mix bus just buckles...

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Post by Sean Sullivan » Fri Sep 10, 2010 6:41 am

Check it, these are plug and play modifications for the Soundcraft Ghost. You can pop in all these components without fear! I lost the document I made for the Ghost when I got a new computer, but here's what could recover:

Channel strip modification:
IC?s 1,3,4,6,7,8 with OPA2134
IC 5,9,10 with Analog Devices OP275.
IC 1 (mic preamp) with OPA2134. You'll need to bypass the voltge divider resistors (R12 and R13) with .1uf/50V ceramic cap to keep it from oscillating.
IC 2 (high pass filter) to TL072 because the stock NE5532 tends to oscillate


Master section:
IC 22 and IC 23 (Control Room Output): LME49860
IC 24 and IC 25 (2 Track A & B): OPA2134

That's all I can remember off hand.

For recapping, use this list:
http://www.underthebigtree.com/wiki/tik ... =Recapping
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Post by Jim Williams » Fri Sep 10, 2010 7:12 am

BurrBrown has a new chip out, the OPA1641/2/4 series. These are fet inputs with low bias current. They are 5 nv/hz/sq noise, 20v/us slew rate and draw only 1.8 ma like the 072. These are "rail to rail" designs so they put out more voltage for a given power supply than standard opamps. That increases headroom as these parts won't clip as early as 072/553x opamps.

Noise is below that of a 5532 opamp and since the inputs are jfets, measurable noise will go down compared to using bipolar input opamps like 5532. This is because resistors in the circuit add more noise than the opamp with fet inputs will.

Drop these in and noise drops, headroom increases, dynamic range expands. They won't require a larger power supply either. They are all SOIC only so require an adaptor for dip layouts.
Their OPA1612 makes a nice summing opamp in the master section.
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Post by underthebigtree » Fri Sep 10, 2010 5:18 pm

I've modded the daylights out of my Ghost, and now that I use it on a daily basis, I couldn't be happier. However, this project is not for the faint of heart. I am very experienced with soldering, having built a lot of DIY outboard gear from scratch, and though I handled all the recapping and cleaning tasks myself, I still sent the boards to Creation Audio Labs for rechipping. The IC's are soldered directly to the board, and the traces are very thin, so removing them is a recipe for immense frustration. The guys at Creation did a splendid job, and the peace of mind that came from them doing the work, and then testing each card before sending them back, was worth every penny.

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Post by Sean Sullivan » Fri Sep 10, 2010 7:21 pm

Having a Hakko 808 desoldering gun will help prevent the risk of pulling traces, as they are thin. I would also install op-amp sockets so you can swap them out easier in the future.

The 2 Track A and B go through TL072s and the master mix goes through NE5542. I used LME49860 in the master mix and OPA2134 for the 2 Track returns.

I really think that spending $50 on capacitors and op-amps for the center section will blow you mind in terms of what you'll get in return. It will be the best $50 you've ever spent on gear. If you aren't comfortable doing it yourself, send it off the Jim Williams or a capable TapeOper.
Last edited by Sean Sullivan on Fri Sep 10, 2010 7:27 pm, edited 2 times in total.
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Post by Sean Sullivan » Fri Sep 10, 2010 7:24 pm

For what it's worth, I find that keeping the meters in the "green" helps the Ghost from folding in. A simple way to do this if you are in Pro Tools or any DAW is to use the Trim plug-in and back off the level going to the console...most people seem to hit the DAW too hard. Yellow is the new red, I heard someone way.
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