Computer Recording Master Section

[dsouku]

Hello all,

I am new to this forum and would like to say Hi to everyone first. Hi. I am sort of new to the DIY thing and would like to dive in and give it a try. So I thought of a project I would like to start with but need some help from others. I have some electronic experience and can work a soldering iron so I am not going in totally blind.

Project: Build a rackmount box that does basic master section stuff from a console. Like Talkback, Speaker Selection, Master Volume, Dim and Cut, VU Metering for the 2 Mix and also would like to have 2 headphone amps that are able to be switchable from the 2 mix to the cue mix.

Examples: There are a couple of these products out on the market today, Like the Dangerous Music MQ, and the PreSonus Central Station, but they are very expensive and I am sure I could build one for a whole lot cheaper. What I am not sure of is getting all of this to work together. I have broken each section down and tried to find a schematic for each section and deal with each one seperatly.

1. Talkback
2. Headphone Amp
3. 2 Mix VU
4. Main Volume, Dim and Cut
5. Speaker Selector
6. Power Supply

What I specifically need is help with laying this out in a schematic and getting this all organized. I have never designed anything like this before and would appreciate the help. I don't think that this is too complicated of a project, but then again I could be wrong. Maybe this is too much to tackle for a first project, but I think if I concentrate on a section at a time it shouldn't be too bad.

Thanks,
David

 

[Kev]

YEP
this is one of my backburner projects and has been so for a while.

I've had a few attempts and these have ended up working models BUT as the customer demands change so easily I haven't been able to come up with a single solution.

New ideas is to make it modular in both building blocks inside each rack box and the rack boxes themselves.

I see a patchable set of rack box solutions to suit needs and be adaptable as needs change.

Talkback and HP amp could be one module
... even then it could have line out to feed other HP amps as the cue sytem gets larger. I have one of these.

2 Mix VU is probably a unit of it's own as it would likely be mounted on the work area. A simple buffered VU box will do the trick ... we all have these.

Main Volume, Dim and Cut ... Speaker Selector ... Power Supply
This is the most difficult as there is a group out there that wants the main signal path to be passive.
Dim Cut ... probably means an active circuit and may use VCA's ... this can be adapted to surround sound OFF a single control pot. I already have one of these.

.. as I said I've tried to make a single solution but have now decided a modular approach is more likely to please more people ...

must be remote controlled as I see no point to bring signal lines up tot he control surface and then back to the monitoring amps.

This will be a project at the DIY Factory ... one day. ... :roll:

 

[synthi]

Very good idea!

I was about to get one of theese master controls but I think they would kill my sound if I get the presonus or mackie stuff, the dangerous and other solutions are expensive, so a DIY master control with (the usual) top quality would be awesome.

Best regards,

Synthi

 

[Guest]

Nice idea
the speaker selection thing has been on my mind too...

I was going to have a look at Hugh Robjohns custom made box - made to a BBC standard
From a article for the magazine he works for (SoS) - this is how the BBC do it..
"but the common facilities are two rotary controls (Volume and Balance), with a trio of lever-key switches giving Dim and Polarity Reverse, Mono To Both and Mono To A, and Cut A and Cut B (BBC terminology for cutting the left and right speakers, respectively).
"
"Note, however, that the BBC monitoring panel doesn't possess a single Cut switch to mute both speakers simultaneously. Instead, a full mute is achieved by selecting Mono To A in combination with Cut A. "
"Finally, the polarity-reversal feature inverts the right (B) channel at a point before the mono switching. Thus, by selecting the polarity reverse and a mono mode together, it is possible to listen to the difference signal (A-B). "

More info in the Oct 04 edition - it is a side bar to the review of the Presonus Central Station

 

[Kev]

We have had a couple of threads here and at the old place about these things.

I feel that once you have an idea of what you need and have trialled it with a simple rats nest of components ... then to rethink it with a complex relay box to allow for remote controlling ... you might then be onto something that many people will like.

Mono in the passive world could still be a slight problem depending on your demands.

I see no problem with having side distribution channels that are active and a set of low priority speakers for the extras like M/S and Diff monitoring.
This side distribution is what also drives the metering and other sends that require active circuitry.

The main path might be passive and even the volume/attenuator could be relay based so as to allow for remote control.

For the digitally smart ones ... a PIC might provide for user stored presets. I would love to do this bit but I have zero PIC knowledge.

 

[Guest]

BUMP!!!!

Piccies of Hugh robjohns BBC Monitor controller here
http://www.cix.co.uk/~hughrobjohns/hr4_020.htm
As part of Frank's DIY Community Monitor Controller Project for the SoS Forum - here
http://www.soundonsound.com/forum/s...&page=0&view=collapsed&sb=5&o=&fpart=1#118645

 

[TomWaterman]

[quote author="Kev"]Main Volume, Dim and Cut ... Speaker Selector ... Power Supply
This is the most difficult as there is a group out there that wants the main signal path to be passive.
Dim Cut ... probably means an active circuit and may use VCA's ... this can be adapted to surround sound OFF a single control pot. I already have one of these.[/quote]

It all sounds good Kev, I'm currently in the middle of designing a mastering console/monitor controller and passive is a pain when you start looking at remote control, mono etc.

Dim cut could be an attenuator section switched in via a relay. User level can be set when built, changing the resitors or use an atty section with a pot for variable level.

must be remote controlled as I see no point to bring signal lines up tot he control surface and then back to the monitoring amps.

Another good point, however remote control means plenty of digital control. I was going for this but I have to admit I got cold feet about it all. Its really complicated, PIC programming doesn't seem so bad but getting PCB layout thats clean and won't pollute the analogue lines with crap is hard.

I looked at opto-coupling etc. Multi-layer board might be a neccessity and a couple of prototypes a muct to improve noise etc....putting the PICs to sleep when not doing anything is a good plan.

I got SCARED!! Its not a project for the average DIY'er.

Problem with passive is balanced/unbalanced.

If you go balanced, large switches are required and any unbalanced connection to/from the box faces the potential to short half of an attenuator.....some form of bullet proof I/O is a good idea for a comunity project.

Its cool if its a build for one guy in particular and they know what its interfacing with but for a crowd of DIYers each with diff requirements, active or transformer balanced seems more appropriate.

I stumbled across that SOS thread last night and like Hugh's suggestion about the Sowter TX attenuator....

I'm personally leaning towards a passive atty buffered by forssell gain stages, no iron in sight.

In the next couple of weeks I'll try and post all my schematics for critque etc. I was trying to go for a mono PCB that was controlled by a master interface. That was 6 boards could be mounted in a rack and control busses paralled for surround in the future.

-Tom

 

[Kev]

[quote author="TomWaterman"]I got SCARED!! Its not a project for the average DIY'er.[/quote]

designing it may be difficult for the average audio DIY'er but trust me ... once the design is done this IS a project for all of you.

most of the work is done but and out there on the net
Mikkel has a unit alive ( I think )

we just need some time to turn it all into a complete , easy to follow project.

if only I had more time

 

[mcs]

[quote author="Kev"]Mikkel has a unit alive ( I think )[/quote]
Yes, and I'll send you some parts to play with, if you want them... :grin:

Best regards,

Mikkel C. Simonsen

 

[Kev]

yes please

the DIY Factory is getting close and I should be able to clean up and move in soon.
This is one of the projects high on the priority list.
I'll force some time.

 

[TomWaterman]

I'm looking forward to seeing what you guys come up with....

Mikkel, do you have a different type of attenutator than the one in the mammoth thread a while back?

I was looking at ways to make other kinds of digitally controlled attenuators....specifically constant impedance bridged-t ones....

I calculated 8 stages; -0.25dB, -0.5dB, -1.0dB, -2.0dB, -4.0dB, -8.0dB, -16.0dB and -32.0dB for bridged-t.

Combinations of the 8 stages provide 0.25dB steps upto 63.75dB attenuation.....however I was worried about the signal going through upto 32 (I think) resistors at one time...noise problems etc.

What have you tried? How does the cascading of say 8 2k5ohm attys affect the input and output impedance of the whole string?

Cheers Tom

 

[pucho812]

I like this right here.

http://www.shadowhillsindustries.com/ coolest looking master section I have ever seen. Made by groupdiy member"mesmer"

 

[mcs]

[quote author="TomWaterman"]Mikkel, do you have a different type of attenutator than the one in the mammoth thread a while back?[/quote]
There were different types mentioned in the thread...

Combinations of the 8 stages provide 0.25dB steps upto 63.75dB attenuation.....however I was worried about the signal going through upto 32 (I think) resistors at one time...noise problems etc.

What have you tried? How does the cascading of say 8 2k5ohm attys affect the input and output impedance of the whole string?

Why would you want 0.25dB steps? I normally use 1dB steps, and that seems fine to me. The attenuators I use have a constant input impedance, but the output impedance changes. I have tested my boards with 100k resistors (with up to 66k output impedance), and it still works fine without noise etc. But keep the cables short of course :wink:

Best regards,

Mikkel C. Simonsen

 

[daArry]

Tom, sounds great - eagily waiting to peep the bits you've worked up so far I'm planning a monitoring/master section atm too...

I think digital control won't be prob to add for ppl that'd like it - what with some of the stuff mcs has cooked up with those Atmel's, or perhaps using the PIC based MIOS system..a modular approach would be cool so you can slice n dice a box to suit...

Mikkel, get anywhere with that p+g belt yet? :grin:

 

[mcs]

[quote author="daArry"]Mikkel, get anywhere with that p+g belt yet? :grin:[/quote]
Yes, I'm working on a new software version for my universal all-in-one multi-purpose control board - and belt fader support is one of the planned features :grin:

Best regards,

Mikkel C. Simonsen

 

[daArry]

:thumb: :guinness: :green:

 

[TomWaterman]

Well after talking to a bunch of MEs about monitor gain resolution, it became clear that fine calibration was a good thing.

If you use the bob katz monitor system it is easier to gauge the amount of compression/limiting applied to a master by looking at the monitor gain position. Smaller steps would mean a more accurate guestimate on levels.

Bob explains all this on his site in 'the honour roll'.
I was initially going for 1dB steps smallest but max attenuation was too large, anything over -60dB may as well be off IMO. So then I added the 0.5dB step, it still seemed like a lot of max attenuation in an 8-bit system, so I planned on 0.25dB. However thinking about it now, it could be cool to use 7 relays for attenuation with 0.5dB/step and the 8th for a hard mute.

[quote author="daArry"]Mikkel, get anywhere with that p+g belt yet? :grin:[/quote]

These sound cool, got a link? Are they expensive?

One stupid thing that I have been planning to look at: If you have 8 2k5 attenuators in series, will the input/output impedance still be 2k5?

The I/O impedance of the bridged-t atty is the series (Z) resistor which would be 1k25 in a balanced system. I'm guessing the I/O impedance will change just as if there were a bunch of resistors in series?

So with all 8 stages in the I/O impedance would be 20k balanced?

Any thoughts? Maybe I'm barking up the wrong tree here....

-Tom

 

[mcs]

[quote author="TomWaterman"]However thinking about it now, it could be cool to use 7 relays for attenuation with 0.5dB/step and the 8th for a hard mute.[/quote]
Sounds like a better idea to me. But why do you have to use 8 relays?

One stupid thing that I have been planning to look at: If you have 8 2k5 attenuators in series, will the input/output impedance still be 2k5?

Depends on the design. Could you post a part of the schematic?

The attenuators I make have a constant input impedance when they are loaded correctly. That way the input impedance stays the same as the input impedance of a single stage. And the impedance is the same no matter how many stages are switched in.

Best regards,

Mikkel C. Simonsen

 

[TomWaterman]

Yeah I spose I don't really need to use 8 relays, I was just thinking about the most resolution possible.

I like the 7 relay idea with a global hard mute.

I'll try and post a schematic this weekend. Its essentially 8 bridged-t sections which are switched in circuit or out of circuit by the relays.

Imagine one big long chain of 8 (or 7) attenuators, all with the same I/O impedance.

Cheers Tom

 

[mcs]

Shouldn't this circuit do what you want (apart from a missing relay)?

http://stiftsbogtrykkeriet.dk/~mcs/6bitatt.gif

Best regards,

Mikkel C. Simonsen