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Old 6th December 2010, 01:53 PM   #21
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Quote:
Originally Posted by Wavebourn View Post
...and they don't need it, if mikes are good and properly placed.

When mastering you can use whatever outboard gear you need, but Baxandals in microphone inputs?!

As Michael said, balanced inserts would be much mode valuable.
I agree that Baxandals ALONE are not the sort of EQ you would expect on what the OP now calls a 'pro' mixer. As I said before they are quite limited but they do have their uses.

What I seem unable to get across to you is that EQ is not just about correcting deficiencies in other parts of the signal chain. It is an artistic tool used to help paint a sound picture so it is quite appropriate to use it on ANY instrument for that purpose.

Cheers

Ian
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Old 6th December 2010, 04:49 PM   #22
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What I seem unable to get across to you is that EQ is not just about correcting deficiencies in other parts of the signal chain. It is an artistic tool used to help paint a sound picture so it is quite appropriate to use it on ANY instrument for that purpose.
I totally agree with you that a paint brush is a good tool! But I can't imagine Leonardo wearing professional belt with many pockets, with flat painter's brush of the same form and size from Home Depot in each pocket...
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Old 6th December 2010, 05:23 PM   #23
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I totally agree with you that a paint brush is a good tool! But I can't imagine Leonardo wearing professional belt with many pockets, with flat painter's brush of the same form and size from Home Depot in each pocket...

Indeed. Nor can I imagine him with no brushes at all.

Cheers

ian
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Old 6th December 2010, 08:54 PM   #24
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The worst case is less than 2K. The 'small signal' output impedance of the CF may be 350 ohms but as soon as you get to realistic signal levels this ceases to be true. 10V rms into 2K is 7mA peak which is pushing it for a 10mA standing current and will certainly give you increased distortion.

Calculating distortion is difficult but in tubes it is almost always directly proportional to signal level. Best thing is to build the stage and try it driving 10V rms into 2K and measure the distortion.

Ian,
could you tell me how you obtained the 7 mA of current loss into the 2 K load?

Last edited by Antonio Tucci; 6th December 2010 at 08:56 PM.
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Old 6th December 2010, 08:57 PM   #25
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Indeed. Nor can I imagine him with no brushes at all.
Right; that's why pockets are needed, to put a needed brush in each, when needed! It is called Inserts for Outboard Gear, speaking Professional Language of Audio Engineers.

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Originally Posted by Antonio Tucci View Post
Ian,
could you tell me how you obtained the 7 mA of current loss into the 2 K load?
For a sine wave, 10V * 1.414 = 14.14V peak.
Ohm's Law: 14/2 = 7

But actual signals on outputs of mixers are not sine waves.
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Old 6th December 2010, 09:19 PM   #26
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Ok
Thank you for your kindness.

Antonio
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Old 6th December 2010, 11:07 PM   #27
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Originally Posted by Wavebourn View Post
Right; that's why pockets are needed, to put a needed brush in each, when needed! It is called Inserts for Outboard Gear, speaking Professional Language of Audio Engineers.
Unfortunately, analogies only work to an extent. Whatever your personal feeling about what a professional mixer should or should not include, the fact is that the majority of professional mixers today have comprehensive EQ per channel (in fact this has been the case for over 30 years). And they all include a Baxandal type HF/LF boost. They may be a more sophisticated version with switched frequencies but they are essentially the same.


They all have inserts too which may occasionally be used for EQ that is not provided by the channel strip but more often they will be used to insert special effects into a single channel.

Cheers

Ian
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Old 6th December 2010, 11:43 PM   #28
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Originally Posted by ruffrecords View Post
Unfortunately, analogies only work to an extent. Whatever your personal feeling about what a professional mixer should or should not include, the fact is that the majority of professional mixers today have comprehensive EQ per channel (in fact this has been the case for over 30 years). And they all include a Baxandal type HF/LF boost. They may be a more sophisticated version with switched frequencies but they are essentially the same.
Do you want schematics of professional mixers? I have some...
First of all, channel strip EQs are more than just Baxandals.
Second, they are zero insert loss, and third they are bypassable.

However, if you mean some cheap mixers for rock groups, they sometimes had Baxandals always on, non-bypassable, but is it your professional feeling on what professional mixer have to look like them?

Good luck!
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Old 7th December 2010, 01:18 AM   #29
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Hi Antonio,

Your general schematic explains a lot about what I meant when I asked the intended use.

From this, it looks like your mixer is for a special purpose:

10 input channels (duh) with mic amps and line inputs, selectable per channel, aikido mic amps.

Each channel has an aikido makeup gain amp ahead of a passive Baxandall filter.

Each channel has an insert that bypasses the makeup amp and filter.

The monitor is set up as four mono sends pre-EQ and pre-fader (despite what's shown on the other diagram...)

There are 3 main buses, 2 mono called "voice" and "bass" and a stereo LR with a pan control.

How the summing on the main buses actually works is not clear but feedback is your friend here.

So far this seems pretty straightforward for a live PA mixer for a small ensemble.

OK, the monitors. What you seem to have in mind is a 4x10 send matrix ala Allen&Heath small PA boards. You'll want to add a master volume for each monitor channel.

You only need one buffer for all 4 send pots on each channel and with the source as shown do not need RC coupling.

Can you calculate the low cutoff frequency of the RC network? Set the values to something that makes sense for your use, like 20 Hz or so.

R4 is not necessary.

For the choice of IC, I'd suggest looking at THAT Corp. for the balanced line driver. They have a nice single chip solution that has good common mode and one-side-shorted characteristics, which will be improvements on your circuit.

For the other opamps, anything with decent gain bandwidth. TL082, NE5532 if you want to get fancy. This is a really uncritical appication.

If you think you might one day want to use your monitor outs as effects sends or aux recording outputs, get a little more picky.

As far as the rest of the signal path, I'd say do go and study some more mixer schematics to look at summing techniques, etc. and start thinking about your gain and level structure interms of nominal level e.g. +4 dBu and headroom to clipping throughout your signal chain inside the mixer. Also think about the noise floor vs. signal levels as you have the gain structure at some extremes.

One example, why would you want more than unity gain from your line input to yout insert return?

How will you control the gain of the aikido stages, and how does that influence the channel noise with the fader all the way up?

Also I'd recommend thinking about your gain/level in dB and dBu, which make it a lot clearer and easier to understand (at least for others in the business).

No phantom power? Direct Instrument inputs?

For the input switching there are some clever ways to arrange relays for phase/mute/P48 bypass.

Anyway, it looks like you have a workable direction for your specific purposes.

cheers,

Michael
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Old 7th December 2010, 04:47 AM   #30
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Michael,

I thank very very much for your long, critical, and helpful reply.

The mixer was born as a project for my son (16 yrs) ... that has a musical group.

After reading your reply ... I got some doubt whether we'll be able to realize such a complex device. I've only a little experience in Electronics and tube amp (I'm a medical doctor), even though I have realized several tube amplifiers and numerous other electronic devices.
In addition, that project requires considerable costs and time (the last not scaring me).

Profiting of your experience (you are an engineer) and before embarking into a such complex project I'd like to ask if you think that the the game worth the candle (effort) ... in order to avoid an icarus flight.

Many thanks ...again

Antonio
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