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Author Topic: Macro-tech 1200 / 2400 in a tri-amp rack  (Read 16175 times)

Samuel Rees

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #20 on: March 02, 2013, 09:45:48 PM »

The step-by-step would involve many calculations having to do with Ohm's law & other electrical formulas.  It's been a while since I compiled the needed calculations and put them into a spreadsheet.  I'll need to work through them again to make sure I still understand them enough to explain them.

If you get a spreadsheet together, post it! I can work backwords.
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Lester Seidenberg

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #21 on: March 02, 2013, 09:51:12 PM »

The .77 reminded me of something buried in the dark recesses of my mind.  After a little research this came up
http://upload.wikimedia.org/wikipedia/commons/0/04/Relationship_between_dBu_and_dBm.svg
The .77 may refer to unity gain on older gear.
Hope this doesn't cloud things up too much
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Samuel Rees

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #22 on: March 02, 2013, 10:13:50 PM »

The .77 reminded me of something buried in the dark recesses of my mind.  After a little research this came up
http://upload.wikimedia.org/wikipedia/commons/0/04/Relationship_between_dBu_and_dBm.svg
The .77 may refer to unity gain on older gear.
Hope this doesn't cloud things up too much

hmmmm
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Corey Scogin

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #23 on: March 02, 2013, 10:50:53 PM »

The .77 reminded me of something buried in the dark recesses of my mind.  After a little research this came up
http://upload.wikimedia.org/wikipedia/commons/0/04/Relationship_between_dBu_and_dBm.svg
The .77 may refer to unity gain on older gear.
Hope this doesn't cloud things up too much

The 0.77 V is technically 0.77459667 V which is 0 dBu.
Run a sine wave through a mixer and turn it up until the output meter reads 0 dBu and you'll get a 0.775 Vrms output.
To my knowledge, all analog mixers are 0.775 V at unity gain but will output as much as +22 dBu or more.  In the digital mixer realm, most meters are referenced to 0 dBFS (Full Scale) but the analog outputs will output +22 dBu or more at 0 dBFS.
« Last Edit: March 02, 2013, 11:16:51 PM by Corey Scogin »
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Corey Scogin

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #24 on: March 02, 2013, 11:09:38 PM »

Corey, did you get the ohm's on the drivers right? The 2445-J is 16 ohms and the high 2404-H is 8 ohms, if they're stock.

I did not get the impedance right.  I didn't see it anywhere in the specs.

So it's
Low - 2206H - 8 ohm - 600W continuous
Mid - 2445J - 16 ohm - 100W or 150W depending on high pass freq. I'll go with 100W
High - 2404H - 8 ohm - 40W continuous

So, for the mid amp:
Macro-Tech 2400
200W "program" into 16 ohms with an input of ~20dBu
Gain Knobs at 9

Gary Weller, Are these numbers making sense to you?  You caught my impedance calculation error so I'm wondering if you have your own method.

If you get a spreadsheet together, post it! I can work backwords.

All this talk has me questioning my calculations.  I'm pretty certain they are close but looking back at it, there are a few things I don't fully understand.  I'll send the spreadsheet if I can get more certain of my results.  I put it together years ago when setting up my QSC powered EV QRx rig.  Then, things were making more sense.  It's been too long since I've done any real math.

I'd love for an expert in this area to give some input.  Is it possible to calculate exact numbers for this sort of thing or is it best to do a hands-on approach of some sort?  How do you all set amp gain?


*EDIT: added detail for mid amp settings.
« Last Edit: March 02, 2013, 11:15:50 PM by Corey Scogin »
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Samuel Rees

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #25 on: March 02, 2013, 11:19:32 PM »

I'd love for an expert in this area to give some input.  Is it possible to calculate exact numbers for this sort of thing or is it best to do a hands-on approach of some sort?  How do you all set amp gain?

I'm kinda super glad that you've now asked the question. I'd kinda love a super pro to come here and drop some mad knowledge on this thread. It'd be one for the archives, I think.
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Corey Scogin

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #26 on: March 03, 2013, 02:05:07 AM »

I'm kinda super glad that you've now asked the question. I'd kinda love a super pro to come here and drop some mad knowledge on this thread. It'd be one for the archives, I think.

I searched for "Amplifier Gain" on the forums here and found a few helpful threads.  It seems it's a complicated topic that most don't want to address.
A sticky post with references would be helpful.

If you're still interested in the calculations I was using, I've put together a more simplified version of my spreadsheet showing the calculations here:
https://docs.google.com/spreadsheet/ccc?key=0Alxj6JiS3mztdHNfQS1nSUEyUUhldl8xV042U0Q3Rmc&usp=sharing

You can download that as an excel file to change the values or use it in Google Docs if you have an account.

This spreadsheet's calculations aren't exactly the ones I used earlier but the results are the same.
In order to use this spreadsheet for the 16-ohm mid driver, you'll need to figure out what the Macro-Tech 2400 is rated for at 16 ohms.  My other spreadsheet was calculating the amp power at a speaker's impedance based on amp sensitivity & gain but I removed those calculations because in some instances my numbers didn't line up with the manufacturers spec.
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Mark Oakley

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #27 on: March 04, 2013, 11:53:37 AM »

Are you familiar with this page?

http://www.poulpetersen.dk/Appn/gblimthr.html

-Mark
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Oakley Audio

Samuel Rees

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Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #28 on: March 04, 2013, 12:20:27 PM »

No, but thanks for the link.

This helps me understand some of the relationships here. I still don't understand how I would choose sensitivity (some have said 26 db is standard, but .775 seems to come up on sites like that a lot). I also don't understand how I could select an amplifier sensitivity and attenuation setting on the front to match a single driver in a triamp setup (especially with an amp with much greater output capability than the driver). I'm reading through some old threads but not sure how much I'm getting this.

How do people learn this stuff? Thanks so much for your help everyone!
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Tim McCulloch

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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #29 on: March 04, 2013, 12:36:38 PM »

At one time this excruciating gain matching mattered a lot, these days not so much with multiple places in a pass band's signal chain to raise or lower drive levels.

0.775v was used for the reason noted above - it matched 0dBu with a 600 ohm load.

From a practical, make-it-work standpoint you're over-thinking this.  Set your amps so their gains are relatively close (with the QSC kind of "in the middle" of the Crown options, I'd pick 1.4v) and make your level adjustments at the DSP.  IIRC gain matching is covered (get out your scientific calculator) in Don Davis' book "Sound System Engineering, 2nd ed."  There is a 3rd edition with chapters on optimization by Eugene Patronis and it's recommended for the updates, but the fundamental engineering material didn't change much if at all; you can probably find a used copy of the 2nd online.
« Last Edit: March 04, 2013, 12:38:26 PM by Tim McCulloch »
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Re: Macro-tech 1200 / 2400 in a tri-amp rack
« Reply #29 on: March 04, 2013, 12:36:38 PM »


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