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miniDSP Low cost, modular Digital Signal Processor (DSP) kits for the DIYer from miniDSP.

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Old 31st October 2016, 09:57 PM   #31
DPH is offline DPH  United States
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You're good to go then.
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Happy DIYing, Daniel
(This space is occupied by the artist formerly known as Derfnofred)
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Old 1st November 2016, 12:48 AM   #32
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Quote:
Originally Posted by DPH View Post
Any chance you can share which models your amplifiers are? I'd have a much better chance giving you a good answer if I could read the user guide/datasheet.
Cheers mate! They are MC2 Audio T500, MC450 & MC650.

MC2 Audio - Full Range of Professional Audio Products
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Old 1st November 2016, 01:14 AM   #33
DPH is offline DPH  United States
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Welcome!

Rated input impedance is 10k (so yes), and the specs qualify that +6 dBm on the MC450 is to drive to peak level, so that's P = Vrms^2/Rload

That's 3.98 mW = Vrms^2/10k = 6.3 Vrms = 9 Vpeak

(Table: Power vs. dBm and Volts)

That's, um, a whole lot more than the T500. Something doesn't seem to add up. If those were either dBu or dBv numbers that were oopsed into "dBm" then they're a lot closer. Might not hurt to email the company. Either way, some serious arc welding equipment there.
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Old 1st November 2016, 01:27 AM   #34
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That's either a huge amount of headroom or we're missing something. Do we need to consider the output impedance? If we took that in parallel we would get a more reasonable value. If it were matched for maximum power transfer, that would lower our result by sqrt(2). Still a large amount (about 4 Vrms), but we can assume the output impedance of the preamp is much lower than 10k. Therefore the voltage to drive the 6 dBm at the input would also be much less.

Last edited by MitchMev; 1st November 2016 at 01:32 AM.
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Old 1st November 2016, 05:09 AM   #35
sangram is offline sangram  India
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dBm is a constant power measurement into 600 ohms. It is not dependent on the input impedance of the power amp. This works out to an input sensitivity of 1.5Vrms for a +6dBm source.
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Old 1st November 2016, 11:01 AM   #36
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Originally Posted by sangram View Post
dBm is a constant power measurement into 600 ohms. It is not dependent on the input impedance of the power amp. This works out to an input sensitivity of 1.5Vrms for a +6dBm source.
So really it's just a conversion of voltage (or current) if you're taking impedance to be constant. Why use this unit if the impedances aren't actually 600 ohms? I understand it's a convention, but why not just use dBu or dBV?
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Old 1st November 2016, 11:23 AM   #37
sangram is offline sangram  India
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I'm not sure why it's rated that way. Maybe to accommodate for voltage sag when the source is loaded down. Maybe it's to allow for worst case sag using long cables (which do load the output somewhat).

I do know some sources do not have constant voltage under load. Some may swing more into higher loads.

It is also possible that the input sensitivity is rather low, and this is not uncommon for professional equipment. +6dBm/10k works out to 6.5Vrms, which is not unheard of in a pro applications specially with requirements of high signal levels to keep S/N ratio up in noisy environments.

The only people who can answer this are the manufacturer, really. It is convention to specify dBm for a fixed impedance. If you would like the input voltage to be referred to the actual input impedance, it is more common to specify the input sensitivity in dBu.
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Old 1st November 2016, 12:06 PM   #38
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Quote:
Originally Posted by DPH View Post
Welcome!

Rated input impedance is 10k (so yes), and the specs qualify that +6 dBm on the MC450 is to drive to peak level, so that's P = Vrms^2/Rload

That's 3.98 mW = Vrms^2/10k = 6.3 Vrms = 9 Vpeak

(Table: Power vs. dBm and Volts)

That's, um, a whole lot more than the T500. Something doesn't seem to add up. If those were either dBu or dBv numbers that were oopsed into "dBm" then they're a lot closer. Might not hurt to email the company. Either way, some serious arc welding equipment there.
Thanks!!!

I'm not surprised by the MCs but the T500 seems unusually low.
9V is fairly normal, they were supposed to be connected to a mixing desk and my Soundcraft has a max output of +26dBu but my crossover will struggle I think with +20dBm.


Jeez dBs themselves are fine but I wish they wouldn't keep jumping about between all those different yet rather similar ones in the spec sheets.


Never thought of my amps as welding equipment. When I was welding my machine put out 160 and 220Amps and all 3 amps together only draw a measly 18A. ;-)

Last edited by Charles Darwin; 1st November 2016 at 12:10 PM.
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Old 30th December 2016, 01:38 AM   #39
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In case it may be helpful, I recently wrote to MiniDSP support asking essentially the same general question about levels. The first MiniDSP I purchased was an original 2x4. When I attempted to connect it directly to the input of a Crown CTS amp I quickly discovered its output level was too low, so I had to purchase a balanced - unbalanced converter box to boost the levels. This kind of threw a wet blanket on things as the converter boxes are about $100 + cables. However there is good news! See my email thread with MiniDSP below, but the short version is that *only* the original MiniDSP 2x4 has output levels that are too low for pro audio amplifiers. All the newer units have output signal levels that are more than adequate for direct connection to pro audio gear...

NOV 01, 2016 | 10:16AM HKT
Tech support team replied:
Hello.
In answer to your questions, it’s valuable to start with a calculator to translate dBu to Vrms (what’s shown on our specs)
dB dBu dBFS dBV to volts audio conversion digital - calculator volt to dBu and dBV dB mW SPL dB decibels 0 dBFS - convert dB volt normal decibels relatioship relation explanation analog audio absolute level true rms convertor converter decibel to dbf
-10dBu = 0.2Vrm
4dBu = 1.25Vrms
So as you can see, quite a lot of our platforms already go at 2Vrms and even much higher.
So for your example (please open datasheet + user manual), you will realize that you don’t need at all to modify the 24balanced. It has more than enough level for a pro amp. (4Vrms)
There is only 1 platform in the miniDSP line up (miniDSP 24, first product we released) that has low level (0.9Vrms). Most have 2Vrms or higher (up to 8vrms) so you’d have no problems. :-)



Just check the datasheet for more details.


Sounds good?
Best Regards

DevTeam

miniDSP Ltd
Office Hours: Mon-Fri 9am-5.30pm Hong Kong Time zone / Thanks for your patience.
OCT 31, 2016 | 06:22AM HKT
Original message:


I would like to know if your MiniDSP units can be used to convert consumer level signal inputs @ -10dB ( CD players, consumer stereo systems etc.) to Pro level @ +4dB out -- concurrently with other functions like EQ, crossover filtering etc...

For example, I would like to to use line level RCA outputs from a CD Player, connect these to a MiniDSP 2x4balanced, do 2-way crossover & EQ apps in the MiniDSP, then bump up the signal level to the level needed by a professional Crown Amp, then connect balanced outputs to the Crown amp's balance inputs.

Thank you!
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