MiniDSP - Page 7

Geeze, as someone pretty much depending upon this device for my sub "project" from what I gathered above I'm pretty disheartened.

I thought the spec sheet said it puts out 2 volts which would be fine, but if it's less than half of that figure we have a problem, Houston.

Penn: you seem to have a different experience with it? Hoping so!

James

The balanced version has 2v output. The unbalanced is limited to 0.9v output.

I'm also just getting into this low output voltage issue. Have been planning to use the Class D amps by HiFiMeDIY as very discussed on the DIY Audio Forum. They require 1.5 (unbalanced) volts for full output. From an old thread there it appears that a couple of resistors can be changedon the amps inputs to allow a lower voltage. I just posted a request for verification at that thread.

Looks like this .9 volt max output on the unbalanced version is a problem, or at least a potential problem for many of us. I'm going to make a post on the MiniDSP Forum "Suggestions" section asking that they have a way to increase their output. Might be helpful if others did the same.

Cheers,
Rod

Discussion at the PE forum. John used the unbalanced model that is why the output voltage is lower, this is a known spec difference and not really a big deal if you know about it ahead of time. If you have a high enough gain amp, or you don't run enough power for it to matter there can be benefits to the lower voltage because it allows the DSP upstream to run at a higher level, which has an impact on resolution in the digital domain. Still it can a problem for some, it would be nice to have some sort of gain (like 0.6-2.0v) adjustment to cover everyone's needs.

Really the apparently non-standard definition of Q at higher frequencies is probably the only real issue, and then only for those of us who measure the speaker, then model the EQ/XO in some software, and want to use those values directly in the miniDSP.

Good qualification...I'm in clear then I guess.

If that's the case it would seem to me everyone would be better served getting the balanced version then and simply running an RCA to XLR adapter, no?

James

This from John: "By the way, how do you get 2 V RMS out of the balanced unit when wiring it for single ended opt? The negative side of the output is shunted to ground which should result in 1 V RMS (max) between the positive side and ground at the input of the power amp."

I don't really anything about XLR, so I have no idea if this how they work or not.

On the standard single ended O/P board, the reason the output is limited to 0.9Vrms is because that is what the ADC/DSP/DAC chip used puts out for 0dBFS and they add nothing after it. Adding gain via say another opamp is getting difficult because it runs on a single +5V rail and most decent opamps won't give a lot of swing run this way. There are some that I might use for subs, but not full range, so a (say) +/-12V supply would be needed for that. That would mean a new board in all probability and not in their 75x75mm format.

For the balanced O/P version, I'm guessing they've just added an inverting opamp to supply the -ve out.

As for the suggestion of just changing the NFB resistors in an existing poweramp to get more gain, I would check with the designer/manufacturer first.

Might the fix for the miniDSP's level issue be as simple as a car-audio line driver (such as an AudioControl Matrix for a multichannel system) on a 12V wall wart?

Would the Behringer MX882 be the best of a good option for multiple outputs.

The last thing I want to do is spend $150+ and wait "x" amount of time for a device that won't allow me to realize 100% use of the amp I also spent $500 on.

So am I now understanding that starting with an RCA at the sub pre-out and going to XLR - minidsp - XLR - amplifier will still result in a voltage shortage at the amp and thus, decreased output?

Wow. If this is the case (low voltage ~1V) with either unit (balanced vs unbalanced), how on earth is ANYONE seeing anywhere near their max output potential while using these?

James

I made a post in the Suggestions section of the MiniDSP forum. Here's the companies response (hope it's okay with AVS to quote it here):

Rod,

Indeed the miniDSP un-balanced outputs 0.9Vrms max. That's based on the fact that it's using a 5V USB supply and supposed to be part of a consumer audio chain of devices. Adding output opamps + modifying the power supply section would mean added cost. Maybe future products based on 12V supply...

If you need higher output capability, using the miniDSP Balanced would be the way to go (2Vrms max). Simply run the input as a Pseudo Balanced/forward referencing which is actually very good at removing the common mode noise inherent to unbalanced connection. Then connect the output as shown on the user manual. The miniDSP could even turns itself into a preamp doubling your gain!

DevTeam

I don't understand what they mean by "run the input as a Pseudo Balanced/forward referencing", nor have I had a chance yet to look at the manual for the output connections. But it does seem as another poster here said that using 1/2 of a balanced 2 volt signal will result in a 1 volt signal. What am I misunderstanding? Think I'll go look at their manual now - but did want to get their response here right away.

Rod

I do not necessarily disagree with you at all, Penn- perhaps except slightly in the DYI point, as I read on their site in multiple areas how they are specifcally attempting to cater to the DYI'er...perhaps just not specifically to this scenario (powering passive subs).

I'm really just saying that this may not be "best" for my particular application and therefore it wouldn't make a lot of sense for me to spend a decent sum of money on it, nor time, if indeed a better option exisits.

That said though, I haven't heard of too many more standalone devices (nevermind external amplifiers) that will give me the only thing I'm really looking for: sub 10hz filtering.

Suggestions?

James

Hi Penn,

If you are talking about the voltage issue, did you see my post above where they responded to my post on their forum?

Rod

Not all pro amps have low input sensitivity.

The Peavery ipr's are .775V, for example.

^ Yep, I'm looking at a QSC rmX 1850 now and that's 1.16- closer than a few at 1.4 I was considering.

As relatively unlearned in this arena I just want to ensure I'm doing everything as "most correct" as possible.

I'd imagine a line driver would still be doable between the minidsp and amplifier if absolutely necessary?

And out of curiosity, can you simply look at an amplifiers min sensitivity required and what you have and come up with an estimate as to your maximum power?

For example: If the balanced version can ouput 1.00 volt and the QSC sensitivity is 1.16 volts sens, can you divide the output by the input (1/1.16), come up with 86% and then look at its max output in bridged 4 ohm load format (2400 watts) and then calculate: 2400 X .86 to arrive at a maximum of 2,064 watts?

I realize published specs are not 100% accurate and that's prolly an 8 ohm sens rating, just wondering if the that's above board in theory.

If it is by chance, I'm sure I'll be fine as it would appear even 1 volt out of the dsp would drive this QSC fine.

Just curious too, I suppose.

thanks,
James

This is a post on my thread at MiniDSP from the DevTeam:

@ John,

Increased output gain of 2Vrms is indeed available on the miniDSP balanced version as mentioned by Theresa. These are meant to run off of a 12V Power supply and therefore can easily derive the split rail supply required for the op amps.

Hoping this clarifies,

DevTeam

The John they are adressing is John.Reekie - I don't think he's the John posting here.

Penn when you get your balanced MiniDSP can you test it's output voltage with a single ended output connection? Would be most informative for many of us here. I also am curious how they can get 1 volt single ended from a 2 volt balanced.

Thanks,
Rod

^ Wait a second...won't must of us be going from an RCA (single) to an XLR to the minidsp to XLR to an amplifier?

So you mean going from a single ended RCA to a balanced output, correct?

Although it's not truly balanced, also correct?

Perhaps I'm lost again though.

James

^^^ Easily, The 'balanced' signal is likely the outputs of a pair of opamps, one + polarity, one - polarity of 1V each. The 2V O/P is the difference between them (1-(-1))=2. So if you short one side to ground you only have 1V.

Edit: my ride turned up as I was typing this this morning, but form one polarity to either + or - will also only give 1V if using it this way.

hey folks, would i need one of these for two sealed 15" subs?

Penn,

This may take a little while to get ready for measurements. Here's how I would go about it (others may have some better ways) and keep in mind a lot of these steps you need to do anyway to use it:

1. Get your instruction manual out.
2. Wire up your 12 volt supply.
3. Hook up the USB to your computer.
4. Install the software plugin you are going to use on the computer and get a little familar with it especially how to set input and output levels.
5. I assume you are going to connect the input to a single ended source (RCA).
6. Get a cable together with RCA on one end for the source and bare wires on the other end. Connect the bare end to the input terminal strip per the instruction manual - Unbalanced connection.
7. For now we wont wire the output to anything. I just hope that the output voltage wont be higher than normal with no load. If someone thinks it might be then we should go ahead and connect it to your amp.
8. I believe you are running balanced to your amp. If so when you do hook it up you will want a cable with an XLR on one end for your amp input and bare on the other end to connect to the Output terminal strip per instruction manual - balanced connection.
9. We will need a steady sine wave signal on the output of your source (Preamp?). Something around one Khz would be good.
10. You will need a meter that will read true RMS. Do you have one? Or a scope?
11. You also need to know what input sensitivity on the MiniDSP you are set for. Is it .9v or 2 volt?
12. I believe their software has an input level display. If so we want this to go to 100% as you turn up the signal on your preamp.
13. Assuming you do have single ended input from your source connect your meter across signal and ground on the input terminal strip. The meter should read either .9 or 2.0 volts depending on the MiniDSP's sensitivity setting.
14. We now know that we have 100% input to the MiniDSP.
15. On the MiniDSP software set the output for 100%.
16. Read the voltage on the output terminals, I believe from + to - since it's a balanced signal. (Someone please correct me if I'm wrong on this.) It should read 2 volts RMS if the factory is giving us the straight scoop.
17. It would be helpful for those of us planning to use single ended in and out if you would read the output voltage with the output connected per the instruction manual for unbalanced output. That is connect a jumper on the output terminal block from S to -. Now read the voltage across + and -. It should still be 2 volts if what the factory is saying is correct. This is the reading some of us are questioning.

Whew - sorry that got so long Penn. Hope it didn't scare you away. As I said before most of the steps you are going to need to do anyway to use it. Basically what we are doing here is to put a 100 % input signal to the DSP, confirming with a voltmeter that it is in fact 100%. We are then adjusting the mini DSP software to give 100% output, and finally reading the output voltage on a meter or scope.

If anyone finds errors or omissions in these instructions, or a simpler way to do some of it, please comment.

Good luck.

Rode

Just wanted to say that I downloaded the two-way advanced plugin last night and it took no more than 20 minutes to manually adjust 5 biquad filters to smooth out my sub response within REW, import that into the plugin, add a high-pass filter as a crossover and upload it all to teh miniDSP. Easy as pie!

I couldn't, however, figure out how to get REW to design the (six) filters automatically. How is that done?

9. We will need a steady sine wave signal on the output of your source (Preamp?). Something around one Khz would be good.

Better yet would be a test DVD/BR with test tones at 0dBFS into the AVR digitally, so you can also measure what levels the AVR puts out at what VC settings too. Anyway, start low and work your way up in level, and remember you will need to give it full scale on the input to get max output.

16. Read the voltage on the output terminals, I believe from + to - since it's a balanced signal.

Correct. Doing this with no load will be fine.

17. It would be helpful for those of us planning to use single ended in and out if you would read the output voltage with the output connected per the instruction manual for unbalanced output. That is connect a jumper on the output terminal block from S to -. Now read the voltage across + and -. It should still be 2 volts if what the factory is saying is correct. This is the reading some of us are questioning.

It will be interesting to hear what numbers come out.

A9X-308 - Good idea on the test tone DVD/BR.

MiniDSP has just posted an FAQ on the I/O voltage levels. It's here:

http://www.minidsp.com/support/faqs/...nidsp-balanced

I've gotta believe that what they are posting is true, so this is good news for those of us needing higher than .9 volt outputs in a totally single ended system. It's just a shame that we have to buy the more expensive balanced kit when we only need single ended.

Penn, unless you just want to do the exercise for learning and to confirm exactly what your system levels are doing (good to know) I'm satisfied with what the factory just put out in the chart. I'm now ready to order 2 balanced kits.

Cheers,
Rod