MiniDSP require signal boost with pro amps

Are we talking about subwoofers or other speakers?

It shouldn't be necessary if you feed a balanced (XLR) signal from the miniDSP to the pro amp especially if the amps are driving bridged mono or low impedance loads.

With the balanced, no.

(And with the unbalanced...also no. I tried it with my unbalanced and a Samson S-Convert, and the result was unacceptably noisy. The bump-box amplifies noise as well as signal.)

Depends on the amp; one reason I got Peavey IPR 3000 was that is that it needs only .775 V for full output

Unless I missed something the LFE output from a reciever is going to be in the several volt range, which is more than enough to push a pro amp to full power. The sub output is 10dB "hotter" than the mains and even if they're under 1V at 0dB (reference volume) the sub will be >3x that.

The balanced miniDSP accepts .9 V or 2V and outputs 2V, 2V should be enough. What amps or what is the input sensitivity of the amps?

Any signal booster does jack up the nosie floor if any; but it depends on what you use it for. As long as it is only for the subwoofer; there won't be any issue. For the mains; it is a big no no.

I am using Art CleanBox Pro to bump up the sub signal from Denon for Crown XLS1000 to run diy sub. I used it on Onkyo 809 also, which had terribly low pre-out signal i.e. 0.2V. Yamahas are no different. Only the high-end avrs like NAD or Rotel have in access of 1.2V pre-out sections.

All these mass market avrs esp Yamaha, Denon, and Onkyo (I've used them all) have terrible output voltage on their pre-outs and are a bad weak signal source to pro amps without a bump box.

If using a unbalanced output to feed the balanced miniDSP you should leave it set to the default .9 volt setting. It will then output 2 volts with a .9 volt input present, more than enough to drive the amp to full output.

I disagree. According to a Pioneer rep THX certified Pioneer Elites have:

output level for -20dBFs input , 0dB VR position => 150mV
output level for -20dBFs input , +12dB VR Position(MAX) => 600mV
output level for 0dBFs input, 0dB VR position => 1.5V

Based on my personal experience I believe the LFE output is even higher. See below.
I would disagree if you're using it on the LFE channel and are after reference level playback. You will definitely clip the input to the MiniDSP playing at reference with the jumper set for .9V. For example, my Pioneer Elite SC-05 can push the input of the of the MiniDSP to 0dB according to it's input meters at -10dB on the receiver's master volume in bass heavy demo scenes with the jumper at .9V and the SW output set at 0dB in the receiver. Even with the jumper at 2V the receiver could still overload the input with the extra 10dB (~3.16x the voltage) of signal level so the SW output would need to be trimmed down some to avoid overloading the input on the MiniDSP.

I wonder if that depends on the subwoofer. Most subwoofer drivers have pretty high inductance, and thus roll off earlier. The ones I specifically tested with the Samson S-Convert (Aurasound NS12-794-4A and Aurasound NS10-794-44A) are exceptions to that rule. The NS10 actually has rising on-axis response from 2-10 kHz, though a lot of that is cone break-up. Still, we're talking about a 10 with 18mm of xmax!

Perhaps with something that has a more "normal" response curve, such as an XLS12 (drops like a rock starting at 500Hz) the extra hash would be inaudible. But with the Aurasound drivers, one definitely hears extra noise when using an unbalanced miniDSP and bump box, compared to using a balanced miniDSP.

Forgive me if this is stupid question.

A typical AVR is almost always capable of driving a pro amp into clipping.
Why then a miniDSP device inserted between the AVR and the amp would make the signal insufficient?

I have directly measured the SW output of a bunch pre-pros or recievers Onkyo, Outlaw, Sony, Pioneer, etc... Every single one of them was capable of at least 5 volts. I've also measured the preout on the main channels a couple of times and these have been over 2 volts. The 3 Onkyo's have been capable of over 10 clean volts out the sw jack. 4-5 volts is plenty to make any pro amp work. The ratings that the manufacturers give for their preamp outputs are not maximum output voltages. There is an audio /home theater magazine that does this testing as part of their equipment reviews. Exactly who it is escapes me right now. (Anybody?)

The minidsp balanced starts clipping around 2 volts out and in which will be borderline with some big amps requiring the amp gain to be set nearly maxed out to reach full power which boosts the noise floor and the mini can be prone to having the input clip unless great care is taken to ensure that the receiver doesn't overdrive it.

If anything the tricky part is getting the mini to play nice with pro equipment not the receiver.

Got it. Thank you

Either you have enough output to clip the amp or not. You either have enough to calibrate your subs with the mains (75dB) or however hot you want to run them, +5, +10dB or whatever, or you do not.

That's it IMO. Determining either requires some objective tests. If you verified you can do neither then you need a signal booster. If you haven't actually verified it with a couple of simple tests then you probably don't need a signal booster.

Edit: I wanted to add that a signal booster boosts whatever signal it is getting so it is going to make the signal obviously hotter and the speakers a lot louder. Subjectively this is a no brainer. You plug the thing in and it jacks the volume way up. Of course there is a difference and of course it sounds better! That is exactly what the piece is designed to do. The question is not whether a booster boosts the signal. That answer is yes. the question is do you need the boost?

This might be a typical scenario.

Receiver is capable of outputting up to 5 volts

Amplifier can make maximum power with 1.25 - 6 volts depending on where the trim is set.
(A booster is not needed to get enough signal into the amp just awareness of where to set the gains)

You add a boost box into the line because you read that it might be needed to match up pro gear with consumer gear and you aren't really blown away with your subs output nevermind the fact that the amplifier trim is set at 50% the SW channel is at 0 and the master volume is at -20 while you listen to some music. So you slap the boost box in line and it amplifies the voltage 10x "Wow I have to turn my amp and receiver levels way down!" "That must be a good thing. I'm going to have way more output now!"

Wrong. It doesn't change the amount of voltage the amplifier takes to reach maximum power or the amplifiers maximum power and your receiver already could have provided that voltage easily. The master volume and channel trim on the receiver do not change how much voltage it can produce at maximum either. The trim on the amplifier does not care if you operate it wide open or at 20%. The amp puts out the same maximum power either way. By adding the boost box you are turning the receiver output way down and barely using any of its potential. If instead you were to use the voltage the receiver is capable of lets say 4.5 volts and set the amp trim to where it clips
at 4.5 volts you will end up with the amplifier trim turned way down and no need for a boost box. Do not be afraid to use the positive range of your receivers SW channel trim. Contrary to popular belief there is no reason not to do this. Clipping the receiver output? Doubtful to say the least, by the time this is happening your amplifier should be clipping and beating your subs mercilessly. If you did it this way you have one less piece of equipment, less cables, lower system noise floor, less response roll off in the ULF range and save yourself some money.
Edited by Ricci - 12/7/12 at 7:32am

+1 to this. I've run Denon to iNuke 12db hot on accident and there was more available. However, what input voltage is ideal for a pro-amp? 2.5v? 5?

One more thing....Is there anyone with a receiver plugged directly into a pro amp who cannot calibrate their sub system to 15dB hot, 90dB with the amplifier trim all the way up and their SW channel trim at maximum? Anyone? I am genuinely curious here. I asked this a couple of times long ago and no one ever replied, which I'm assuming means something.

Josh,

I have a follow up question to the gain structure walk through you posted in another thread.
Is anything changed when sub signal is split to multiple subwoofers? I have three subs, one powered by a pro amp and the other two are active.
when I am setting the trim level on the pro amp should I have the other two subs connected and powered to present realistic load? I general, how do Y splitters affect the signal?

It depends on the amp and the load. Usually pro amps need less than 2.0Vrms to make full power into 8 ohm x2. For subs no one using pro amps has a stereo 8 ohm load. The voltage requirement goes down with lower impedance loads.

Just FYI, I clipped my Crown XLS1000 today, connected directly to a HK AVR146. No amplifier box in between - so if I can clip, I don't need a booster.... Gain on the amp was at ~70% and I'm running the HK 6db hot. Again - I don't see why I'd need a boost, and there is no noise or hum - certainly nothing I can hear at clipping

Wrager, you might want to try this. I just received my Balanced MiniDSP and were in the same boat as you. I tried to run the MiniDSP with my system calibrated the way that it was but I was barely getting any sound out of my subs with the current setup. I have a Samson S-Convert that I was just using but wanted to eliminate anything I could in the chain so I decided to test out a theory that I had.

First, make sure that the jumpers are set to .9v. Mine came set to 2v on each input.

Second, I originally calibrated my system with my main levels at 0 and adjust my center and surrounds accordingly.

Here was my originaly level setting:

Mains: 0 dB
Center: -4 dB
Surrounds: -2.5 dB
Subwoofer: 0 dB (I previously didn't have a sub)

At these levels with my Onkyo Processor at -20 dB my speakers were very loud but the sub was nonexistant.

Third, lower all your speaker levels at the same rate EXCEPT for the sub. You might need to bump the sub up a little bit if needed. I kept on adjusting it until it was how I wanted it. I adjust all my levels down -8 dB except for the sub which is now at +3 dB. I had my Crown XLS 2500 amp dial 2 notches from max (just under clipping).

Here is my new level settings:

Mains: -8 dB
Center: -12 dB (The lowest setting possible for me)
Surrounds: -10.5 dB
Subwoofer: +3 dB

Four, which these new settings the levels of all your speakers remain the same but you'll notice that at the same volume setting as before (-20 dB for me) it won't be nearly as loud and you'll have to crank the volume knob up however much you lowered your levels. Since I dialed everything down -8 dB I had to crank my volume to -12 dB to get the same volume as before out of my speakers but what this did was give my sub out signal more power which is what my amp needed to be driven to its max. With this method and just a +3 dB increase in the sub I was able to clip my Crown (with it dial at max) at loud action scenes! Of course I dialed the crown back a little bit to prevent it from clipping.

I don't know what youre settings are but if you're able to give what I did a try it might work out for you. My onkyo sub level can go up to +15 dB or something like that. I didn't want to push it that high so that I didn't clip the signal going out. I instead decided to try to lower all my other gains to compensate. I don't know if it's psychological or not but by doing this the sound comming out of my speakers seemed to be a little fuller and my surrounds seemed to be a little more noticable than before. Overall, I'm pleased with the test and will adjust some more when I get done with my dual ported 10's build as it's going to be a lot louder than my sealed 10's that I'm running now.

Your Yamaha is probably capable of outputting far more than the Minidsp. I doubt it has anything to do with your Yammie at all and everything to do with the Minidsp only accepting and putting out 2 volts.

How high was the SW channel trim in the Yammie set during this? Maxxed?

This is really good advice. I do have a question though?.......Why should one set the minisdp input voltage to .9v? Would that clip the input on the dsp? I am about to receive mine in the mail and am learnig the best possible settings for the device before integrating it into the sub chain.

You most likely shouldn't if you're using it on your SW. You will clip the input if you push the volume.

ok that is what I figured.

So just out of curiosity, what harm is done by adding a bump box? Are there any significant reasons for not using them?

At least one of them has been shown to not have a flat frequency response. Meaning it will artificially roll off your bass.