Unbalanced to Unbalanced Cleanbox like Gain - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 69 Old 06-15-2019, 08:52 AM - Thread Starter
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Unbalanced to Unbalanced Cleanbox like Gain

I have some amps that are just straight amps but I'd like to have a gain knob on them, not just an attenuation knob. The amps only have an RCA (unbalanced) input. I used an ART CleanBox and it really can add gain but my AVR has unbalanced and the Cleanbox can only output balanced when the input is unbalanced.

Basically, I would like the CleanBox gain but in an unbalanced to unbalanced configuration.
Not sure if something like this would work: https://www.performanceaudio.com/rol...ine-mixer.html
I like how on my plate amps they have a gain knob. Thoughts on how to add gain knob like functionality to a consumer amp?

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post #2 of 69 Old 06-15-2019, 08:55 AM - Thread Starter
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This is promising: https://www.amazon.com/rolls-MX22S-M.../dp/B007EY7MH4

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My old Yamaha receiver has always had a weak subwoofer signal, I used the ROLLS MINI MIX to increase the LFE signal to my two home theater subs. What I really liked about it is, you can really fine tune exactly how much bass you want without menus or EQ calibration.
https://www.amazon.com/gp/customer-r...SIN=B007EY7MH4

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post #3 of 69 Old 06-15-2019, 11:15 AM
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The gain knob on your plate amp is likely also an attenuator, even if they label it as a gain adjustment. Amps generate a static voltage gain to the input signal, typically 26dBU, 32dBU, etc. depending on the application. So irrespective of the knob setting and if it’s mounted to a plate or inside a box, the gain being applied to the signal is static.

When you add another box like you describe you are basically adding another amp stage, which just has its own much lower static gain, plus its own attenuator knob. Any noise added in this stage is also being amplified by the next amp and might also be more input voltage than your existing amp can handle, requiring you to then attenuate back, so you should be careful and ensure you really need it.

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post #4 of 69 Old 06-15-2019, 03:51 PM - Thread Starter
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Originally Posted by FriscoDTM View Post
The gain knob on your plate amp is likely also an attenuator, even if they label it as a gain adjustment. Amps generate a static voltage gain to the input signal, typically 26dBU, 32dBU, etc. depending on the application. So irrespective of the knob setting and if it’s mounted to a plate or inside a box, the gain being applied to the signal is static.

When you add another box like you describe you are basically adding another amp stage, which just has its own much lower static gain, plus its own attenuator knob. Any noise added in this stage is also being amplified by the next amp and might also be more input voltage than your existing amp can handle, requiring you to then attenuate back, so you should be careful and ensure you really need it.
So my Rhythmiks get that much louder than my MBM's? The rythmiks are at about 12 oclock to hit the 75dB calibration. I would never run them with the knob at full tilt. They would be very imbalanced. I bet the sub channel on calibration would be -15dB.

How do amps with no gain knobs work? How could I run the speakers connected to those hot?

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post #5 of 69 Old 06-15-2019, 05:28 PM
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Originally Posted by tjcinnamon View Post
So my Rhythmiks get that much louder than my MBM's? The rythmiks are at about 12 oclock to hit the 75dB calibration. I would never run them with the knob at full tilt. They would be very imbalanced. I bet the sub channel on calibration would be -15dB.

How do amps with no gain knobs work? How could I run the speakers connected to those hot?
amps with no gain knob provide a fixed amount of gain.

If you want increased levels out of them, you adjust the output level of your avr.
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post #6 of 69 Old 06-16-2019, 05:25 AM
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Quote:
Originally Posted by tjcinnamon View Post
Basically, I would like the CleanBox gain but in an unbalanced to unbalanced configuration.
Not sure if something like this would work: https://www.performanceaudio.com/rol...ine-mixer.html
Did you check the specs on that thing? No frequency response spec, no THD spec, no S/N spec. Why would you want something like that in your signal chain?

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post #7 of 69 Old 06-16-2019, 07:10 AM - Thread Starter
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Originally Posted by Wayne A. Pflughaupt View Post
Quote:
Originally Posted by tjcinnamon View Post
Basically, I would like the CleanBox gain but in an unbalanced to unbalanced configuration.
Not sure if something like this would work: https://www.performanceaudio.com/rol...ine-mixer.html
Did you check the specs on that thing? No frequency response spec, no THD spec, no S/N spec. Why would you want something like that in your signal chain?

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I would have liked to avoid it but the Crown XLS2002 .775 mode doesn’t work. This was the only way I could get any appreciable volume out of it.

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post #8 of 69 Old 06-16-2019, 07:50 AM
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You can easily convert the Clean Box’s balanced output to unbalanced with an XLR to RCA cable.

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post #9 of 69 Old 06-16-2019, 08:58 AM
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So my Rhythmiks get that much louder than my MBM's? The rythmiks are at about 12 oclock to hit the 75dB calibration. I would never run them with the knob at full tilt. They would be very imbalanced. I bet the sub channel on calibration would be -15dB.

How do amps with no gain knobs work? How could I run the speakers connected to those hot?
The plate amp might just be designed to hit max power with lower input voltage, run at higher static gain, etc, so the sub could seem like it's louder relative to competing products to buyers. Maybe it's coincidence. Attenuator knobs don't necessarily apply their attenuation in a standard or consistent manner either, so the '12:00' position on one knob could be attenuating the input signal -3dB and the another could be -12dB. If you're really confident that you aren't hitting max power because you can't give the Crown amp enough input signal and don't want to use the clean box you have now, perhaps something like a MiniDSP2x4 balanced (or 2x4 HD if the in/out voltage is sufficient) is worth considering since it will produce several volts output and also allow you to apply DSP and/or static digital gain. And you'll be able to BEQ movies using the 3ll3d00d GitHub app.

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post #10 of 69 Old 06-16-2019, 09:10 AM
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What is your AVR trim setting? Turn it up to feed the MBM amp more signal, and turn down the gain on the Rythmik accordingly.

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post #11 of 69 Old 06-16-2019, 12:01 PM - Thread Starter
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Originally Posted by FriscoDTM View Post
The plate amp might just be designed to hit max power with lower input voltage, run at higher static gain, etc, so the sub could seem like it's louder relative to competing products to buyers. Maybe it's coincidence. Attenuator knobs don't necessarily apply their attenuation in a standard or consistent manner either, so the '12:00' position on one knob could be attenuating the input signal -3dB and the another could be -12dB. If you're really confident that you aren't hitting max power because you can't give the Crown amp enough input signal and don't want to use the clean box you have now, perhaps something like a MiniDSP2x4 balanced (or 2x4 HD if the in/out voltage is sufficient) is worth considering since it will produce several volts output and also allow you to apply DSP and/or static digital gain. And you'll be able to BEQ movies using the 3ll3d00d GitHub app.
With regards the the attenuation, if the gain knob is maxed it's 0dB (full signal) and will be outputting whatever is being sent from the AVR with no attenuation meaning that if it were flat and uneq'd there would be no possibility of clipping assuming I had enough power in the amp?

With regards to the MiniDSP 2x4HD, the .9 input on the MiniDSP 2x4 works great. However, the 2.0 input on the HD version is abnormally quiet similar to the Crown Amp without the Cleanbox amping up the line-input. I purchased both and had to return the HD model despite wanting to keep it. It seems that the LFE on the NAD 758v3 is too quiet for something that requires a higher input. The NAD 758 is a very old AVR that receives upgrade modules so it's not out of the realm of possibility that the LFE is weaker.

Low Output on Crown: https://www.avsforum.com/forum/155-d...rown-amps.html

MBM's not what I thougth: https://www.avsforum.com/forum/155-d...ng-so-far.html

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There were 2 issues: 1) the XLS voltage of .775 doesn't play nice with some AVR's. I purchased a CleanBox and that fixed it immediately. 2) I had the Mag tuned to about 60 and once I tuned it to 43ish Hz it sounds GREAT!!!
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The Crown XLS 2002 issue

So I had some serious issues getting the proper sound out of the Crown Amp even at .775v. It was brought up that a cleanbox would pump the gain. However, it made a large thud if I turned it off in the wrong order and I also didn't like all of the cords and (right or wrong) I didn't trust it.

You can enjoy the long threads here:

https://www.avsforum.com/forum/155-d...rown-amps.html
https://www.avsforum.com/forum/155-d...ng-so-far.html

The bridged amp solution

I tried some consumer amps and got great results. So I began to search eBay and bought 2 Rotel 981's that I can run in mono for an alleged 360W. They sound great. In classic AVS fashion I figured I'd try to blend via active crossover the MBM's with the mains and then run double bass (fronts to large).

Blending the mids and fronts with no LFE

So in order to do that I needed another amp (Rotel 981) in stereo and a MiniDSP 2x4HD because the regular miniDSP is not high fidelity enough for full range (and I needed the ports).

Input sensitivity issue (I think)

I had the same issue as I did with the pro amp and MiniDSP HD. I speculate it had to do with the input sensitivity on my NAD.

https://www.avsforum.com/forum/91-au...l#post57157676

So that went out the window. I needed to return the MiniDSP HD and one of the amps (on ebay, not easy).

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post #12 of 69 Old 06-16-2019, 12:02 PM - Thread Starter
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Originally Posted by FriscoDTM View Post
And you'll be able to BEQ movies using the 3ll3d00d GitHub app.
What is BEQ? Does that only work with the MiniDSP 2x4HD?

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post #13 of 69 Old 06-16-2019, 12:04 PM - Thread Starter
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Originally Posted by Augerhandle View Post
What is your AVR trim setting? Turn it up to feed the MBM amp more signal, and turn down the gain on the Rythmik accordingly.
I left the AVR alone but upped the miniDSP 2x4 (non-HD) for the MBM channels. The problem is I'm adding 2 more subs and will be out of outputs on the miniDSP. I'll have to get another one because I'm going to convert the MBM's to nearfield and want to run them super-hot but also will have them on a switch to turn them on and off. On for special occasions only.

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post #14 of 69 Old 06-16-2019, 12:40 PM
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What is BEQ? Does that only work with the MiniDSP 2x4HD?


Check the Bass EQ thread in the sub forum for info. It is a method developed by forum users to EQ bass using the DSP units. Most of the people seem to use the HD DSP but I use the Balanced DSP.

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post #15 of 69 Old 06-16-2019, 01:37 PM
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Originally Posted by tjcinnamon View Post
With regards the the attenuation, if the gain knob is maxed it's 0dB (full signal) and will be outputting whatever is being sent from the AVR with no attenuation meaning that if it were flat and uneq'd there would be no possibility of clipping assuming I had enough power in the amp?
You might want to try to measure the output voltage from your AVR or look up the specification, so you understand what the full signal voltage is. Every DSP or amp device is designed around a specific maximum voltage, and when the signal is under that value the signal should not clip but once you exceed the max input voltage the peak of the signal will clip and be limited to the maximum voltage. So if your AVR produces a maximum 1V signal and you use a DSP (or amp) unit that is designed for 0.5V maximum, any signal over 0.5V will clip and pass a flat top wave. For comparison if the DSP unit is designed for a 10V input signal and you pass a 1V signal, you should never clip because you'll never hit 10V.

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Originally Posted by tjcinnamon View Post

With regards to the MiniDSP 2x4HD, the .9 input on the MiniDSP 2x4 works great. However, the 2.0 input on the HD version is abnormally quiet similar to the Crown Amp without the Cleanbox amping up the line-input. I purchased both and had to return the HD model despite wanting to keep it. It seems that the LFE on the NAD 758v3 is too quiet for something that requires a higher input. The NAD 758 is a very old AVR that receives upgrade modules so it's not out of the realm of possibility that the LFE is weaker.
Based on this, it sounds like your AVR produces a max signal somewhere under 1V. Are you sure you didn't have the HD jumper set to the 4V input position? If you've got it set to 2V in and 2V out, it should pass the the signal right through, but if you have the jumper for 4V in and 2V out it would produce less voltage than is coming out of the AVR. With the HD unit set to 2V in, you should be able to pass a 1V signal and boost it further via the digital gain in the DSP.

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post #16 of 69 Old 06-16-2019, 07:14 PM
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Here we go again. I would be shocked if your pre-pro will not easily put out more voltage than your amps require to clip. The MiniDSP 2x4 is generally unsuitable for subwoofer duty if you listen loudly because it's has inadequate voltage input and output capability. It ends up clipping the input fairly easily and has an anemic output.
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Lol, my AVR puts out over 9V clean on the rca. I know not all do this, but most people just aren't setting their levels right or have some other issue.

fs input over hdmi, +12db mv, +10.5db subs


fs input over hdmi, +12db mv, +11db subs
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post #18 of 69 Old 06-17-2019, 03:06 PM
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Lol, my AVR puts out over 9V clean on the rca. I know not all do this, but most people just aren't setting their levels right or have some other issue.

fs input over hdmi, +12db mv, +10.5db subs


fs input over hdmi, +12db mv, +11db subs
The Denon's I've measured will do about 4.6Vrms when they start clipping. The Pioneer and Onkyo units I measured will do more (not as much as the 9Vrms you measured).
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post #19 of 69 Old 06-17-2019, 03:10 PM
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Originally Posted by Stereodude View Post
The Denon's I've measured will do about 4.6Vrms when they start clipping. The Pioneer and Onkyo units I measured will do more (not as much as the 9Vrms you measured).
That was a Denon 5308 btw.


Even 4.6Vrms is plenty.
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post #20 of 69 Old 06-17-2019, 03:13 PM - Thread Starter
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Originally Posted by Stereodude View Post
Here we go again. I would be shocked if your pre-pro will not easily put out more voltage than your amps require to clip. The MiniDSP 2x4 is generally unsuitable for subwoofer duty if you listen loudly because it's has inadequate voltage input and output capability. It ends up clipping the input fairly easily and has an anemic output.
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Lol, my AVR puts out over 9V clean on the rca. I know not all do this, but most people just aren't setting their levels right or have some other issue.

fs input over hdmi, +12db mv, +10.5db subs


fs input over hdmi, +12db mv, +11db subs
I'll run some tests once I get a miniDSP HD. I'm not sure what is wrong but the unbalanced input on the Crown is way quiet and unbalanced on my consumer amp works well. My Rythmiks kick the tar out of my MBM's irrespective of the frequency. Granted they are double ported but each are 12" woofers and the MBM's are running 98db sensitive with 380W on the consumer amp. Not sure why there's such a disparity between the 2.

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post #21 of 69 Old 06-17-2019, 03:17 PM - Thread Starter
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Originally Posted by Stereodude View Post
Here we go again. I would be shocked if your pre-pro will not easily put out more voltage than your amps require to clip. The MiniDSP 2x4 is generally unsuitable for subwoofer duty if you listen loudly because it's has inadequate voltage input and output capability. It ends up clipping the input fairly easily and has an anemic output.
How does that explain the low output on the HD version vs the NonHD? I'll order another one and check the voltage for the jumper.

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post #22 of 69 Old 06-17-2019, 03:52 PM
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Originally Posted by tjcinnamon View Post
How does that explain the low output on the HD version vs the NonHD? I'll order another one and check the voltage for the jumper.
Well, when set up correctly the HD is going to cut your output by 6dB (voltage in half). 4Vrms input setting since it only has 2Vrms output. The nonHD can't be set correctly for sub duty IMHO since it has only .9Vrms output and no input setting that will accept a realistic reference level receiver LFE out. However, they both have jumper settings that will let you achieve unit gain through the device.

Where do you have your master volume and your subwoofer level trim?
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post #23 of 69 Old 06-17-2019, 06:27 PM
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@tjcinnamon if you don't mind sir, I'd like to piggyback off of your thread as it seems we share a similar issue
@Stereodude I was wondering if you could help me out. I goofed up and bought a regular minidsp 2x4 for sub duty, thinking the .9v - 2v jumper/selector was in regards to the output I have a couple of the ROLLS MB15b Promatch and More, will this make up for the .9v limitation of the mini 2x4?

Will the following allow me to achieve a proper gain structure...no clipping?

1. Turn off Audyssey on my avr (SR7011), set MV to 0.
2. Ensure input sensitivity jumper is set to 2v on the mini
3. Play a 0db 40Hz test tone (Subs disconnected) and measure the sub out rca and adjust the sub trim until the output is 2v
4. Connect the sub out of the mini to the "ROLLS MB15b Promatch and More" and adjust the output knob until I get a desired non clipping signal to my amp (FP20000 clone)?
Am I good so far? Instead of a 40Hz tone, should I use pink noise?
Let's stop there for now. BTW, my meter has an oscilloscope feature so I can monitor the signal using it.

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post #24 of 69 Old 06-17-2019, 06:34 PM
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Originally Posted by johnson636 View Post
@tjcinnamon if you don't mind sir, I'd like to piggyback off of your thread as it seems we share a similar issue
@Stereodude I was wondering if you could help me out. I goofed up and bought a regular minidsp 2x4 for sub duty, thinking the .9v - 2v jumper/selector was in regards to the output I have a couple of the ROLLS MB15b Promatch and More, will this make up for the .9v limitation of the mini 2x4?

Will the following allow me to achieve a proper gain structure...no clipping?

1. Turn off Audyssey on my avr (SR7011), set MV to 0.
2. Ensure input sensitivity jumper is set to 2v on the mini
3. Play a 0db 40Hz test tone (Subs disconnected) and measure the sub out rca and adjust the sub trim until the output is 2v
4. Connect the sub out of the mini to the "ROLLS MB15b Promatch and More" and adjust the output knob until I get a desired non clipping signal to my amp (FP20000 clone)?
Am I good so far? Instead of a 40Hz tone, should I use pink noise?
Let's stop there for now. BTW, my meter has an oscilloscope feature so I can monitor the signal using it.
Generally, I'd say your method will not quite work. You seem to be overlooking a few things.

0dB 40Hz test tone from what source and in what format?
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post #25 of 69 Old 06-17-2019, 06:38 PM
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Generally, I'd say your method will not quite work. You seem to be overlooking a few things.

0dB 40Hz test tone from what source and in what format?
it is an audio file used in the Steve Mead DD-1 test disc. If that is insufficient, will the pink noise in REW work?

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post #26 of 69 Old 06-17-2019, 07:19 PM
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it is an audio file used in the Steve Mead DD-1 test disc. If that is insufficient, will the pink noise in REW work?
Well, if you only listen to CDs on your system and don't use any content with a .1 channel the test disc might work fine. Are you running all your speakers as large?

Otherwise you need a test signal that has a 0dFS sine wave in the .1 channel. I think REW with a HDMI output using ASIO can do this. Then you need to allow for extra signal level from redirected bass to not clip the input either. By the time you're done I expect you'll find you can only just barely adjust the subwoofer trim in your receiver low enough to ensure you can't clip the input on the MiniDSP 2x4 at reference with near worst case scenario content (with it at the 2Vrms setting). I'd expect the subwoofer trim will be at something like -12dB.
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post #27 of 69 Old 06-17-2019, 07:31 PM
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Originally Posted by Stereodude View Post
Well, if you only listen to CDs on your system and don't use any content with a .1 channel the test disc might work fine. Are you running all your speakers as large?

Otherwise you need a test signal that has a 0dFS sine wave in the .1 channel. I think REW with a HDMI output using ASIO can do this. Then you need to allow for extra signal level from redirected bass to not clip the input either. By the time you're done I expect you'll find you can only just barely adjust the subwoofer trim in your receiver low enough to ensure you can't clip the input on the MiniDSP 2x4 at reference with near worst case scenario content (with it at the 2Vrms setting). I'd expect it will be at something like -12dB.
Currently, all speakers are set to small. So your statement holds true for the 2x4 HD as well? Are you saying neither the regular 2x4 nor the HD is the correct piece of equipment for bass duty? In regards to input clipping avoidance.

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post #28 of 69 Old 06-17-2019, 07:47 PM
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It all depends on the gain of the amp.
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post #29 of 69 Old 06-17-2019, 08:01 PM
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Well my amp is the FP20000. As is everyone, I'm trying to get full output from the amp without any clipping.

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post #30 of 69 Old 06-17-2019, 11:02 PM
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Well my amp is the FP20000. As is everyone, I'm trying to get full output from the amp without any clipping.
Max output from the minidsp is 0.9Vrms.

The FP can be set to 44db of gain. It's max voltage output is 195V peak.

44db of gain is a voltage ratio gain of about 158.5. This gets you ~143Vrms output from the FP, which is ~202Vpk.

So the max output of the MiniDSP can max out the FP if it's set to 44db of gain and the level knobs in the front are not attenuated at all.
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