Unbalanced to Unbalanced Cleanbox like Gain - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old Yesterday, 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 15 Old Yesterday, 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 15 Old Yesterday, 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 15 Old Yesterday, 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 15 Old Yesterday, 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 15 Old Today, 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 15 Old Today, 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 15 Old Today, 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 15 Old Today, 08:58 AM
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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?
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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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 15 Old Today, 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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Originally Posted by tjcinnamon View Post
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 15 Old Today, 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 15 Old Today, 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 15 Old Today, 12:40 PM
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Originally Posted by tjcinnamon View Post
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 15 Old Today, 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.

Display 2013 Samsung 75" UN75F6300 TV Media Xbox One X, Dune Solo, QNAP TS-453A NAS
Pre/Amp Marantz 7702mk2 Processor + DIY 11ch Icepower 50ASX2BTL Monoblock Amp Amp Build Link
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