This is diyaudio you could simply and cheaply add op-amp buffers to the passive volume control you already have
Hi scottjoplin,
I found this [1] that seamed appealing and ships in my region and this page [2] that explained what you said, but when I started thinking of how to do everything I realized that I also need a stable 5V power supply, insulation for everything, jacks, cables, it became to complex for my wishes and I can't guarantee the fidelity of the result (we paid 3000€ on the system and I don't want to reduce it's quality with my lack of electronics skills). Are you sure that there are no simpler ways of fixing this?
If changing the connections or limiting the volumes would work, then it would be perfect. Otherwise I would like to stick to simple tings, at most solder a resistor or, if absolutely needed, buy an extra device, but something that doesn't rip our pockets.
I feel bad for disappointing you, but even thou I like to handcraft things for my personal projects, I wouldn't like to go that path here.
I realized this is diyaudio and this is why I asked here, thinking that people here know the insides of how things work and thus offer pertinent advices, and indeed you do, but I know my limitations and hope that with your help I can achieve a good result in this problem.
I hope I don't sound lazy, I just don't feel comfortable to modify that much for this specific project.
[1] LM4562MA/NOPB Texas Instruments | Mouser Romania
[2] https://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.html
I found this [1] that seamed appealing and ships in my region and this page [2] that explained what you said, but when I started thinking of how to do everything I realized that I also need a stable 5V power supply, insulation for everything, jacks, cables, it became to complex for my wishes and I can't guarantee the fidelity of the result (we paid 3000€ on the system and I don't want to reduce it's quality with my lack of electronics skills). Are you sure that there are no simpler ways of fixing this?
If changing the connections or limiting the volumes would work, then it would be perfect. Otherwise I would like to stick to simple tings, at most solder a resistor or, if absolutely needed, buy an extra device, but something that doesn't rip our pockets.
I feel bad for disappointing you, but even thou I like to handcraft things for my personal projects, I wouldn't like to go that path here.
I realized this is diyaudio and this is why I asked here, thinking that people here know the insides of how things work and thus offer pertinent advices, and indeed you do, but I know my limitations and hope that with your help I can achieve a good result in this problem.
I hope I don't sound lazy, I just don't feel comfortable to modify that much for this specific project.
[1] LM4562MA/NOPB Texas Instruments | Mouser Romania
[2] https://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.html
This is how impedance works in very simple terms.
The preamp output stage may be either a 'perfect voltage source', which most preamps come close to, or it may be configured to have a true 600 ohm impedance. The first example (the perfect source) may be described as '600 ohms capable' meaning it can drive 600 ohms without issue. That is really the most likely scenario.
If the preamp is giving 1 volt output we see that both outputs also have 1 volt present. The two traces overlay each other as both are the same.
Now we connect a 600 ohm load to each. The first output, the 600 ohm capable doesn't change, the true 600 ohm sees the voltage fall by half as the voltage is split equally across the two 600 ohm impedances.
Now we add a second 600 ohm across each. Again the 600 ohm capable output simply maintains the level. The true 600 ohm output sees the level fall again as now two thirds of the signal are across the 600 ohm and one third across the (now) 300 ohm load.
So the big question is what the output of the preamp is. Is it a true voltage source capable (as most preamps are) or is it really 600 ohm.
You could check this with a test tone (around 400 Hz) and measure the AC voltage at the output pins of the preamp. Set the volume to give say 1 volt AC and then add a resistor load (say 470 ohm or 680 ohm) and see if the level drops. If it drops a lot then the output really is 600 ohm. If it maintains level then its more of a perfect voltage source.
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Hi, no problem, I understand, it may serve your purpose to use as it is, you won't do any damage so don't worry about that. Adding a resistor(s) in series will attenuate the signal, the input impedance is measured across the input
Hi Mihai,
I would just give it a try without anything else.
As you see, the advice from TOA is rather useless, as adding a serialresistor will significantly reduce level. The outout impedance of the Behringer MDX is only 50 Ohms and can easily drive even two 600 Ohm inputs.
And as you supposed, the volume controls, when not turned up completely in fact increase the impedance that is seen by the driving source. The worst thing could be a bass rolloff, but I don't even expect that.
Alternatively, although it is not optimal of course, you could swap the positions of the compressor and the feedback killer in the signal chain and insert the Nanos between them. As the FBQ *should* cause no big difference in overall level this should work too.
Is this for some conference installation or similar?
I would just give it a try without anything else.
As you see, the advice from TOA is rather useless, as adding a serialresistor will significantly reduce level. The outout impedance of the Behringer MDX is only 50 Ohms and can easily drive even two 600 Ohm inputs.
And as you supposed, the volume controls, when not turned up completely in fact increase the impedance that is seen by the driving source. The worst thing could be a bass rolloff, but I don't even expect that.
Alternatively, although it is not optimal of course, you could swap the positions of the compressor and the feedback killer in the signal chain and insert the Nanos between them. As the FBQ *should* cause no big difference in overall level this should work too.
Is this for some conference installation or similar?
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Thank you very much for the responses.
Mooly, thank you for explaining, I think I understood that some amplifiers are affected by the resistance they drive while others not and we don't know which is the chase for the ones I mentioned. It's hard to test thou because the problem is the input to the power amplifier, not the output.
GeorgeK, I will try this and tell you how it goes.
The installation is for a church and having in mind that everything is stone (walls, floor, ceiling) we can only use quarter-half of the station's volume because of feedback, so, in our case at list, adding a resistor or limiting the controllers volume is no problem at all 🙂
Firstly we will let it work for a few days and then see if there are any differences in tone when using the processors in bypass mode / not using the processors at all and post the results. If there are slight differences I think they can be corrected with the graphic EQ or maybe we will add the resistors.
Thank you.
Mooly, thank you for explaining, I think I understood that some amplifiers are affected by the resistance they drive while others not and we don't know which is the chase for the ones I mentioned. It's hard to test thou because the problem is the input to the power amplifier, not the output.
GeorgeK, I will try this and tell you how it goes.
The installation is for a church and having in mind that everything is stone (walls, floor, ceiling) we can only use quarter-half of the station's volume because of feedback, so, in our case at list, adding a resistor or limiting the controllers volume is no problem at all 🙂
Firstly we will let it work for a few days and then see if there are any differences in tone when using the processors in bypass mode / not using the processors at all and post the results. If there are slight differences I think they can be corrected with the graphic EQ or maybe we will add the resistors.
Thank you.
The output Behringer MDX is rated at 50 Ohms unbalanced, so no problem here.
Specs for the FBQ's output read 60kOhms (60000 Ohms!), which I really think is a mistake in the manual. The german manual reads 60 Ohms, and I am sure this value is the correct one. Give it a try.
That's it 🙂 and we don't know which variety this is.
(If you did want to test it then you don't actually need a power amp connected, you are just measuring the preamp output voltage, first with a load and then without and seeing if there is a difference.
Alternatively, you can measure the AC voltage across the speaker output and see if the level is maintained as you parallel the amplifiers. You would not need a speaker attached to test... it would be to noisy anyway. Again a level of around 1 volt fine and most digital meters would measure that reliably)
Ok, one test done: the FBQ was the last processor, driving the amplifiers, and everything seams to work fine. And no volume change is noticeable at the interior (first amplifier) while changing the volume at the exterior (second amplifier) with the monitor controllers, nor when disconnecting the exterior amplifier, so I think this is good 🙂 If it holds a few days, I will put them in the correct processing order. Sometime later, when doing measurements for room equalization, we will see if inserting the processors changes the sound quality. For now, what is noticeable, something that sounds like clipping/distortion at loud input sounds into the microphones, but all the levels are far from clipping. I will try to see into this some other time because this could be a different problem (TOAs work at max 1v and the processors at +4dBv).
Seeing no change in volume when the exterior amp is connected sounds good.
You should test to see whether the clipping and distortion disappears when this exterior amplifier is removed.
If the distortion remains then the clipping is another issue.
If it does not clip then it means that the preamp feed to the amplifiers is distorting under the additional loading.
You should test to see whether the clipping and distortion disappears when this exterior amplifier is removed.
If the distortion remains then the clipping is another issue.
If it does not clip then it means that the preamp feed to the amplifiers is distorting under the additional loading.
Thank you, I will do that. And while I'm at it, maybe I'll add the resistors too. What do you thing, is this good [1] for connecting one at the red wire for each PWR AMP IN? From my little electronics knowledge it should lower the line level from the +4dBv of the processors to the 2v PP (I think this is what they mean by 0dB = 1V from their specification) of the amplifiers and should also increase the input impedance a bit, 2 in one 😀
[1] 750/0.25 W 1%
[1] 750/0.25 W 1%
Its not really possible to put an exact figure on how much the resistor would cut the level because it works in conjunction with the input impedance figure (which we don't know for sure).
Adding the resistor will raise the impedance but it will only 'add' to the unknown figure. If that is quite high then the effect becomes negligible.
For example a 10k input impedance on a power amp would be just 10750 if you add the resistor.
I think you need to test it first (as I mentioned earlier) and see if the distortion is caused by the additional loading of the second amp. If it is not then you can leave things as they are and look elsewhere for the distortion problem.
Adding the resistor will raise the impedance but it will only 'add' to the unknown figure. If that is quite high then the effect becomes negligible.
For example a 10k input impedance on a power amp would be just 10750 if you add the resistor.
I think you need to test it first (as I mentioned earlier) and see if the distortion is caused by the additional loading of the second amp. If it is not then you can leave things as they are and look elsewhere for the distortion problem.
Yes, I presumed the power amplifier is a true 600 ohms, thus from the 4.5V of the processors a bit less then 2V would remain for the amplifier. If the levels don't change (because now with the levels at half for the processors the amplifier clips) then we would also know the amplifier is 600 ohm capable and not true 600 ohms. I'm glad I understood this 🙂
This would have been nothing we would have expected. Lo-Z outputs like the Behringers' can drive their loads nearly independently from each other or total load, as long as you do not go below a certain minimum load impedance.
I told you that the worst thing that I expected to happen would have been a slight bass roll-off. And even if so, this pobably would not do any harm in a church environment.
Did you use the volume controllers? How do they work?
So far they seam to work perfectly, constant and gradual attenuation on the entire race of the wheel. It however seams a bit more abrupt at high volume, but not something to bother. And I don't hear sound coloration at different volumes.
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