I am thinking the 'standard' equipment is becoming more standard than ever.
I have
multiple digital sources S/PDIF >> SRC2496 AES/EBU >> DEQ2496 >> DCX2496 >> Active volume control >> amps/speakers
the SRC (in passthrough-mode) acts as a digital source selector
The DEQ for room correction and pretty lights
The DCX is DAC and active crossover, with some driver correction
I use the Altronics K-5600 (modified) as a volume control.
I won't mention the amps and speakers at this stage, as they are not much to speak of, and will be changing soon-ish.
I have
multiple digital sources S/PDIF >> SRC2496 AES/EBU >> DEQ2496 >> DCX2496 >> Active volume control >> amps/speakers
the SRC (in passthrough-mode) acts as a digital source selector
The DEQ for room correction and pretty lights
The DCX is DAC and active crossover, with some driver correction
I use the Altronics K-5600 (modified) as a volume control.
I won't mention the amps and speakers at this stage, as they are not much to speak of, and will be changing soon-ish.
Pulse-R said:
As long as you're using the analog inputs and outputs of the Behringer equipment, then there shouldn't be any need for the outboard volume control, right?
Besides, my Pioneer Elite receiver doesn't have a digital output for the 7.1 channels. It's all just regular unbalanced RCAs. However, I am using a Rane Balance Buddy BB-22 to bring that unbalanced signal to balanced +4dBu before it hits the EQ and xover.
No.chops said:
the analog outputs will be set relative to the digital stream running through the processor.
The digital side must be run at near 0db for the highest signal/channel in the processor. This will give a 775mV output which will drive many power amps to maximum. And leave no adjustment for volume control.
The tiny +-15db adjustment in the digital domain is more intended for balancing signal levels rather than volume adjustment and it is not recomended that these digital attenuators be used for such.
Even -15db will leave the analog signal too high for most listening occasions. I used around -25db to -40db of attenuation on the output before feeding my power amps.
AndrewT said:
I'm lost...
My receiver ONLY has analog outputs, just regular old RCAs. They are the preamp outputs for the front channels and center channel. Obviously, their output will vary with my turning the volume up and down on the receiver.
IOW, I will not be feeding this equipment a digital signal at all. It will all be totally analog. I don't want to be adjusting the system volume through the Behringer gear.
Are there any simple opamp-outputs (preferably balanced) that gets rid of the DC filter cap alltogether? Why is it even needed in a differential system?
And how 'bout a simple single ended input circuit?
I read through this whole thread a couple of months ago, and I can't remember any good answers to these.
And how 'bout a simple single ended input circuit?
I read through this whole thread a couple of months ago, and I can't remember any good answers to these.
Hi Novec,
I'm not aware of how to get rid of the DC voltage without caps but you can use Polyprop types to improve quality and you can use smaller values for tweeter and mid (C-µF * F-Hz = 1000). Without filtering the DC voltage the following opamp(s) might get a CMRR problem.
Here you get a simple and good analog IN circuit. C1 and C2 should be at least MKT (eg. Wima) type. For IC1 I would use LM4562. With R8 you can change gain setting. Instead of R10 there could be some kind of a zener diode.
I'm not aware of how to get rid of the DC voltage without caps but you can use Polyprop types to improve quality and you can use smaller values for tweeter and mid (C-µF * F-Hz = 1000). Without filtering the DC voltage the following opamp(s) might get a CMRR problem.
Here you get a simple and good analog IN circuit. C1 and C2 should be at least MKT (eg. Wima) type. For IC1 I would use LM4562. With R8 you can change gain setting. Instead of R10 there could be some kind of a zener diode.
Attachments
Thanks, oettle. Problem is I need a single ended input. It's probably a very simple thing to do, I just don't know how, and can't get any good search results on the forum. I won't need a DC input filter with the sources I've got now.
I'm still uncertain why a differential signal needs DC caps at all - doesn't the nature of differential eliminate the need for ground reference?
I'm still uncertain why a differential signal needs DC caps at all - doesn't the nature of differential eliminate the need for ground reference?
Thanks, Jan, I think I'll keep it single ended and go for that. I have some LM4562 left from the group buy, so I'm pretty much set to go.
I have a whole lot of good 2.49k resistors, but no 1k - is there any way I can use them instead? I don't need anywhere near the 4.8V output level the original circuit gives.
Oettle: I guess it's the IC2's job to generate the 2.5V for ADC reference? And the same chip can be used for both channels? And just to clarify - when going single ended, the negative input is shorted to ground?
Thanks a lot!
I have a whole lot of good 2.49k resistors, but no 1k - is there any way I can use them instead? I don't need anywhere near the 4.8V output level the original circuit gives.
Oettle: I guess it's the IC2's job to generate the 2.5V for ADC reference? And the same chip can be used for both channels? And just to clarify - when going single ended, the negative input is shorted to ground?
Thanks a lot!
Hi,
looking at the original DCX output circuit I would say that the first opamp stage is just the same as on the AK4393 data sheet. But at the output of this opamp Behringer uses a 47µF AC coupling cap. Reason for it might be that if the R values doesn't match exactly there will be some small DC voltage on the output?
looking at the original DCX output circuit I would say that the first opamp stage is just the same as on the AK4393 data sheet. But at the output of this opamp Behringer uses a 47µF AC coupling cap. Reason for it might be that if the R values doesn't match exactly there will be some small DC voltage on the output?
chops said:
I'm lost...
My receiver ONLY has analog outputs, just regular old RCAs. They are the preamp outputs for the front channels and center channel. Obviously, their output will vary with my turning the volume up and down on the receiver.
IOW, I will not be feeding this equipment a digital signal at all. It will all be totally analog. I don't want to be adjusting the system volume through the Behringer gear.
Anyone have anything to say about this?
One other thing I wanted to add...
"The digital side must be run at near 0db for the highest signal/channel in the processor."
Now how can the input signal stay at 0dB if music gets quiet and loud? That doesn't make any sense. Whether you keep the master volume at one spot or not, the signal is going to change regardless. People don't sit around all day listening to sine waves, at least I hope not anyway.
Hi,
assume any of your digital sources are going to send a max signal sometime during the performance. This is 0dbfs. Your digital processor should be set to allow that theoretical maximum to pass through so that none of the channels clip on this worst case signal.
Similarly, the analog input attenuator should be set to pass your highest signal input without clipping in any of the channels.
If you set the attenuators with spare to allow overhead as one does with an all analogue signal chain you will lose performance.
To maximise performance you must set your digital processor right at the top end (almost clipping) on a fully modulated input.
Setting this way does not allow any attenuation after the processing to alter volume.
The analogue outputs should be attenuated to alter your volume. Better would be to alter the gain of the following amplifiers but very few if any can do this and remain stable for all levels of gain likely to be needed for a normal range of volume adjustment.
assume any of your digital sources are going to send a max signal sometime during the performance. This is 0dbfs. Your digital processor should be set to allow that theoretical maximum to pass through so that none of the channels clip on this worst case signal.
Similarly, the analog input attenuator should be set to pass your highest signal input without clipping in any of the channels.
If you set the attenuators with spare to allow overhead as one does with an all analogue signal chain you will lose performance.
To maximise performance you must set your digital processor right at the top end (almost clipping) on a fully modulated input.
Setting this way does not allow any attenuation after the processing to alter volume.
The analogue outputs should be attenuated to alter your volume. Better would be to alter the gain of the following amplifiers but very few if any can do this and remain stable for all levels of gain likely to be needed for a normal range of volume adjustment.
chops:
What you are looking to do is utilize every bit (pun) of the digital range. Unlike an analog signal that you lower the volume using resistance and you haven't really hurt the dynamic range, just shifted it, with a digital signal if you don't use all available bits, i.e. loudest at 0 dbfs, then you have lost resolution, not volume. This is why you want to run the DCX2496 at its highest level at the input to the unit and attenuate the signal in the analog domain after it leaves the unit. But 6 channel high quality volume controls are not readily available. Jan Diddens is the best I have ever seen, but I also built one with a 6 section ALPS motorized pot that can be adjusted using a remote control.
Someone with a better grasp of the subject can probably explain in more technical detail than I can what goes on when using digital signals and why you want and need to take advantage of full use of the signal available for best fidelity.
What you are looking to do is utilize every bit (pun) of the digital range. Unlike an analog signal that you lower the volume using resistance and you haven't really hurt the dynamic range, just shifted it, with a digital signal if you don't use all available bits, i.e. loudest at 0 dbfs, then you have lost resolution, not volume. This is why you want to run the DCX2496 at its highest level at the input to the unit and attenuate the signal in the analog domain after it leaves the unit. But 6 channel high quality volume controls are not readily available. Jan Diddens is the best I have ever seen, but I also built one with a 6 section ALPS motorized pot that can be adjusted using a remote control.
Someone with a better grasp of the subject can probably explain in more technical detail than I can what goes on when using digital signals and why you want and need to take advantage of full use of the signal available for best fidelity.