Question for DCX2496 owners - Volume Control

[Branwell]

Question for DCX2496 owners

For my three ways, I have a DCX2496 running into two Panasonic Digital Receivers. The setup works well, but I need more power, and so am planning on getting a larger amp, something like the ATI 1806.

Here is the question:

How to control the volume ?.

One could go:

CD Digital Out
Behringer
volume control
Amp

Or

CD Analog Out
Volume control
Behringer
Amp

The issue is how the Behringer reacts to a low volume analog input, i.e. having the volume control before the Behringer unit feeding it an analog signal. Some have suggested that Digital crossovers loose resolution if fed this way.
I have tried it with the Behringer so I don’t know.

Has any one any experience with this ?.

Thanks,

Branwell

[Petter]

If you can possibly feed a digital signal to the Behringer then do it.

That means you need the volume control after the Behringer. This causes a problem - you need up to 6 channels of tracking volume control.

It is a strategic mistake by Behringer of not including at least a rudimentary volume control on the output.

Petter

[pinkmouse]

Originally posted by Petter
It is a strategic mistake by Behringer of not including at least a rudimentary volume control on the output.

No, not really, as it is designed for use in the pro audio world, where all gain control is implemented on the desk. Extra gain controls in the main audio lines just give more chances of being tweaked accidentally, causing problems that you then have to try and troubleshoot.

It would also increase the cost of the unit, for a feature that most users would not need.

[Vadim]

Here is what I did. I bought 10 dual linear 10k motorized Alps pots from allelecronics.com at $3.5 each. They are 1 inch square and real nice. I wired the motor of each pot to the infrared remote control board through relays so that I can control each pot independently through a common hand-held remote control.

To solve the tracking problem, I placed a resistor in parallel with the output of each pot, -now all pots are matched to at last 1%. This resistor also turned the pots into the logarithmic devices.

I then buffered all inputs and outputs with BB2604 op-amps and also place a 20 dB attenuator in a form of a resistor divider before the opamp driving the pot. End result is that I can now feed 10 V peak signal into the DCX2496. This 10 V are turned into 1 V by the attenuator and then further controlled by the pots.

I am in the process of building an 8 channel system with active speakers. My fronts are 3-way dipoles, so I need 6 channels just for the fronts. My volume control ultimately will manage 16 channels.

At this time I have the fronts working and the volume control is operational, but I think I might change the attenuator value to -15 db or so. Otherwise everything seems to work.

[Thunau]

Could you post a schematic Vadim? I'm doing something similar, except my crossover will be my Alesis 8 channel audio interface fed from my remote controlled media server computer with an RME Hammerfall ASIO card in my basement. The Alesis has a +4/-10dB switch, so I won't need the voltage divider. I'm doing VST plugins on the individual outputs for crossover filters. I have gathered a few candidates and will start actual testing this weekend. The freebies actually look like they have the most potential. I'm thinking I could use the serial port for controlling the volume pots.

[Vadim]

Jan,

I apologies for the late response. My schematics are just plain hand written pages. However, I can describe the project, which is a work in progress, a bit better. There are several elements to my Master Volume Control Box. They are, - the buffer boards, the motor control board and the relay board. When all put together, I should be able to control any combination of about 6-8 motorized potentiometers with a common hand–held remote.

I got all my boards from Mikkel, see http://stiftsbogtrykkeriet.dk/~mcs/Remote/index.html for details. Mikkel is a very nice guy and he ended up designing some of the boards to my specifications.

Here is what I do, - I connect a relay in series with each pot. I then connect all pot-relay combinations in parallel. The Motor Control Board is then connected to control the entire thing. The motor control board is pre-programmed by Mikkel to accept commands from the hand-held remote’s keypad in order to control the relays and to turn ‘on’ and ‘off’ the H-bridge that controls the potentiometer’s motors.

The Buffer Board contains two identical non-inverting op-amp configurations with provisions for gain, attenuation and signal by-pass.

In my particular case, I use the DCX2496 for most cross-over functions except the open baffle EQ. This open baffle EQ is done in analog by the buffer board. It is just too much gain for DCX to handle.

So, I feed the DCX a nearly 10 Volt peak analog input and after the DCX I attenuate the signal by the 20 dB resistor divider on the Buffer board. I then use the non-inverting op-amp circuit to do the EQ. The signal is then sent to the pot for volume control and then buffered by another op-amp on the Buffer board.

All-in-all I have it all nearly working now. When I am done with this project I will try to put together a complete data-base with schematics for all the boards involved.

Vadim

[nowater]

How does putting a resistor in parallel with each pot mean they are matched to at least 1%?

Are you only referring to the total resistance, or to tracking at all volume levels?