[tortugaranger]

Being a big fan of active crossovers using DSP (digital signal processing) I'm seriously considering offering a 4-channel derivative of our LDR preamps for active DSP applications involving 2 way speakers. Could be expanded to accommodate 3 or even 4 ways as well.

Very interested in getting comments on this.

Also, here's a recent article we posted on the subject of Active DSP Crossovers. http://www.tortugaaudio.com/articles/case-active-dsp-crossovers/

[JohnR]

Hi Morten, interesting idea  In your diagram though, the analog source needs to be connected further upstream (via an ADC).

[tortugaranger]

Hi Morten, interesting idea  In your diagram though, the analog source needs to be connected further upstream (via an ADC).

Good catch John. Have corrected and updated. 

[WC]

So would the 4 channel preamp just be 2 V2.5 boards, one as master and one as slave?

I was considering building speakers and making them active, but the complexity of it stopped me from considering it. The issue I had with it was that I was trying to implement the active speakers into a system where the speakers were shared between 2 channel and multi-channel use. In this application, I would most likely put something like the miniDSP 2x4HD on the outputs of the 2 channel preamp if I want to run as active speakers. It will cost less than adding another DAC and an additional 2 channels in the preamp. May not be the best sounding option, but if it is not better sounding I could just use the passive crossover. If I had an all digital only 2 channel system it would be simpler.

[tortugaranger]

So would the 4 channel preamp just be 2 V2.5 boards, one as master and one as slave?

I was considering building speakers and making them active, but the complexity of it stopped me from considering it. The issue I had with it was that I was trying to implement the active speakers into a system where the speakers were shared between 2 channel and multi-channel use. In this application, I would most likely put something like the miniDSP 2x4HD on the outputs of the 2 channel preamp if I want to run as active speakers. It will cost less than adding another DAC and an additional 2 channels in the preamp. May not be the best sounding option, but if it is not better sounding I could just use the passive crossover. If I had an all digital only 2 channel system it would be simpler.

Yes, 2 V25 boards would be needed.

After thinking about it I can see where accommodating both 2 channel and multi-channel might get very complex but a system diagram on things like this would help a lot. I read your note several times and I'm sure I'm not sure I understand the issues.

[WC]

Main issue with multi-channel signals is the signals can be transferred via HDMI, USB, and analog. You can't split off the front channels digitally via HDMI, so the only way to split the channels is via analog. USB is limited to 8 channels and connecting via USB from my Raspberry Pi server could be problematic.

If I only had a 2-channel system, it would be simpler. I am connecting the Raspberry Pi server to DAC via I2S, which I could insert a DSP in between. So the Toslink/Coax connections to my DAC on my input board become useless, but additional digital inputs to the DSP would replace the ones not being used to the DAC. I also have an analog input from my turntable which would need to be connected to the DSP. This requires an ADC to get it into the DSP. When you add up all the IO into the DSP, it ends up costing quite a bit.

In the end I decided to go with this train:

Raspberry Pi via I2S > DAC > Preamp > amp > Speakers (with passive crossover)

If I am not satisfied with the passive crossover I can always add a miniDSP 2x4HD or greater if I want more sub control.

Raspberry Pi via I2S > DAC > Preamp > DSP > 2 stereo amps > Speakers (2 way active)

I can also use the other inputs on the preamp for phono and HT (Front Left and Right):

Phono or HT > Preamp > amp > Speakers (with passive crossover)
 or
Phono or HT > Preamp > DSP > 2 stereo amps > Speakers (2 way active)

[tortugaranger]

Main issue with multi-channel signals is the signals can be transferred via HDMI, USB, and analog. You can't split off the front channels digitally via HDMI, so the only way to split the channels is via analog. USB is limited to 8 channels and connecting via USB from my Raspberry Pi server could be problematic.

If I only had a 2-channel system, it would be simpler. I am connecting the Raspberry Pi server to DAC via I2S, which I could insert a DSP in between. So the Toslink/Coax connections to my DAC on my input board become useless, but additional digital inputs to the DSP would replace the ones not being used to the DAC. I also have an analog input from my turntable which would need to be connected to the DSP. This requires an ADC to get it into the DSP. When you add up all the IO into the DSP, it ends up costing quite a bit.

In the end I decided to go with this train:

Raspberry Pi via I2S > DAC > Preamp > amp > Speakers (with passive crossover)

If I am not satisfied with the passive crossover I can always add a miniDSP 2x4HD or greater if I want more sub control.

Raspberry Pi via I2S > DAC > Preamp > DSP > 2 stereo amps > Speakers (2 way active)

I can also use the other inputs on the preamp for phono and HT (Front Left and Right):

Phono or HT > Preamp > amp > Speakers (with passive crossover)
 or
Phono or HT > Preamp > DSP > 2 stereo amps > Speakers (2 way active)

Thanks. That all makes complete sense to me.

What got me thinking about the 4 channel preamp is the fact that a 2 channel preamp plus DSP more or less forces you into the scenario you outlined above which is essentially how I've been running for several months now.

Dedicated Windows 10 PC Music Server via USB >  DAC > 2 channel Preamp > DSP > 2 stereo amps > Speakers (2 way active)

When I get some time to set up a 4 channel V25 preamp I will change this around to the arrangement below and assess. The DSP I'm using is the miniDSP 2x4HD which is remarkably flexible and a solid performer.

Dedicated Windows 10 PC Music Server via USB >  DSP > 4 channel Preamp > 2 stereo amps > Speakers (2 way active)