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End game Open Baffle speaker design, digital active crossovers, DSP & Room EQ.


rv295
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Guys, is there any reason I couldn't use an AV pre/processor to control the volume (placed between the dac and power amps?).

Quite a few processors have 8 (the magic number) analogue DVDA/SACD inputs and matching pre-amp outputs.

Just for examples sake: http://www.ebay.co.uk/itm/151975464479

$_57.JPG

If you look at the picture it has an 8-channel input (top left) and matching pre-outs near the middle at the bottom.

The only potential issue I see with something like this is the need to use (for example) the centre channel and the sub channel for the left and right bass drivers. (I don't know if the sub channel is treated differently from the others and therefore whether there would be a noticeable difference between the signal sent through the channel marked sub and matching channel marked centre.

It seems like a way to get a decent quality volume control for not a lot of money (there are much cheaper 2nd hand options out there with the same connections). Many of the units also have a pure direct mode where the digital processing is shut down and a simple input - volume control - output circuit is used.

If this is possible I don't understand why I haven't come across any other DIY set-ups doing this. Most people go for something like the MVC-1 or an equivalent DIY build.

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So long as it works in pure analogue pass through with nothing funny on the bass channel it would work. I have no interest in using something so complex as just a volume control, I did however experiment using an hdmi receiver before I bought an 8 channel sound card. A lot of AV equipment will digitise any analogue input.

An spl volume 8 http://www.thomann.de/gb/spl_volume_8_black_b_stock.htm?ref=prod_rel_266872_1&sid=76f2de21c5955574aa7bb50dd0aefd67 wouldn't be much more, and is fully balanced.

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Agreed, there is a lot of unnecessary components in AV processors but on the other hand; there doesn't seem to be many options for 8 channel (analogue) volume control (for those who can't build their own). I'd really like a remote control too.

If the pure direct functions are minus AD/DA then it is an option I'd consider, I can live with the fact the unit does lots of stuff that I don't need as long as it's not detrimental to its ability as a multi channel pre-amp.

I'll see if I can dig up anything with regards to the implementation of the bass channels in these units and the AD/DA situation of a few potential models. I could buy one and test it but that's a risky option.

I had come across those SPL products but I was hoping to find something similar but with a remote control. They are on my list of options though, it's a very small list.

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I really think you're over complicating this.

You are only using your PC/Jriver as a source, then out to the miniDSP, then onto the multichannel DAC, then possibly onto an analogue 8 channel volume control.

As discussed earlier even the low power PC you said you were using will have more than enough power for processing all the audio stuff. The volume control in Jriver is 24 bit so more than enough resolution for volume control and filters without loosing your original bits. Just plug in a remote receiver for IR control. Jriver is also MUCH MUCH more powerful than the miniDSP box you bought, however now youve got the lucid which hasn't got a PC interface I guess you'll have to use it to get the audio out.

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I really think you're over complicating this.

You are only using your PC/Jriver as a source, then out to the miniDSP, then onto the multichannel DAC, then possibly onto an analogue 8 channel volume control.

As discussed earlier even the low power PC you said you were using will have more than enough power for processing all the audio stuff. The volume control in Jriver is 24 bit so more than enough resolution for volume control and filters without loosing your original bits. Just plug in a remote receiver for IR control. Jriver is also MUCH MUCH more powerful than the miniDSP box you bought, however now youve got the lucid which hasn't got a PC interface I guess you'll have to use it to get the audio out.

I do genuinely listen at low volumes quite a lot and I also like to crank it up sometimes. For higher volumes I understand I don't need anything (I already use an app that can control the volume of JRiver and the nanodigi has IR and can be used with a remote control) but there is a question over the quality of reproduction at low volumes with the digital volume controls I have available. That is where I see an analogue volume control could bring a benefit.

I'm not going to add another box in the chain to start with but I'd like to have all my bases covered.

It seems like some AV processors could be just the ticket. Here is a quote from Arcam about one of their processors (the AV8/9) which has the 8 channel in and out:

The multichannel input is suitable for use with sources that decode the surround channels internally, such as DVD-A or SACD players. The AV8 switches these analogue inputs directly to the analogue outputs via its own volume control circuit. This direct path maintains the best possible sound quality for DVD-A and SACD sources.

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Have been watching this with interest as I'm looking at designing some actives and using a Nanodigi and was considering something like this for volume control..

http://www.dact.com/html/multi-channel_preamps.html

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Hi Matt, That looks great (although lacking a remote) but the components seem rather expensive. The DACT 8 gang attenuator alone is €619 which makes that SPL volume 8 seem like a bargain.

The 6 way is €485,60 if you were doing a passive pre for a 3-way active set-up.

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Your right they do seem expensive but I'm sure that something similar could be put together at a fraction of the cost with a bit of research and perhaps a custom attenuator?

As I am looking at putting together a 4 or 6 channel preamp I am considering a Kozmo 6 channel attenuator and 3X pass B1 Buffers and just cheap Alps mono pots for level matching and the Khozmo can be purchased with a remote control..

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I question the value of a 6 or 8 way passive pot for active loudspeaker use, as opposed to multichannel use. For actives, the pots are used for fading all the amplifiers simultaneously, maintaining the frequency response unchanged. This requires that the tracking be well within 1dB, ideally 0.1dB, impossible with conventional pots.

For multichannel use, it's less critical, as all that'll change is a small change in image balance, less critical than a change in frequency response as volume changes.

I would either use an electronic fader, which can track 0.1dB fairly easily, or as I've done, have the volume control on the stereo input to the ADC.

S

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That sounds great Matt and I do wish you luck! Sadly I couldn't build that unless someone gave me a shopping list and a set of very simple instructions to follow to the dot. I'd like to get to that stage one day. :)

There are plenty of people on here who could do it in their sleep though and I'd love to hear how you get on if you do.

Edit: Just seen Serge's post and :notworthy:

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Edit: Just seen Serge's post and :notworthy:

as have I so might have to get back to the drawing board although not sure my middle aged ears would notice such inaccuracies ?

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Stepped attenuators like the Kozmo with matched resistors will have no issue with tracking between channels. A few of the other solutions use things like the pga2311 which is basically a stepped attenuator on an ic, again should be no issues with tracking.

I plan on using a fairly rough system, 2-3db steps using relays, with fine/remote control via software. No remote on the pre needed.

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Stepped attenuators like the Kozmo with matched resistors will have no issue with tracking between channels. A few of the other solutions use things like the pga2311 which is basically a stepped attenuator on an ic, again should be no issues with tracking.

I plan on using a fairly rough system, 2-3db steps using relays, with fine/remote control via software. No remote on the pre needed.

Once again I have to bow to your knowledge!

I have seen people building 3 and 4 way DIY active speakers that knocked up their own multi-channel pre although the implementation was different to mine. Plus I don't have the understanding required to judge how effective their solutions would be.

I'm going to start off controlling the volume digitally but adding in an analogue pre-amp is an itch I will probably scratch at some point in the near future. It also offers a certain level of protection from accidents or computer malfunction as I know with an analogue volume control that I can make sure the system volume is right down when turned on.

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I agree with Serge, the analogue volume control will end up giving sub optimal results for a high price.

I don't have much of a problem using a digital volume control, despite listening at a range of volume levels, compressed pop and quiet classical. Just set the digital volume max to your max listening level, assuming that you have gain controls on each amp.

If you don't have volume controls on each amp, you can end up with significant digital attenuation on some channels. This is to be avoided if possible, although it may not be audible. Choose your amps wisely!

If you are desperate to have a quiet/loud setting, I would use a simple attenuator system, which used L-pads to switch in 10 or 20 dB of attenuation onto each channel. This way, a single switch would change the level. Such a system would be easy to build.

Sent from my Hudl 2 using Tapatalk

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I agree with Serge, the analogue volume control will end up giving sub optimal results for a high price.

I don't have much of a problem using a digital volume control, despite listening at a range of volume levels, compressed pop and quiet classical. Just set the digital volume max to your max listening level, assuming that you have gain controls on each amp.

If you don't have volume controls on each amp, you can end up with significant digital attenuation on some channels. This is to be avoided if possible, although it may not be audible. Choose your amps wisely!

If you are desperate to have a quiet/loud setting, I would use a simple attenuator system, which used L-pads to switch in 10 or 20 dB of attenuation onto each channel. This way, a single switch would change the level. Such a system would be easy to build.

Sent from my Hudl 2 using Tapatalk

Digital crossovers like my DCX2496, do all the processing in DSP, including filtering, level adjustment, time delays, phase adjustment, parametric EQ. It uses Sharc processors, which are DSPs designed for audio applications. The 6 analogue outputs that result from the processing are correctly dithered and converted to analogue, such that there's no loss of resolution with level adjustments for different sensitivity amplifiers and drivers. The only thing that can be an issue, and was in my case, is that the analogue outputs provide +22dBu at 0dBFS, which is close to 10v RMS and so with most power amps there's about 16-20dB more output than they need, and 16-20dB more noise than they want. Without attenuating the analogue outputs, a small amount of hiss was audible, especially in the sensitive midrange driver, and also the crossover had to be operated some 20dB below optimum levels resulting in a theoretical loss of resolution. By attenuating the crossover's analogue outputs by 16dB, and adjusting the internal gain bearing in mind the gain of the preamp I'm using for source selection and volume control, the noise and resolution have been optimised.

I would expect any DSP-based digital crossover, whether stand-alone hardware like mine, or implemented on a PC, to work in the same way.

S

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