Behringer UltraDrive DCX 24/96 or Other Digital Loudspeaker Management Systems

[Victor]

Intelonetwo,

I must agree with Steve here. Do not shy away from the Digital EQ option only because it seems daunting. You can definitely use your DEQ in the tape loop of the receiver, so the RTA is within your reach. As for the DCX it is also possible on the tight budget. Here is the $30 product that may work for you.

http://www.decibelhifi.com.au/prod18.htm

It is a 6-channel passive attenuator. Why don’t you get one to control the signal to your power amps after the DCX. So in the end you will have a DVD-A decoding. You will need to get one inexpensive pre-amp. There are many used units out there for at most $100 on ebay. Assuming you get this pre-amp the signal chain for you may be as follows:

SACD player 5 channel analog outputs gets split with front channels going to the pre-amp. From the pre-amp the analog signal goes to DEQ, then to DCX then to $30 passive attenuator box. The attenuator would produce 2 sets of 3 outputs for you Right and Left front channel for a total of 6 channels all together.

Take those six outputs and feed them to your receiver’s main-in inputs. You are now using your receiver to amplify all the channels for you 3-way front speakers.

You need more amps for you center and your rears. Get them! Assuming that you rears and the center use passive crossovers a single 6 channel receiver will do the trick.

So, here you have it, - a SACD capability for the additional $150 at most. Did I miss anything?

Victor

[Victor]

Dennis,

Victor, I think you misunderstood me. I'm assuming you would set up your gain structure so everything clips at about the same time.

Yes, I must have misunderstood.

That most likely means a fixed attenuator between the EQ and the power amp and that would set the noise floor.It also assumes you have enough voltage available from your preamp to drive the EQ to full scale. So, now the noise is at a constant and presumably acceptable (inaudible) level.

The noise floor cannot be set-up with the resistor you are talking about. You see, the LSB (least significant bit) voltage is directly proportional to the full scale voltage (input amplitude). So it follows that if the input is not high enough the LSB will be indistinguishable from noise. In fact, not just the LSB alone but the lower bits in general may be completely masked by noise. The theoretical noise floor for A/D converter is fixed and it is a function of bit resolution. For example for the 16 bit A/D converter it is 98 dB, for 24 bit device it is 146.24 dB, - which is naturally unachievable.

The noise won't increase if you turn down the volume before the EQ, the signal just decreases. The noise should remain inaudible at all times.

No, unfortunately it can’t happen this way. As you decrease the input signal the noise will rise exponentially. The mathematics shows that LSB (in volts) is equal to the full scale voltage input divided by the two to the power of the number of bits that A/D is using. Once LSB and other low order bits are gone as a result of the low input voltage the A/D is no longer the 24 bit device but a lower bit device, hence higher noise. It may be difficult to see what I am saying here.

For example, for the 24 bit A/D that DEQ is using, the LSB voltage is 1.2 microvolt providing that the input amplitude is +/- 10 Volts. This is the reason why you can never have 24 bit resolution. Look at 1.2 uV number and compare this number with the thermal noise that the resistors around the A/D are generating. The LSB and the few neighboring bits are already gone and we are at the maximum input. So this 24 bit converter is 24 bits in name only, - we will be lucky to get 16 bits out of it. If you decrease the input further, the problem only becomes worst.

Regards,
Victor

[sfdoddsy]

Intelonetwo,

Did I miss anything?

Victor

I think so unfortunately :?

The Yamaha RXV-1 only has three Main Ins - for Front, Left, and Center.

Something I missed was an earlier post from i1/2 about using the dual subwoofer outputs from the Yamaha to the a/d/s subwoofer amplifiers.

There are two problems here. The first is that I would bet those dual sub outputs are mono, and I'm sure you want your bass towers to be stereo.

The second is that if you use the main ins after the DEQ, the sub channels will not be EQed, and they are the ones that will benefit it most.

So, assuming you wait on the DCX, you will need to split the output from the DEQ, sending one lot to the the Main Ins and thence your head units, and the other to the a/d/s amps and then your subs.

The attentuator box Victor mentioned could be used in this setup as well. I have one and it is very handy.

A better soltion would be to incorporate the DCX now, so you go Main Outs to analog in DEQ, digital out DEQ to digital in DCX, analog out DCX to attenuator, then mid/highs to Main In on Yamaha and lows to a/d/s.

Later, when funds permit, you could do the full triamp setup on the mains. Or you could use the spare input on the DCX to biamp/EQ your center.

Hope this is not too confusing.

Steve




Steve's DIY Dipoles

[Dennis H]

Victor, I think I understand what you are saying but I think we're talking about two different things.

As you decrease the input signal the noise will rise exponentially.

I think you must be talking about relative noise, i.e. S/N ratio. I'm talking about absolute noise level in dB SPL. If I put a voltmeter on my speaker terminals, I don't think turning down the volume control on the preamp will cause the reading on the meter to increase.

we will be lucky to get 16 bits out of it.

I think that's plenty for my room. The background noise in my room seldom (if ever) falls below 20dB SPL. That's really very quiet. Let's say the loudest the system will ever play is 105dB SPL. Subtract 96dB for the 16 bit dynamic range and that means the quietest sound I can reproduce at full volume is 9dB SPL -- well below the ambient noise floor of my room. If I put a smaller signal in, say 80dB SPL peak I do significantly reduce my dynamic range to 71dB, and increase S/N ratio but does it matter? I can still reproduce a 9dB sound and it's still below the noise floor of the room. Even the quietest analog gear wouldn't do any better in my room with an 80dB SPL signal. Fortunately, very few recordings have a dynamic range of actual musical material that comes anywhere near 70dB. The only thing that quiet is tape hiss, etc.

I know from a purist engineering point of view, it's not as good as it could be but I take a more pragmatic approach -- can you hear the difference?

[Victor]

Steve,
Yes, you have a point regarding this Yamaha receiver. Oh, well…

Currently, I have a 12dB shelving filter based at 100Hz, 6 dB octave, which EQs for the fall from 400 or so down.

Yes, that is 2 octaves and it is doable. Unfortunately I need more then that. My baffle is about as wide as yours, but I would like to cross the drivers from 70 Hz to 500 Hz. The theoretical peak is at 640 Hz. So I need to EQ from about 550 Hz down to 20 Hz. I guess I am out of luck here and must do analog shelving filter, as it is out of range of the Digital Box.

You know, if you use 2 filters, one low-pass and one high-pass, then you can kind of configure the overall response to look like a shelving low-pass extending all the way down to -12 dB.

For example, set-up a low-pass 6dB/Oct shelving filter at let us say 20 Hz with amplitude of 15 dB. That would mean we have 12 dB of gain at 20 Hz (-3dB). Then set-up a hi-pass 6 dB/oct shelving filter at 640 Hz at -15 dB. Again considering a -3dB specification the filter would appear to have -12 dB at 640 Hz. So now we have 5 octaves spanning 30 dB from +15dB down to -15 dB and from 20 Hz all the way to 640 Hz. It seems to work. What do you think of this?

Victor

[Dennis H]

Victor, I just realized you have the perfect setup to test the audibility of the two methods. You can attenuate the signal either before or after the EQ, using either the preamp or the pots. Have you actually tried it both ways? Can you hear a difference when you turn the pots up "pretty loud" and then cut it back down to "pretty quiet" with the preamp?

[intelonetwo]

Steve and Victor
Ok, I think I got it.

A better soltion would be to incorporate the DCX now, so you go Main Outs to analog in DEQ, digital out DEQ to digital in DCX, analog out DCX to attenuator, then mid/highs to Main In on Yamaha and lows to a/d/s.

In this setup the preamp that Victor specified is left out. Is it necessary for this setup? The A/D/S subwoofer amplifier is just a good deal and honestly will not go in the system if the DCX is to remain, just because of the dollars. I do not have many of them.

Now knowing that the A/D/S subwoofer would not be in the chain if the DCX is to remain in the chain, can my Yamaha still power the front speakers as in the setup outlined above? Are you saying for now that I do not have to purchase separate ampifiers for the front mains? I would love to do this, however I did not think it was possible. As I said many times before, I do not care for my center, and surrounds to have any processin applied to them....yet.

How do you think it would cost for me to pay someone to build this 6-channel attenuator?




MI-II-CENTS
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The TailWind Generation I

[sfdoddsy]

Victor,

I programmed the filter you suggested into the Driverack, and it does indeed give the boost you indicated. I can't see any reason why it wouldn't work with the DCX. You'd obviously need to fiddle with levels, but I would assume you need to cut the levels of your mids relative to the treble and bass anyway.

Intel,

You could drop the DCX from the path above. But you need a crossover between your bass modules and the main modules. You mentioned earlier that the a/d/s amps have typical sub amp capabilities. If they have a built-in crossover, you could use that, depending on what sort of crossover they incorporate, but it might include both a high pass and low pass section so your head units would be run full range. The attenuators mentioned by Victor can be bought assembled. Just email the company.

However, I have another cunning plan for you :roll:

You could use an analog crossover such as the Behringer CX2310 after the DEQ equalizer. The CX2310 is a nice simple crossover (I have one) that is very quiet. But the nifty thing is that it has gain control on the inputs, and then for each output. You can actually attenuate the signal by up to 20dB, which should be about right to get the best possible signal into the digital EQ.

The best thing is the cost. They are around $80 from online stores, or $75 here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2559573478&category=23793

So your signal path would be (takes a breath) Yamaha Main Outs to analog DEQ inputs for room EQ. Then DEQ analog outs to CX2310 for crossover and attenuation. The mid/highs go to the Main Ins on your Yamaha then your head modules. The lows go to the a/d/s amps and then your bass modules.

Easy.



Steve




Steve's DIY Dipoles

[intelonetwo]

Steve
I like the idea about the Behringer analog crossover. I figured that since I already have the DCX I might as well keep it and use it. I just do not want to have to purchase another 6 channel amplifier to tri-amp as this is a rather large expense that I can not afford the present time. If I can use the DEQ, DCX, 6-channel attenuator and RX-V1 to power the speakers that would be great. I would drop the A/D/S amplifier from the setup. However when I do so, the last portion of the setup falls apart.
Where do the lows go if I am not using the A/D/S sub amp?

A better soltion would be to incorporate the DCX now, so you go Main Outs to analog in DEQ, digital out DEQ to digital in DCX, analog out DCX to attenuator, then mid/highs to Main In on Yamaha and lows to a/d/s.

Here is the setup.

Main Outs analog to DEQ inputs for Room Eq. Then DEQ out digital in to DCX. Then analog out to attenuator, then mid/highs to Main In on Yamaha and lows to ???

I am trying understand why the DCX cannot provide the necessary signal attenuation before reaching the ampliifers? This would eliminate the need for the 6-channel attenuator. Is it an impossiblity or is it a sound quality issue (resolution). ALso Steve, on my Yamaha receiver, the unit actually has 3 sub outputs. 1 is mono (Main, Center, Rear), 2 and 3 are what they call SPLIT jack which output stereo separation for the main and rear channels and split mono signal for the the center and LFE channels.

How are the speaker driver actually connected to this convoy or equipment? To the analog in's of the DCX?

I found a great article over at Newform Research regarding the Behringer DCX and believe it or not a Panasonic 6-channel digital receiver/amplifier. It is very interesting. However I am confused about how they are using the Panasonic Receiver to bi-amp the speakers they are using. http://www.newformresearch.com/whats-newfr.htm

I finally got the DEQ into the system this morning. It is placed between the Yamaha Preout and Main In connections as specified by many of you here. Thanks. It does have a million adjustments that can be done, however since I am only using very small MTM speakers for the fronts the DEQ does actually have much to do. I will be trying out the auto eq function in the next few hours and fiddling around with the unit to get familiar with its operations. Boy you gotta love the RTA readout. Looks impressive. Friends came over and are all stoked about it.




MI-II-CENTS
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The TailWind Generation I

[sfdoddsy]

Yep, you same to have the hookup right for your current speakers, but the results will depend a bit on how they are setup from the Yamaha. Do you have them set to full range, no sub? That's how you should do your testing.

The problem is going to be when you do your DIY speakers. Namely that you simply don't have enough amp channels available. At some stage you are going to need separate power amps to drive at least a part of your mains.

You could just get the a/d/s you mentioned. But in the long run it will be much cheaper to think ahead.

By far the easiest way of doing it would be to get a multichannel power amp. I'm not sure what power your speakers will require, but with thwe doubling of the drivers you mentioned, and going active, you probably won't need a heap of power.

For example, a Parasound 806 will give you 6 x 80 watts and should be around $400 used on eBay or Audiogon.

The Rotel RMB 976 is 6 x 60 watts and sells for around $300 on eBay.

There is an even cheaper RMB 956 that sells for around $200.

A good thing about all of these is that they have input gain controls so you can attenuate the signals, ie no external attenuator needed. They can also be bridged to give various configurations of 6-2 channels.

My pick of these would be the Parasound unit.

The Newform article is an interesting one. I used to own Newform speakers and they are pretty good for the money. John Meyer has long been a fan of digital amps, so if he is recommending the cheap Panasonic receiver there is probably something to it, weird as it may seem. He wouldn't sell it with his best system if it sucked.

I would assume that it is being connected through the external 5.1 inputs, so it essentially just a six channel amp with a volume control. Again this would be good for you since the volume control would allow you to attenuate the signal, although there again might be questions about attenuating a signal coming into a digital device.

Finally, the reason you wouldn't attenuate using the DCX, is that it does this in the digital domain, and that may reduce resolution.

If it were me, I'd bite the slight bullet and get something like the Parasound 806 instead of the a/d/s amps. You will probably want the extra channels sooner or later, or you could triamp now, and they are very nice amps.

I actually wish I'd got a 1206 (the big brother) when I set up my system. In fact I am bidding on one now.

Cheers

Steve




Steve's DIY Dipoles

[intelonetwo]

You are right I do not have enough channels to drive the DIY 3-ways. Where are those spare amplifiers when you need them?

If I wanted to use the Panasonic to amplify my speakers would the connections be as follows:
Out: Yamaha (analog) Preout
In: DEQ
Out: DEQ (AES/EBU)
In: DCX
Out: DCX (6 analog ouputs)
In: Panasonic (5.1 inputs)
Out: Panasonic Speaker Level terminals to 3-Way DIY's.

In Yamaha Main In from DEQ.

This would give me the necesay attenuation and volume control although not on all channels. Is this a problem?

I really do want to purchase one of the ampifiers that you suggested. And I just may bit the bullet and do it.




MI-II-CENTS
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The TailWind Generation I

[Spearmint]

I have both The DEQ & DCX 2496, and have a question re the input levels.

I see Victor is using a pre-amp to increase the analogue input levels into the Behringer, I was looking at getting one those di boxes to change the level from consumer to pro, and the other unit I am currently looking at is the Behringer Ultramatch Pro SRC2496.

http://www.behringer.com/SRC2496/index.cfm?lang=ENG

Can any tell me if these would do as good or better job as a pre amp, both units are coupled via digital, it is just raising the input analogue level I am looking at.

[Victor]

Wow! The blast from the past! This is an old thread indeed. Well, Yes I am still using my Bryston BP-20 as an analog input level booster and it works just fine. Do not forget that once you increase the input level to the required pro amplitude of about 5-6 Volts peak, the output level gets scaled also to the same maximum. So you will need an attenuator just as well. Behringer makes an interesting (and cheap!) product called ULTRALINK PRO MX882 which is very suitable to ‘fix’ input and output levels in and out of DEQ-DCX combination. Check it out

http://www.behringer.com/MX882/index.cfm?lang=ENG

The specs of MX882 look pretty good and I am sure if need be it can be modified to become a more politically correct audiophile-type product. Although with S/N at 95 dB or better and THD of 0.002% at max signal and 1 kHz, I can’t see any problem with it as is. The THD will decline as the signal goes lower then +4dBu, but still those specs tell me that MX882 is quite transparent.

Vic

[Dennis H]

Doesn't the DEQ have a switch on the back to set input and output voltages to either pro or consumer levels? In the +12dBU position, most consumer gear should be able to drive it without an extra preamp.

[Victor]

Dennis,

The +12 dBu is still about 4 Volt peak signal. Perhaps some commercial gear can do that, but I would not expect even 2 Volts for the most part. For instance, my anemic and old Technics AC-300 AC-3 decoder cannot master anything past about 1.2-1.4 Volts even though its output is advertised as a 2 Volt maximum. Go figure! I am afraid the pre-amp at the input of DEQ is necessary.

You know, the interesting thing is this, - when I use SPDI/F input into the DEQ I often observe clipping. I understand that it is nothing to worry about because the signal is digital, but still it occasionally clips my output on the DCX and the limiters kick in, - very unnerving to say the least. If I use analog inputs to the DEQ and use my pre-amp to set the maximum input levels at about -3 to -5 dB, I hear absolutely no difference vis-à-vis the SPDI/F input. This tells me that those AKM A/D converters in the DEQ are rather good.

Vic

[Davey]

Vic,

The output from your decoder is pretty low. For most folks there's only another 3.8db gain possible from an outboard preamp. +12dBu is 3.1 volts RMS and the typical output from most CD players and DAC's is about 2 volts RMS for FS recorded signals. That's getting pretty close.....I'm not sure it's worth the trouble for most.
In your case why don't you get inside the DEQ and simply change resistors and increase the gains of the input stages?

I've also noticed the clipping when using the digital input of my DCX. A user has to be aware of this when setting the levels. Maximum recorded level sine waves are usually not a problem, but input waveforms with high crest factors can easily cause clipping on the outputs.

Cheers,

Davey.

[Spearmint]

Thanks for the info Victor,

Its funny I had come across the MX882, while looking for a di box on the Behringer site. Anyway yesterday I went to my normal Music Shop haunt to buy a cheap di box, and ended up ordering the MX882 c/w 4x XLR interconnects and 2x 1/4" phone jacks to XLR 1 each male & female XLR.

I use my DCX for my 5x subs, so I am going to use channel 6 of the MX882 as an unbalanced gain amplifier for the DEQ and of course the DCX as well, then the other 5x I will use as attenuators, on the output of the DCX, I am hoping that the outputs of the MX882 are muted at power on/off.

The reason I ended up going this way was after playing with some of the other Behringer analogue pots they have micro steps and appear to have a nice smooth action, also the MX882 was only $50 AUD more than a di box. You can get some good discounts on Behringer gear.

I told them I will be back later in the week to pick it all up, if you guys are interested, I can post some findings on the weekend.

Dick

[sfdoddsy]

You've piqued my interest Dick. I need a couple of new toys and may get one of these either in Oz or when I visit the States next week.

How much did you pay here?


Steve

[Victor]

Vic,

The output from your decoder is pretty low. For most folks there's only another 3.8db gain possible from an outboard preamp. +12dBu is 3.1 volts RMS and the typical output from most CD players and DAC's is about 2 volts RMS for FS recorded signals. That's getting pretty close.....I'm not sure it's worth the trouble for most.
In your case why don't you get inside the DEQ and simply change resistors and increase the gains of the input stages?

I've also noticed the clipping when using the digital input of my DCX. A user has to be aware of this when setting the levels. Maximum recorded level sine waves are usually not a problem, but input waveforms with high crest factors can easily cause clipping on the outputs.

Cheers,

Davey.

Yes you have a point and I will go inside the DEQ soon and fix the input amp gain. While there I will also deal with the coupling caps!

Also, how do you propose to deal with this clipping? Since the input is digital do you just turn down the gain of the A and B inputs on the DCX?

Regards,
Vic

[Victor]

Thanks for the info Victor,

Its funny I had come across the MX882, while looking for a di box on the Behringer site. Anyway yesterday I went to my normal Music Shop haunt to buy a cheap di box, and ended up ordering the MX882 c/w 4x XLR interconnects and 2x 1/4" phone jacks to XLR 1 each male & female XLR.

I use my DCX for my 5x subs, so I am going to use channel 6 of the MX882 as an unbalanced gain amplifier for the DEQ and of course the DCX as well, then the other 5x I will use as attenuators, on the output of the DCX, I am hoping that the outputs of the MX882 are muted at power on/off.

The reason I ended up going this way was after playing with some of the other Behringer analogue pots they have micro steps and appear to have a nice smooth action, also the MX882 was only $50 AUD more than a di box. You can get some good discounts on Behringer gear.

I told them I will be back later in the week to pick it all up, if you guys are interested, I can post some findings on the weekend.

Dick

The MMX882 is a good solution for the money, but it is not a master Volume control. In Australia you have several outlets selling a very interesting box, - a 6 channel master volume control. Look at

http://www.decibelhifi.com.au/prod69.htm

There are others, like the alltronics.com

You can get this in a kit form for less then $200US. It uses a very good monolithic attenuator from National Semiconductor with THD+N specs better then 16 bits, - which great. It is not a VCA design. Also it works with common remotes. I think I might get a kit and use better parts in the process. One good thing about it, is that it can deal with high input level signal while the VCA based attenuators may have a problem. We need that since the DCX outputs 5-6 Volt peak.

Vic

[Davey]

Vic,

Yes, adjust the input gains to approximately -1 to -3db. Then, as long as you don't program any outputs to exceed the 0db level the outputs will not clip...guaranteed.

I noticed the Alltronics unit awhile back. It looks good.

There isn't any problem with using the VCA-based attenuators directly on the outputs of the DCX.....provided you don't enable the 6db boost by jumpering pins 1-3...provided you don't increase the DCX gains above 0db...and provided the particular VCA can handle the input. The SSM2018T VCA's I used will clip at their inputs with 4.2 volts RMS (if a +/-12VDC power supply is used,) and the DCX will output approximately 4.3 volts RMS (from each polarity to ground) at clipping so it's a pretty good match. A simple, fixed attenuator of a few db is an easy addition for peace of mind. Anyway, there's still way more than enough voltage available to drive any power amp to its rated output.

Regards,

Davey.

[Victor]

Vic,

Yes, adjust the input gains to approximately -1 to -3db. Then, as long as you don't program any outputs to exceed the 0db level the outputs will not clip...guaranteed.

Good point! Indeed this is a way to go.

I noticed the Alltronics unit awhile back. It looks good.

There isn't any problem with using the VCA-based attenuators directly on the outputs of the DCX.....provided you don't enable the 6db boost by jumpering pins 1-3...provided you don't increase the DCX gains above 0db...and provided the particular VCA can handle the input. The SSM2018T VCA's I used will clip at their inputs with 4.2 volts RMS (if a +/-12VDC power supply is used,) and the DCX will output approximately 4.3 volts RMS (from each polarity to ground) at clipping so it's a pretty good match. A simple, fixed attenuator of a few db is an easy addition for peace of mind. Anyway, there's still way more than enough voltage available to drive any power amp to its rated output.

Yes I can see now that the VCA’s can handle the input from the DCX. I would gladly consider the VCA-based solution if I can only get the circuit board somewhere. It is just I do not have the time to do the entire thing these. I can design it, but it takes a lot more time building it, particularly the metal work, etc.

This is why the monolithic attenuator box from Australia looks so appealing to me. They send you everything including the metal box and it is a ready to go kit. I can definitely make it a lot better in terms of overall quality by using more sophisticated parts and cleaning up the power supply along with even discrete component buffers.

The question is which is a better way to go, - a VCA-based volume control or a monolithic attenuator based volume control? Both have similar specks. Although the THD in VCA solution stays fairly constant over the audio band, while the monolithic attenuator’s THD does rise a bit, but still is low enough to be innocuous.

Regards,
Victor

[Spearmint]

How much did you pay here?

Hi Steve...

I got the unit and cables for $200.00 AUD

Okay I got the unit last night and installed it into my rack.

Works an absolute treat...

I muted the outputs of the DCX, set the LFE on the pre/pro to 0. The MX882 feeds the analogue inputs of my DEQ; I set the Pre/Pro to ref level and ran the test tone. I adjusted the gain on the MX882 to just on clipping of the DEQ, and then I backed the gain off so that clipping did not occur at all.

Next I un-muted the outputs of the DCX, and attenuated the outputs of the MX882 to calibrate the subs.

Pros:
- No audible hum from the power xformer
- No thump when powered on
- Pots are smooth with micro notches, very easy to match each other up for quick adjustment
- Excellent range of adjustment from full attenuation to + 15dB
- No audible coloration of the signal

Cons:
- Small thump when unit is powered off, nothing to worry about though
- Split/Mix buttons are illuminated in mix mode only, and are a little on the bright side sitting in the rack, not over the top though

This unit is being used as a set and forget item, for the price, and the fact that I can use balanced inputs and outputs, has meant I have a level matched and hum free subwoofer setup.

Dick.

[RonS]

I've just emailed DecibelHiFi about their K3 kit, want to find out if they sell a version for 110V NA standards.

Has anyone used one? Care to comment on the sound quality? I would most likely upgrade much of it, use OPA2134 opamps, eliminate the coupling caps etc.

I couldn't find anything similar on the alltronics.com site, can someone point me to the proper item? I could build Davey's VCA design, but I just dont' have the time to design boards and make them. Also, has anyone bought the boards from Bdipoala? They fit right inside the DCX unit itself. Wondering about the quality of those as well.

Cheers,
Ron

[capslock]

Hi

Nope not me, I find the entire low buck digital EQ idea somewhat problematic. I may pick up something quick and dirty for prototyping and there are some PC based EQ's that are free..

Thomas, what PC based solution are there that are free? I have Soundeasy, and Igmar's Lsplab does the same thing, but the are not free. I am aware of BruteFIR , but that needs Linux.

[ThomasW]

I was referring to BruteFIR.
An interesting thread
If you read through the thread you'll find that very little Linux knowledge is needed. These guys are booting and running a Linux PC from a USB Memory stick (no hard drive).

I'm sure Ed Wildgoose would be happy to send you a copy of his complete system on a CD. He's a very nice guy, I've corresponded with him about other topics.

[Davey]

Thomas,

Thanks, that IS an interesting thread that I hadn't see before. I wish I was better versed in Linux and not such a non-geek computer type.

Davey.

[RonS]

For those in North America who are interested, I heard back from Decibel HIFi about their K3 kit. First, it is out of stock until mid April. Second, a 110V transformer is an additional $40AUS. Insured mailing to Canada runs another $95AUD. All in all, too expensive for what it is. By the way, the kit is based on an article published in SiliconChip magazine, in two parts. I bought the first part, which has a full parts list, pcb layout and schematics. It's based on a National LM1973N 3 channel resistor attenuator chip. The biggest problem in building one is that there is a PIC chip that needs to be programmed. Anyone know of a place that will program them? Otherwise, the unit is pretty straight forward to build. Distortion starts to rise above 1kHz, but that may be due to the use of TL072 opamps (they're used as output buffers), something better like an OPA2134 might help.

Ron

[Davey]

Ron,

I have that article in the files section of the DCX forum. (Six pages.)

http://groups.yahoo.com/group/DCX2496/files/

Davey.

[RonS]

Thanks Davey. I hadn't realized that you had it up there, guess I could have saved myself $8

Any opinions about the National part vs. the AD part that you used? The fact that I have board patterns makes using the National part easy. I'm still torn between building my own, or getting Bdipoala's boards. He has a very elegant solution, but it's not cheap, for either the boards or the parts. I'll spend almost as much on his solution as the DCX unit itself!

Cheers,
Ron

p.s. I don't seem to be getting email notification from HTGuide anymore, wonder what's up with that?

[Davey]

I don't know about the LM1973 solution...never used them. Thorsten (who doesn't like any electronic solution) says he dislikes the LM1973's the least. For whatever that's worth.

Bdipoala's setup is nice, but I like the idea of building a separate external unit. That way you can use it for other purposes or other crosssovers in the future.

I'm getting a little tired of folks bad-mouthing or passing judgement (generally without auditioning) on the setup I came up with so I'm not following the threads too close anymore. I still think it's a viable solution, but needs to have remote capability and a few improvements to make it more attractive. I'm working on a re-designed PCB which will have everything, but it's not high on my priority list right now.

Cheers,

Davey.

[RonS]

Thanks Davey.

I'm tempted to go with your design, as I already have the 6 SSM2018T chips at hand. Problem is that I don't have the time/inclination to design a board, and remote control would be very nice indeed.

If I could figure out a way to do remote control easily, I'd go for it, but I'm more a woodworking/speaker building kind of guy, not very deep into the sparks end of things (I can follow a schematic, but forget about designing something from the ground up!)

Cheers,
Ron

[Victor]

For those in North America who are interested, I heard back from Decibel HIFi about their K3 kit. First, it is out of stock until mid April. Second, a 110V transformer is an additional $40AUS. Insured mailing to Canada runs another $95AUD. All in all, too expensive for what it is. By the way, the kit is based on an article published in SiliconChip magazine, in two parts. I bought the first part, which has a full parts list, pcb layout and schematics. It's based on a National LM1973N 3 channel resistor attenuator chip. The biggest problem in building one is that there is a PIC chip that needs to be programmed. Anyone know of a place that will program them? Otherwise, the unit is pretty straight forward to build. Distortion starts to rise above 1kHz, but that may be due to the use of TL072 opamps (they're used as output buffers), something better like an OPA2134 might help.

Ron

Hi Ron,

I looked at this design too. The THD rise above 1 kHz is due to the LM1973. The OP-amps although dated are not at fault. I was considering this kit until I noticed the rather high THD numbers. I think you are right that the overall price with 110 V conversion and shipping is kind of high.

Anyway I ended building the potentiometer based five channel volume control with infrared remote based on Alps motorized pots. Each channel has 3 single pot sections. I can achieve better then 0.5% tracking channel to channel for all 15 sections. As for the controllability I can control any combination of channels from 1 to 5 with the remote.

I think if you want a solid state solution you will be better of with Analog Devices or TI VCA parts. The amount of work needed to built such volume control is the same as in the case of LM1973, but you will definitely get a better overall solution.

Regards,
Victor

[RonS]

Hi Ron,



Anyway I ended building the potentiometer based five channel volume control with infrared remote based on Alps motorized pots. Each channel has 3 single pot sections. I can achieve better then 0.5% tracking channel to channel for all 15 sections. As for the controllability I can control any combination of channels from 1 to 5 with the remote.

I think if you want a solid state solution you will be better of with Analog Devices or TI VCA parts. The amount of work needed to built such volume control is the same as in the case of LM1973, but you will definitely get a better overall solution.

Regards,
Victor

Victor, can you elaborate on your remote control solution? I'm very tempted to go with the AD VCA parts (I have them at hand) but remote control would be a very nice addition to Davey's efforts.

Cheers,
Ron

P.S. We should get together one day, I'm in mid town Toronto.

[Dennis H]

Let's not forget the cheap prefab solution. Buy some cheap receivers used on Audiogon. Some of them have decent though low-powered amps to my ear but I've been accused of being deaf before. Anyway, you get amps and remote volume control all in one box. You can use as many boxes as you need and they will all operate from one remote. If you need more power for some channels, use the receiver's preamp outputs to external amps.

[Victor]

Victor, can you elaborate on your remote control solution? I'm very tempted to go with the AD VCA parts (I have them at hand) but remote control would be a very nice addition to Davey's efforts.

Certainly Ron, - here it is,

My volume control project was motivated by the need to have quite a few channels, - at least 12. You see, my HT has dipole speakers in all 4 corners, - the fronts are 3-way and the rears are 2-way. I use two DCX2496 to control them. So far I need 10 channels, but I may need as many as 16 once I add some subwoofers and possibly side surrounds. I do not use a front center channel.

So, the volume controller must have better then 1% tracking error, have infrared remote capability and can also be used as a kind of balance control, i.e. any combination of channels must be independently controlled. To top it off,- I also wanted to use good old mechanical potentiometers.

In order to solve the tracking problem I needed linear pots. The solution is simple, - turn linear pot in to the log pot by adding a resistor from the wiper to ground. The pot to resistor ratio is about 1:7. So, my pots are 10k linear and I use 1.46k resistor. The parallel combination of the resistor and the pot forces the overall resistance value to be dominated by the 1.46k resistor while giving me a logarithmic law. Also, this resistor can be a high quality 1% unit which goes nicely with one of my compulsions of using good parts whenever possible. In the end all pots are now tracking to better then 1 %.

Next problem was to fix the rotation speed of the pots. The pots I got are Alps 2-channel motorized units and I have 10 of them. You can get them for $3.50US here

http://www.allelectronics.com/cgi-bin/category.cgi?category=470010&type=store

The motors track to within 2 seconds from each other for the full turn. Naturally this is a problem. After all I need at least 3-channel pot for my front speakers and I must have all 3 channels turning together at the same rate. So my solution was to turn 2 channel pot into a 4 channel pot. I place 2 pots back to back and use a shaft connector to bind the shafts together. Now the entire thing acts as one 4-channel pot. Actually because of how those pots are wired internally it becomes only a 3-channel pot, which is also fine for my purposes. All I have to do is wire one of the pots electrically as a mirror image of another. Pairing up the pots also solves the rotational tracking problem to a greatest degree. Additionally the resistors can be used to completely optimize the rotation speed so it is identical for all pots.

Finally, I got a module on the net that give me a motor control with infrared remote using standard Philips codes. I also got a relay switching matrix board that enabled me to activate any or all of the relays with the same remote control. The motor control board gets wired to the pot’s motors through the relay board.

And here you have it, - out of 10 dual motorized pots I now have five 3-channels pots that I can control independently. No tracking problems at all. All pots rotate with the same speed and show identical resistance with the required logarithmic law. It takes about 40 seconds for a full turn, which makes the control very sensitive.

I know that my approach is kind of out of the left field, but with the overall cost of about $120US I now have what is considered to be a very high quality multi-channel volume control with remote.

The VCA approach is also very credible, particularly with Analog Devices chips. You will have no tracking problems with VCA’s and multiple identical channels are possible. The THD of the VCA approach is also low enough. You can easily add a remote control to the VCA design by simply getting a cheap single channel motorized linear pot and an motor control board with remote capability and you are done.

[RonS]

Hi Victor,

Thank you for the detailed description of your setup. Can you tell me where on the net you bought your remote control setup? That's the piece of the puzzle that I'm currently missing. I found a place in Europe, but it's pretty expensive.

Cheers,
Ron

[Davey]

Ron,

Maybe something you're not interested in, but how 'bout a multi-channel receiver functioning as volume control and power amplifiers?

http://us.marantz.com/shop/_templates/Proddetail.asp?model=7&cat=15

The Marantz SR4500 is a pretty cool unit.

Cheers,

Davey.

[Dennis H]

That Marantz looks pretty nice. It has a 7.1 input. Most of the cheap ones only have 5.1 inputs so two of the amp channels go unused.

[RonS]

Ron,

Maybe something you're not interested in, but how 'bout a multi-channel receiver functioning as volume control and power amplifiers?

http://us.marantz.com/shop/_templates/Proddetail.asp?model=7&cat=15

The Marantz SR4500 is a pretty cool unit.

Cheers,

Davey.

Davey, I had thought of that scenerio as I can get extremely good deals on NAD gear (I'm their photographer). Problem is that most of these multi channel amps, even the ones that have 5.1/7.1 inputs redigitize the signal so that they can do all of their processing magic. I really want to avoid that. But it is a cheap way of doing it. Maybe I'll call NAD tomorrow and ask them about their units.

By the way, I've ordered a rack case for the volume control, decided to build the VCA design that you made. I'm going to use a trick that I learned from Bob Pease over at National Semiconductor. It's basically hardwiring everything, but you use wirewrap IC sockets, which you tack solder to a copper clad board which acts as a ground plane. You use a socket that has more pins than the IC device that you are using, so I'll be using a 20 pin socket, and soldering the 2 pins on either end to the copper clad. the remainding pins get bent up and the various parts soldered to them. Makes for a very quick prototype board. It will be the first time I've done this, but I think it should work well.

Cheers,
Ron

[Dennis H]

Very few of the cheap receivers digitize the multichannel inputs. It costs money to put in all those ADCs. And those that do usually give you a straight passthrough option. So you're looking at a straight analog preamp, volume control and power amp. Maybe not "audiophile" (rhymes with pedophile ) quality but that Marantz has a 105dB S/N ratio -- not to shabby for a preamp, power amp combo.

[RonS]

Hmmm. I'll have to look into this more carefully. Now that I've spent money on a rack case :cry: It would sure make for fewer boxes though.

Ron

[Davey]

My understanding is the same as Dennis' that in most (and I'm fairly sure the Marantz) the signal remains analog if using the optional multi-channel inputs. I think it would encounter the volume control first thing and then probably some sort of analog preamp section before heading to the power amplifier channels.....discrete in this case. It seems like a neat solution for the problem. I've seen the 4500 for approximately $400, and the earlier 4400 for about $300 at various places.

Ron,

I'll send you a schematic for simplified and improved control voltage generator vice the one posted the web page.
I've seen the copper-board-used-as-a-ground-plane-with-prototyped-circuits-stuck-to-it method used before, but I've never tried it. Sounds like it should work great.

Cheers,

Davey.

[sfdoddsy]

If you're just after fixed attenuation Decibel have the passive six channel thingy which I had for a while until I lost it. But for variable I have to agree with the other guys about a cheap low noise receiver. If you could find one of the H/Ks or Marantzes from a few years back with pre-ins and outs you could get yourself a cheap power amp too.

Steve

[RonS]

Ron,

Maybe something you're not interested in, but how 'bout a multi-channel receiver functioning as volume control and power amplifiers?

http://us.marantz.com/shop/_templates/Proddetail.asp?model=7&cat=15

The Marantz SR4500 is a pretty cool unit.

Cheers,

Davey.

Davey, have you used the Marantz SR4500 in a system like the Orion? If so, can you give us some feedback on your opinion of it (sound wise)? How does it cope with lower impedance loads? (manual states no lower than 6ohms, with paralleled mids my speaker easily drops lower than this).

Thanks!
Cheers,
Ron