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Old 18th December 2004, 05:52 PM   #1
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Default DCX2496 Volume control

I have a couple extra PCB's for a volume control circuit used on a DCX2496 crossover project. The circuit uses 12 solid state digital pots (Xicor X9C102).
Electrically the pots are positioned between the D/A converters and the output op-amp circuit. No modifications to the DCX2496 are necessary. The circuit plugs in between one of the ribbon cable connectors inside the 2496. (see attached picture) I cannot hear any difference in sound quality my system when the pots are inserted. I have made many electrical performance measurements to make sure the circuit works correctly.I am tri amplifying a pair a klipsch Lascala's with a sensitivity of 104db @1w and very sensitive to noise in the system, no increase in noise was measured or herd even with my ear next to the horn outputs.

The PCB's were made using a 4 layer FR4 with solid ground plain on the inner layers and controlled impedance trace widths. This type of layering construction is extremely expensive since the board house first makes two double sided PCB and then laminates them using an inner pre-preg layer. The board run cost over $1000 at a high quality shop not a cheap proto house you find on the web.

I would like to get $80 for the board. I know it is a little high but the quality is top notch and if you make a cheap double sided board this size at a web base shop it will cost you all of that. a schematic and parts layout drawings are included. all parts are available from Digi-key.

Volume adjustments can be made using a rotary control or an IR remote control with some additional hardware.The remote control inputs require a short to ground for an Up level increase on one input pin or a short to ground on the other input for down adjust. This can be accomplished with a relay contact or an open collector output from your IR remote receiver circuit ( not included in the PCB layout).

There is one small design error on the PCB that requires one trace to be cut and two jumper wires connected. This error was caused when I used Xicors application notes as a reference for the pin configuration. The app notes are wrong, this ****ed me off, the notes are supposed to help you not make things more difficult.
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Old 18th December 2004, 07:53 PM   #2
tg3 is offline tg3  United States
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Very nice design. A few ?s come to mind:

* estimated cost of completing the project
* PS requirements (including mA)
* adaptability for non-DCX2496 application (should be easy)
* looks like everythig is SMD except for PS caps

A schematic would also be nice to get some idea of the project complexity. You can email me if you don't want to post it.
Folly befits a fool.
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Old 19th December 2004, 12:39 PM   #3
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Default project cost

The most expensive parts are the digital pot IC's at $3.44 each.
You will need 12 of them if you are using the 6 balanced outputs. You would only need 6 IC's for unbalanced. Figure about $8 for all the other parts depending on the resources available to you.

The PCB is powered from the +/- 15 regulated supplies on the DCX2496. Current draw < 15mA. If running separate, you would need to supply the power from another source.

The design could easily be used for projects other than in a 2496. The PCB has a 2" X 2.5" "perf board" section for easy implementation of additional custom circuitry. This is basically a bunch of plated through hole at .1" centers.

I have no problem posting the schematic but I do not have it in a format that can be easily read. It is in Viewdraw CAD system. I will see if I can translate it into a pdf file.
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Old 19th December 2004, 05:35 PM   #4
tg3 is offline tg3  United States
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I use pdf995 to 'print' PDF files. Perfect for this type of application. Its free with a nag box, $10 otherwise.
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Old 19th December 2004, 05:58 PM   #5
Cobra2 is offline Cobra2  Norway
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Default User interface?

Can you read/see the volume/attenuation - value anywhere?

Arne K
Don't believe everything you think...
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Old 19th December 2004, 06:36 PM   #6
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How do you control the volume settings?

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Old 19th December 2004, 07:18 PM   #7
Davey is offline Davey  United States
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Excellent. Nicely done.

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Old 21st December 2004, 07:31 AM   #8
AR2 is offline AR2  United States
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I am interested in getting two boards if they are still available. Please let me know.
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Old 21st December 2004, 09:06 AM   #9
405man is offline 405man  Scotland
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I would be interested in one board if you have any available...Stuart
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Old 23rd December 2004, 07:17 AM   #10
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Default volume control schematic

OK, hopefully the schematic will answer some of your questions. See attached.

Sorry for the funky schematic symbol for the digital pots.

The volume control can be adjusted several ways. You can connect a couple N/O momentary switches to P14 to GND for Push vol. up or Push Vol. down function. The rate of change can be adjusted by tweaking a resistor value. Another technique is to connect the P14 to a couple of relay outputs on a remote control board. This is one of the ways I use it. The remote control transmitters and receiver board are available for $20 to $30 on the web.

The third way to adjust is to use a digital encoder controller (switch) This is a quadrature type switch I got from Dig key, the part number is on the schematic next to P15. P15-3 pin will need to be jumpered to P14-1 for this to work.

In the box labeled "Optional Circuitry" can be used for whatever. I am using U19 to provide a 0-1Vcd signal to a digital panel meter that displays the volume level. The schematic does not show the 1 V reference connection to H36 that is needed. I am using a digital Pot with a linier taper for this. The DPM then will display the number 0-100 for a level indication.

I am also using U16 to control an analogue (7th) channel for my subwoofer. The subwoofer volume tracks the levels of the other channels. I have mounted a couple of RCA jacks on the back of the DCX2496 for this.

In the top right corner of the schematic is a switch that can be used to program the volume at power up. If this switch is not used, the volume level at power up will be the same as it was at power down.

The attenuation level of the control will depend on the type of digital pot used. Xicor has several that will drop in the circuit. You can select one with different number of steps, tapers and max attenuation. Some of them go to infinity.

Please note that the schematic shows some components that do not have pads on the PCB. I have tacked some of them on where needed. These components are one with the? marks next to the ref. des.

Itís not clear in the low grade picture I attached earlier but the PCB fits nicely in the DCX2496 enclosure. So the only wires exiting the box are the 3 control wires. You can use some of the unused pins on the network connectors on the back of the 2496 for the control lines. This assumes you don't need the connectors for networking. This makes for a nice clean solution.

I currently have 4 unpopulated PCB's for anyone interested.

Please e-mail me at bdipoala@aol to make arrangements.

If any of you still have questions, just ask.
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