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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 3rd February 2011, 01:13 PM   #21
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I took this one, HD44780 compatible, 5VDC power supply, driven by a PIC.

Click the image to open in full size.

Here is, where you can buy it:

LCD Display HD44780 2x16 BLUE 16x2 Blau white weissFSTN bei eBay.de: Bauelemente (endet 03.02.11 21:29:55 MEZ)


Price: 4.00Ä

Best regards - Rudi_Ratlos
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Old 3rd February 2011, 03:00 PM   #22
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I see there is a long ribbon cable coming off the lcd.

my current design and build preference is to follow a so-called 'backpack' style, such as:

Click the image to open in full size.

and in use on a test bed:

Click the image to open in full size.

there is an LCD/IR/motorPot 'remote head' and it controls a volume control engine (that big motherboard thing) via a simple i2c+power cable. the ribbon just needs 4 wires (I use 6 to double up on power and gnd) and then it can control any downstream i2c device as well as give or get power from it (in this case, the mobo gets power and sends it *to* the display/control head).

you can see this can even be a distributed setup where the remote head is in one fancy display box and the back-end that handles the mess of wires is somewhere else. you *can* put them in the same box, but you don't *have* to. control is digital and audio path is pure analog.

anyway, I now try to do my control over i2c instead of bulky parallel cables. and since the PGA chips are SPI (more chips means more chipselect lines) I'd prefer to front-end all SPI devices with bit-banged i2c (not great for speed but fast enough for the application).
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Last edited by linuxworks; 3rd February 2011 at 03:03 PM.
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Old 6th February 2011, 03:13 AM   #23
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I'm now $30 poorer but the $30 bought some nice new results for me

AMB Laboratories DIY Audio • View topic - VFD display experiment

Click the image to open in full size.

Click the image to open in full size.

its pretty much plug and play! I made some minor adapting from my lcd edge connector so that pin3 for contrast is 'open' and pins 15,16 are also 'open':

Click the image to open in full size.

and that keeps the backlight on the controller from doing anything on the lcd as well as that contrast pot pin (that normally should be N/C but just in case, its REALLY a N/C now).

power it up and it says hello

Click the image to open in full size.

to be really complete, you should have some way for the controller to know if its lcd or vfd and if its vfd, send 4 levels of brightness on the bottom 2 bits of a special control byte, you send over the 4 bit interface. if its lcd, you vary the pwm output to pins 15,16. but if you don't care about brightness, then this should just power on and work as-is.

(tested on my own controller; no idea about the ebay one but I'm not planning on using the ebay controller; just the ebay vol control engine/board and interfacing my controller to that).
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Old 6th February 2011, 08:11 AM   #24
ads2 is offline ads2  France
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That's is the good news of today :-)
Waiting for this board to be available....
Any plan to have a board for the PGA2311 also?
Regards

Armindo
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Old 6th February 2011, 08:38 AM   #25
Draki is offline Draki  Macedonia
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Default 6 ch volume control e-bay

Anybody familiar with this 6-ch volume control? Looks like it may work with 2 or 3 way active crossovers (such as DCX).

6Way M62446 5.1 Volume Remote Control Preamplifier Kit - eBay (item 260706403227 end time Feb-08-11 20:21:36 PST)
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Old 6th February 2011, 12:56 PM   #26
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I can't tell what chip that uses for vol control on that ebay board.

and like us, you will get little support and probably the wrong or outdated schematic ;(

also, the pcb layouts on these cheap chinese boards are really BAD. no decent ground planing, inputs near outputs or inputs near clock sources, bypass caps too far away from chips, etc. just really a bad effort overall. and depending on how mean the seller/maker is, they can even SCRATCH OFF CHIP MARKINGS on chips before selling to you. you can't know what the chip is or even if its fake. want to replace it later? good luck. ;(

also note, the ribbon cable is probably where your analog-out goes (!). does that look audio grade to you? not me.

I got my kit knowing it would be a test bed for me but not to use in real life. afterI got my kit, looking at the really bad trace layout and design of the board, I still feel it would not be suitable for use in anything but a kid's first stereo set. not really audiophile grade, imho.

almost every time I buy from china, I regret it for one reason or another; so I can't really recommend using these systems as-is. heavily modified, maybe they will be ok.
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Last edited by linuxworks; 6th February 2011 at 12:59 PM.
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Old 6th February 2011, 02:14 PM   #27
ads2 is offline ads2  France
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I have just finished this temporary kit.... very disapointed.
sound loose a lot of detail. sound is more detailed on my Dac Zero using the integrated preamplifier (that don't use a HDAM on this stage) than Direct RCA output using HDAM and with this kit.
LCD display is a real bad choice. White text on a blue background, at 2 meter I can't read it, nothing compared to my DIY CD transport with VFD display.
Will wait for LCDuino (or VFDuino) and a good PCB board for the PGA2311 to use with.
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Old 6th February 2011, 02:55 PM   #28
Draki is offline Draki  Macedonia
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Tend to agree that e-baying from China is a high risk. Anyway I ordered one so let's see what comes. Indeed it doesn't say which volume chip is used. The output opamps are NE5532 (luckily easily replacable, probably with LM4562's), I see the tantalum bypass caps fairly close....
I will post information here once I receive it.... Worst case, like you said: goes to kid's room. But let's see first.
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Old 6th February 2011, 03:56 PM   #29
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more good success today with that damned thirty dollar vfd (lol)

Click the image to open in full size.

I just dropped it in, after removing my old 'classic' lcd. its not mounted but the same screw holes (on 16x2) should work - that's kind of the whole point of a drop-in

I have not tested the audio path yet. no idea if a metal shield is needed or useful or ferrites or what. I just 'dropped it in' and at least at the logical level, it works. the same exact lcd routines I used to write to lcd's also seem to work unchanged, even with the bargraph graphics. no brightness control on unmod'd firmware but I plan to add the 2bits of levels and some way to config the thing (at install time) to tell it to treat it as an lcd or a vfd.

it also draws hundreds of ma. my regulator is getting warm now (7805). be aware of this.

I still think it might be good to have a 7805 just for this display and then 7805 for the arduino/rest of system. maybe overkill but it seems like a proper design decision unless we find its really totally not necessary.

there is also burn-in with vfd's. the spec sheets even mention that. so a screen saver is needed or an auto turn-off after non-use. I have that working in my lcd-based code (display can optionally fade off after 4 secs or so of non-IR or knob use) but I have yet to add that code for vfd's.

this color seems to match the logitech squeezebox (I have an SB3) and for that, I'm kind of happy. this new box will probably sit right next to the SB3 and so the colors and style will match, at least on the display parts.
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Old 6th February 2011, 03:57 PM   #30
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Quote:
Originally Posted by Draki View Post
Tend to agree that e-baying from China is a high risk. Anyway I ordered one so let's see what comes. Indeed it doesn't say which volume chip is used. The output opamps are NE5532 (luckily easily replacable, probably with LM4562's), I see the tantalum bypass caps fairly close....
I will post information here once I receive it.... Worst case, like you said: goes to kid's room. But let's see first.

there is no photo of the vol chip. I wonder... maybe its the surface mount version and its under the board. hope its not some 'wonder chip' with scratched off markings ;(
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