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Old 4th March 2011, 04:05 PM   #81
alkasar is offline alkasar  France
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Interesting. Not much difference.

you know that you can load two measure sets in RMAA and show both on the graphs. Helps to visually compare
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Old 4th March 2011, 04:59 PM   #82
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is it possible to set the atten at a few other levels (on the pga) and then do the rmaa?

i wonder how noise and distortion change as you ask the pga to vary its atten range and even more so, what happens once you go into the + range and get actual gain from its internal op-amp.

I was not disappointed, overall, with the pga boards I tried but once you got over 0 db, the noise level did go up audibly.

I loved having the gain, though. at the time I was using a media streamer that had some 'movie mode audio bug' that would play 5.1dd/dts movies about 10db lower than they should have, when downmixed to 2.0. I needed and extra 10 of gain just to watch movies and hear the sound, and a pure attenuate-only control would not go high enough. yes, the media streamer was at fault, but still, it was nice having the 'above zero' gain for when it was needed.
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Old 5th March 2011, 03:15 AM   #83
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Hi,

Apart from the crosstalk (high end definition muddied by digital noise ?), the tests just show this volume control is performing at least on a par and potentially better than the sound card. I need better gear and better knowledge of the software to really test this thing.

And while the numbers are nice to know, to be honest, I'm far more concerned with real listening tests. Add in my time restrictions and, well, sorry, but that's it for me. Someone else's turn..... ;-)

For sure, I'm happy that this baby is good enough for the AV role it'll play.

Tom
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Old 22nd March 2011, 06:49 PM   #84
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I have the beginning of a test bed:

Click the image to open in full size.

Click the image to open in full size.

this is a 6 channel (3 PGA chips) ebay board that I'll use to test out my code and interface. the perf board is something I made last nite that will interface i2c down to bit-banged SPI (for the PGA). I have headers on my board and placed headers on the PGA board. now I have to make an adapter ribbon to map my bit definitions to the ones the PGA board expects. after that its a matter of connecting the analog in's and out's from patch points on the board to my rear jacks (not shown).

the case and lcd unit were from a previous build, so I saved a lot of effort on that. I installed this test bed of guts on a slide-out piece of plexiglass (still with white paper backing on it). it was easy to lay that on the case, lay the boards on top, mark wtih pencil and drill holes. very cheap and dirty for rapid prototyping and it keeps things in place. when I want to work on it, I slide the whole bottom layer out and work on it out of the case.

I was able to see lights on my LED strip blink 'as they should' when I turn the volume knob on my software. I have had this working in the past and so I think the software will still work today. I used the following bits:

bit0: common SPI clock
bit1: common SPI data
bit2: chip-select PGA-0
bit3: chip-select PGA-1
bit4: chip-select PGA-2
bit5: common MUTE

previously, I've always hard-wired mute to + and left it there, then just used software zeroes to mute the thing; but I had a spare bit in PE so might as well export it. I'll probabaly always OR in the ~MUTE bit as a 1 but at least if I want to play with it, the bit is there.

perhaps today I'll finish wiring this and give it a test run. laying down the phys infrastructure is never really the fun part, for me I put it off as long as I can; but if there's no infrastructure, there's no test bed and therefore, no software can be developed/tested.
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Old 22nd March 2011, 11:12 PM   #85
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update: it works!

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

only 1 chip is wired in right now but the software works and so does the board.

I can't comment on audio quality but that was never my purpose with this kit. I did avoid installing the front end resistors, caps, relays and driver transistors. input selection is happening in another module, not here.

so, proof of concept is complete. volumaster (my software for the arduino) is updated to include the PGA driver. if you want to use it you will have to build the i2c port adapter or patch the code to use direct arduino pins, if you want to go direct SPI (nothing wrong with that but I prefer i2c for universal and 'remotable' control).
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Old 23rd March 2011, 02:13 AM   #86
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Nice! this is exactly the implementation of the LCDuino I'm planning, is there a way to implement individual volume control, say for bi and tri-amping aplications?
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Old 23rd March 2011, 02:28 AM   #87
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right now, there's no provision at all for varying volume out of the 'gang' relationship. to do balance or fade and do it even somewhat well would mean another 500 bytes or more of code and I can't easily find that. yes, its that tight (out of about 30k of actual machine code). I've spent some time breaking things into 'ifdef' bundles so that people can choose which options to omit in order to be able to build AND load the image to the cpu.

once you hit a wall like that, I can't think of any other way than to give people choices at build time. for example, it takes a lot more code to support non-sony IR remotes and by removing nec/rc5/rc6, you gain at least another 500 bytes. really valuable room! seriously. so I can disable non-sony IR style remotes, choose to use a sony-device mode on some multibrand remote and be able to unlock a bunch of other goodies that I do want to have onboard. others may want full multibrand remote support and so would not be able to have relay and pga support, for example. or no spdif switch and d2 switch support. or remote bigfonts support.

back to my testbed, I wired up the other 2 channels (in my build) and they work, now, too. there's also a pic of the 'old shell' that was a single board stereo 127db relay atten and the new shell that is the PGA engine - but using the same exact face and cpu and code! I really wanted to have some pluggable vol engine support and I got it. also pluggable i/o selector support, for delta2 relay based OR 2 kinds of spdif/other switch (addr and bitmap modes on a port expander; that would select 1-of-n fabric for spdif or anything else you want). you can mix/match, too; pick pga for vol and spdif for i/o or pick d1 for vol and spdif for i/o, but only 1 from columnA and one from columnB (lol).

Click the image to open in full size.

very blurry handheld snapshot but the light was fading and I really hate using flash. (I also hate using camera flash, too. lol)
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Old 23rd March 2011, 02:37 AM   #88
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to properly answer the question, I think a combo of BOTH relays and a silent PGA would be idea. I think I'm going to do that.

with relays, you can pick your resolution. for 'balancing' or matching, i want a lot more than half-db. on the pga, you can only go down to a half, from one thing to the next. its there for completeness but I don't see any hifi use in it, to be honest.

what I want to solve this is what I call a 'trimmer box'. that device is there to normalize things and you'd have one on each amp's input, for example. those things are not full range vol controls but maybe only 20 or 30 db range (if even that) but carve those slots up into tinier pieces. the relays can do this extremely well and with high accuracy and pretty low cost, too. I did an 8bit tenth-db (25.5db max) build and it was meant as a subwoofer 'trimmer box'.

the neat thing about trimmer boxes is that you do NOT actively vary them. you set them, calibrate them if you will, then leave them alone.

with these latching relays, you could, in theory, bury a relay module IN your amps, 'calibrate' it and then remove both the controller and power from it. it will retain its last state until told otherwise. ie, never its passive and just 'runs' after its set. ideal for a trimmer!

I could envision a whole set of amps and speakers and each one having a trimmer module and a 'management port' that you connect to, one by one, calibrate and then move onto the next. I've never seen this done before and it might be a brand new idea, in fact. but its removing a 'calibration part' and saving cost and space along the way. just an idea..

anyway, the pga ganged volume pot would always move in unison and any downstream trimmer would adjust that 'common level' to whatever the subentity needs. the relays never move in vol-up/down operation and they never need power. the pga's move but they never make relay clicking.

win/win.

but you need 2 levels of box. toplevel and a bunch of sublevel trimmers.
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Old 23rd March 2011, 02:37 AM   #89
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would having several lcduinos running off of a common pot for master volume, and having several pots run off of its wiper for individual control? One main screen on the master of course.
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Old 23rd March 2011, 02:46 AM   #90
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you could series-run these. in fact, that's the whole idea on the distributed 'main vs trimmer' topology.

the top guy could be a relay guy or pga or regular analog control. the ones below could also be various technologies.

what I thought was key is that the lower ones offer very fine db resolution and ideally, they should be set-and-forget so they stay out of your way.

you could have a pga on top with 3 chips (like my board) and run 3 sets of stereo outs (tri-amp processed from a crossover). then those 3 sets would go to 3 trimmer boxes or one big box with 3 trimmer setups in it.

a custom version could be made that sets the offset level on each 'board' and leaves it there. that would be the cpu that talks to the trimmers.

the main vol cpu and display would not know or care of the eixstence of any downstream boxes. its ONLY job is to vary all 6 channels in sync and give the user half db up/down incrs. the daily use knob.

you could use ldr's downstream if you configure them for fine steps. or even motor pots whatever you want. but I do think the notion of trimmer is separate (when its a multi amp config) from the main vol attenuator.
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