Cheap Surround sound buffer/level shifter

[JR.]

pop'd all the TH parts... disregard all the missing parts on the legend... they are for JIC tweaks. Looking at the picture reveals a missing cap for the V/2 (since pop'd).

Next step is to apply 5V and see what catches fire...

two wires for every input and output times six... 5V will come here first, and then go to decoder. So 30 individual wires to connect and solder.

JR

PS: I haven't settled on how to order the channels for logical dancing LEDs display... My thinking now goes from left to right I will show; L surround, L front, center, sub, R front, R surround. The channel LEDs are green and one far right LED is red for overload. This display is a variant on my old FLS patent that will light only one green LED for the loudest channel. This will either be slick or a dud... time will tell.

[update- no smoke but no love,,, first the v/2 was shorted to GND by a solder blob... after clearing that it is now 1.8V so better and a few channel of op amp appear biased up... a few not... more debug to go, but this is more straightforward, with parts of it working. /update]

[JR.]

Damn.... I was trying to troubleshoot my blinky light circuit, and I was measuring OK junctions but in my overload red LED circuit, the NPN (3904) was behaving like it had really low hfe, dragging down its bias string? Hmmm NPNs used backwards with collector and emitter leads swapped still work and show typical junction diode drops all around but exhibit low hfe. Ding ding ding, I had somehow grabbed a bogus GP NPN SOT23 footprint in the eagle schematic capture library.

My stash of to92 2n3904s was out of hand but I found a bag of MPS-A06 a higher voltage gp npn... I tacked two of them in and that circuit started working but i still have 6 backwards 3904s on the individual channels. I might be able to place the sot23 package upside down, and bend the leads in the other direction..

I have given up looking pretty... Now I just want it to work,,, but this is hugely irritating.

[update- these sot23 devices are too small to hold and bend the leads up instead of own, but tacking resistor leads to the pads and tacking the device in upside down works.... don't tell anybody. /update]

JR

PS: I deleted the bogus footprint but i think it said IPC standard or something like that... arghhhh

[mediatechnology]

So are your blinky lights working now that you inverted the transistors?

[JR.]

So are your blinky lights working now that you inverted the transistors?

It turns out I wasn't able to use the sot23 transistors upside down, so I tacked to92 TH devices in and that is working better. I haven't really been able to give this project uninterrupted attention, but every time I sit down I find and fix another problem.

Late today I finally powered up my scope and test set for the first time in years to bang some sine waves through it... It took me a half hour this afternoon rooting around in my back lab to find a 1/4" plug to go into the TS-1 output to get a sine wave out. My audio test bench is in pretty sad shape from neglect and lack of use.

After beer oclock today i found the latest instability... The input pots/attenuators are designed to get their ground from the digital decoder. which isn't connected yet, so they were floating. Tomorrow I will ground all those input trims that should make things more stable.

I still fell lucky, but that stencil/solder paste experiment was a fail... Too much paste in some places and not enough in others.

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But I have other distractions tomorrow, I'm putting new tires on my ride, because the old ones are showing signs of dry rot. That shouldn't take too long.The new tires will be more of a pain in my pocket. I finally have the mustang running strong like when it was new, but the check engine light is still on. Might be time for some black tape over the check engine light. I checked and the engine is still there.

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I figured out a solution to another different problem... I finally cut holes through a few walls and mounted the air blower to my bathroom ceiling. For summer cooling I just leave it powered up all the time, but last winter for heat assist I had the blower being controlled by the thermostat in my back bedroom. My new solution for winter heat is to run an extension cord inside the 8" air duct feeding the back bedroom. I can plug that in where I did last winter to get thermostatic control. In the bathroom to select between heat mode and cooling mode I will use a 120VAC DPDT relay. When I turn on the wall switch in the bathroom for summer cooling, the energized relay disconnects power from the bedroom thermostat and connects to the bathroom mains power. I have a suitable (30a) relay on order so this will be sorted soon enough. I wasted some time trying to design a solid state circuit to automatically steer the power between the two feeds, but the relay is simple and robust. I don't want to leave behind too many inexplicable systems for the next owner to figure out. I will only need to label the bathroom wall switch summer/winter.

JR

[JR.]

Sorry for the delay but putting new tires on my car took a lot out of me (like $750 ).... Actually I have several projects backing up but I got back on the bench today.

With all the gain trim pots grounded the circuit is much better behaved. 5 of the 6 channels are passing signal cleanly and the light show is working, even the red overload LED is behaving perfectly . (that is probably patentable as an improvement patent to FLS but so what?)

So next I need to fix the one channel, probably more bad solder connections.

mo lata...

JR

[JR.]

I have all 6 channels passing clean sine waves. I don' feel lucky about the quality of the solder job, or the TH transistors tacked to SMD pads. I already lifted one top pad/trace. If I don't use TH LEDs I can use one of the plated thru holes for the transistor collector lead that will make a robust connection.

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I don't want to make too big of a deal about the IMO clever overload add-on to the FLS steering circuit. This is not that much of an advantage for the typical FLS GEQ application that only has one or two audio paths... BUT, one of the latter mixers I designed at Peavey a 24 input monitor console had a FLS (loudest input) LED on every mixer input strip... The concept was to help the operator identify which mic input was causing the feedback during a feedback event.

My FLS variant overload circuit added to that 24 input loudest channel indicator, could tell the headroom status of the entire console with one LED. If the OL LED lights the operator knows one channel is hot, and then the operator can scan across the inputs to see which input is overloading from the per channel FLS LED.

This would have been a brilliant idea if I had it 20+ years ago... Thats life.

JR

[JR.]

More delays, I was sold out of drum tuners so had to build a couple more... now done.

===

Next step is to label the speaker jacks and plugs, then proceed to final integration.

mo lata...

JR

[update- speakers and jacks labelled ... check
TH transistors all grabbing at least one plated thru hole... check
next... fire in the hole. [/update}

[update 2 no smoke, loud, but noise floor is not where I want it. /update]

[JR.]

Apparently I had a false sense of confidence in telescoping the the single ended output and ground from the decoder out through my bump board. After a few simple experiments it appears that my level trim pots were acting like noise antennas.

To KISS I removed all the input pots and fed direct into the first gain stage. Instead of telescoping each output channel ground through the pots, I bused all those input grounds together and tied them over to the power ground. In theory this creates a ground loop, but the proof in the pudding is that I now have a quiet noise floor, and the extra 8 dB of gain.

My light show is pretty much a fail... While I could see good results on the bench with one sine wave input at a time, in practice the sensitivity does not make a blinky display.

I'll need to soak that in beer for a few days, but I accomplished my original goal, louder and clear....

JR

[mediatechnology]

Glad its quiet!

[JR.]

Glad its quiet!

Loud and quiet a good combination....

I think I have a plan to make the blinky lights start blinking but not tonight.

The extra 8dB of level makes a good difference.

JR