Bassblaster
Super Member
Once i figure out what kind of demand we have ill place another order for a panel. to give me an idea everyone who wants these boards like this post so i can just look at the numbers.
PA1002A workaround / replacement
- Thread starter Bob@FM
- Start date
Bassblaster
Super Member
Ive been off this project as ive only gotten 2 or 3 requests for boards, BUT good news ive been getting all my DIY projects piled up and when i order ill be getting a few small panels of these boards. would be 90 of them so probably last my life time lol
How have you been doing on the muting function?
Don't be discouraged by large time gaps, I see plenty of long gaps on the Constant Current Sources.
Of course, DIY instructions are out there prominently for those.
Bassblaster
Super Member
I Never done it has a never got a schematic from the original designer unless i completely missed it. Remember i just made the PCB's
KB4437 is a legitimate substitute for the PA1001A MPX decoder IC. There are still some of those floating around.
I would be interested in a couple of the PC boards, as I only have one KB4438 left, and have not been able to find any more.
Thanks
Bob
Thank you for the info Bob, it's appreciated!
Ya, I just finished a Pioneer SX-1280 that had both the PA1001A and the PA1002A ICs bad. I now only have one of each KB4437 and KB4438 left in stock. I found a source for some KB4437's (PA1001A) but the KB4438's (PA1002A) are apparently now made of UNOBTANIUM.
I would definitely be interested in some of the PC boards
I would definitely be interested in some of the PC boards
Bassblaster
Super Member
I HAVE 3 BOARDS! i was saving them for someone but after months he ever got back to me so back in the public they go.
shoot me a PM
shoot me a PM
Bassblaster
Super Member
Mouser BOM parts list. Might make a digikey list one of these days but i dont have a digikey account
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=4ea6de02c1
the muting board never got made as i never got the complete schematic from the thread starter Bob@FM
Bob@FM
Well-Known Member
The UK seller Little Diode has KB4438 and sells on Ebay. I ordered one for $15 delivered and it tested and worked fine.
https://www.ebay.com/itm/KB4438-Sem...152152?hash=item2602d33058:g:2ugAAOSwerRbmo8Z
I never tested the muting circuit, as I got sidetracked on other stuff, and apparently there is very little interest overall, probably as KB4438 are still around. The seller above has more than 10 available.
The PA1002A circuit/board I designed will let you use any op-amp you want, but no muting, yet... That is another board. Adding those two boards will be a lot more work than just popping in a new KB4438.
For some using a modern op-amp instead of the PA1002A/KB4438 may make a meaningful sonic upgrade, for others it may be a "don't care". I tend to think most may be in the second camp, and just want the tuner or receiver to work again. So the muting board is probably not worth pursuing, unless there is more interest (now or later).
Oldsansui441
Super Member
Good to know Bob as l have just recently ordered one also.
WOW!!!
I just finished working out the muting add on to the "Work Around" PC board. It uses a very small DPDT relay for the actual muting. It disconnects the chip output (pins 5 and 12) from the op amp output (pins 4 and 13), and connects the chip outputs (5&12) to their respective rail splitter outputs in mute (5 connects to 7, and 12 connects to 8) The relay coil + goes to VCC and the relay return is controlled by the collector of a 2SC1815 transistor to GND. The base is fed through a circuit with a timer for VCC on delay, and a circuit from pin 8 for normal muting.
Now that the KB4438's are available again, I don't think there is any need to continue with my adaptation.
MANY THANKS!!!!!! Bob@FM for finding the source. I have purchased a few for stock.
I just finished working out the muting add on to the "Work Around" PC board. It uses a very small DPDT relay for the actual muting. It disconnects the chip output (pins 5 and 12) from the op amp output (pins 4 and 13), and connects the chip outputs (5&12) to their respective rail splitter outputs in mute (5 connects to 7, and 12 connects to 8) The relay coil + goes to VCC and the relay return is controlled by the collector of a 2SC1815 transistor to GND. The base is fed through a circuit with a timer for VCC on delay, and a circuit from pin 8 for normal muting.
Now that the KB4438's are available again, I don't think there is any need to continue with my adaptation.
MANY THANKS!!!!!! Bob@FM for finding the source. I have purchased a few for stock.
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Oldsansui441
Super Member
Installed the KB4438 and can report the same result as Bob@FM, the new IC works very well, had to adjust VR2 slightly for proper muting function. I would say looking at the silk screening that they are a Chinese copy but they are advertised as generic so all good 
.
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I have learned over the long term not to count on odd (and inherently sporadic) sources for old parts.
I had enough fun year to year with mouser parts number changes, company sales (Fairchild being bought by On-Semi etc...) and entire series of capacitors being discontinued.
I would be grateful if you could either send me the interim work, (with appropriate non-disclosures, approbation, credit etc - I have done it before) or post it here for others to build on.
MY work on the output muting stalled until I could determine if the muted outputs are grounded(and what impedance, like ohms, kilo ohms or millivolts) ,
or high impedance as seen from the outside of the chip, and what is presented to the internal drives for the op-amp outputs.
I can post a schematic of my muting add on to the work around PC board. The only issues not yet complete yet are the R and C values for the turn on timing delay, as I have been experimenting with different values, and delays. The current prototype is just built up in "spider Web" construction. I can include a photo but I don't think it will help much (it's rather a mess)
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Bob@FM
Well-Known Member
My mute design simply takes the outputs to ground, through an optically switched solid state FET relay, controlled by another FET from the stock tuner mute signal. It can be added anywhere before the output phono jacks. I tested the unit with no muting for both turn on and turn off pops, and heard none (that were very loud), so did not worry about that. This is still untested. I have a couple different relays here I wanted to test. I wanted to do a universal design I could use for other projects, like outboard MPX decoders and home made preamps.
I have been testing the work around in a Pioneer TX-7800 Tuner, so the turn on and turn off pops are very apparent in the connected amp. In a Pioneer Receiver, I don't think they will show up because the protection relay is open when the turn on pop occurs, and I suspect the protect relay opens again before the +13 volts drops causing the turn off pop. In the tuner there is nothing to stop the pop from reaching the amplifier. The design I am working on is an addition to the "Work Around" PC board, so it will be "Plug and Play" for the PA1002A (no additional connections). I have the normal inter station mute working properly, the turn on pop issue figured out (still working on ideal timing values), and I still need to design some circuitry to take care of the turn off pop.
Bob@FM
Well-Known Member
OK, it makes sense to do a new design / board with it all on there. I hope figuring out the rail splitter / op-amp stuff helped a little.
I don't have big speakers hooked up in my lab, so how apparent the low end pop is can be relative. Most guys know to turn the volume down anyways, I am hoping? Switching things on and off in with the volume cranked up is never something I recommend to anyone, but shirt happens.