Hello
I have been trying to get hold of a Sinad meter for a while now to setup and test my large collection of CB radios and ham radio gear, problem being that they dont show up for sale very often and when they do they are often in the states which attracts high shipping and duty costs, not to mention many dont work properly and need new capacitors and significant maintenance to work correctly, there is a fellow on youtube who repairs one and shows it at the end "working" when it actually isnt working
I posted a request on here for a meter in the wanted section with some helpful links suggested by some users, I tried the software versions of all types but there is significant hysteresis and lag which makes them very cumbersome to use, you after all cannot replicate the speed of a true analogue signal in real time without any conversion.
Inspired by the very helpful Wendymott a user on here who supplied me with some very useful information i started the build.
I already had vero board in stock, I picked up a pack of LM348N op amps from ebay for 2 pounds and a single 2N3819 J-Fet for the AGC part of the circuit, I already had the transistor in stock.
All the other components I had in the shack trays, I used 1% tolerance resistors and I matched the capacitors in the 1Khz notch filter to ensure it balanced properly, took about half a day to build the board and another half a day to find my faults, mostly not breaking the tracks on the back of the board.
Once built I tested the board using my dual channel scope and signal generator and got a lovely tight band block at 1Kz, so then I moved on to the case.
I designed the case in Design Spark, a free download from RS in the UK, really nice and easy program to use, the only other item I had to design the case around was the meter, I picked up a 200V moving coil meter from Amazon for 6 pounds, I removed the large series resistor, copied the scale from the Original Sinadder and printed it off, you can see on the back of the meter the offset adjustment pot I calibrated it with, meter with resistor removed was 0.5V FSD.
Just for fun I popped the original logo on the front of the case as this circuit is based on the Sinadder 3 original circuit without the analogue volt meter switch as I didnt need that facility, so i have a basic 3.5mm Audio jack on the side, an Illuminated orange push button on the top and the meter, all runs off my 12V bench supply, the illuminated button draws more current than the circuit does.
Before anyone asks its orange because I needed to use up the reel of plastic on my 3D printer as it was getting old and needed using up, besides I wont lose it now.
I have been testing it for a day or so and it works absolutely superb and matches all the software versions without the annoying lag, such a very useful tool to use for alignment.
I only built the AGC section, the filter and the rectifier to drive the meter, I also popped in the voltage divider circuit and supply capacitors as well as the Op Amps are dual rail.
Hope that inspires others to give it a go, it takes up very little room on the bench and I think it looks rather jolly as well, any questions I am happy to answer them.