Cadet V Scaler BOM error for voltage reference, +/-5V to 0-1V [fixed]

cadet

#1

The version C BOM for Cadet V Scaler says DNP for U3 and U4, however, the circuit is obviously needed to offset the zero referenced +/-5V to the 0-1V output. All of the circuit resistors are in the BOM.


#2

Caps C5 and C9 for op amp U4 should also be populated.


#3

It’s been fixed, thank you!


#4

1v to 5v version has some errors too – the schematic and BOM don’t match. The schematic asks for TL072, but the BOM lists LM6172, which I’m hoping is correct, as I’d like to add some gain to video signals. Also, the vref. circuit looks a little strange – there’s an op-amp just connected to ground? I built some simple LM6172 amplifiers on strip without a reference and they didn’t work the way I expected.


#5

If you are doing video to video voltage conversions then use the very high bandwidth LM6172 parts. If you are doing audio to video or video to audio conversions then the TL072 op amps are more than adequate at 1/10th the cost.


#6

The vref circuit is not needed for 1V to 5V conversion since it is just a straight x 5 amplification. No DC offset is needed.


#7

The vref for U1 and U2 should be tied to ground in the 1V to 5V Alt A schematic. If the schematic is correct then it ties to nothing. I dont have a Scaler board in front of me so I cant check what happens in the actual board.


#8

I made a couple of LM6172 single-channel chiclets on strip to boost the outputs of some utility video mixers, and DUH, my circuit was biased weirdly not because of the vref (which I just had connected to GND) but because I didn’t tie the ground rails together. They work fine now. It was user error. I followed the schematic and just used LM6172 instead of TL072.

THANK YOU!


#9

Correcting my statement on the C5 alt A schematic, 1V to 5V. U4 is used solely to provide the ground to “vref” of the 4 scaler op amps. An LM6172 is a waste of money there. I would just use a TL072 for U4 regardless of the signal speed.


#10

Yeah, TL072, or you can probably jumper it easily! This was a case where I designed the C5 board and tried to include population options for a lot of things. Some of the alternate BOMs are a bit awkward, but it does show examples of flexible build possibilities (which was the intention.) In my case I wanted a board where I could do whatever preset amp/attenuation/offset arrangement I needed.


#11

Back to the Alt C BOM for +/-5V to 0-1V, there is an error in the value for R7. The BOM shows 10K, it should be 20K. 10K gives only -0.5V at the Vref output, which is halved by the inverting scaler op amp stages, giving +0.25 V offset for the 1 Vpp signal. Changing R7 to 20K fixes the offset range.


#12

Thanks @microtonal for creating this thread :grinning::+1:t3:
For everyone else, here is a link for the C5 Scaler page to find the updated BOMs and other info files just for the sake of speed.