Pro Audio Design Forum

Another question for you - since I'm using it in a high-Z circuit (passive filter), is charge injection going to be a major problem? Maybe even make this a dead end ?

I think it would be an issue. That's why I suggested the H11M1 OptoFET which has 0 charge injection.

1. If I understand you correctly, i can go ahead as per the drawing in the data sheet? Yes, correct. 2. learning here so bear with me, what is lBias? There has to be some path for the bias current at the input of the 1240 op amp to flow. That's true of all op amps. That current flows through one or...

FWIW The 1510 datasheet has just been updated with the protection and T-bias changes:

http://www.thatcorp.com/datashts/1500data.pdf

I didn't exactly say the right thing. One of the inputs has to have a DC path, not necessarily to ground. If you tie one of the 9Ks to an op amp output (as you intend to do) the bias current will have a DC path. Both inputs (pins 1 and 3) cannot be AC-coupled since there's no DC path for Ibias. If y...

1. in the parallel section can a 1246 drive 2x 1646's? Yes, but what Roger said. 2 in the summing section, can i add a mute switch and attenuator where indicated? What Roger said. 3. and can i use the 1240 in summing mode as the data sheets specifies using the ref input so you have two matched 9k i...

Yes, exactly. Though a center detent may not be necessary. The center is fairly wide. Most of the action is near the ends. I'd say about a third of the rotation in the center is subtle. The outer thirds are where stuff starts to happen. An ideal solution is a dual stepped switch with a bias resistor...

Guys - I just did some crosstalk measurements on the matrix board after modifying it. In precision bypass mode* the 20 kHz crosstalk was: L into R -81.5 dBu R into L -75.5 dBu * Full encode/decode but with the encoder's 1646 and the decoder's 1246 bypassed. From points C to F here: http://www.picoco...

I'm OK but one thing, I'm confused by the padding resistor you mention? we are talking about the 2x 22k resistors? Yes, those are the padding resistors for an ideal pot. With an inexact pot (all those without ground taps in the center), one of the 22Ks will have a third resistor in parallel to make...

1. the potential divider resistors across the pot,is there a value suggestion here? or just trial and error? you mention a trimmer also, would this replace and sit in any position of the divider? I think I used 22K resistors and the reason for choosing that value was to give it a better "feel....

The simpler 1240 can be used stand-alone.