Search found 5447 matches

by mediatechnology
Mon Dec 29, 2008 1:24 pm
Forum: Pro Audio Design
Topic: Mid Side M-S Matrix Uses No Precision Resistors
Replies: 271
Views: 619307

Re: Mid Side M-S Matrix Uses No Precision Resistors

I also tried the precision bypass mode and the crosstalk improved. I swapped the L&R channels from prior measurements. By hand picking 1246/1240 combinations I can make the L to R as good as the R to L numbers. Unfortunately on this prototype the left channel 1246 is soldered to a flying lead. T...
by mediatechnology
Mon Dec 29, 2008 12:08 pm
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

They were advised by THAT to use separate pads and buffers at + and - control ports. One inverting buffer and one non inverting buffer. This prevents hitting the VCA with a correlated noise source (in first buffer?). This seems like it should be a modest phenomenon but perhaps measurable with noisy...
by mediatechnology
Mon Dec 29, 2008 10:24 am
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

I do want to forward Igor's article to THAT however and ask about the differntial Ec drive. I really need to print it but I don't think I've seen that approach used before - just differential audio path and parallel is what I've seen.

Thanks for sending it Igor and joining us here in the forum.
by mediatechnology
Mon Dec 29, 2008 8:41 am
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

Wayne, have you ever discussed something like this with lads at THAT? The schematics you posted shows the typical parallel up a bunch, but that's to drop into some old sockets to make up for smaller geometry transistors. I wanted to show the Cv pads and buffers. The parallel-up-a-bunch doesn't make...
by mediatechnology
Sun Dec 28, 2008 2:06 pm
Forum: Pro Audio Design
Topic: Mid Side M-S Matrix Uses No Precision Resistors
Replies: 271
Views: 619307

Re: Mid Side M-S Matrix Uses No Precision Resistors

When I originally designed the matrix I was concerned about gain build-up during encoding in the Mid (L+R) channel and also in the decoder which produces not L and R, but 2L and 2R . In anticipation of that I designed the following circuit and then allowed myself to get talked out of using it off-fo...
by mediatechnology
Fri Dec 26, 2008 1:54 pm
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

The LM833 is compared by Douglas Self to the NE5532 with slightly higher noise and somewhat less drive capability. I think the 833 was National's answer to the 5532 and it's not a bad choice either. There may be a modest need for speed and output current in this stage to keep the output impedance fr...
by mediatechnology
Fri Dec 26, 2008 12:00 pm
Forum: The Peabody Lounge
Topic: Merry Christmas!
Replies: 3
Views: 7741

Re: Merry Christmas!

It's 77 here right now at noon with a high in the low 80s predicted. Great weather for doing after-Christmas cleanup.

If it dries out I may go for a bike ride. We've had really high humidity and things are very slick for 1-1/4" English racer tires.
by mediatechnology
Fri Dec 26, 2008 11:52 am
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

so low gain opamp noise is not as much of a concern as source impedance at control ports. You are correct that the op amp should buffer the pad or have less than unity (inverting) gain. I misspoke previously. An op amp's impedance rise vs frequency is particularly critical with most BIFETS showing ...
by mediatechnology
Thu Dec 25, 2008 7:49 pm
Forum: The Peabody Lounge
Topic: Merry Christmas!
Replies: 3
Views: 7741

Re: Merry Christmas!

Merry Christmas Roger and everyone!

Just back from a long day of eating....
by mediatechnology
Wed Dec 24, 2008 11:40 am
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 214225

Re: OTB Mixer Using Current Summation

John - One op amp driving one port would be best. We might consider however having a resistive attenuator at the Ec and using something more like 20dB/V rather than the native 6.1 mV/dB. As long as the source impedance at Ec is low the attenuator would not add significant noise or CV modulation. Off...