Search found 67 matches

by ilya
Mon Dec 11, 2017 3:28 pm
Forum: Pro Audio Design
Topic: Incorporating LPF in the FET input stage
Replies: 9
Views: 7907

Re: Incorporating LPF in the FET input stage

Series Rin will be too noisy. I estimated a suitable R as 500K, which gave me a -97dBv Johnson noise. Cap on the output worked though. Where is it better to connect it? Before R56 or after? I'm getting different values of the cap depending on its position (roughly 100 times difference in capacitance).
by ilya
Mon Dec 11, 2017 1:00 pm
Forum: Pro Audio Design
Topic: Incorporating LPF in the FET input stage
Replies: 9
Views: 7907

Incorporating LPF in the FET input stage

I'm building a simple FET DI input and it has too wide bandwidth as it is. What is the best way to incorporate an LPF in this design? I've tried different things, but the most obvious is a cap across the resistor as shown (470p gives a good cut-off frequency). Are there any drawbacks to this method?...
by ilya
Fri Nov 24, 2017 1:18 pm
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 16557

Re: THAT 202XL recreation

JR. wrote:
Fri Nov 24, 2017 12:53 pm
enjoy the math (I don't) http://www.thatcorp.com/datashts/dn128.pdf

JR
Ugh..... Seen than. This stuff is far above my math grade unfortunately((((
by ilya
Fri Nov 24, 2017 12:26 pm
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 16557

Re: THAT 202XL recreation

I don't think that's correct. If you look at the 2181 datasheet page 2 table 3 it shows a +0.33% gain control tempco. You still need -0.33% to correct it. Also see equation 1 on page 5 of the 2181 datasheet for the delta-T term in the denominator: http://www.thatcorp.com/datashts/THAT_2181-Series_D...
by ilya
Fri Nov 24, 2017 10:20 am
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 16557

Re: THAT 202XL recreation

Sent a letter to THAT and it turned out I don't need tempcos for 2181 any more because it's already there on the chip. Now, if I understand correctly, I just remove the tempco (R8 in the 202XT circuit). Do I still need the R7 (6R8)? Can't figure what its function is. Everything else seems to be pret...
by ilya
Thu Nov 16, 2017 4:12 am
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 16557

Re: THAT 202XL recreation

I hate always being the wet blanket but WHY??????? (maybe I don't hate it, or I would stop doing it). I actually have a patent for a VCA (US04818951 roberts 1989), and stopped using my own after we (Peavey) could buy better ones from dbx.... The last generation IC VCA from THAT corp is superior to ...
by ilya
Wed Nov 15, 2017 8:47 am
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 16557

THAT 202XL recreation

I'm thinking of building an equivalent ov 202XL VCA for my compressor. I've studied the documents here: http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=34 While circuits look simple enough, there're a couple of things I'd like to clarify. All circuits use 3300ppm tempco resistor. Al...
by ilya
Thu Oct 12, 2017 2:53 pm
Forum: Pro Audio Design
Topic: Strange simulation results
Replies: 9
Views: 8197

Strange simulation results

I'm playing with a simple DI circuit in the simulator and here's a very strange thing that's happening. I'm following the output of the DI with a basic non-inverting op-amp block. When I use JFET op-amps, everything is fine. But when I put BJT op-amp, the input and output pins show a huge DC offset....
by ilya
Tue Sep 19, 2017 4:59 pm
Forum: Pro Audio Design
Topic: Log switch using binary coded relays - possible?
Replies: 6
Views: 5144

Re: Log switch using binary coded relays - possible?

This is an EQ project, so replacing a pot with a rotary switch is a very useful option. Especially if this pot is a dual rev log beast. My concern is tracking between the decks (which in rev log may be horrible). Slugging is an option, but it will require a higher resistance value pot, in my case ar...
by ilya
Tue Sep 19, 2017 2:43 pm
Forum: Pro Audio Design
Topic: Log switch using binary coded relays - possible?
Replies: 6
Views: 5144

Re: Log switch using binary coded relays - possible?

No luck with relays. It takes too many of them to cover any useful range of the log pot. I started to look in the direction of JFET switches which led me to one interestion TI app note with the schematic of video switcher. I played with it in the sim and it looks fine, I don't get any drastic increa...