Search found 11 matches

by Igor Dockx
Mon Nov 06, 2017 6:19 am
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 4870

Re: Digital gain control w/ analog VCA: PTAT

Thanks Wayne, U4 also inverts the current. I haven't found a way to make the LM334 sink current, as to be able to omit U4... In my application, the DAC's live in a 19" rack a couple of meters away from the console which holds the VCA's I'll have to double-check, but the DAC rack is probably quite st...
by Igor Dockx
Sun Nov 05, 2017 1:18 pm
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 4870

Re: Digital gain control w/ analog VCA: PTAT

Okay, I'm not a designer and I'm not familiar working with current mode devices... But here's an attempt: DAC VCA balanced drive PTAT compensation draft.png The LM334 current source produces -10V at the output of U4 at room temperature; R8 turns this into a current of about -30,5µA which shifts the ...
by Igor Dockx
Tue Oct 31, 2017 2:58 pm
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 4870

Re: Digital gain control w/ analog VCA: PTAT

If I understand correctly, at VCA gains different from 0dB, the VCA's gain drops as temperature rises. The solution proposed by That Corp in their Design Note 02 does connect between the DAC's output and the rescale buffer, and thus seems to be needed per DAC channel... Since all eight VCA's in my a...
by Igor Dockx
Mon Oct 30, 2017 3:18 pm
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 4870

Digital gain control w/ analog VCA: PTAT

Hi, I am looking into controlling eight VCA's by a single-chip 8-channel DCA with 5V supply. I digested what I could find about the subject on this forum, and came up with the following existing balanced-drive schematic, which I simulated and proves to be working according to my requirements: DAC VC...
by Igor Dockx
Mon Jun 19, 2017 1:33 pm
Forum: Pro Audio Design
Topic: Linearize 'log' VCA's response
Replies: 13
Views: 7684

Re: Linearize 'log' VCA's response

Hi Wayne and John, Thanks for your valuable comments. I'll certainly look at John's proposed economic solution; a good opportunity for me to further explore LT Spice. I simulated the EDN-circuit with inverted reference current; applying +5V DC as reference voltage gives 0dB thru the VCA if the input...
by Igor Dockx
Thu Jun 15, 2017 3:12 pm
Forum: Pro Audio Design
Topic: Linearize 'log' VCA's response
Replies: 13
Views: 7684

Re: Linearize 'log' VCA's response

Hi Wayne and John, I spent a couple of hours behind my computer today and decided to give LT Spice a try. I found a 2181A model and did some simulations. I can proudly report that Wayne's assumptions were correct; I managed to obtain linear VCA control with two 2181's using the schematics in my firs...
by Igor Dockx
Wed Jun 14, 2017 1:31 pm
Forum: Pro Audio Design
Topic: Linearize 'log' VCA's response
Replies: 13
Views: 7684

Linearize 'log' VCA's response

Hi All, Some time ago I built a linear VCA using two sections of the SSM2164 quad VCA, following an old schematic, see attach. It works great. I am wondering if the same trick can be done using two THAT 2181 VCA's. Ultimately my goal is to build a linear VCA to allow me to add VCA automation to some...
by Igor Dockx
Sat Jan 30, 2010 4:11 pm
Forum: Pro Audio Design
Topic: Sum bus theory and practice
Replies: 37
Views: 39316

Re: Sum bus theory and practice

Hi John, Thanks for your reaction! Here's another question; I hope it's okay to post it in this thread since it has nothing to do with current summing. I have this Amek Channel in a Box; it has a trafo-coupled line input that can be converted into a virtual earth mixer by bypassing the 5K1 resistors...
by Igor Dockx
Tue Jan 26, 2010 3:22 pm
Forum: Pro Audio Design
Topic: Sum bus theory and practice
Replies: 37
Views: 39316

Re: Sum bus theory and practice

Dear John, Would you comment on how you'd go about implementing the current summing principle in a conventional mixing desk with mono input channels, and a pan circuit between the fader and the current summer? So actually my question is, what would a "current panner" ideally look like, if it were to...
by Igor Dockx
Sat Jan 03, 2009 4:07 am
Forum: Pro Audio Design
Topic: OTB Mixer Using Current Summation
Replies: 137
Views: 152173

Re: OTB Mixer Using Current Summation

Hi John and all, Happy new year! Yes, let's get the best out of your design so one more vote for differential drive. Nothing comes for free; I think the use of two more opamps is justified here. It might always be considered to make use of the That Analog Engines, which offer VCA, RMS-detector and t...