Search found 10 matches

by diffuse371
Sun Feb 18, 2018 5:08 pm
Forum: Pro Audio Design
Topic: LME49720 DECT Cordless Phone EMI Susceptibility
Replies: 7
Views: 5116

Re: LME49720 DECT Cordless Phone EMI Susceptibility

I wonder how frequency sensitive this is? It would be interesting to see how this plot changes with a different spectral pattern, it may just be that the internal geometry of the opamp has some structural resonance at 100Hz and it's harmonics. Whenever I see the die footprints for many modern ICs th...
by diffuse371
Tue Nov 14, 2017 7:13 am
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 5964

Re: Digital gain control w/ analog VCA: PTAT

That's a nice idea. 8 AD633s is hard to justify the cost of. You need to be careful about gain staging too, but it's easier that than hand trim the offsets. I can confirm that the LM234 is a good performance technique for compensating gain control elements in timed circuits like VCOs or filters thou...
by diffuse371
Mon Nov 13, 2017 11:18 pm
Forum: Pro Audio Design
Topic: Digital gain control w/ analog VCA: PTAT
Replies: 9
Views: 5964

Re: Digital gain control w/ analog VCA: PTAT

For temperature compensation of the kT/Q term of a VBE you need to multiply by the PTAT reference. All you have at the moment is a constant that is compensated. You are not compensating the voltage control coming from the DAC. For a pure voltage controlled amplitude application a resistor with tempe...
by diffuse371
Sat May 20, 2017 5:11 pm
Forum: Pro Audio Design
Topic: Super Low Distortion Ultra Pure Audio Oscillators Revisited
Replies: 40
Views: 33273

Re: Super Low Distortion Ultra Pure Audio Oscillators Revist

From an EMC point of view (radiated and through common power supply impedence) an RMS detector and a variable gain cell is a whole lot quieter than grabbing the peak of the cosine at the zero crossing of the sine, which is in the case of the HP8903 is 5 comparators, some logic and a monostable. I th...
by diffuse371
Sat May 20, 2017 2:34 pm
Forum: Pro Audio Design
Topic: Super Low Distortion Ultra Pure Audio Oscillators Revisited
Replies: 40
Views: 33273

Re: Super Low Distortion Ultra Pure Audio Oscillators Revist

Diffuse(?)... It looks like you have spent a lot of time on this. Did you ever mess with the trig identity (sin^2+cos^2=1) from quadrature outputs of a SVF to make a ripple free rectifier source? Of course this is never completely ripple free unless the two quadrature outputs are perfectly matched ...
by diffuse371
Sat May 20, 2017 12:52 am
Forum: Pro Audio Design
Topic: Super Low Distortion Ultra Pure Audio Oscillators Revisited
Replies: 40
Views: 33273

Re: Super Low Distortion Ultra Pure Audio Oscillators Revist

(quick caveat, most of my post is focussed on wide range VCOs) The trigonometry compensation method that I explored performs very well, although there are harmonic distortion products from the various nonlinearities of the 4 quadrant multipliers. With 3 untrimmed AD633s and 2 THAT2180As in the main ...
by diffuse371
Fri Mar 11, 2016 5:31 pm
Forum: Build
Topic: Low Distortion Sine Wave Oscillator
Replies: 6
Views: 9091

Re: Low Distortion Sine Wave Oscillator

Multiple similar products have reduced the component count by many factors using FPGAs and PICs. There are several technical reasons for generating sound in the analogue domain, but the one that I like the most is subatomic particle behaviour. An oscillator in a loop is very interesting when observe...
by diffuse371
Fri Mar 11, 2016 11:57 am
Forum: Build
Topic: Low Distortion Sine Wave Oscillator
Replies: 6
Views: 9091

Re: Low Distortion Sine Wave Oscillator

The AD534 is Gilbert's design, I would suspect he had a hand in it's revised version the AD734. I *think* the AD633 is based on the AD534 as well, but without much concern for laser trimming at the factory. I require heavy use of linear multiplication in my designs, and the above 4 quadrants multipl...
by diffuse371
Thu Mar 10, 2016 4:49 pm
Forum: Build
Topic: Low Distortion Sine Wave Oscillator
Replies: 6
Views: 9091

Re: Low Distortion Sine Wave Oscillator

There's a Barrie Gilbert patent called the Pythagorator that slims down the concept into a single IC.

http://www.patents.com/us-5714911.html

I tried quite a few variations on this topology and this one just works very well without any mess.
by diffuse371
Thu Mar 10, 2016 1:19 pm
Forum: Build
Topic: Low Distortion Sine Wave Oscillator
Replies: 6
Views: 9091

Low Distortion Sine Wave Oscillator

Hi all. I'm designing modular music synthesizers. I've made available for non commercial purposes a sub circuit of one of my designs. After considering some of the options available for low distortion sine, I preferred the idea of a real time compensation system that uses the trigonometric nature of...