Analog Devices ADG413--Incredible Audio Switch IC

Two of my favorite social media (S&M) things: IMSAI Guy's Chip of the Day vlog and finding a great surplus electronics deal on the web. 

This time I do both: my own chip of the day (more like chip of the quarter?  I blame my day job...): an audio/video frequency switch IC I found online at a great surplus price, Analog Device's ADG413BR.

MUX AND FLUX

Audio/digital switch IC's--MUX'es or "multiplexers"--are extremely useful for what we do. The classics contain them; inside Roland's Jupiter 8 (schematic here) and Oberheim's OBXa (here) you find CD4053 and CD4051 mux IC's. 

Details about MCU control of this IC family can be found here and here. 

The ADG413 is a 4-channel switch with superb specs: 50V rail-to-rail supply range compared to the CD4051's 20V, for instance.  

The problem with these high performance switch IC's is their expense. Digikey US sells the ADG413BRZ for $9.08USD in small quantities, compared to 79c each for 4051's on Amazon. 

I'll stick with CD4051's?

Not so fast!! An AudioDiWHY favorite, The Electronic Goldmine, had ADG413BR's on sale recently for $1.79USD each. The 413BR is an obsolete version of the current BRZ IC. The only difference I could see was that the surplus parts were not RoHS compliant. 

(Better to use non-ROHS parts than throw them away--but if they have to go, please get rid of them sensibly....)

An aside: I love The Electronic Goldmine. Hobbyist-friendly surplus stores are a dying breed with many of the great ones like Haltek long gone. Goldmine keeps fighting the good fight. Sign up for their 4AM daily email flyer (here)--good way to start your work day. 

Lifetime buy....

The IC's arrived quickly. I got them ready for the bench.

SOIC: an adapter was needed for breadboarding

Ready to roll....

QUICK WORD FROM THIS BLOG'S SPONSOR

Many thanks to PCBWAY for sponsoring the AudioDiWHY blog and for all the help they've provided over the years. You can help out this blog in a big way by checking out PCBWAY, here. 

As soon as I get my first ADG413 based PCB laid out I'll send the gerber to PCBWAY along with any other fabrication needs, including 3D printing and assembly. 

PCBWAY is super fast, super friendly, and does great work. Please consider using PCBWAY for your next audio project. 

MAKING BALLOON ANIMALS

With two ADG413's soldered up, time to see if I could lay out basic switch circuits.

I still hate breadboarding....

....but I'm slowly getting better. I have found extreme patience, along with using a quality breadboard and checking my work early and often, gets the job done.

Using the 413 to switch LED's off and on (doh). Seems working!

 

Wiring used for ADG413 tests. "IN" represents logic inputs. Yes, the 10K pulldown was necessary; I used 12V for Vdd, GND for VSS, and 5V for logic but found the IC accepted a surprisingly wide range of voltages for rails and logic. Nice! Also, Pins 6/7 are one of 4 I/O pairs and for all I/O audio or DC voltage can flow source to drain or drain to source, makes no difference. 

For breadboarding sanity I used a CD4069 hex inverter for ADG413 pins "IN2" and "IN3". Using an MCU control I'd do this inversion in software.

 A few ideas....

The ADG413 let me create common switch configurations without needing a lot of logic signals:

1-to-4 multiplexer:

Dual SPDT's:

4 SPST's:

DPDT:

1:8 multiplexer using a 74HC595. Use more IC's and get as many channels as you want.

Good tutorial for the 74HC595 IC is here.

OUTTRO

OK enough for now. I bought a lot of ADG413's so (hopefully) they make it into future designs--hours of fun! 

In the meantime, ROHS well, AI well, and above all: don't breathe the fumes.

Dual 13700-based LFO: Mo' Hotta, Mo' Frya

Readers--this is a work in progress, you can see the schem and pcb on the one page website here.

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Hidee Ho! This time I tried to turn a working OTA LFO design (post here) into a dual LFO/small PCB, based on a SOIC SMD LM13700 OTA chip. 

Guess what?  Damn thing didn't work, the LM13700 kept heating up, and I had no idea why. Update 9-14-25 ModWiggler to the rescue! got it working; update at the bottom of this post.

"Seems not working"

 Started as a PCB n' stencil, from the blog's sponsor PCBWAY

Lately I have been using SMD non-framework stencils extensively; speeds up fabrication

SPONSOR TIME....

PCBWAY has been instrumental in keeping this blog up off the ground.  

Serene, my totally friendly handler at PCBWAY, told me to tell you: this month they are having specials in addition to their usual great pricing: 

1. Purple Solder Mask: In September, it's free--they won't charge an extra fee for purple cool color PCB's. That's to say, for 10 purple 2-layer 100x100mm PCBs, it's only $5USD, rather than $38.43USD.

2. TPU(FDM) in 3D printing: TPU is good for you! This super-useful material starts from $12.45USD, but in September, it's priced from $7.96. The heavier the weight, the bigger the discount, which can be up to 80% off. Go Getim!

And as always--PCB has all sorts of cool services tailored to what we do; you can help this blog immensely by checking PCBWAY out via the link here. Thanks!

USELESS (?) BUILD PHOTOS

Back to the blown up dual LFO....

Maybe if I look at these pictures long enough I'll find a build fault. but really, it all looks pretty good to me.

Glooped paste and picked/placed parts pre-bake--looking good I think

As usual, I heated up the plate to 215C, let it sit a minute, then back down to 150C. I am always surprised how well this works and how forgiving the process is. 

Next I soldered in THT parts like trimmers and a few caps:

Finally soldered the edge connector:

Test time...nope! 

My power supply immediately went haywire--the voltages maxed out at about .25 to 2V while the current went to the 30mA limit on each rail. Not good. 

NASA we have a short--the 13700 got really hot, quickly. 

Removing the 13700 the short went away but (obviously) the LFO's didn't work.

So why doesn't this work (besides having removed the LM13700) ??

Was the 13700 a cheap fake? I replaced the LM13700 with chips from two different vendors (Digikey, Tayda), same problem; I removed the PNP transistors thinking maybe I had a I-abc issue, nope.  

I spent a couple more evenings troubleshooting, wishing the design was through-hole (I usually am glad it's not) so I could lift up IC pins. No love.

There was a time in my DiWHY journey where I would have kept slamming away on this until fixed, but I have built so many LFO's at this point that I realized: the hell with it, I can redesign it, pitch it, and/or move on. 

Above all, I had to make sure I was having fun, and more evenings troubleshooting this didn't feel like it'd be that.

I posted to the modwiggler DIY forum to see if those folks had ideas--maybe they'd save my bacon, they had before. 

If not, this one might be one and done for the dumpster.

update 9-13-25: Modwiggler to the rescue! In short order synthiq saw the problem:

If you look at the schematic (here), the power rails to the quad op amps are flipped!!!

That's at least part of the problem, right? 

Not sure why this foobar heated up the OTA and didn't smoke the TL074's, but, things definitely wouldn't work as-is. 

I wanted to test the rest of the design. I removed the TL074's and put on new ones flipped 180 degrees (quad op amps are fully symmetrical--so this counter-intuitive fix worked! Flipping quad op amps to solve audioDiWhy stupidity is another awesome tip from MW's resident genius "guest").  

Finally, I used trimmers TR1 and 2 to set the frequencies to about 200hz, then used 4.7K for R21 and R14, and 39K for R7 and R20, to get the output waveforms closer to 10V P/P. Finally tested CVs at input --which modulated the LFO's frequencies. HA!! WORKS!!!

Post TL074 flip: no more short circuits--made me very happy indeed.

Battle damage post-fix. Lots of flux spoojim visible. As I fix repair SMD boards I find myself using no-clean flux more and more. For SMD work it's crucial, the flux inside fine gauge solder doesn't get it done. No-clean leaves a mess; I honor it by not cleaning.

Testing post-fixes. I will lay this board out again.Flipping the TL074's is a clever fix but energizes my OCD buzzer.

I will have another round of boards fabricated and try again. Stay tuned, and don't breathe the fumes.