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Old 14th March 2014, 03:47 PM   #1
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Default Opionions on analog switches vs vacrols

I'm probably one of thousands who in times gone by has used VACTROLS such as their vtl5c3 (Newark Reference) to re-route low level audio. For me, I've typically used it in situations where I wanted to control several older style guitar effects pedals that typically use a mechanical SPDT flore stomp button. By leaving the pedal "ON" and using a few VACTROLS and a control voltage, i could easily either route the audio chain through the pedal, or bypass it. Often I'd use some OP amps in the chain, but just as often it wouldn't be necessary. The quick yet NOT instantaneous response of the VACTROLS always made for a smooth pop-free transition.

But now I'm considering an updated version of the above pedal control methodology, and I've become intrigued at the apparent high quality of solid state analog switches such as the ADG1612 (Analog dev. reference). Its very tempting to use these because a single unit contains 4, making its cost/gate about 1/4 of what VACTROLS are going for (unless I get a VACTROL equivalent knock off from alibaba.com).

So do any of you have any opinions here? The off isolation of the AD chips are touted at -70dB (not bad), and while they don't have the slow roll off time I've come to like in the VACTROLS, real mechanical pedal buttons never had ANY such delays, and I'm thinking they may be a better fit. I understand that for controlled analog systems, like building a compressor/limiter, the VACTROLS are still great. But for simple switches maybe they are overkill?
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Old 14th March 2014, 08:22 PM   #2
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No specific first-hand experience here. I suspect the solid-state switches will never be as smooth and click-free as optically coupled devices like the Vactrol. (The updated and improved successors are made by Silonex.) Whether anybody cares about, or even notices, the difference is another question.

Vactrols could be effectively used with program signal levels all the way from transducer levels (a few millivolts) to line levels (tens of volts). Solid state switches will probably require more thought to the voltage levels being switched - I think they are all limited by their supply rails.

The Vactrols et al most DEFINITELY offered the possibility for isolating the control signals (with their related switching noise, ground loops, etc) from the program signals.

Dale
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Old 14th March 2014, 09:16 PM   #3
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I tend to agree dale. A vactrol will never have the added issues of having to add capacitors when powered from a single ended supply. I guess what even got me looking for alternatives was the prices. Perhaps I haven't found the magic stash yet, but except for those possible allibaba substitutes from china, I haven't found any company stateside making a comparable part for less than $4. Once upon a time I didn't care because anything I made was generally just for me. These days I hardly make anything without considering the possibility of marketing, which of course makes any possible savings on parts important. Do you know of any place to get the optos cheaper?
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Old 14th March 2014, 09:38 PM   #4
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Old 15th March 2014, 12:48 AM   #5
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Quote:
Originally Posted by Peter Pan View Post
I've become intrigued at the apparent high quality of solid state analog switches such as the ADG1612 (Analog dev. reference). Its very tempting to use these because a single unit contains 4, making its cost/gate about 1/4 of what VACTROLS are going for (unless I get a VACTROL equivalent knock off from alibaba.com).
Ooh, cool, Vactrols. Linear response optocouplers. I didn't know about these. The datasheet from excelitas technology is so clear. I had previously found some led-CDS cell optocouplers by chinaledproduct.com but their datasheet was so weird I gave up the idea of using them. The product number is LCR0202 and LCR0203. No charts on the copy of the chinaledproduct.com datasheet I found. So that gives you another source of a similar product, besides 'alibaba".
I backed into these by looking up parts used in 1963 Wurlitzer organs, where an incandescent bulb/CDS cell Wurli made device was used for volume control etc. It struck me as just the thing for current controlled gain amplifiers, with a cds cell in the feedback loop. Apparently according to the wikipedia VCA article (voltage controlled amp) the concept of cds cells in the feedback loop has been used before.
I know from my work in geophysics that switched input high gain channels using relays get a huge pop when the input switches. And I don't expect an analog switch to be a lot better, although with a CMOS flip flop as driver (74HC74 or 4013b) the switching transient might be so high in frequency as to be capable of elimination by RC high cut filter.
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Last edited by indianajo; 15th March 2014 at 12:51 AM.
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Old 15th March 2014, 04:41 AM   #6
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As it turns out, the LCR0202 and LCR0203 are the very china made products I found on alibaba. I wouldn't mind trying them, but there is a 1000 pc minimum, and then there is the shipping from China.
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Old 15th March 2014, 05:52 AM   #7
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Originally Posted by Peter Pan View Post
. . . . except for those possible allibaba substitutes from china, I haven't found any company stateside making a comparable part for less than $4. . . . Do you know of any place to get the optos cheaper?
It appears that Silonex was bought by an outfit called "Advanced Photonix Inc" about a year ago http://advancedphotonix.com/optosolutions/ . If you waste enough time rooting around their website, you eventually stumble across a slick marketing page that brags about how great their analog optocouplers are, but doesn't give a single performance measurement, or model number, or link to any technical info . . . . so I don't know if they intend to actually sell the things, or just use the web page as vaporware to keep the stock price up and fleece investors.

Allied Electronics still seems to have some in stock : http://www.alliedelec.com/search/res...ex,optocoupler
You can find Data Sheets attached to most of Allied's product pages for the Silonex couplers. The Silonex web page used to have a very good technical section - including, as I recall, reference designs, SPICE models, etc. Perhaps you can find some of these documents stashed on other folks' web sites.

Dale
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Old 15th March 2014, 07:03 AM   #8
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ssm2402.jpg
This device (2 pole) and SSM2404 (4 pole) feature ramped break before make operation...iow clickless switching.
Extensively used in audio broadcasting (radio) and pro-audio worlds.
These are unfortunately nowadays obsolete, but eBay and Google show current sources.
ADI have extensive range of analog switches and crosspoint switches also.

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Old 15th March 2014, 08:57 AM   #9
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SSM2402 and SSM2404 both in stock here. Tried to sell them but no one was interested.
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Old 15th March 2014, 10:35 AM   #10
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Originally Posted by jean-paul View Post
SSM2402 and SSM2404 both in stock here. Tried to sell them but no one was interested.
Nobody here knows what they are !.
What prices/quantities are you offering ?.

Dan.
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