[sdiy] Discrete OTA

[Tom Wiltshire]

Two things that'd be high on my list would be lower noise/higher signal level, and buffers that work. Log/Lin CV inputs would be a nice touch.

On 1 Apr 2014, at 13:51, Dan Snazelle <subjectivity at hotmail.com> wrote:

> my main question about your $5 discrete ota product would be what it would offer that a  1-2 dollar 13600 would not.
> 
> thnx
> 
> 
> Sent from my iPhone
> 
>> On Apr 1, 2014, at 5:22 AM, "Neil Johnson" <neil.johnson71 at gmail.com> wrote:
>> 
>> Rutger Vlek wrote:
>>> Haha, thanks for the enthusiasm! It is very tempting to reveal what I have been working on, but I'm a little hesitant at the moment. As I explained to you I'm looking to move away from academia. I just finished my PhD, but working under the enormous pressure in a high-tech lab environment has resulted in a severe burn-out.
>> 
>> Ha ha ha ... try the real world :)  Academia is *easy*.  Unless you
>> have a big pot of cash (or a working partner) to keep you fed I would
>> suggest getting a day job and tinkering with synth stuff in the
>> evenings and weekends.
>> 
>>> I'm slowly getting back on my feet again, but this is taking long. For the future, I'm looking for a different way to earn money. This is why I'm thinking about starting up a company.
>> 
>> So you'll be working evenings and weekends anyway :)
>> 
>>> I absolutely love working on synth design (especially in the DIY community).
>> 
>> Great.
>> 
>>> Normally I would be all for "open source" and sharing the ideas that I have, but the intellectual property may now become relevant for my income. That's why I'd like to figure out some way of protecting the IP. Any thoughts on that? I see many companies currently doing the "open hardware" licensing thing.... Would that provide enough protection for designs, schematics and layouts to prevent someone el
>>> se from slavishly copying and making money off my designs?
>> 
>> Unless you have a lot of money the only real defence mechanism you
>> have is community pressure.  Copyright won't protect you.  Patents
>> cost money, and only worth having if you can afford the legal costs of
>> defending them.  Something like this would be difficult to keep as a
>> trade secret as it won't take long for someone skilled in the art to
>> work out what you've done.
>> 
>>> Ok, now the more interesting part..... I have something on my test bench that contains VCAs and a VCF design with discrete OTAs. I haven't tested the VCF yet, but the VCA performs pretty good. I don't want to make any strong claims at this point about it, since I'm not a skilled electrical engineer. Just a hobbyist with general scientific skills.
>> 
>> If you're serious about setting up as a hi-tech company then this is
>> not the place to discuss it.  You need to keep quiet until ready to
>> ship.  You already have competition - George Hearn does a range of
>> potted modules (op-amp based, not discrete), there are clones of
>> Yamaha and Korg hybrids out there, and Barrie Gilbert has published
>> extensively on the subject of variable gain architectures, and you can
>> make a discrete VCA out of a CA3046.
>> 
>>> My goals were roughly to develop a discrete OTA that can be made moderately cheap. I have not been aiming to beat high quality alternatives (2164, THAT-chips, etc), but was rather aiming for an alternative with a bit of character (think of the way the ca3080 saturates). There are several ways my prototype could be made available to others, and I'd like to hear about your preferences:
>> 
>> Character is good.  I like to add a certain amount of character.  Does
>> your OTA add too much character?  Or the wrong character?  Can I
>> change your character to my character?  Or would you say it is better
>> to minimise your own character and allow people to add what they want?
>> Strive for perfection, and then customers can add imperfection that
>> *they* want.  The CA3080 is by no means perfect: some like its
>> character, some don't.
>> 
>>> 1) Because of the topology it will never be an exact drop-in replacement for any existing OTA, but I believe it is possible to fit a single discrete OTA on a tiny DIP8 daughterboard. For good temperature stability it probably needs potting too. If I had to estimate a price, it would probably be around 5 or 6 euro's, possibly a bit cheaper in larger quantities. Is this still feasible for the DIY community?
>> 
>> As a stand-alone product?  How many do you need to sell to break even?
>> Or even make a profit?  Or are you happy to personally subsidise
>> other people's hobbies?
>> 
>>> 2) I could also turn the entire discrete OTA-based VCA into a tiny daughterboard, including lin/log option for the current source, etc.
>> 
>> See George Hearn's potted modules.
>> 
>>> 3) I could turn the prototype into 'ready made' or DIY-kit Eurorack modules, VCA, VCF. I already have some other innovations for a VCF on the bench too, so that would be included.
>> 
>> Would you be looking at competing at the high end with MOTM, the
>> mid-range (Intellijel), or bargain-basement (Doepfer)?
>> 
>>> ps. Any experience with companies that do potting (with heat-conducting epoxy)? Or can this be done cleverly DIY, yet still for high quantities?
>> 
>> If you don't need vacuum encapsulation then you could do it on your
>> kitchen table.  Or farm it out to a company that would be able to do
>> it to a higher standard, consistently, quicker.
>> 
>> Neil
>> --
>> http://www.njohnson.co.uk
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