Big Fat Mama - Portmanteau reply

[Chris Thorpe]

Wow! When I posted the Big Fat Mama message, I anticipated getting
flamed from Virginia to Vladivostok. Instead, several people seem at
least interested, even enthused. I don't want to further fragment the
thread by replying separately to everyone so this is a big fat
portmanteau answer.
________________________________________________________________________
From:  Steffan Davies <pinetop at dircon.co.uk>
> I don't have anything like the electronics needed to comment on the
> technical side of the proposals, but a cooperatively-designed set of
> cheap modules would be a godsend, at least until I can afford that
> VCS3.

Yes - quick & dirty rules. Especially for those looking for a MIDI 
controlled source of accident & wierdness.
________________________________________________________________________
From: MSISteve at aol.com
Re hardware costs
> Fatman panels are only 20 bucks, it's worth considering. Also, Chris
> List's panel for the ASM-1 is expected to be only around $25 and it's
> a four unit job and damned nice looking as well.  Either of these
> would probably be cheaper than the FracRack if you start adding it
> up...
Re PSUs
> Wouldn't that be nice?  Stable, readily available, cheap power
> supplies. You couldn't begin to build one for the price at which PC
> PSs are sold...

> Count me in.  If you're banished from the list as a heretic by
> the EE guys with their  o'scopes, keep in touch okay?  I'd
> like to try something a little serious.  If  it sounds weird I'll
> probably like it.

Yes, I think that's the right attitude for this! I checked out the
circuits you attached from AH - a whole synth built with cheap discrete 
transistors! Now that's wierd! The author of that wrote - 
> Building simple analog hardware is a lot of fun !!!
Couldn't agree more. A mate told me last night that I shouldn't use PC 
PSUs as the switching electronics will generate too much audio noise. 
Thing is, these days, the things are practicallly free if you know where 
to look so I may use one just to get me going and finish up with a nice 
smooth PSU afterwards.
Take your point about the panel hardware costs.  
________________________________________________________________________
From: "john.." <jat5 at york.ac.uk>
> Yeah, go for it!!
> I've been looking into building some `cheap' circuits and I'm pretty
> sold on the LM13700 as a `do it all' chip.... The National
> Semiconductor databook has schems. for VCA, VCO, VCF, and Ring
> modulator circuits.
> It's cheap too!
> If you have a PDF viewer you can go to the Nat Semi web pages and get
> a copy of the data book pages....
> http://www.national.com/design/
> and search for `13700'
Did that - these circuits look useful. Chip selection is a big part of 
making this kind of box work. There are also some useful looking wide 
range, temperature stable, voltage to frequency converters on the Nat 
Semi site and see also the separate thread on the Exar xr-2206.
________________________________________________________________________
From: Erik Forsling <e6erikf at etek.chalmers.se>
> Like you say, it all depends on what you're after. I'm about to start
> building, and I can't say I have an ambition to build something bigger
> and better than everyone else, but I do know this: I want it to be my
> own. Of course, my first functional modules will probably be someone
> else's design and all that, but I'm aiming at learning something here
> as well. And if you do your own designs, you can do them as cheap or 
> as expensive as you like.

OK - personally, I like cheap. Also, I don't have as much electronics 
design expertise as I need to be totally self-sufficient. What I really 
want to do is start making music NOW! I'll just say, when you do design 
something great - please share it with the rest of us.
________________________________________________________________________
From: Troy Sheets <tsheets at xanadu.cyborganic.com>
> Well, when you are talking about cheap modulars, what are you going to
> skimp on?  It seems that the price of the components are all about the
> same. Are you talking about making very simple circuits that require
> few components?

Yes, probably. Also, by splitting features into separate modules, you 
gain flexibility at the expense of patching complexity, rather than 
building super-modules that each contain every possible feature. A point 
more eloquently made by CList below...

> I am putting a whole lot of effort into my ASM-1 synth.  I could cut
> corners here and there and save a little money or a little time.  But
> instead, I am electing to do it as first-class as possible.  When I
> finish it, I want something that is going to look and sound really
> great...  its going to be something I look forward to showing off on
> my web page ;)

I'm not arguing, but, if the ASM-1 is a Porsche, isn't there also a 
place for a Ford Escort? Nah, make that a 500cc trail bike.
________________________________________________________________________
From:  Christopher_List at Sonymusic.Com
> 1. The cost difference between a v/Hz VCO and a v/oct VCO is
> negledgable UNLESS you want it temperature stable. If you don't care
> about the temp sensitivity, the parts count can differ by as little as
> 1 transistor, one op-amp and a handful of resistors. Since MIDI-> CV
> converters that output v/Hz are often more expensive than those that
> output v/oct you might want to think about the cost trade-off. You've
> got to generate an exponential scale <<somewhere>> in the system. The
> Fatman does it via sneaky use of the uProc and table look-ups. If you
> really don't care about mapping your notes to a keyboard (ie you just
> want to make cool synth noises) then you shouldn't care about temp. 
> stability - so make a cheap expo. converter for in the VCO (i.e.
> normal transistors and no temp-compensating resistors)

I'm still semi-undecided on this issue. I would think teperature 
sensitivity is still important even for surf-thrash synth devotees. One 
UK company is able to sell a single channel MIDI/CV converter with 
exponenetial out for as little as £75! So I think the all important 
converter part can still fit within the budget whichever way the scaling 
goes.

> You'll probably save more money by putting the whole thing in a big
> plastic box ... than you ever possibly could by simplifying the
> circuits.  

Yes, I could see doing that. Or use cheap plastic boxes for each module 
and build a kind of pigeon-hole cabinet to stack them in.

> Along the same lines, super-simplifying your modules can save cost,
> but will lead to more patching. For instance, you could take the
> "depth" knobs for FM and PWM off of all of your VCOs and just have a
> couple of separate "stand alone" attenuators. Do this with all of your
> modules and you'll save a lot parts - but you have to do a lot more
> patch cord routing.

In a few words, more modularity, less knobularity. I like that - it'll 
work. 

> Just some food for thought. While I tend to be a proponent of fancy
> parts (just because higher tolerances help cover up my lack of EE 
> skills :) - 
> I think a lot of the circuits discussed here are simple and
> economical. Most of them come from Electronotes and they were 
> definitely striving for simple low-cost designs. I think the
> Electronotes Preferred Circuit Collection is exactly the sort of
> collection you're asking for - provided you don't follow every circuit
> to the letter and make some of the adjustments and substitutions I
> described above.

I last looked at samples of the Electronotes stuff many years ago and it 
was great but the idea that we could instigate the whole thing online 
amongst ourselves brings a warm glow. Also, while Bernie Hutchins does a 
great job with Electronotes, I'm afraid my cash is going on chips rather 
than paper. Of course, Bernie, if by any chance you're reading this,
I'll trade you a set of everything in return for which I'll turn it all 
into indexed Acrobat files so you can publish the CD ROM version...
________________________________________________________________________
Anyway, thanks to all who've replied - you have provided me with exactly 
the kind of inspiration & advice I was looking for. Think I'll start 
soldering soon!

- Chris