[sdiy] "obsolete" 2N3906

[jhaible at debitel.net]

> > Remember, everything a musician likes about an instrument
> > is based on technical features in the end.
> 
> oooo, no no no no....
> Musicians want something that sounds good, not something that looks good on
> paper!

I didn't say a word about paper. I was talking about the physical
reality. (With specs on paper it's just as with statistics: they may
represent the reality, or they may be not. Most often they do not.)


> > Bigger instrument - larger distance between circuit
> > parts - less chance of VCOs to interlock because of
> > electric or magnetic fields.
> 
> good one, though if properly designed this shouldn't be an issue.

Right. The demands on "properly designed" may be higher if the
components are closer together, though. If you get the same results
in a smaller space, your work was better. 8-)


> > Bigger instrument - less problem with power consumption
> > (heat!) - allows use of low noise and no-crossover-
> > distortion class A circuits
> 
> You can still do this with surface mount, or did I miss something?

If you produce the same amount of heat in a smaller space,
temperature gradients are likely to be larger, so your VCOs (if you
have VCOs) will be harder to keep in tune.
Try to build a polysynth with 10mA class A in each buffer stage,
and you'll run into heat problems pretty soon.

> I mean, we're talking power amps here just VCAs, VCFs, etc.

Yes, VCFs, VCAs, that kind of stuff. What again was the current
thru a Minimoog VCA ?

> agreed, but this doesn't say much about surface mount Vs Thru hole.
> I've seen switch modes made from through hole..

I have nothing against surface mount. In a noise _source_, such as
a switcher, small size is _good_ to reduce interference.
But then again, _distance_ to sensitive circuit parts is positive
as well, so we're back again at a larger size of the instrument ...


> > Also, high quality capacitors are rather big. This doesn't mean
> > that a large instrument must automatically contain the best
> > components, but it means that in the smaller instrument there
> > isn't even _room_ for the better ones!
> 
> this is true, but Im sure these will come with time..
> You can already get some good Non-polarized SMD caps upto around 22uF.

I hope this will come with time.
At the moment, if you want to make a SMD version of a circuit which
has polystyrene caps in its big incarnation, these would most likely
be replaced in the SMD version.

Please don't get me wrong: I would not support a "big is better" hype.
This would be as ridiculous as the "discrete is better" hype that
already has some followers.
And nevertheless, when we have laughed about the generalisations
of such hype, there are still reasons why often such instruments
(big, discrete, to name these two) are _likely_ to have an advantage.

Of course you can totally ruin a big & discrete circuit, and of
course you can get remarkable results with miniaturised circuits.
But I think the original mail was about a _tendency_, not a rule,
and I think this has a physical background.


> > And don't forget that one: If someone claims the small version
> > "contains the same circuit as the big version", this isn't
> > always true. For example, if the Alesis A6 with its highly
> > integrated circuits doesn't sound like a big Moog module, it
> > might not just be the same circuit downsized, but it might be
> > an entirely different circuit
> 
> What is the sound of a moog module?
> I mean, I've seen clones of moog VCFs (and heard many many of them) and they
> all sound slightly different, the sound is very subjective..

Certainly. I just picked this example because there has been a hype
for this particular instrument to sound very similar to a specific,
early implementation of the Moog ladder, and while the hype was spread
I had my doubts because of the miniaturisation involved, and when
I finally heard the end result, I had to laugh out loud because it was
much farther from the original than I had expected in my worst
estimations. But I hope I made it clear that I cannot tell if
this is _because_ of the miniaturisation, or because of other factors.
But I still doubt that the bigger capacitors of the original have been 
included in the ASIC version, even as external components, without 
causing other side effects. Of course I may be wrong. If somebody has 
the schematics for this (inside and outside the ASIC), I will gladly 
discuss the details of the original which they have kept, and which 
they have lost.
But that's a different story. My argument is just that miniaturized
circuits normally follow different design rules than less miniaturized
circuits, so a difference is to be _expected_.


> > So, there are good reasons to "go big", if you can afford it!
> > (And there are other good reasons for going small, too. (;->) )
> 
> 
> space being one of the biggest, build a polysynth, oh and fit in a 3U rack
> :-)
> Its hardwork, if you stick by all your rules (big caps/space between
> oscillators/etc) you simply wont do it..
> A compromise is inevitable.

Exactly. That's precisely what I wanted to say. (Except the "rules"
stuff.)
I admire the good sound of my OB-8 every time I turn it on, and I
admire the good compromise they have found, and the non-locking
free running operation of its VCOs _despite_ the high density of its
boards. If I look at a pair of huge elektor Formant VCOs, and they give
me the same (or better) free running VCO behaviour, my admiration is
not as high, because it was "more likely" to get it that way, with such
a physical size.

JH.

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