Cgs synth

hey guys,

so ive ordered the pcb's for the synthacon project but i have a few
questions about ancilliary stuff for it.

i was planning on setting it up in a 1ru case as a stand alone mono
unit (early plans for stereo have been shelved for the moment, maybe
in the future ;) )

the layout is here: http://users.bigpond.net.au/xpander/filterpanel.gif

aux1 and 2 on the front panel are d punches for neutrik locking jacks,
the input circle is a rotary switch (with led's that will indicate
which is selected). the bp hp lp circles are toggle switches for
feeding signal in to each input ;) level freq and resonance are pretty
self explanatory. then i have a couple of led bars that i intend to
drive off lm3915's to give a visual indication of in and out levels.
then bypass is a 4pdt toggle that will completely bypass the signal
from the unit and just send it straight back out without touching
anything.

the power switch is on the back, as will be the power input, and d
punches for neutrik locking jacks for the main input and the output.

i purchased a black 1ru 19" case from altronics in australia (im in
oz) and its got some funky extruded front panel. i should be ok
getting the panels drilled and punched (my housemate works in
electronics and said he'd do it at work or at his dads place for me).
but having never done any front panel labelling, i was wondering how
you guys do it? getting it silk screened would be pricey i think.
inkjet transfers afaik, don't offer white lettering on to black. so
should i get some model transfers to try? or would i be better off
buying a labelling machine that does white text on clear tape?
obviously both options id want to put a matt clearcoat over the top to
stop it rubbing off.

but i was hoping some of you synth guys would be able to offer some
advice on labelling panels up.

now i move on to powering the unit. i was thinking about getting a
switchmode power supply, having that plug in to the back of the case,
then before the power goes to the synthacon, have a 7815/7915 circuit
to smooth the power out even more for better sound quality. but im a
bit confused as to what wall wart to buy. to get +/-15v out of the
regulator circuit i assumed i needed like a 18vdc wall wart, but that
only gives +18vdc or does it give +/-18vdc? this is where i am confused.

and if that is the case then i was thinking about going the +/-12vdc
option that ken mentions can be used with the synthacon and getting a
24vdc wall wart and running that in to the regulator circuit (based on
the assumption that wall warts always output higher voltage then they
are meant to, it should give enough so that +/-12vdc can still be had
out of 7812/7912). would this work?

with the op amp, i've come from building headphone amps and have
disliked the TL-07X and TL-08X series for a while, i just find their
sound to be very average. i have a couple of single channel op amps
floating around left over from other projects. theyre opa134 and
opa227, both DIP chips, and i think i may even have a spare opa627 and
637.

would i have any problems running these op amps in place of the
TL-071? i understand the opa637 doesnt like to work at unity gain, but
i was more interested in using the opa227 or opa134 in the unit. the
627 seems to be a bit overkill for the synthacon.

do you guys have any pots you could reccomend that are nice high
quality ones? i was thinking about sticking in just some ordinary
alpha pots. then getting some boourns or alps ones later. i was
tempted to use the 9mm sealed alpha pots but with the size of the
knobs i was going to use, theyre just too light. the values i was
planning on using were 1k linear, 100k linear, 50k log.

finally what caps would you guys reccomend for the electrolytics? in
the past ive had good experiences with the panasonic FC's, but their
values arent really whats required in the synthacon. i havent received
my pcb's yet so i can't see what the largest is that will fit on the
pcb, but i was contemplating using panasonic m series this time.

Hi,

I suggest looking through the Yahoo archives for this group for
synthacon related posts. You will find a lot of good information. I
discovered that it is important to beta match the transistors.

hiriseau wrote:

Thanks for the reply !

> Use a good quality machined pin IC socket. Then you can experiment. I
> doubt you will find much audible difference whatever op amp you use.
> The sound quality of this filter depends more on the other parts,
> expecially the quality of the capacitors and how well beta-matched the
> transistors are.

After reading the archive I've gotten a heap of transistors and plan
on spending a lot of time matching them. I had also been intending to
experiment with the capacitors later down the line.

> For the bypass caps, 10uf and 47uf, the Panasonic would be fine. I did
> not use electrolytics for the three caps in the signal path,
> substituting 1uf polyester, Mouser #75-MKT1826510064. I also
> substituted a 100nf cap for the 1uf specified for the CV input at the
> base of the 2n2222. For the 2n2 caps in the filter section, you want a
> high quality polystyrene, such as Mouser #23PS222.
>
> -Richard Brewster

its good to know i can substitute the electrolytics in the signal path
for non electros. i have some BC, wima, and avx caps that all could
work in place of the mkt you used. the 2n2 i had intended to use a
ceramic cap initially. i will look in to a polystyrene one though :)

my power supply research has lead me to the conclusion ken offered.
18vac plug pack into rectifier then regulator circuit :) i will knock
one of these up tonight.

i mounted a few different pots i had in to a panel to play with them
and see which i preffered the feel of most. as this unit will be
travelling with me to dj gigs and live performances, on the fly
tweakability is essential. i think i've decided on the sealed 9mm
alpha pots. had good luck with these in the past. what are you guys
using for your pots?

thanks for all the help :)

sean