Cgs synth

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:

>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.
>
>
>

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.

>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.
>

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