| piglet <erichpwagner@hotmail.com>: Dec 13 08:45PM On 13/12/2020 3:52 pm, Don wrote: > paid the bonus (to Steve Jobs) Atari didn't understand how Woz's circuit > worked. > Danke, Well in this design he didn't optimise enough. I can't see the need for R14, but if needed for adjustment range R15 could be increased in value to 200R. And R19 and R20 are providing an offset voltage of 1.5mV but to a diff amp made from presumably unmatched and non-isothermal Q6,Q7 and whose other input is derived from a vanilla zener and follower. Even across minor room temperature changes the drift could be horrible. I am baffled by that 1.5mV offset, bet you can just tie the base to ground and save two resistors. Also the polarity of C3 C4 C5 looks strange? piglet |
| "Don" <g@crcomp.net>: Dec 14 02:36AM > On 13/12/2020 3:52 pm, Don wrote: >> In sci.electronics.design piglet <erichpwagner@hotmail.com> wrote: <snip> > horrible. I am baffled by that 1.5mV offset, bet you can just tie the > base to ground and save two resistors. > Also the polarity of C3 C4 C5 looks strange? At some point there was a small ~ 1" x 4" scrap of paper included with my documentation. It was an addendum, which noted how D4 was now 5.6 V instead of 6.8 V. (A fact duly recorded on my paper schematic in ink, but missing from the PDF, which was uploaded then shared with the group.) IIRC it also said Q6, Q7 were a matched pair. Of course, the scrap of paper with irreplaceable information on it got misplaced. Nonetheless, if you seek to match Q6 and Q7 to make the pair as isothermal as possible, will this circuit do the job? https://crcomp.net/paia/matcher.png The D3 kludge is easy enough to grasp. But R19 and R20's eccentricity is a little too far out for me. Simonton's next generation VCO removes some unsavoriness: https://crcomp.net/paia/4720.png Danke, -- Don, KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night. |
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