Greg Mayman wrote in a message to Roy J. Tellason:

 -=> Roy J. Tellason said to Mike Ross
 -=> about "BAG OF CHIPS" on 01-12-04  12:06.....

 RJT> yet,  they didn't even switch by decades or anything.  So finally I ran
 RJT> across a chip which would do it (the number escapes me at the moment). 

 GM> Hmmm... the number 3038 comes to mind, but i can't find any data
 GM> sheets to check it.

Close.  It was an 8038!  :-)

 RJT> Here's the thing,  though -- you get real low in frequency,  and all

 GM> How low do you mean by "real low"? Below 100Hz, 10Hz, 1Hz?

The original target was the audio range,  so I'd picked values to go down
to 20 Hz.  There's a number of trimpots in there,  and one of them will
make this effect go away -- but it also raises the minimum output frequency
up toward 50-60 Hz.

 RJT> of a sudden the output waveform gets *real* distorted.  Sine or
 RJT> triangle waves have a chunk out of the middle of the top part.  I can't
 RJT> recall offhand what squarewaes do.  I showed this to one guy,  and he
 RJT> said to me "get that power supply out of the box",  but it being a

 GM> I wonder what he was thinking of -- interference from the power
 GM> supply, or did he just want to have a look at it?

No,  you could see it -- I'm guessing he thought it was interfering with
things.  I'm inclined to think that perhaps there's some aspects of the
power supply in there that could be designed a little better.

 RJT> transformer and the rectifier and filters being on-board,  that's a
 RJT> little difficult to do.  I did add more filter capacitance at one
 RJT> point,  and that didn't help much.  I think that what I'm likely to try
 RJT> next is removing the zener diodes that are in there currently and
 RJT> sticking a couple of 3-terminal regulators in there instead,  since I
 RJT> have them on hand.  Along with associated caps and such.  Other than
 RJT> that,  I don't know...

I don't remember now whether the transformer/rectifier/filter combination
will put out enough to support 3-terminal regulators.  I don't have the
instrument handy to measure,  either.

 RJT> You guys have any ideas on this?

 GM> I suspect you might be running out of current in the power
 GM> supply. You mention that you are using zener diodes -- I'm
 GM> guessing that you have series limiting resistors to feed the zener
 GM> regulated output. So the output stage can't pull any more current
 GM> than the series R will allow to flow.

I'm going to have to dig out the schematics for this thing,  if I can find 'em.

 GM> Since you obviously have some way of looking at the waveforms, what
 GM> do you see if you put the CRO on the power supply lines to the
 GM> unit? I'd look at the lines both before and after the zener
 GM> regulators.

Good idea.  I do have a scope,  but it's not set up at the moment -- no
place to put it!  Working on that...

 GM> Where did you connect the extra filter caps? Were they before or
 GM> after the zener regulator?

Before,  across the ones that were there.

 GM> Yes, by all means use 3 terminal series regulators. They are so
 GM> cheap and they will supply all the current you need, within
 GM> reason.

I just don't recall offhand if the transformer I have in there gives a high
enough output voltage that will allow for them.  And if I have to go with a
different transformer that could get awkward.  It's a pretty full case...

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