[sdiy] asm1 lfo and power supply

[>>>marjan<<<]

Hi Nils,

> 
> Once again an asm-1 question. I have trouble getting the lfo to work. (shame
> on me, it's such a simple circuit). Is this circuit sensitive on a "not
> really good" power supply?
> 

Huh, it rather tends to make PS _worse_ , it's good practice to 
decouple lfo opamp with 100 ohms is series with each rail and
filter it with 100U and 10n caps to gnd from opamp power pins.

> To be honest I'm still working with a very bad powersupply built around a
> 7815 and 7915. Worse is, that I have -17V instead of -15 (don't ask me why -
> only the 7915 knows...).
> 

You have serious problem there. It's not normal. check the orientation
of the regulator (different pinout than 7815) and try different
brand, do you measure it without rest of the cct? Try 2k2 from reg
out to gnd. Use 10U on output not more (without reistor or choke
decoupling). Heck, check the archives for my and other members
advices. We had that recently. You can build decent PSU even with
78/79xx but you should consider some things. 

> I've read a lot of times, that a good power supply _is_ important.

Yep! 

> Mine is a
> pice of junk. It has ripple, it does the wrong power, it's noisy, and each
> time I'm, working with it remember that I'm just a mortal (you can touch the
> wires of the mains). 

It's piece of junk cause you made it that way. Few simple upgrades
will make it right.

> But nevertheless - it did it's job for over a 5 years
> now. It supplied my guitar preamp. 

Hmm, guitars... Even more hmmms, guitarists... 

> It supplied all my experimental
> diy-circuits, and it survived uncounted short circuits.
> 
> Back to the LFO:
> 
> I checked my pcb a couple of times, changed opamps, measured here and there,
> and everything looks fine. Could it really be my sucking power supply?,`Even
> if it's a pice of junk I never had serious problems with it.
> 

If you get +15 and -17 maybe you fried opamp? That's 32V across the
sucker.
Maybe he didn't like it. Check the wiring, pots, integrating cap,
resistors
(hey those red bands can easily be orange etc). Maybe a lifted pad or
solder
bridge? 


-- 



marjan


me    : Marjan Urekar
e-mail: urekar.m at eunet.yu
s-diy : http://surf.to/marjansystems
music : http://go.to/forcemajeure