[sdiy] More op amp distortion troubles

[Seb Carr]

Thanks to all for the replies.As i wasn't too sure which the coupling 
capcitor was i systematically changed valueson two of the caps:
1) an electrolytic running in series with the signal input one op amp input.
2)a cap between the diode clipping stages and the negative rail, neither of
which offered any schange in performance as i could perceive.
    another fault which seems to have developed is an intermitency in the
amoubt of gain. Initially i checked all solder joints and connections, no
obvious dry joints or shorts.  As a few of the diodes were ripped from an
earlier project, i read these were tep sensitive. could these be faulty and
thus be irratic in there forward voltage?
    As one last attempt at improving things  i ran the circuit from 2
batteries, in an attempt to improve headroom (but still not running as a
bipolar, just as 0v, 18v) and this made no change. any more
ideas/suggestions?

thanks a lot.

Seb Carr

----------
>From: "Happy Harry" <paia2720 at hotmail.com>
>To: star at all-carrs.demon.co.uk, synth-diy at node12b53.a2000.nl
>Subject: Re: [sdiy] Op amp distortion unit
>Date: Tue, May 1, 2001, 10:14 pm
>

> The 5534 is one power sucking SOB... maybe not too good for
> battery power.
>
> However... your problem is more likely a coupling capacitor
> at the opamp input... IMHO.   There's probably some bias current
> problem or the like that causes a DC level shift when you stomp on
> it... and takes a little time to drift back.
>
> Same thing happened to my Moog Ladder not long ago (last week...)
>
> As to clipping stages, use back to back LEDs germanium diodes,
> transistor base-emitter junctions... whatever you like.
>
> H^) harry
>
>
>>From: "Seb Carr" <star at all-carrs.demon.co.uk>
>>To: synth-diy at node12b53.a2000.nl
>>Subject: [sdiy] Op amp distortion unit
>>Date: Tue, 01 May 2001 20:04:26 +0100
>>
>>Hi all, thanks in advance for any help.
>>
>>     Okay, i just built a small (1 op amp, 6 diodes, a couple of caps)
>>distortion unit (soft distortion from practical elctronic musical effects
>>units, R.A. Penfold) for guitar and while it generally sounds great, and
>>i'd
>>recommend it, mine has a small glitch: When the input level rises too high,
>>the gain is reduced resulting in the sound fading to a clean sound then
>>back
>>again. If the input level rises any hifger then the sound cuts completely
>>(annoying as i like to play guitar quite hard).  I wasn't sure if this was
>>due to the input level clipping ( the op amp in question is a low noise
>>ne5534p) due to input gain, or if the high output gain draws more current
>>than the 9v pp3 battery can supply (it was designed to run from one of
>>these).  i cannot say if the problem changes with output gain as it is
>>fixed
>>for simplicity.
>>     Another query is, what would be the effect of replacing the 6 diodes
>>(OA91) with something germanium or leds.
>>     If the above problem is due to lack of current supply, would using 2
>>pp3's help, and if the supply voltage was changed would more diodes be
>>needed to be added?
>>
>>Thanks
>>
>>Seb Carr
>
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