[sdiy] Op amp distortion unit

[Happy Harry]

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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