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<TITLE>More op amp distortion troubles</TITLE>
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<TT>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: <BR>
1) an electrolytic running in series with the signal input one op amp input.<BR>
2)a cap between the diode clipping stages and the negative rail, neither of which offered any schange in performance as i could perceive.<BR>
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?<BR>
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?<BR>
<BR>
thanks a lot.<BR>
<BR>
Seb Carr<BR>
<BR>
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>From: "Happy Harry" <paia2720@hotmail.com><BR>
>To: star@all-carrs.demon.co.uk, synth-diy@node12b53.a2000.nl<BR>
>Subject: Re: [sdiy] Op amp distortion unit<BR>
>Date: Tue, May 1, 2001, 10:14 pm<BR>
><BR>
<BR>
> The 5534 is one power sucking SOB... maybe not too good for<BR>
> battery power.<BR>
> <BR>
> However... your problem is more likely a coupling capacitor<BR>
> at the opamp input... IMHO. There's probably some bias current<BR>
> problem or the like that causes a DC level shift when you stomp on<BR>
> it... and takes a little time to drift back.<BR>
> <BR>
> Same thing happened to my Moog Ladder not long ago (last week...)<BR>
> <BR>
> As to clipping stages, use back to back LEDs germanium diodes,<BR>
> transistor base-emitter junctions... whatever you like.<BR>
> <BR>
> H^) harry<BR>
> <BR>
> <BR>
>>From: "Seb Carr" <star@all-carrs.demon.co.uk><BR>
>>To: synth-diy@node12b53.a2000.nl<BR>
>>Subject: [sdiy] Op amp distortion unit<BR>
>>Date: Tue, 01 May 2001 20:04:26 +0100<BR>
>><BR>
>>Hi all, thanks in advance for any help.<BR>
>><BR>
>> Okay, i just built a small (1 op amp, 6 diodes, a couple of caps)<BR>
>>distortion unit (soft distortion from practical elctronic musical effects<BR>
>>units, R.A. Penfold) for guitar and while it generally sounds great, and <BR>
>>i'd<BR>
>>recommend it, mine has a small glitch: When the input level rises too high,<BR>
>>the gain is reduced resulting in the sound fading to a clean sound then <BR>
>>back<BR>
>>again. If the input level rises any hifger then the sound cuts completely<BR>
>>(annoying as i like to play guitar quite hard). I wasn't sure if this was<BR>
>>due to the input level clipping ( the op amp in question is a low noise<BR>
>>ne5534p) due to input gain, or if the high output gain draws more current<BR>
>>than the 9v pp3 battery can supply (it was designed to run from one of<BR>
>>these). i cannot say if the problem changes with output gain as it is <BR>
>>fixed<BR>
>>for simplicity.<BR>
>> Another query is, what would be the effect of replacing the 6 diodes<BR>
>>(OA91) with something germanium or leds.<BR>
>> If the above problem is due to lack of current supply, would using 2<BR>
>>pp3's help, and if the supply voltage was changed would more diodes be<BR>
>>needed to be added?<BR>
>><BR>
>>Thanks<BR>
>><BR>
>>Seb Carr<BR>
> <BR>
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