[sdiy] Blown LF13741 and suitable replacement?

[Michael E Caloroso]

I would be MUCH more concerned with the 102VAC potential between shield and
ground before replacing that opamp.  Or even operating tha rogue device,
that is a lethal electric shock waiting to happen!!

MC

On Sat, Jan 31, 2026 at 9:12 PM Adam (synthDIY) <synthdiy at adambaby.com>
wrote:

> Are the cap and resistor shown here on the output cooked as well? I'm
> wondering why just that op-amp blew....
>
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> > On 1 Feb 2026, at 10:40, Richie Burnett <rburnett at richieburnett.co.uk>
> wrote:
> >
> > Hi all,
> >
> > An unfortunate tale, a lesson learnt, and a question for the analogue
> experts...
> >
> > Today I was giving my old Roland SH-09 a quick test with some powered PC
> speakers that I had handy on my work bench plugged into the line output
> socket.  (Creative T10 multimedia speakers powered from their own Class-2
> wall-wart power supply.)  I played it for about an hour through these
> little speakers and all was fine.
> >
> > Then I decided to plug it into my mixing desk to record some sounds.
> When I pulled the jack cable connecting it to the powered speakers there
> was a loud crackle (despite me having turned down the volume on the powered
> speakers.) The SH-09 then played out of tune when I connected it to the
> mixing desk! It was initially about 8 semi-tones flat, and playing notes an
> octave apart resulted in less than an octave span in pitch.  This behaviour
> had me stumped, so I pulled the audio cable connecting it to the mixing
> desk, and plugged the multi-media speakers back in again.  Now the VCO
> plays the same frequency (about 6Hz!) regardless of what note I play.  Not
> a good day for the SH-09, or me :-(
> >
> > On investigation it turns out that the LF13741 JFET op-amp in the
> keyboard CV sample-and-hold circuit of the SH-09 has been cooked.  Playing
> C notes an octave apart on the keyboard presents 1V, 2V, 3V to the input of
> the op-amp, but always about -3.5V coming out.  For what it's worth the VCO
> still responds to changes in the synth's VCO octave range switch, LFO mod,
> and the pitch-bend lever, so I don't think anything else has been damaged.
> Fingers crossed!
> >
> > Can anyone recommend a modern replacement for this part, before I pay an
> arm and a leg for what might turn out to be a counterfeit LF13741 on ebay?
> The device in my SH-09 is actually a circular metal can package, but the
> pinout matches a standard single op-amp DIP-8 package, so I'm guessing a
> plastic DIP version would suffice?
> >
> > I'm just cross that I didn't think of the *potential* for damage
> connecting/disconnecting Class-2 speakers to a piece of Class-1 earthed
> equipment.  My multi-meter shows 102VAC between the shield on the audio
> cable coming from the Creative powered speakers and mains earth!  Modern
> gear is probably more tolerant than 1980's technology, but definitely
> something for others to be aware of to reduce the risk of damage to other
> vintage gear.
> >
> > -Richie,
> >
> > --
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