[sdiy] Blown LF13741 and suitable replacement?

[Adam (synthDIY)]

> On 1 Feb 2026, at 13:09, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
> 
> 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




Agreed, but I think Richie measured the aberrant voltage on the powered speakers, not the synth


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