[sdiy] Blown LF13741 and suitable replacement?

Sun Feb 1 14:00:26 CET 2026

Thanks for all the tips and suggestions guys.

I de-soldered the TO-99 LF13741 and tacked a trusty junkbox 741 in it's 
place just to test, (as I don't have a TL071 at hand.)  Everything seems to 
work again, so I think I've been lucky and nothing else got damaged.  The 
pitch swoops down like a dive bomber when you release a key though!  ...so 
I'll obviously need to get a proper JFET TL071 ordered and fitted in there 
so it holds the keyboard CV properly after you release a note :-)

Regarding Class-2, I love your summary Steve R... "So, probably legally 
safe, but still cr4p."  Couldn't agree more!  I've got a laptop at work with 
a metal back to the screen/lid and you can clearly feel the buzz of 
electricity if you run your hand over it when it's charging.  The current 
from my Creative powered speakers Class-2 "ground" to mains earth was 180uA 
when I just measured it with the DVM.  I've actually got two pairs and both 
measured the same.  Interestingly when I connected the ammeter between the 
sleeve of the audio cable and the earth post on a nearby Class-1 bench power 
supply, one of this PC's monitors blinked off for a split-second and came 
back on!  So although the steady-state current is tiny, the peak current 
upon connection is like a mini EMP weapon!!! (>.<)

Regarding the damage to the SH-09 I think I might have just been unlucky. 
As others have said maybe that 46 year old JFET op-amp was almost ready to 
give up the ghost anyway.  Normally the powered speakers are permanently 
plugged into the PC in my home office, so they're grounded through the PC, 
and I kind of forgot about the hazardous voltage when they're not grounded 
via something else.  Modern synths are built to pass ESD, transient, etc. 
EMC tests though, so I think they're designed to withstand this kind of 
event from the outset.

To be honest, you're all probably thinking that it was sacrilege to play 
analogue synth bass through crappy 3" desktop PC speakers anyway! ;-))  Oh 
well, lesson learnt.

-Richie,

-----Original Message----- 
From: Tony Mowbray
Sent: Sunday, February 1, 2026 5:04 AM
To: Adam (synthDIY) ; Michael E Caloroso
Cc: Richie Burnett ; synth-diy mailing list
Subject: Re: [sdiy] Blown LF13741 and suitable replacement?

Switch mode power supplies nearly always need grounding as their outputs 
float, I've seen them as high as 60volts. One can often feel the difference. 
Never trust anything always check first and protect your gear.

I've built a few guitar pedals and before I a was educated, I had all sorts 
of earth loops and clicks and pops, not to mention electrified fingers on 
the guitar.

Thrilling.

Might also be the original ic was past its due by date, this happens too

Regards
Tony Mowbray

Sent from my Samsung Galaxy smartphone.

-------- Original message --------
From: "Adam (synthDIY)" <synthdiy at adambaby.com>
Date: 1/2/26 2:17 pm (GMT+10:00)
To: Michael E Caloroso <mec.forumreader at gmail.com>
Cc: Richie Burnett <rburnett at richieburnett.co.uk>, synth-diy mailing list 
<synth-diy at synth-diy.org>
Subject: Re: [sdiy] Blown LF13741 and suitable replacement?

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

A

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....

> 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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