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[sdiy] Blown LF13741 and suitable replacement?

[sdiy] Blown LF13741 and suitable replacement?

2026-01-31 by Richie Burnett

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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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Mike Bryant

I'm quite sure a TL071 will be fine.  Can't see anything special in what is a very old design.

As for your speaker PSU, what country are you in ?  The problem with class 2 (to my mind) is that it assumes neutral is connected to earth somewhere, but in some countries earth sits half way between line and neutral, whilst in others the whole concept of line and neutral is a bit irrelevant as they are often swapped over on the wall socket.
________________________________
Show quoted textHide quoted text
From: Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Richie Burnett <rburnett@richieburnett.co.uk>
Sent: 01 February 2026 00:40
To: synth-diy mailing list <synth-diy@synth-diy.org>
Subject: [sdiy] Blown LF13741 and suitable replacement?

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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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Oren Leavitt

I think other JFET op amps (TL071 et al) should work - just need to 
adapt it the TO-99 can of the LF13741.

Weird situation - I've used a pair of class-2 wall-wart powered Harman 
Kardon multimedia speakers for various monitoring. Never had a problem. 
Sounds like the Creative speakers power supply is not to well isolated 
from the line.

- Oren
Show quoted textHide quoted text
On 1/31/26 6:40 PM, Richie Burnett 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,
> 
> 
> --
> This email has been checked for viruses by AVG antivirus software.
> www.avg.com
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy@synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace@synth-diy.org

Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Gordonjcp

On Sun, Feb 01, 2026 at 12:40:28AM -0000, Richie Burnett wrote:
> 
> 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?

The datasheet says it's a 741 with FET input buffers so I'd just fire in a TL071 and see how that goes.

It might need recalibrated, it might not. It's got a better chance than what's in it now.

-- 
Gordonjcp

Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Adam (synthDIY)

> On 1 Feb 2026, at 10:40, Richie Burnett <rburnett@richieburnett.co.uk> wrote:
> 
> 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.


102 volts!!!???
I would never have thought of this....

A

Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by rburnett@richieburnett.co.uk

On 2026-02-01 02:08, Adam (synthDIY) wrote:
> 102 volts!!!???
> I would never have thought of this....

I know. You can actually feel it! Some choice words were uttered I can 
assure you Adam.

> Are the cap and resistor shown here on the output cooked as well? I'm 
> wondering why just that op-amp blew....

I don't think so, but I'll do some more probing around tomorrow to 
check.

I was equally perplexed at why the keyboard CV sample-and-hold op-amp 
would get fried as a result of a current surge from the line output 
socket to the mains ground (earth.)

I think it might have something to do with how Roland took the line 
output socket's ground via the little volume control board with the 
bender and portamento controls on it, before it returns to the main 
synth board.

You can see this on that schematic in the service notes... All the CV 
jack's and headphone jack have their grounds go straight to the main 
synth board ground, but the audio output jack's ground goes via the 
volume/bender/portamento board first for some reason.

So a current surge coming in on the line output jack's ground goes "all 
around the houses" before it finally gets to mains ground (earth.) The 
S&H amplifier gets its CV input from this volume/portamento board too, 
so I'm guessing that is why it got cooked by the surge.

-Richie,

(Newcastle, UK)
Show quoted textHide quoted text
> 
> 
> 
> 
> 
> 
> 
> 
> 
>> On 1 Feb 2026, at 10:40, Richie Burnett <rburnett@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,
>> 
>> --
>> This email has been checked for viruses by AVG antivirus software.
>> www.avg.com
>> ________________________________________________________
>> This is the Synth-diy mailing list
>> Submit email to: Synth-diy@synth-diy.org
>> View archive at: https://synth-diy.org/pipermail/synth-diy/
>> Check your settings at: 
>> https://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace@synth-diy.org
> 
> 
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy@synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: 
> https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace@synth-diy.org

Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by 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
Show quoted textHide quoted text
On Sat, Jan 31, 2026 at 9:12 PM Adam (synthDIY) <synthdiy@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@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,
>
> --
> This email has been checked for viruses by AVG antivirus software.
> www.avg.com
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy@synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace@synth-diy.org

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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Adam (synthDIY)

> On 1 Feb 2026, at 13:09, Michael E Caloroso <mec.forumreader@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
Show quoted textHide quoted text
> 
> On Sat, Jan 31, 2026 at 9:12 PM Adam (synthDIY) <synthdiy@adambaby.com <mailto:synthdiy@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@richieburnett.co.uk <mailto:rburnett@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, 
>> > 
>> > -- 
>> > This email has been checked for viruses by AVG antivirus software.
>> > www.avg.com <http://www.avg.com/>
>> > ________________________________________________________
>> > This is the Synth-diy mailing list
>> > Submit email to: Synth-diy@synth-diy.org <mailto:Synth-diy@synth-diy.org>
>> > View archive at: https://synth-diy.org/pipermail/synth-diy/
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>> > Selling or trading? Use marketplace@synth-diy.org <mailto:marketplace@synth-diy.org>
>> 
>> ________________________________________________________
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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Tony Mowbray

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



On 1 Feb 2026, at 13:09, Michael E Caloroso <mec.forumreader@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@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@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,
>
> --
> This email has been checked for viruses by AVG antivirus software.
> www.avg.com
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy@synth-diy.org
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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by S Ridley

Measuring approx half mains voltage on class 2 mains equipment "0v" is not uncommon. It's generally due to mains filter caps forming a capacitive divider between live and neutral. The caps should be relatively small and mains rated, so should meet safety standards and is unlikely to provide a dangerous current, but you can sometimes feel it, and on connection or disconnection to properly grounded equipment a cap may discharge through other equipment. So, probably legally safe, but still cr4p.

Steve


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On Sun, 1 Feb 2026 at 01:59, Adam (synthDIY) <synthdiy@adambaby.com> wrote:


On 1 Feb 2026, at 10:40, Richie Burnett <rburnett@richieburnett.co.uk> wrote:

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.


102 volts!!!???
I would never have thought of this....

A
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Re: [sdiy] Blown LF13741 and suitable replacement?

2026-02-01 by Ingo Debus

> Am 01.02.2026 um 04:09 schrieb Michael E Caloroso via Synth-diy <synth-diy@synth-diy.org>:
> 
> 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!!

That’s most probably the Y capacitors in the speaker’s power supply. Remember, a modern voltmeter has a very high impedance, so you’ll measure some high voltage between live and ground even with a quite low capacitance in series with the voltmeter. If the DMM can measure AC current, measure the current from the audio cable to mains ground (same as when you measured the voltage, but DMM in AC current measure mode). I’m willing to bet that the current is so low that there’s nothing to worry about (but if it’s not so low, you should indeed not use that power supply anymore).

I just picked randomly one of the class II SMPS wall warts here and measured both AC voltage and current from its output to mains ground. Voltage is 80 volts but the current is only 0.06 mA.

Probably this leakage current wasn’t the reason for the fried opamp at all.

Ingo

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