[sdiy] Blown LF13741 and suitable replacement?

[rburnett at 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)



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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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