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I'm quite sure a TL071 will be fine. Can't see anything special in what is a very old design.</div>
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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.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Richie Burnett <rburnett@richieburnett.co.uk><br>
<b>Sent:</b> 01 February 2026 00:40<br>
<b>To:</b> synth-diy mailing list <synth-diy@synth-diy.org><br>
<b>Subject:</b> [sdiy] Blown LF13741 and suitable replacement?</font>
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<div class="PlainText">Hi all,<br>
<br>
An unfortunate tale, a lesson learnt, and a question for the analogue <br>
experts...<br>
<br>
Today I was giving my old Roland SH-09 a quick test with some powered PC <br>
speakers that I had handy on my work bench plugged into the line output <br>
socket. (Creative T10 multimedia speakers powered from their own Class-2 <br>
wall-wart power supply.) I played it for about an hour through these little <br>
speakers and all was fine.<br>
<br>
Then I decided to plug it into my mixing desk to record some sounds. When I <br>
pulled the jack cable connecting it to the powered speakers there was a loud <br>
crackle (despite me having turned down the volume on the powered speakers.) <br>
The SH-09 then played out of tune when I connected it to the mixing desk! <br>
It was initially about 8 semi-tones flat, and playing notes an octave apart <br>
resulted in less than an octave span in pitch. This behaviour had me <br>
stumped, so I pulled the audio cable connecting it to the mixing desk, and <br>
plugged the multi-media speakers back in again. Now the VCO plays the same <br>
frequency (about 6Hz!) regardless of what note I play. Not a good day for <br>
the SH-09, or me :-(<br>
<br>
On investigation it turns out that the LF13741 JFET op-amp in the keyboard <br>
CV sample-and-hold circuit of the SH-09 has been cooked. Playing C notes an <br>
octave apart on the keyboard presents 1V, 2V, 3V to the input of the op-amp, <br>
but always about -3.5V coming out. For what it's worth the VCO still <br>
responds to changes in the synth's VCO octave range switch, LFO mod, and the <br>
pitch-bend lever, so I don't think anything else has been damaged. Fingers <br>
crossed!<br>
<br>
Can anyone recommend a modern replacement for this part, before I pay an arm <br>
and a leg for what might turn out to be a counterfeit LF13741 on ebay? The <br>
device in my SH-09 is actually a circular metal can package, but the pinout <br>
matches a standard single op-amp DIP-8 package, so I'm guessing a plastic <br>
DIP version would suffice?<br>
<br>
I'm just cross that I didn't think of the *potential* for damage <br>
connecting/disconnecting Class-2 speakers to a piece of Class-1 earthed <br>
equipment. My multi-meter shows 102VAC between the shield on the audio <br>
cable coming from the Creative powered speakers and mains earth! Modern <br>
gear is probably more tolerant than 1980's technology, but definitely <br>
something for others to be aware of to reduce the risk of damage to other <br>
vintage gear.<br>
<br>
-Richie, <br>
<br>
<br>
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