Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on August 17, 2022, 08:17:02 am
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Was looking at the schematic on my Sunn Model A and the input voltage on my JRC4558 chip for the reverb is -21 vdc. The RC4558 data sheet says 18 volt max. The schematic shows a direct feed of -21 vdc to pin 4 of the RC4558. I have been looking at other chip data to swap out the 4558. Any suggestions?
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It’s helpful to provide links to info being referred to.
Are you sure the 4558 isn’t +/-18V?
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It’s helpful to provide links to info being referred to.
Are you sure the 4558 isn’t +/-18V?
Yes it has + & - rails. Im trying to find the online page i saw last night. I didn't bookmark it. I have little knowledge of OP amps.
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+/-18V means a 36V limit between pins 4 and 8.
Your amp puts 22V between them, so there shouldn’t be a problem.
https://el34world.com/charts/Schematics/files/Sunn/Sunn_model_a.pdf
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+/-18V means a 36V limit between pins 4 and 8.
Your amp puts 22V between them, so there shouldn’t be a problem.
https://el34world.com/charts/Schematics/files/Sunn/Sunn_model_a.pdf (https://el34world.com/charts/Schematics/files/Sunn/Sunn_model_a.pdf)
Ok i think i'm starting to understand. I'm like a sponge taking in everything i can learn about OP amp driven circuits. This amp has been a learning experience.
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other chip data to swap out the 4558. Any suggestions?
TL072, NE5532, OPA2134
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other chip data to swap out the 4558. Any suggestions?
TL072, NE5532, OPA2134
Thanks tubeswell. I have a NE5532FE from 1981. Just tinkering with reverb sound. I really don't have a noise issue with the 4558 in the amp now. Just was doing some reading on quieter OP amps and wondering.
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In case you are looking for very low noise the TLE2072 is the one.
https://www.ti.com/product/TLE2072
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don't the bjt op amps (1458/4558/5532) have more current drive capability than the fet op amps (tl0x2)?
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> don't the bjt op amps (1458/4558/5532) have more current drive capability than the fet op amps (tl0x2)?
The name is the INput device. "Drive" usually means the OUTput device, which is often different.
Trust Sunn. Older op-amps were intended for bipolar power (so they could do DC computations and give answers like "5 feet below ground level" for an airplane trainer). And it got very conventional to use plus and minus 15V supplies (30V total), with an 18V max for a little leeway. The actual limit for a JRC4558 is +/-22V or 44V total, which assumes their "40V process" is working extremely well.
At just one negative 22V rail, you are way within bounds. For this or most "30V" opamps. (5V even 3V opamps now exist but I don't fool with them.)
I would NOT change this opamp. The '4558 is a wonderful audio device for reasonable signal voltages. Sounds good. It is not a microphone amp or a studio output amp, but I've had rigs where all the amps in the middle were 4558 types and were pleasing.
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I tried a 5332 this morning. Then switched back to the 4558. The 4558 sounds better. A tad more clarity to my old ears.
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Give the Burr Brown (TI) OPA2134 a try. They are awesome sounding op amps, IMO much better sounding than 4558 & 5532.
--Pete