Bass amp opamp tweaking

[PaulBass]

I have a bass amp thats all NJM4558 opamps. There are 3 in the preamp section and 2 on the power board. I got tired of the hissing so I replaced them with sockets and popped in NE5532's. The sound is now more clear and way less hiss. So I tried LM4562's and it was a noisy mess from the oscillating. I was wondering are there more modern opamps I can use for even better performance that won't oscillate?

[Leo_Gnardo]

That's another "bridge too far" story. I'd back up to the 5532's and park it there. Some of what you get with improved, high-performance chips is more bandwidth, into the multi megahertz region. Gigahertz even. Then you have oscillations and you can spend your time compensating for them which just reduces the excess bandwidth back to a stable point . . . or simply reinstall op amps that worked noticeably better and don't bother trying to improve it even more.

[bob p]

IMO chasing bandwidth in an audio circuit is a fool's errand. it just forces you to tweak the feedback circuit.

[J M Fahey]

Specially in a Bass amplifier.

[darkfenriz]

OPA134/2134/4134 will give you JFET inputs (=lowest current noise), very low voltage noise and reasonable gain-bandwidth product. Perfect audio op-amp in 99% of applications.

[bob p]

OPA134/2134/4134 will give you JFET inputs (=lowest current noise), very low voltage noise and reasonable gain-bandwidth product. Perfect audio op-amp in 99% of applications.

JET are the perfect audio op-amp in 99% of applications? I'd disagree with that.

FET input stage op-amps such as OPA2134, OPA134 tend to sound best when input resistance is 50k or higher.
IMO when input resistance is low biopolar op amps like the OPA2227, OPA227 are a better solution.

[darkfenriz]

Some technical reasoning behind one's guts feeling comes handy, if it comes.

[alexradium]

There is a book for that, Small signal audio design

[darkfenriz]

Well, there's a book on anything, usually a couple of books, some good, some bad. Some people are book advisors, others are book readers and some folks write them too.

To the point: there's nothing wrong with JFET inputs, especially at high source impedances, but they are just as good at low source impedances.
Their biggest advantage is nearly no input current and no input current noise - in contrast with Bipolars input current noise starts to dominate usually at the 10kOhm source Z range or even lower.

The only areas where JFET inputs may be inferior are DC precision (unless laser trimmed, like OPA627), slightly lower DC gain and more dramatic degradation at high temperatures, all of those seem not much applicable to audio.

[Enzo]

And don't lose sight of the fact your preamp is not a couple op amps sitting on a plate. it is entire circuits, and ALL of those circuits contribute to noise.

[PaulBass]

JET are the perfect audio op-amp in 99% of applications? I'd disagree with that.

FET input stage op-amps such as OPA2134, OPA134 tend to sound best when input resistance is 50k or higher.
IMO when input resistance is low biopolar op amps like the OPA2227, OPA227 are a better solution.

I tried one TL072 on the preamp board and it didn't squeal on me. I have a some OPA2227 samples and I'll pop a few in

[nevetslab]

TI's TLE2072 is a recent improvement over the standard T L072 series, having twice the bandwidth, better output current drive, and doesn't have the nasty clipping behavior of Bi-FETs like the TL072. I do think they cost a bit more than TL072's, but I've had very good luck with them.

[PaulBass]

I got 5 free samples of TLE2072 years ago and they are being used in another device. I was going to buy more but the price never goes down. It's always around $4. If I'm going to pay that much I might as buy a better opamp. I bought 5 OPA2134's and the sound is incredible.

[Leo_Gnardo]

I bought 5 OPA2134's and the sound is incredible.

Kool, where do you buy yours?

[PaulBass]

Digikey. I don't trust any sellers on ebay not even the US ones