New Doug Self pre-amp design...

[Mooly]

counter culture has just earned himself a short break for commenting on moderation.

[abraxalito]

Yes, its internally a current feedback opamp disguised as VFB. They've done this by adding in an extra buffer prior to the (normally low impedance) inverting input. Stability is indeed a little more tricky than a 5532 but not too difficult, its unity gain stable.

The biggest issue to check on is the input bias currents - around 10X greater than for the 5532, so definitely check over the resistor values in the biassing and feedback networks. Other than this you'll be good to go. Its 3kV/uS incidentally and 36V absolute max supply.

Yes I've been using it for some time in active XOs and like the sound I get.

[SY]

Originally Posted by Kindhornman

Sy,
A follow on to my last post. I went to the Linear Audio site and registered for it. So this is a publication to purchase, a technical self published journal in effect. Is there somewhere that I can go to read this article without having to buy an entire volume of papers?

Not "self-published," Bruno doesn't have anything to do with publication other than as an author (as am I, Doug Self, Ed Simon, Dick Marsh, and several other diyAudio participants). The publisher, Jan Didden, has Bruno's article available on the site for free download.

[owdeo]

Originally Posted by abraxalito

Yes, its internally a current feedback opamp disguised as VFB. They've done this by adding in an extra buffer prior to the (normally low impedance) inverting input. Stability is indeed a little more tricky than a 5532 but not too difficult, its unity gain stable.

The biggest issue to check on is the input bias currents - around 10X greater than for the 5532, so definitely check over the resistor values in the biassing and feedback networks. Other than this you'll be good to go. Its 3kV/uS incidentally and 36V absolute max supply.

Yes I've been using it for some time in active XOs and like the sound I get.

Ok thanks for the info. There are a couple of sections in the preamp where the offset resulting from higher input bias currents could be high enough to reduce headroom, so might require more extensive mods to make it work ok. I'm interested though and will order some to try.

[Fast Eddie D]

Originally Posted by MOER

Same issue with the opamp story. The signal in the recording chain goes through a "mudbath" of ICs, bad capacitors, bad cable and the gurus moan and groan about a few opamps in a pre-amplifier.

Ha ha, that is so true. You can even hear a good mix from a bad one on a mid fi tabletop stereo.

I will say the same thing about the 5532 that I said about capacitors. If you design the circuit to work with the device, it will provide excellent performance. And the limitations of the 5532 vs discrete or more complicated op amp designs is a no brainer. For line level signals, you can make it do whatever you want.

The use of parallel buffers offers greatly enhanced performance at very low cost. I applaud this design.

[owdeo]

I'm curious to know why you think the design is so praiseworthy when as far as I can see you're implying that all recordings are already so degraded by lower performance (than this design) mixers etc and as such nobody needs to listen to them on anything other than mid-fi gear. According to your logic there is no need for the higher level of performance provided by this design over any other bog standard opamp mid-fi preamp. I mean what's the point of going to the trouble of paralleling 5532s to get higher SNR and/or better driving ability when single 5532s already provide adequate performance by comparison with the recording chain?

Presumably you have built it and listened to it then?

Paralleling 5532s might offer significant cost vs performance benefits to manufacturers, but for hobbyists buying only a few opamps this simply not the case - eg taking Element14 as an example supplier and ordering in qtys of < 25 pcs:

1 x On Semi 5532ANG: $2.60. 4 in parallel brings the cost to $10.40
1 x Nat Semi LM4562: $6.37.

This does not look like "very low cost" to me.

[owdeo]

Originally Posted by abraxalito

Yes, its internally a current feedback opamp disguised as VFB. They've done this by adding in an extra buffer prior to the (normally low impedance) inverting input. Stability is indeed a little more tricky than a 5532 but not too difficult, its unity gain stable.

The biggest issue to check on is the input bias currents - around 10X greater than for the 5532, so definitely check over the resistor values in the biassing and feedback networks. Other than this you'll be good to go. Its 3kV/uS incidentally and 36V absolute max supply.

Yes I've been using it for some time in active XOs and like the sound I get.

Abraxalito, what sort of decoupling did you use with those super fast beasties? This preamp has 0.1uF across the supply rails (not to gnd) and not one for every opamp package so I'm wondering if that will be adequate. I did use polypropylenes instead of polyester, though suspect it doesn't make much difference...

[AndrewT]

Originally Posted by owdeo

I did use polypropylenes instead of polyester, though suspect it doesn't make much difference...

That could be the mistake.
esr has a big bearing on the damping provided by the local decoupling cap.

What you must not have is oscillation due to a fast change in current demand.
That oscillation is damped by the esr.
A low esr cap like a polypropylene could be allowing a corrupted signal to pass.

Hi-K ceramic are usually good for local decoupling. An alternative could be a high esr polyester !!!!

[Fast Eddie D]

Originally Posted by owdeo

I'm curious to know why you think the design is so praiseworthy when as far as I can see you're implying that all recordings are already so degraded by lower performance (than this design) mixers etc and as such nobody needs to listen to them on anything other than mid-fi gear.

That's not the main point that I'm making. In fact, the quality of recordings varies from absolutely awful to squeaky clean and dynamic. Anybody that listens to music on a decent system and has any kind of ear knows this. Some recordings are so awful that they sound subjectively better on a "mid fi" system.

My point is that if you design a circuit with the parameters of a 5532 in mind, you can get excellent performance out of it. It can certainly be improved on. The point of diminishing returns is a subjective thing.

The 5532 can't do everything. It would be a poor choice for a microphone preamp. It would make a poor instrumentation amp (the lowly TL072 would be better). But for low impedance (less than 500K) line level circuits, it is right at the sweet spot for cost vs performance.

I wholeheartedly encourage you to design higher performance circuits. I would never argue with advancing the state of the art.

I said the same thing about capacitors. A properly designed circuit will give excellent performance with cheap electrolytic coupling and bypass capacitors. Marginal and somewhat subjective improvements can be made by employing fancy pants capacitors.

I mean what's the point of going to the trouble of paralleling 5532s to get higher SNR and/or better driving ability when single 5532s already provide adequate performance by comparison with the recording chain?

Actually, I explicitly praised the parallel buffers. I have used such schemes myself. It is a simple way to improve performance.

Have you ever looked inside a typical mixer? It has 5532s out the ying yang. A typical headphone amp inside a mixer is parallel 5532s. It works great! But of course we can do better with the resources we have here.

Presumably you have built it and listened to it then?

There's nothing earth shattering about this circuit. It is just an optimisation of everyday circuits. It is well thought out. And I have built most (if not all) of the circuits contained in it at one time or another.

Paralleling 5532s might offer significant cost vs performance benefits to manufacturers, but for hobbyists buying only a few opamps this simply not the case - eg taking Element14 as an example supplier and ordering in qtys of < 25 pcs:

1 x On Semi 5532ANG: $2.60. 4 in parallel brings the cost to $10.40
1 x Nat Semi LM4562: $6.37.

This does not look like "very low cost" to me

Well do it then. This is a website where we try different stuff and compare notes. Go for it.

[Fast Eddie D]

One thing you must understand is that I studied electrical engineering before op amps were used in industry. Op amps like the 741 only existed on paper. All we had was the 748 which isn't even worth using. When the 741 and the 709 came out, it was the advent of practical op amp circuits. When the 3140 came out, it was considered the very best op amp for most audio applications. We have come a very long way.

Engineers are trained for cost vs performance objectives for industry. I personally applaud all the efforts here to extract the last little bit of performance from circuits. I've learned a lot here. Don't think I'm a hater.