Discrete Op Amps

[woolie]

I've been building a lot of old school microphone preamps, compressors and EQs of late, and the one thing they seem to do a lot of is use discreet op-amps. I was wondering if anyone has tried these in pedal builds. They are much larger than IC op amps though.


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[jholmes]

I am also interested in thoughts on this, a good question. 

[jholmes]

Ok, I'll take a stab at this...  I would suspect that it is because pedals are inherently NOT designed to be transparent (since they provide an effect), unlike recording gear.  So, they would not receive the same benefits of upgrading to discrete op-amps.

I am not an engineer, but take a marijuana joint as a metaphor, with the joint being the circuitry, the outside air as sound/signal input, passing through the joint (circuitry), and then the THC+air mix as sound/signal output (LOL!).  In a pedal, you'd want a higher THC-to-air ratio in the output, or at least you'd want a way to control the ratio--i.e. you'd light the joint and inhale as much (or little) smoke as you like.  But for a recording gear situation you'd want an unlit joint so that THC-to-air ratio is as close to zero as possible.  Actually, the recording engineer might prefer to have no joint at all, but that is not possible since we must electronically store the recording.  Now, since mary jane is really stinky (in a nice way if you are lucky), even if the joint is unlit you'd still get some stank air in your mouth when you inhale through it.  Just like even if the gear is as transparent as presently technically possible it will still alter the signal in some way.  When we are using vintage recording gear like analog stuff, we should keep in mind the technical limitations that existed when it was designed/built and the resulting way in which it colors the signal.  Sometimes that color can be desirable.

The recording engineer's problem is that electronic gear alters the signal due to physical limitations of the circuitry, like the tiny IC in the signal path.  If left unchecked, this would produce a recording which is unfaithful or non-flattering to the musician's original performance.  A discrete op-amp is designed to minimize that alteration by giving the engineer more control over the discrete component selection instead of forcing him/her to comply with the qualities inherent in the packaged IC.  In an effect pedal we are generally not worried about the signal alteration since we are already drastically altering the signal on purpose by using the effect itself, and so a discrete op-amp would be moot and not worth the trouble.

In the end, the engineer is often recording a mix of a direct signal and a mic'd amp.  The direct signal could maybe, potentially, have some benefit of discrete op-amps being used in the pedal if the effect was perhaps only very slightly intended.  But in the mic'd amp signal it would be moot since the signal chain is colored so much after the effect: instrument output-->the discrete op-amp effect pedal-->a wisely chosen but super colorful (engineer's perspective) amp+cab or combo amp-->projected from speakers into the air-->mic.  From that point on the goal for the engineer is generally transparency and so they go to great lengths to achieve it.  This is why they have a 1000 channel mix desk with 10 racks of outboard gear, a million tracks of overdubs each using a different mic, non-parallel walled live rooms, iso booths, etc.  This is so that their recording represents the artist's performance as closely as possible and in the most flattering light.  For the artist/guitar player, the goal is not transparency in the gear, but instead it is to create a good expressive/artistic performance itself.  If you need discrete op-amps to achieve a good expressive/artistic performance, then you might want to try it.  But IMHO the player would (usually) benefit more from practicing and from acquiring greater life experience (maybe smoking a joint?).  Hah.

Cheers.

[midwayfair]

There is a discrete op amp project on DIYSB.

Jason Lilly did a Hotcake with a discrete op amp. IIRC it sounded good but was finicky.

I'll just go ahead an echo that almost all of the time a discrete op amp would be a needless complication for us. We run guitar pedals with unbalanced signals on 9V into a guitar amp that will distort and make its own noise. We don't need the power dissipation, headroom, maximum voltage, noise figures, or any other characteristic of a discrete op amp compared to the gobs of DIL8s that cost pennies.

[warriorpoet]

There is a discrete op amp project on DIYSB.

Jason Lilly did a Hotcake with a discrete op amp. IIRC it sounded good but was finicky.

I'll just go ahead an echo that almost all of the time a discrete op amp would be a needless complication for us. We run guitar pedals with unbalanced signals on 9V into a guitar amp that will distort and make its own noise. We don't need the power dissipation, headroom, maximum voltage, noise figures, or any other characteristic of a discrete op amp compared to the gobs of DIL8s that cost pennies.

Not to mention the size difference.

[peterc]

In the 60s and 70s there were no low noise, high current devices. The 5534 (also known as the TDA10??) was the first to do this in the 70s. Studer, NTP and Jensen were the pioneers.

Great devices for high end studio gear imho

[woolie]

After making a whole bunch of them for my recording stuff, I was curious. Thx for the discussion.


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