active versus passive

[Jerryz1963]

Any strong feelings about active versus passive tone controls? Beyond the greater insertion loss of the passive? Is passive commonly found because of economies or is there a sonic reason I'm unaware of?

I haven't found an article that really clearly spells it out, just kind of a wishy-washy noncommittal dissertation.

[rdjones]

Any strong feelings about active versus passive tone controls? Beyond the greater insertion loss of the passive? Is passive commonly found because of economies or is there a sonic reason I'm unaware of?

I haven't found an article that really clearly spells it out, just kind of a wishy-washy noncommittal dissertation.

Do you mean a tone circuit that uses a frequency modified feedback loop to control tone ?
I think they're fairly rare in tube based guitar amps.
A whole lot easier to implement with op-amps than tubes.

rd

[Jerryz1963]

I have an intense dislike for op amps. I got into a bit of a heated discussion with an EE about that. He starts quoting figures like distortion and slew rate. that's all well and good, but my ears tell me discrete components work better and I theorize it's because the more stages you run the signal through, the worse it sounds. My own experience seems to bear that out. So, long way of saying, I avoid use of op amps to the maximum extent possible.

After posting, (it always seems to work that way) I found an article wherein the majority of guitarists when polled stated a preference for passive, feeling it sounds more "natural," or "organic." Those in favor of active said it sounded "cleaner" to them.

[Stevem]

The early 70s Soundcity 120 model had a active preamp section and it sounded ok for and in the Bass model of the 120, but for guitar it really kinda sucked to be short about it!

[sliberty]

The early 70s Soundcity 120 model had a active preamp section and it sounded ok for and in the Bass model of the 120, but for guitar it really kinda sucked to be short about it!

+100

Sound Shitty

[VacuumVoodoo]

Passive vs. active EQ is always an interesting discussion, often turning into a heated debate.
Players trying out my Tubewonder amps usually praise the tonal range offered by the EQ. A minority will make an effort to find something to criticize - it can't be that good, can it? Well, they find the horse to beat when informed that the EQ is 100% active. And also find it difficult to believe that it's all tube based.
For some reason many associate active circuits only with opamps and such. Excuse me, aren't all tube circuits active? - yes we can debate rectifiers
All analog filter and EQ topologies were developed with tubes, long time before silicon entered the stage.

[vibratoking]

...but my ears tell me discrete components work better and I theorize it's because the more stages you run the signal through, the worse it sounds.

I don't know why you think discrete components mean less stages? You may not like opamps, but opamps don't equal more stages. Things like distortion and slew rate are present in discrete circuits as well as opamps. Discrete circuits don't offer a panacea.

I like active and/or passive depending on the circuit and how it is designed. No need to discriminate based on superficial judgements. Poor active designs can suffer from things like nonlinear phase shift and group delay. There are quite a few established passive designs that are predictable in this way. These get used a lot because most amp builders aren't breaking new ground. So copy what is known. There is no risk. Kudos to your active designs. Take risks, experiment, think outside the normal box. I wish I could play through your amp. Alek.

[Leo_Gnardo]

Those Sound City amps used passive filters to divide the spectrum into 4 sections, then pass thru a "voiced" preamp then summed together. Kind of trying to make a pig out of sausage. Not really "active" either, just filters (lossy) followed by gain, followed by mixer (lossy) followed by more gain. In spite of their design, I've been able to make 'em work well for some customers.

Another more successful filter-then-boost design is found in old Pultec (and similar Lang) EQ's. They came in "treble & bass" varieties or just midrange. Highly sought after by studios, these old beasts now sell for thousands of bucks.

Intended to be put inside the guitar or bass, the treble & bass controls on an Alembic pickup kit are AFAIK active, and sound wonderful to my ear. Steeper curves and a more aggressive tone by far than regular passive "cut treble only" tone controls.

[vibratoking]

BTW, I owned a Music Man HD130 in the late 70s. Opamp front end with a tube PA. That was a damn good amp. I wish I still had it.

[Jerryz1963]

...but my ears tell me discrete components work better and I theorize it's because the more stages you run the signal through, the worse it sounds.

I don't know why you think discrete components mean less stages? You may not like opamps, but opamps don't equal more stages. Things like distortion and slew rate are present in discrete circuits as well as opamps. Discrete circuits don't offer a panacea.

The INSIDE of an integrated circuit is many stages. If you peruse the datasheet, you see this clearly as they often show not just the "equivalent circuit," but the actual circuit, and the actual circuit is a lot of active and passive devices. that is indeed many stages. It matters not that the stages are crammed into a tiny package, they are still stages. I try not to get boxed in by absolutisms 'cause I have ended up with egg on my face too many times. That being said, MY experience with opamps has been one of disenchantment. For example, I went through two op-amp based electronic crossovers(One a RANE brand) and then built one out of discrete components. It was ZERO contest, the discrete component crossover (simpler in design to boot) sounded much better. I'm of the opinion (and I'm not alone) that the oodles and gobs of negative feedback associated with sand state in general, op amps included, has a lot to do with the (perceived or real) reduction in sound quality. I take some comfort in the knowledge that I'm not alone in that opinion. I'm pretty sure that at least part of the beauty of valves is that massive amounts of negative feedback are not applied.

[vibratoking]

I have designed many opamps... I design integrated circuits. They are not all multiple stage circuits. There are many different topologies depending on the purpose. There are significant differences and lumping them all into a single category is kinda short sighted. But I won't try to force you to like something you don't.

I have to admit that I don't know what you mean by gobs of negative feedback associated with sand state?

[eniam rognab]

my musicman RD50 110 has the same setup as VK with a 12ax7 driver tube

love love love it, no idea if the TS is active or what but its my favorite

[Jerryz1963]

I have designed many opamps... I design integrated circuits. They are not all multiple stage circuits. There are many different topologies depending on the purpose. There are significant differences and lumping them all into a single category is kinda short sighted. But I won't try to force you to like something you don't.

I have to admit that I don't know what you mean by gobs of negative feedback associated with sand state?

With solid state, there is a lot more gain. To get impressive numbers in terms of distortion, engineers trade-off gain for improved distortion by applying a lot of negative feedback globally and locally. Valves don't have the gain of solid state, so engineers tend to apply feedback more sparingly with valves. I experiment a lot 'cause I'm curious. I noticed (as have many others) that removing the negative feedback in their stereo valve amps results in improved sound quality, often times dramatically so.

when you say you design IC's, do you mean you design circuits WITH IC's or you are a semiconductor engineer: The way you worded it makes me think you are involved in the fabrication of integrated circuits, work in a clean room, and all that.

Whenever I look at what's really inside an IC, it is invariably countless transistors, resistors, and capacitors. I admit I don't do this as a matter of course. Nowadays, the data sheets just show the "effective equivalent" of the circuit. When I was a teenager and in my early 20s, they sometimes showed what was REALLY inside the IC. Sound Blaster at one point was bragging that their high end sound card had so many millions of transistors (in ICs of course). I'm not an IC expert, so I concede there may BE ICs that aren't hundreds or thousands of active devices. You may very well have much more knowledge in that regard than I do. I'm not going to BUILD an IC, so, I'm only curious to a point. I would be intrigued by an IC that was designed for audio in which the engineer tried to make one without a lot of stages, trying for sound purity instead of impressive figures.

[VacuumVoodoo]

Well, you might want to have a look at "complementary bipolar dielectric isolation process"
exceptionally suitable for analog bipolar circuit for audio. Developed once by
Harris Semiconductor and now used by THAT Corp exclusively.
In short, it makes it possible to truly integrate a discrete circuit by virtue of
total absence of parasitic p-n junctions which are common in other processes.
BTW if you're using FX stompboxes you are putting opamps and such right in front of your signal chain.

[Jerryz1963]

thanks for all the answers. think i have more testing to do