Hi Folks,
I'm currently putting together a passive summing mixer for use in my modest home studio. I thought it would be good if I added some sort of make-up gain stage to bring the output of the mixer up to something like line level.
Ideally I'd like the gain stage to be relatively clean up until, say, 80% of its maximum, with the last 20% introducing some subtle distortion.
I realise that there are a lot of different ways that this can be done - amplifier stages (Neve BA340), op amps (API 2520), older amplifier designs like the ETI 340, etc. This led me to "light" overdrive pedals like the Mona Lisa.
So what I'm not clear about is the difference between an overdrive pedal design and an amplifier design. Is the overdrive essentially an amplifier running at its limits and then having its output reduced? Is that the basic idea?
Would it be possible to modify something like the Mona Lisa so that it kept its distortion characteristics and at the same time acted as an amplifier?
I realise that this is a vague design question but it's something that I'm not clear about.
Cheers,
Chris
I'm currently putting together a passive summing mixer for use in my modest home studio. I thought it would be good if I added some sort of make-up gain stage to bring the output of the mixer up to something like line level.
Ideally I'd like the gain stage to be relatively clean up until, say, 80% of its maximum, with the last 20% introducing some subtle distortion.
I realise that there are a lot of different ways that this can be done - amplifier stages (Neve BA340), op amps (API 2520), older amplifier designs like the ETI 340, etc. This led me to "light" overdrive pedals like the Mona Lisa.
So what I'm not clear about is the difference between an overdrive pedal design and an amplifier design. Is the overdrive essentially an amplifier running at its limits and then having its output reduced? Is that the basic idea?
Would it be possible to modify something like the Mona Lisa so that it kept its distortion characteristics and at the same time acted as an amplifier?
I realise that this is a vague design question but it's something that I'm not clear about.
Cheers,
Chris
Amplifiers and distortion effects are the same basic thing, just smashed to the limits.
IMHO you don't want a mixer to distort. You generally do not want multiple instruments distorted against each other (the exceptions I know displease me). Each source gets its own distorter, player-controlled for level (degree of distortion).
A for-purpose distorter will be selected (maybe designed) for "nice distortion". Some amplifiers sound like crap when distorted. This is much harder than just designing a clean amp.
The infamous "FuzzFace" was a general-purpose preamp, intended to bring 50mV to 200mV. But when pushed much harder guitarists liked the distortion.
IMHO you don't want a mixer to distort. You generally do not want multiple instruments distorted against each other (the exceptions I know displease me). Each source gets its own distorter, player-controlled for level (degree of distortion).
A for-purpose distorter will be selected (maybe designed) for "nice distortion". Some amplifiers sound like crap when distorted. This is much harder than just designing a clean amp.
The infamous "FuzzFace" was a general-purpose preamp, intended to bring 50mV to 200mV. But when pushed much harder guitarists liked the distortion.
Yes, it does depend on whether you're talking about a "niceness" effect for audio amplifiers as Douglas Self sarcastically describes it, or a strong distortion effect for single musical instruments, where it usually becomes an essential or dominant part of the sound.
I trust others realise that passing all the audio program of a multi-track production through a distortion effect circuit or circuits would sound just awful and virtually kill off any entertainment value in the resulting grunge. Otherwise, adding subliminal levels of distortion in response to particular levels and frequencies could actually have pleasant or bad effects. It's then a matter of which audio gurus you follow and the type of client/ music program they cater for to make the best of the effects; be it Rock, classical style, solo jazz vocals etc.
I trust others realise that passing all the audio program of a multi-track production through a distortion effect circuit or circuits would sound just awful and virtually kill off any entertainment value in the resulting grunge. Otherwise, adding subliminal levels of distortion in response to particular levels and frequencies could actually have pleasant or bad effects. It's then a matter of which audio gurus you follow and the type of client/ music program they cater for to make the best of the effects; be it Rock, classical style, solo jazz vocals etc.
It's actually a pretty common technique in the rock and pop world.
Fusion | Solid State Logic
Neve – Master Buss Processor
Silver Bullet - drBill's Stereo Tone-Amp™ - Louder Than Liftoff
Cheers!
Fusion | Solid State Logic
Neve – Master Buss Processor
Silver Bullet - drBill's Stereo Tone-Amp™ - Louder Than Liftoff
Cheers!
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So if you can imagine a transfer function as a straight line, passing through zero, in the first and third quadrant of an x-y plot. When you get to "80% of the maximum", the line starts to get a bend in it, such that the y axis "gain" starts becoming less as x swings higher in amplitude. You could design a circuit like that using non linear elements (such as a diode or zener) in the feedback loop of an op amp.
The difference between a distortion pedal and what you described with the 80% clean is where the bend in the curve starts. In a pedal, it's going to start nearly immediately as the signal comes off zero, to some +/- value. That's how you get a constant amplitude signal from a exponentially decaying electric guitar note. Of course, that's just the rudiment of it.
I read comment here on a 12AX7 input stage where they tied both halves of the 12AX7 in parallel; something like oh look, how they put a second harmonic distortion generator at the input of this amp. The idea being one 12AX7 triode half has some bend in its amplification curve, two in parallel has more bend. But not anything close to a distortion pedal.
I'd wager that's what some of these "tube warmer" effects do. Whether they are a box with a real tube in it or a DAW plug in, that puts a bend in the curve mathematically. I once had a schematic for a log amp that used an IC transistor array - all transistors identical. Transfer function appeared linear through zero, with a nice, symmetrical round bend at higher +/- values. 35 years and I never built the thing; chip still taped to the paper schematic copy, legs all smashed...the last time I saw it.
The difference between a distortion pedal and what you described with the 80% clean is where the bend in the curve starts. In a pedal, it's going to start nearly immediately as the signal comes off zero, to some +/- value. That's how you get a constant amplitude signal from a exponentially decaying electric guitar note. Of course, that's just the rudiment of it.
I read comment here on a 12AX7 input stage where they tied both halves of the 12AX7 in parallel; something like oh look, how they put a second harmonic distortion generator at the input of this amp. The idea being one 12AX7 triode half has some bend in its amplification curve, two in parallel has more bend. But not anything close to a distortion pedal.
I'd wager that's what some of these "tube warmer" effects do. Whether they are a box with a real tube in it or a DAW plug in, that puts a bend in the curve mathematically. I once had a schematic for a log amp that used an IC transistor array - all transistors identical. Transfer function appeared linear through zero, with a nice, symmetrical round bend at higher +/- values. 35 years and I never built the thing; chip still taped to the paper schematic copy, legs all smashed...the last time I saw it.