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Author Topic: Preamp stages, clipping and tone control.  (Read 433 times)

Oooscar

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Preamp stages, clipping and tone control.
« on: May 11, 2020, 10:47:11 AM »
Hello,

I am studying different preamp schematics. I am inclined to minimal amps or amps with not so many parts, just the ones needed to produce a given sound for guitar practice/bedroom playing purposes. I have several questions:

1.- Is it good to add a boost stage initially before any overdrive/soft clipping in terms of sound?
2.- Is it better to add a tone control stack before any clipping or after, in terms of sound?
Let's say you make: guitar, boost, tone control/tone stack, soft and/or hard clipping, out.
3.- Does it worth to add a classic tone stack with bass, trebble, mid respect a single pot tone control, or a BMP with some mid control (Jack Orman mod I believe...)?

It seems to me that with a simple tone control (or maybe two pots) you can get a wide range of sounds, but I am learning, and I would like to understand how many stages can have a guitar amp, and the purpose of those, to see how can I simplify or minimize them, and still get a good and wide range of sound. For instance, adding preamp stages to an LM386 can give you a good sound with control. I have tried hard clip diodes with a TL072, and the sound to me gets better. Nicer.

Thank you very much for your attention.

Regards, cheers.


joecool85

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Re: Preamp stages, clipping and tone control.
« Reply #1 on: May 12, 2020, 10:31:54 AM »
Hello,

I am studying different preamp schematics. I am inclined to minimal amps or amps with not so many parts, just the ones needed to produce a given sound for guitar practice/bedroom playing purposes. I have several questions:

1.- Is it good to add a boost stage initially before any overdrive/soft clipping in terms of sound?
2.- Is it better to add a tone control stack before any clipping or after, in terms of sound?
Let's say you make: guitar, boost, tone control/tone stack, soft and/or hard clipping, out.
3.- Does it worth to add a classic tone stack with bass, trebble, mid respect a single pot tone control, or a BMP with some mid control (Jack Orman mod I believe...)?

It seems to me that with a simple tone control (or maybe two pots) you can get a wide range of sounds, but I am learning, and I would like to understand how many stages can have a guitar amp, and the purpose of those, to see how can I simplify or minimize them, and still get a good and wide range of sound. For instance, adding preamp stages to an LM386 can give you a good sound with control. I have tried hard clip diodes with a TL072, and the sound to me gets better. Nicer.

Thank you very much for your attention.

Regards, cheers.

For the ultimate in control of EQ and still simplicity, the two band Vox style works amazing well.  The great thing is even though it has no mid control, you can control mids by way of the treble and bass controls.  IE - you want very little mid scoop, set treble and bass to half.  Want a giant mid scoop, put the bass all the way up and treble matched (or a little down).  Check out the TSC calculators here: https://www.guitarscience.net/tsc/vox.htm

When using the TSC calculators, I find it very helpful to click and drag on the graph to highlight from 82hz to 10,000hz as this is the guitar range.

You can do a lot with a modified BMP single tone control, but you are still locked into a certain type of sounds.  I've got one variant of it that will be going into the SSGuitar kit I'm putting together and it works quite well, but it is still limited compared to 2 band or 3 band EQ.
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edvard

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Re: Preamp stages, clipping and tone control.
« Reply #2 on: May 21, 2020, 01:04:21 AM »
Hello,

I am studying different preamp schematics. I am inclined to minimal amps or amps with not so many parts, just the ones needed to produce a given sound for guitar practice/bedroom playing purposes. I have several questions:

1.- Is it good to add a boost stage initially before any overdrive/soft clipping in terms of sound?

It depends on the circuit.  Some circuits sound just fine creating their own gain, like discrete transistor designs and most Op-Amp designs, but oftentimes boosting into a circuit that is wired for low gain will get better tones than the circuit itself wired for high gain.  In my experience, MOSFET inverter stages are like this, perhaps some others.  Counter-intuitive, I know...

Quote
2.- Is it better to add a tone control stack before any clipping or after, in terms of sound?

Again, it depends on the circuit and what you want it to do.  Personally, I've found that tone controls before the clipping/gain stage work best with low- to mid-gain circuits, for Blues and Classic Rock.  High gain circuits can tend to be noisy and "mushy" sounding with the tone control in front, though that might sound good if you want more of a Fuzz effect from your high-gain channel.  Post-clipping tone controls can sound "sterile" with lower gain circuits (but not always, there are many exceptions, I'm sure), but can be powerful tone shaping tools after a high-gain stage.

Quote
Let's say you make: guitar, boost, tone control/tone stack, soft and/or hard clipping, out.
3.- Does it worth to add a classic tone stack with bass, trebble, mid respect a single pot tone control, or a BMP with some mid control (Jack Orman mod I believe...)?

The best answer I can give is to simply try it.  I've used single-knobs, two knobs, 5-band EQs, they all have their advantages and disadvantages.  If you want to keep it simple, then a BMP with mid control sounds like it could be nice, but as joecool85 said, it can be TOO limiting.  Give it a shot, start breadboarding and take notes on which ones you like.

Quote
It seems to me that with a simple tone control (or maybe two pots) you can get a wide range of sounds, but I am learning, and I would like to understand how many stages can have a guitar amp, and the purpose of those, to see how can I simplify or minimize them, and still get a good and wide range of sound. For instance, adding preamp stages to an LM386 can give you a good sound with control. I have tried hard clip diodes with a TL072, and the sound to me gets better. Nicer.

Thank you very much for your attention.

Regards, cheers.

Most of the "extra" stages and parts of a preamp have to do with either tone shaping, bandwidth limiting, or protection.  Solid state gear is really good at simply re-creating whatever is put into it, but that includes signals you didn't intend, and so we have a thousand schemes to clamp oscillations, eliminate sub-sonics, and protect an op-amp from frying itself.  Many of those can be eliminated, but it is oftentimes what gives certain circuits their "feel".  Would a Tube Screamer sound like it does without that famous mid-hump?  Nope, it'd sound like any other generic OD/Distortion boxes out there, but maybe that's what you like; only YOU can make that distinction.

For the record, I prefer: Op-amp clean boost to a tight (2-pole) hi-pass at about 100Hz into a chain of low-gain MOSFET inverters, just about any FMV tone control circuit, (pre-gain for clean channels, post gain for dirt), make-up gain and single pole low-pass at ~5-7kHz depending on the circuit

joecool85

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Re: Preamp stages, clipping and tone control.
« Reply #3 on: May 21, 2020, 08:12:28 AM »
For the record, I prefer: Op-amp clean boost to a tight (2-pole) hi-pass at about 100Hz into a chain of low-gain MOSFET inverters, just about any FMV tone control circuit, (pre-gain for clean channels, post gain for dirt), make-up gain and single pole low-pass at ~5-7kHz depending on the circuit

That's also close to what I like.  I've found that I like to have a hi-pass set to around 80hz running into most any clean boost (op-amp or BJT typically) into a 2 band Vox or 3 band FMV tone control (always post gain), some make-up gain if the power amp doesn't like the amount coming out of the preamp, and then a low pass set to around 10-12khz.  For built-in dirt I like to use back to back red LEDs, though my 5th Gear OD uses a red LED and 1n914/1n4148.

Also, I'm currently on a single channel kick.  I really enjoy being able to turn back the gain and have a nice crystal clear clean.  Turn it up a little for a slightly edgy/jangly voicing, or wind it up for anywhere between classic rock and just below 80's metal.  For further gain I'm fine running a pedal.

Everyone has their thing, that's for sure!
Life is what you make it.
Still rockin' the Dean Markley K-20X
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