matt239 wrote:phatt wrote: I doubt you will ever reach **group consensus**
Perhaps not..
- but maybe, at least, a kind of general agreement on a range of acceptable design parameters for a specific case?
One of the nice things about this forum, is not everyone's opinion is set in stone, & in general we seem open to evidence/science.
I really don't have an "opinion" on the issues I've asked about here; I knew I didn't have a complete understanding. I just want to know what will work, what the compromises & tradeoffs are, & what peoples reasoning/thought processes were..
DrNomis wrote: Well, I reckon you probably will need a buffer of some sort to provide a high enough input impedance for a guitar, the output of a guitar is usually at a high impedance (for passive pickups), a buffer will make the effect sound brighter, personally I think it's good design practice to design for a high input impedance, and a low output impedance anyway....
Right, but one of the things postulated here was that an op-amp as a non-inverting amplifier, with some gain, - could have a high enough input impedance on its' own..
I don't think we've reached a definitive conclusion.. ???
Hi Matt,, obviously you are still a bit confused. LOL
>>Sadly the possibilities in electronics is just so vast that what might work in an **ideal perfect text book world** is more often than not,,, going to have
issues in a Real World application. Again I stress each techno freak has differing views on this but this is my way.
I tend to listen carefully when folks have built Real world equipment and are working LIVE players or at least worked a lot with stage equipment.
If max power transfer was the game then we would all be using oxygen free copper wire to join the nodes and hang 10 meg resistors off every input,,Ker??
Cricky This is an amplifier not a race car!!
Go turn up ALL the sliders on your graphic EQ and you have max tone but of course it's useless used in that manner,,There has to be loss for it to work well.
The trick is knowing where to use that loss to maximise the effect of tone shaping.<<
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The pic should give a rough idea of how to keep the noise gremlins OUT.
Replace the opamp buffer with a transistor if you wish,,The opamp is obviously better.
Open a lot of pro gear and you will often find an opamp buffer is the very first thing the signal passes thru. If it's good enough for a lot of the better
equipment makers,,, then it's good enough for me,, wink.
With operational chips costing only a few more cents than a single transistor you may as well use opamps.
Note; I've not bothered to use exact values on the pic so up to you to work out the gain stuff.
I'd breadboard this stuff anyway so you soon get to work out what values to use.
As should be obvious, these 2 circuit have close to identical outputs,,, the first (u1) will be quite, while the gain is kept small but if you crank up R4 and R11 the circuit with the buffer (u2-u3) will be substantially quieter.
Re hi freq loss due to lower input impedance;
Consider this,
Some of the most revered Amps of yesteryear have absolutely shocking hi freq response. Those old Marshall Amps are devoid of treble above 4,000 CPS.
Yet most desire something resembling **THAT kind of TONE** and are often prepared to pay big dollars to get it.
Yet some tecks STILL constantly quote text book hifi influenced data which may well be correct for hifi but good guitar sound/tone is worlds away from flat.
As to the claim about loading of the PU's due to low imp input rolling off hifreq.
well yes if it's plugged into an old tape deck input or some other pathetic low Z input but an opamp buffer with 300k input is plenty high enough.
Yes your PU will loose a bit of hi freq content but most of it is not worth bothering with and it's DEAD easy with modern gear to have too much hi freq content,,,
Don't you guys what the famous tone ????????????????????
Go work it out for yourself,, no electronics involved!!!!
FACT;
90% of the notes you can play on a guitar have a fundamental freq below 1,000 CPS
(1khZ).
For those with 24 frets the highest possible fundamental freq is a tad over 1,300hZ.
Now double it for some harmonic content, 2,600. x2 again for some sibilance, 5,200.
Now I'm the first to admit I'm crap at maths but you will find most of the Hi Freq loss that some babble on about is well above what's important for good
****LIVE Rock guitar****. (a recording studio is a whole other subject)
If heavy rock guitars where a high freq instrument the amp would have a 3 way hifi crossover setup much like a hifi speaker,,, go try it,, see how long you
can bear the sonic insult of distortion pedals through hifi speakers. Yukas-Pukass!!!!!!
Frankly It's up to your ears to work out what sounds better as we all hear differently,,but my money is on limited bandwidth.
If you still complain of tonesuck you likely have other deeper issues happening.
Try turning up treble on most modern gear and you are also turning up a lot of unwanted crap higher up the frequency bands which will mostly have a negative
impact asto much hifreq destroys good OD sound.
If You are not able to cut through,,,your problem is you have NO MID BITE.
THIS is due to The Whole circuit design NOT tone stacks or poor quality opamps
The Whole Amp has to work together and once the Amp cranks up you need to defeat the higher frequency content. Your tone stack on it's own CAN'T DO THAT.
**It's the severe lack of hi freq content that makes those old amps worth so much**
Someone once stated that a good Marshall had a mid range HONK that no other amp could deliver at that time,,, and I have to agree.
But that honk is not derived from GAIN in the mid band,,,,, confused yet?
It is the *massive cut* above 4khZ (and also below 100hZ) that allows for the Amp to be played hard and loud and cut through. By subtraction you emphasize
the mid freq you need for good mid treble response so now when turned up the result is MID BOOST.
Bingo mid boost by ***Subtraction***
If you start building your own gear in the end you will find far greater TONES by cutting out frequencies that are not desired rather than trying to boost
the freq you do want to hear.
ADDING GAIN at freq you want will almost always add NOISE.
Tiss far better to wipe what is not used THEN turn up the gain.
PS,, if someone can give me a REAL World Example of 1 meg or 10 meg resistors delivering very low noise levels with off the shelf components while developing massive gain from one operational chip,,,,them I'm quite prepared to try it.
Until then I'll use buffers and medium input values. Winky.
A CARVIN Legacy with it's 220k grid resistor has more good guitar Mid/Treble that you will ever need. Replace it with a 1 meg and you WILL have issues.
I should know,, as I've done that. winky
Have fun,, Phil.
Cheers,, Phil.