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Author Topic: Phabbtone  (Read 8611 times)

sjturbo

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Phabbtone
« on: February 25, 2014, 08:58:35 PM »
I am interested in building the Phabbtone and I have a couple of questions.
1) If v3.5 the latest and greatest from the creator?
2) Has anyone done a vero layout of this?
3) Has anyone used this as the front end of an od?

Thanks!

smackoj

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Re: Phabbtone
« Reply #1 on: May 03, 2014, 07:59:53 AM »
hi; I just built one of these Phabbtone pre's from the 3.5 ver. schemo. absolutely love it. I have only tried it with my mahogany body franken-strat but strat tone is my measuring stick for new builds. I don't play much humbucker stuff these days. This pre gives a sweet, transparent sound and a nice natural compression. I did not use the full size pots, I used trim pots for my initial build. I ran out of real estate so I used a fixed 39k resistor instead of the 100k trim pot shown on the schemo by the output. here are a couple pics.

I have not tried it with any other pedals/effects.

phatt

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Re: Phabbtone
« Reply #2 on: May 04, 2014, 08:38:26 AM »
Hi smackoj,
Well done  :dbtu:

Glad to hear you enjoyed the result.
I have not made comment as I felt it best to let the circuit speak for itself First. 8)

With pedals try it both ways ,, in front and after let your ears be the judge.
When used In Front of distortion pedals I've found it can tame over gained pedals and PU's in a subtle way which may suit those who are looking for a simple way to take back control of their sound.
You will get a little more edge with less control when used After pedals
Cheers Phil.

smackoj

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Re: Phabbtone
« Reply #3 on: May 07, 2014, 07:05:45 PM »
senor phatt; thanks. question; have you used other pedals to specifically boost the signal ?  or, maybe what I would really like to know is, have you done any mods like adding another IC or mosfet to boost the signal more without changing the basic sound/tone?

thanks, jack

phatt

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Re: Phabbtone
« Reply #4 on: May 08, 2014, 08:21:14 AM »
Hi jack,
Well yes you can stick any booster you like in front or after this circuit.
Obviously the results will vary depending on the structure of the unit you use.

If it helps,, A while back I had the chance to test drive nearly all the boss pedals on one big Demo board and the OS 2 was the brightest of all the dirt pedals on that board.
Most of the other Boss distortion boost pedals where notably darker in tone.

This is where you have to have some idea of where you are heading as to the tone you like.
If you make all the stages in your system bright you will end up with a very harsh tinny sound and no amount of knob twirling will remedy the situation. If your basic amp sound is very dark then you may need a brighter pedal circuit to balance it out.

Pedals can be a help but also a hindrance to great sound simply because there are just so many options. Some pedals change the sound/tone so much that they only work if they are left on all the time.
Ideally you want several sounds with no engaged circuit/booster altering the sound so much that you need to stop playing and adjust the tone controls on the gear.

Keep in mind that every circuit (even if similar in design) may impart quite different tone response curves on the signal,, even one component value change can make a big difference.
you really do have to suck it and see if it works for you there is no RIGHT way when tone is in question.
Always test the gear you want to buy on Your own Amp rig and guitar,, never trust the shops gear.

Something to consider with just tone controls;
Nearly all the passive tone circuits suffer what is termed *Insertion loss* which simply means that a 1 volt wiggle at the input will result in a much smaller wiggle out. You can loose 70% of the signal just to have tone control and you need to make that up either before or after that point.

You can go Active tone but in all the years of guitar amps passive seems to suit guitar amps. Active alone does not seen to impart a useable sound. I actually use both passive and active filters for tone shaping.

As of late 2012 I use this for my live sound.
http://www.ssguitar.com/index.php?topic=2895.0
Might give you some clues as to how far you can tkae this idea of boosting/OD and mixing tone tricks. 8)

Again either way you approach this there will be something gained while something else is lost.

As to the PhAbbTone,, you could always insert a buffer front end. Look at the front end of a TS9 schemo for clues. If you want everything going in with no loading then *Roly* likes Fet buffer stages right at the guitar. I can't seem to find right now?

I'm not so keen on getting ALL frequencies  as I've found that just makes more trouble down the line. Sure if all you do is strum chords with a super clean guitar through a 20/20 bandwidth digital chorus,,then yes Full bandwidth may well be more appealing but full blast Rock Distortion,,,, No way it's a horrible sound with far too much hi frequency hash.
And In my humble observation (having played guitar since my early teens) higher than needed bandwidth is the number one reason a lot of modern gear sounds crap.

My PhAbbTone is not a one hit wonder box that does all it's just another unit one can use to build your tone but it may prove to be more useful than the tone controls on some big expensive brand name Amplifiers. winky.
Phil.

Roly

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Re: Phabbtone
« Reply #5 on: May 08, 2014, 10:12:08 AM »
Just to clarify a point, the effect of a high impedance buffer such as a FET doesn't automatically produce wide bandwidth - what it does is liberate the natural resonance of the pickup, and by altering the resistive and capacitive loading in a controlled way, rather than just leaving it to the chance of cable and first device, you gain control over this pickup resonance.

In fact when loaded with a suitable amount of capacitance the natural pickup resonance can be brought right down and, as this plot illustrates, the rolloff above that frequency is quite steep.



This is a front end circuit I devised that allows you to individually change the resistive and capacitive loading (best built in, but should work as a belt pack);



One of the reasons that low-insertion-loss (0dB) active tone controls are unsatisfactory for guitar is that the Baxandall is really the only game in town, and the response curves it produces are very different to the classic guitar amp passives (loss typically -20dB or to one-tenth).

The Baxandall has become almost universal in everything from ghetto blasters to up-market stereos because it is very well suited to reproduction EQ in typical situations, but guitarists like "mid-band scoop" in the response and that simply can't be obtained with the classic two-knob Baxandall.  If you have a play with Duncan's Tone Stack Calculator you will soon see the point.

HTH

{normal Phabbtone service will now be resumed  :cheesy: }
If you say theory and practice don't agree you haven't applied enough theory.

smackoj

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Re: Phabbtone
« Reply #6 on: May 08, 2014, 11:23:58 AM »
thanks gents. I like the discussion about frequency and I made a copy of Roly's adj CR schemo. I generally set the tone and volume when playing and leave it there. I switch pickup positions often but not the basic tone and vol. I have several different types of buffers already built so maybe I will try some combinations with the Phabbtone and see what sounds good.

adios for now,   :tu:

phatt

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Re: Phabbtone
« Reply #7 on: May 11, 2014, 07:28:42 AM »
Hi *Roly*,
Thanks for the input, One day I'll have to test that circuit for real but meantime a question.
I'm assuming that big peak you show at 10khz is at the high Z end of the scale?
If so then it makes sense that the higher the Z (sensitivity) then you open the door for big peaks.
In my limited understanding resonant peaks might be something some designers might wish to avoid depending what you are trying to build. With modern guitar gear I'm thinking this might be inviting oscillations and needless feedback at high gain settings.

Long story short via a real world experience. (think I mentioned this to you once before?)
Anyway for the benefit of others I'll relay it again.

Got to hear A top Aussie guitar player a few years back. (not something I often get to do these days) Great player with top notch gear. On the way out the door I glanced at the amplifier He used.
So I went home and Googled the name and to my surprise I found the schematic for that Rig.
Interesting to note that The Carvin Legacy circuit no longer had the classic input of 1 meg grid leak,
NO 220k instead, hum?
Yes that amp is a multi stage high gain modern rig and my bet is that if you used 1 meg at the input you would have trouble keeping it stable at high volumes.
 Even the input to the PI section is reduced to 100k and having done exactly that to one of my home built Valve amps it certainly did help to keep things under control.

That player is well known as loud and BRIGHT and having heard Him live I totally agree His Sound is not lacking in the treble (if anything it's too bright). I'd bet that higher Z input would bring little benefit to his already bright sound and likely cause problems. I doubt I'd a job as his amp teck by doing such things. (subtle but very evident once you add lots of distortion)

@ smackoj,
                   Your idea sounds good to me. :tu:
Yes it's taken me years to get that balance to happen but it leaves one to focus on the songs you play and not having to have to be constantly distracted tweaking knobs.
Phil.

Roly

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Re: Phabbtone
« Reply #8 on: May 11, 2014, 12:23:00 PM »
Basically it works a bit like a parametric, shunt capacitance moves the resonance down in frequency (which can be quite a lot), and load resistance reduces the amplitude of the resonant peak.

The curves I've plotted are from Helmut Lemme's measurements of a bunch of real world pickups, so the only real difference my circuit makes is that it brings these two factors under control rather than just being left to chance and good luck as they are at the moment (the VariTone aside).

Crank the gain of any loop high enough and it will take off into oscillation at some frequency, mikes and PA's being the typical example.   After reading about how Leo Fender spent so much time futzing around with pickups, and discovering the electrical characteristics of his pickups (and looking at some of his other circuit designs, in particular his much misunderstood Harmonic Vibrato), I formed the opinion that he was more of a cunning old techo-fox than he is given credit for, and that this resonant behaviour of his pickups was where a lot of his classic Tele and Strat sound came from - but this pickup characteristic is still not widely known, and largely ignored.

With an input resistance of only 220k the typical pickup will be loaded until it is Hi-Fi flat, and we know that much higher figures up to 1 Meg are a lot more common.  My workshop test guitar is a Casino, a cheap Strat copy, and I've experimented with input resistances up to 10 Meg, but between 1M and about 4M7 you get a noticeable increase in the chimy-ness, it "sings" more; but above that little difference.  So for my taste and this guitar about 2M7 seems to give the "richest" result.

Signal content is easy to get rid of, but if it's killed between the guitar and amp no amount of anything is going to restore it.

So this idea was two-fold, get everything off the pickup into the amp, and be able to "game" the pickup itself.
If you say theory and practice don't agree you haven't applied enough theory.

smackoj

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Re: Phabbtone
« Reply #9 on: May 13, 2014, 09:44:00 AM »
Mr Phatt; I use a transducer pickup in my big body acoustic guitar. These do not use any active components and the signal strength is minimal. Most preamps do not work because the input sensitivity is too poor. Could you make a suggestion on whether the Phabbtone could be modified to amplify such a small signal?

thanks, jack

phatt

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Re: Phabbtone
« Reply #10 on: May 13, 2014, 10:12:45 AM »
OH poo,
       Yeah You picked the very one thing the PhAbbTone can't do. lol.

As Most Piezo PU's nowdays come with onboard HiZ preamps built in then it's no problem for the PhAbbTone,,,
BUT IF you have a totally passive ceramic PU with no preamp you are up the creek in a barbed wire canoe without a paddle and the tide is going the wrong way. :'( :'(

This is where Roly's circuit or similar will NOW be super useful. :dbtu:
Just watch the high freq output of some piezo preamp circuits as some don't pay much attention to the low pass filtering that is needed for a realistic tone reproduction.
A lot of early acoustic preamp ideas where insane bright and picked up every last fingernail scratch making for a very harsh non realistic tone, though some like that :-X
But I'm sure when Roly climbs out from under the maze of wiring in his shed he will have more helpful advice for you. 8)

Also look for the Don Tillman fet circuit it might give you some ideas.
Phil.

smackoj

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Re: Phabbtone
« Reply #11 on: May 13, 2014, 07:23:25 PM »
do you think that adding something as simple as a small audio transformer to change the input Z would be a real fix so it would "pickup" a small transducer signal?

thanks, jack

QReuCk

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Re: Phabbtone
« Reply #12 on: May 14, 2014, 08:42:49 AM »
I use passive Piezzo occasionaly (on a nylon). I found it kinda realistic if you take care of where you put it on the guitar. I would recommand close to the bridge, as this is where the amplitude of the bass content is the greatest.
Anyway, buffering this signal close enough to the guitar itself (beltpack maybe) is the way to go. I do use my GE7 for this purpose also (adding some clean boost + a convenient cut of 200Hz to prevent uncontrolable feedback to happen), but a buffer followed by a good parametric would probably do the trick better.

J M Fahey

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Re: Phabbtone
« Reply #13 on: May 15, 2014, 10:23:42 AM »
Any realistic transformer won't have input impedance into the megohms which you need.

Build this simple FET preamp/buffer , just omitting the "pickup" and volume control shown which are meaning an electric guitar.

The 1M input resistor will work fine, you can rise it to 3M3 if you wish for a little better bass.

smackoj

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Re: Phabbtone
« Reply #14 on: May 15, 2014, 07:48:24 PM »
thanks friends; simple FET buffer makes lots of sense. I have a few already made laying around I will scrounge up and give 'em a whirl.

question; does the piezo type 'transducer' (passive) have a hi Z?

gracias again

smacko jack     8)