Fulltone - OCD  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Postby bajaman » 12 Sep 2007, 00:35

OK - thanks for that - TL082 more transparent - anyone else noticed this :?:
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Postby analogguru » 12 Sep 2007, 06:43

OK - thanks for that - TL082 more transparent - anyone else noticed this
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Interesting news, for 30 years TI made me believe that the TL072 has the same chip architecture as the TL082 and the TL072 are only selected for lower noise specs from the same production run of TL082....
In other words:
A TL082 is a TL072 which doesn´t achieve the required noise specs of 17nV/SqR-Hz. Before it is thrown away, it is sold as TL082.

Hmmm....

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Postby soulsonic » 12 Sep 2007, 07:20

The higher noise = improved "transparency" follows with my theories of how noise modulating a signal changes it's tonality, psychoacoustically.
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Postby analogguru » 12 Sep 2007, 07:25

Let´s agree with that:

...my theories of how noise MASKING a signal changes (SUBJECTIVE) it's tonality...


Because white noise adds frequencies which haven´t been there before....they maybe have been missing for the subjective feeling of the listener.

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Postby soulsonic » 12 Sep 2007, 07:32

Agreed. Let this be the new official way to explain "mojo-effect" to people who swear noisy components sound better.
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Postby bajaman » 12 Sep 2007, 08:28

very interesting - a bit noisier = more transparent - I, like AG, believed that the TL082 used the same chip architecture as the TL072 - just not as good low noise specs. Does anyone know for certain that this is true, or does it have different architecture. By the way, lxh2 (check out his website) has built several Fender and Marshall simulators etc. - he always advises to use the TL081, 82, or 84 types - he reckons they distort differently to the TL071, 72, or 74 type chips :!:
Anyone else shed some light on this mystery :?:
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Postby JHS » 12 Sep 2007, 09:47

Both have J-FET-inputs, but 081 sound different compared to a 071, that's all, that doesn't mean better or worse. A JRC 072BD sound different than a TI 072 too.

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Postby soulsonic » 12 Sep 2007, 10:00

Well, the different noise specs can have an effect on the way they distort. I think noise really is the key to why similar components can have different tones. I AM a believer in one kind of resistor or component potentially sounding better than another that's almost the identical, I'm just trying to think of a logical reason WHY. I really think self noise is the biggest factor.
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Postby snoof » 12 Sep 2007, 21:42

I've noticed I've been preferring the 82 over the 72 lately as well. My last 3 opamp dist builds have all gotten 82's. With the gain past noon, I found I didn't care for the tone much either as stated by another poster.
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Postby celadine » 13 Sep 2007, 02:36

The 072 data sheet says 'low harmonic distortion and low noise', so perhaps whatever tricks they used to lower noise/distortion might make them less 'transparent' than 082s. Of course, we want a good amount of harmonic distortion here!
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Postby analogguru » 13 Sep 2007, 05:29

The 072 data sheet says 'low harmonic distortion and low noise', so perhaps whatever tricks they used to lower noise/distortion.....


If you have a look at the chip schematic, you will see that there is absolutely no difference between these two chip. So which "tricks" should this be ?

For your information:
A BC 546A ist from the same chip waver as a BC547B and the same as a BC549B or a BC 550C. All the BC5xxx are produced at the same time with the same chip-architecture and only later selected for their specs.

Is this chip noiseless ? Then it will become a BC 550
Is Vce more than 65V ? Then it will become a BC 546

The worst transistors will be stamped BC548 (without A, B or C) - but I am sure for true believers they will be "the best sounding ones", ..."whatever tricks.."

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Postby CS Jones » 13 Sep 2007, 06:52

How much tone does a pull down resistor suck?
How does the t-boost boost and what is it boosting?
How does switching the second stage bias from a multisource TS style to straight dc coupling make for fat and thin?
How does a parallel pair of caps do anything to a topend which a single cap of similar value couldn't do?
What would the topend be?
What am I listening for again with the 120k switch to parallel the 500k pot? I've forgotten.
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Postby soulsonic » 13 Sep 2007, 07:34

You're just too damn jaded to understand the true mojo... :lol:
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Postby JHS » 13 Sep 2007, 11:26

A 1M pulldown R sucks a lot of the treble, compresses the dynamic and the sound will be muddy and undefined, picking nuances get lost. Even a 10M cut highs, and it's audible. IMHO a 1M pulldown R turns a good sounding FX into a piece of soft sounding shit. You can swap a blanket over your amp to emulate the effect of a pulldown R in a FX.

My Strat produces softer treble ring if I only swap the vol-pot, 240k in reality compared to the mounted 255k. Both are 250k pots from the same brand and lot. A 1M pulldown R will drop the value of a 250k git-vol pot to app. 200k, a 10M decreases the actual pot value about 4%. Furthermore a pulldown R has a big influence on the RC-combination of the guitar tone circuit which is even more worse.

BTW: Switches and IC/trannie sockets suck tone too (there's no ideal contact in a switch or socket), so I try to avoid them whenever possible.



t-boost = treble boost, the cap switched in will produce slightly peakier treble response (technical, it compensates the treble loss caused by the 10uF electrolytic).

With the 220k switched in the sound is more compressed an has more mids, w/o it you'll have the input-impedance of the opamp (the opamp has a FET-input so the imp. w/o any additional BIAS-R is very high).
The 220k drops the input-imp. to a very low value, technical it's a low pass, cutting highs.



A 1uF output cap sounded fine to me. I don't like electrolytics for coupling, the frequency curve of those caps is not very linear (decreased high and lows), I like MKT output caps with nearly linear response.
A 1uF O-cap will give clearer, more defined treble response.

IMHO A 1uF MKT highend cap is very good for coupling, but also quite expensive and not stock in radio shacks. Hifi circuit designers do the this trick if they want to emulate an ideal 1uF MKT cap with nearly linear frequency response for cheap. They wire two cheap 470nF MKT and a 100p styro in parallel. With the 100p, treble was to peaky for me, so I dropped it.



The output cap and the vol-pot in combination is a simple low pass filter.
A 1uF/100k LP-filter (V1) cuts more treble than a 1uF/500k LP-filter (V2/3) and I don't like switching between two vol-pots (100k and 500k).

If the 120k is switched in parallel to the 500K pot, the 500k pot is converted into a 100kpot.
(app. 96k in theory, depending on the real value of the vol-pot, it can differ app. +/- 20%).

96k is OK, a 100k pot will have a value between 80 and 120k in reality).

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Postby MKB » 13 Sep 2007, 13:03

FWIW, most of the magic of the OCD isn't as much in the topology but in the details. You can't just add a few resistors to a VLOD and have it sound the same. I laughed when I saw the tantalum signal caps (to be avoided most of the time) and the TL082, but the design sure snapped into shape when these were added. IMO what you are paying Fulltone for is the ears and knowledge to combine such tiny mojo effects together to make a superior whole.
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Postby analogguru » 13 Sep 2007, 13:04

A 1M pulldown R will drop the value of a 250k git-vol pot to app. 200k, a 10M decreases the actual pot value about 4%. Furthermore a pulldown R has a big influence on the RC-combination of the guitar tone circuit which is even more worse.


Sorry but this is absolutely mojo-nonsense.....

At the time when we are listening a sound we are not dealing with DC, we are dealing with AC, so for this reason we are not dealing with resistance we are dealing with impedances.

So when we look at the schematic we havew a pulldown resistor (1M or 10M) a capacitor 22n (with a reactance of 20k at 400 Hz) a 10k resistor a 470k resistor and a capacitor of 10µF (reactance of 40 Ohm at 400 Hz) which is loading the pickup (or poti).

So letds neglect the 40 Ohm then we have already an impedance of (470k+10k-20k=) 500kohm which is loading the pickup. When we now add a pulldown-R of 10M in parallel the impedance now loading the pickup becomes 476k.

Before we have a guitar-cable with about 100pF/m (unless you are using PE-foam-cables with 30pF/m) so lets say we use 5m cable, we have 500pF capacitance. This gives a reactance load of about 700k /400Hz or 70k at 4kHz.

lets repeat: 70k load at 4kHz only from the cable.....treble-area

At 4kHz the pickup is already loaded with 70k. Now lets parallel to this the stompox load of 500k (476k with pulldown). The pickup-load without pulldown-R now becomes 61k and with pulldown-R 60,5 k at 4kHz.

After this is an Overdrive/Distortion which produces harmonics. And you want to tell me now that you can listen the difference of 61k to 60,5 k ?
Which guitar are you using: a Fender Elite Stratocaster ?

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Postby analogguru » 13 Sep 2007, 13:11

IMO what you are paying Fulltone for is the ears and knowledge to combine such tiny mojo effects together to make a superior whole.


No....: You pay for that that you are so stupid to believe the mojo-lies which are spreaded around and that you believe this Mojo-unit will improve your skills.

When you listen to zeppellin, purple, moore, chaquico, knopfler: they sounded without fuller or zvex.... they sounded much better than 99,99 % of what I listen today WITH Zvex, Fuller & Co (and clones).

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Postby MauroR » 13 Sep 2007, 13:27

About TL082, TL072 etc.

I have TL082 NS datasheet and the internal chip schema it's like the LF353!!

Instead the TI TL082 datasheet chip schema it's like TL072:
which is the true?

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Postby markm » 13 Sep 2007, 13:36

MauroR wrote:About TL082, TL072 etc.

I have TL082 NS datasheet and the internal chip schema it's like the LF353!!


This could explain it's better sound.
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Postby kagaxdx » 13 Sep 2007, 14:10

analogguru wrote:
A 1M pulldown R will drop the value of a 250k git-vol pot to app. 200k, a 10M decreases the actual pot value about 4%. Furthermore a pulldown R has a big influence on the RC-combination of the guitar tone circuit which is even more worse.


Sorry but this is absolutely mojo-nonsense.....

At the time when we are listening a sound we are not dealing with DC, we are dealing with AC, so for this reason we are not dealing with resistance we are dealing with impedances.

So when we look at the schematic we havew a pulldown resistor (1M or 10M) a capacitor 22n (with a reactance of 20k at 400 Hz) a 10k resistor a 470k resistor and a capacitor of 10µF (reactance of 40 Ohm at 400 Hz) which is loading the pickup (or poti).

So letds neglect the 40 Ohm then we have already an impedance of (470k+10k-20k=) 500kohm which is loading the pickup. When we now add a pulldown-R of 10M in parallel the impedance now loading the pickup becomes 476k.

Before we have a guitar-cable with about 100pF/m (unless you are using PE-foam-cables with 30pF/m) so lets say we use 5m cable, we have 500pF capacitance. This gives a reactance load of about 700k /400Hz or 70k at 4kHz.

lets repeat: 70k load at 4kHz only from the cable.....treble-area

At 4kHz the pickup is already loaded with 70k. Now lets parallel to this the stompox load of 500k (476k with pulldown). The pickup-load without pulldown-R now becomes 61k and with pulldown-R 60,5 k at 4kHz.

After this is an Overdrive/Distortion which produces harmonics. And you want to tell me now that you can listen the difference of 61k to 60,5 k ?
Which guitar are you using: a Fender Elite Stratocaster ?

analogguru
Wow AG :) What an interesting view! Thanks for writing that, very clear!
@ AG now about this same kind of analise, how would it be on the output of an FX with let's say a tipical 100K volume pot, if we have it midway(linear pot) then we got a 50K (series resistance) and then it goes thru a cable that have a 100pF X meters.... :shock: :shock: forming a LOW PASS FILTER ??? :?:
Now if we do the math for a 500K vol pot go figure where would it have the LP filter 3db corner frequency :shock: :shock:
Thank you...
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