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Post subject: Comments On The Clapton Circuit.......
Posted: Mon May 18, 2015 6:57 am
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I have been in contact with Paul Gagon, former Vice President of Technology for BBE Sound. When he worked for Fender in the early 1980's he developed and patented the TBX [Tone Boost Expansion] control. He also developed the MDX [Midboost Expansion] circuit board. These were intially intended for the Elite Series guitars and ultimately found their way into the Clapton Stratocaster.

My reason for contacting him was a curiosity about the functioning of the Phase One Clapton guitar I own. It is the early design featuring a mini-toggle mode switch which activates the preamp. [This was ultimately discarded in favor of the stereo jack.] On my guitar, with the circuit in passive mode, there is no function other than some minimal input from the TBX. The guitar's output is at a fixed level for all pickup settings, and the volume and DBX controls are silent. In active mode, everything cooks.

I made a copy of the guitar's wiring diagram which I found in A.R. Duchossoir's book and took it, along with the guitar, to a very knowledgeable tech, of Gagon's ilk in electronics, for a cleanup, setup, and trouble shooting. The final diagnosis was that all was in order. He traced out the signal path for me in passive mode.

I reviewed all this with Paul Gagon and here is his reply: [Understand that the mode switch idea came into being AFTER he left Fender]

[u]'The mode switch is a bit puzzling. Since the volume control is AFTER the first preamp stage, it CAN'T be used passively. I'm guessing that the only reason to have such a switch is as a bail out function. If the battery or preamp died in the middle of a gig you could at least hit the mode switch and bypass the active circuitry."[/u]

In some respects that corroborates what my tech told me when I asked him how one would handle the volume requirements. He replied that it would have to be done through the amp.

Apparently the MDX also acts as a passive filter that feeds the midboost control. In order to be passive the signal must be taken from the pickup selector/TBX junction. Hence, the guitar cannot be wired so that a passive signal feeds into the boost at end of the chain permitting both active and passive configurations by a flip of a switch.

In essence, one can only assume that the guitar was NEVER designed to be played passively, but fitted with an external control to activate the boost circuit. Understandable why Clapton eschewed it in the final design. There's no one at FMIC presently who can provide any further feedback on the R&D thinking which went into the guitar. Believe me.....I've tried.

That's all folks. :wink:


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Post subject: Re: Comments On The Clapton Circuit.......
Posted: Tue May 19, 2015 1:10 am
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Thanks for sharing us this useful information! :D


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Post subject: Re: Comments On The Clapton Circuit.......
Posted: Thu May 21, 2015 6:43 pm
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I'm not sure how useful...at least for me...but interesting for sure...nice investigative work Doc.

I had puzzled over this...anticipating a build with the Mid Boost Circuit...

...finally deciding that carrying an extra battery and using the AXcess Trem cover would have to do...


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Post subject: Re: Comments On The Clapton Circuit.......
Posted: Fri May 22, 2015 3:10 am
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danagos wrote:
I'm not sure how useful...at least for me...but interesting for sure...nice investigative work Doc. I had puzzled over this...anticipating a build with the Mid Boost Circuit...
...finally deciding that carrying an extra battery and using the AXcess Trem cover would have to do...

The investigation answered a question for me, as to why the guitar played as it did. It also provided a bit more insight into the workings of the circuit. Most interesting coming from its inventor. In your case, and mine with the Pewter model, the wiring follows the final upgrade made when the guitars went into production. Xhefri observed that the mode switch then serves as nothing more than a battery saver. In the upgrade, the same effect requires unplugging the guitar between uses. On a gig, that would mean, between sets. Elsewhere, at home for example, you'd have to remember to do this when done woodshedding. What we're lacking is any literature which came along with the guitar nearly 30 years ago. Guess wel'll never know.

BTW: How's that battery placement working out for ya?? I figured that one out over a decade ago when I fitted a Strat with the Gilmour circuit.

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Post subject: Re: Comments On The Clapton Circuit.......
Posted: Fri May 22, 2015 3:52 am
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ZZDoc wrote:
danagos wrote:
I'm not sure how useful...at least for me...but interesting for sure...nice investigative work Doc. I had puzzled over this...anticipating a build with the Mid Boost Circuit...
...finally deciding that carrying an extra battery and using the AXcess Trem cover would have to do...

Xhefri observed that the mode switch then serves as nothing more than a battery saver. In the upgrade, the same effect requires unplugging the guitar between uses. On a gig, that would mean, between sets. Elsewhere, at home for example, you'd have to remember to do this when done woodshedding. What we're lacking is any literature which came along with the guitar nearly 30 years ago. Guess wel'll never know.

BTW: How's that battery placement working out for ya?? I figured that one out over a decade ago when I fitted a Strat with the Gilmour circuit.

I remember reading that you had your tech install that...Great Idea...

...I'm not using the Tremolo so it works fine with this guitar...ala Clapton...unplugging the guitar is now second nature...mostly :lol:

I have the Aged White Trem cover...for the new owner...which looks SOOO much better. :D

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