Mesa Flux Drive [traced]

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Mesa Flux Drive [traced]

Postby zoetrop » 05 Jul 2016, 09:42

I traced a Mesa Flux Drive. Some thoughts:
- there's a LED on the board which just lit and has no other function. It draws arounf 1.2 mA.
- basically a TS dlipping circuit with baxandall tone controls
- Schematic around C1, R10, C17, R11 lloks strange, but I double-checked it.
- funny: two protection diodes, one serves as a voltage clamping diode for 15 volts, but it would still conduct if biased forwards, so, whats the point of D2?
- R23 and R26 for reducing switching noise

Please note: The photo of the bottom side is mirrored. I'm not sure I marked every connection, since I was continuity checking, schematic drawing and marking the tracks on the pcb at the same time. My main focus was to draw the schemtic, maybe I forgot to mark some tracks on the pcb...

Please discuss =)
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Re: Mesa Flux Drive [traced]

Postby EddieTavares » 06 Jul 2016, 00:12

BB-preamp clone? Who is the older?

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Re: Mesa Flux Drive [traced]

Postby zoetrop » 06 Jul 2016, 07:46

Good catch, EddieTavares! There was amissing GND-connection in my schematic, please find a new version attached (input and output resistors were not grounded). I also rearranged the circuitry around the second part of 4558 to improve readability.
I also found another schematic of the BB-preamp, which is dated april 2006. Seems like the Mesa is the clone here (they were launched late 2012, iirc).
Only major difference is the resistor arrangement around the second opamp. I desoldered some resistors and continuity-checked and am quite sure that my version is correct. Also, the flus drive has two clipping diodes in each direction.
And, if you compare BB preamps schemtic from 2006 with the Flux drive, the circuit between the 4558 and TL072 has the C-R-C-R arrangement which I believed was wrong in my schematic, but it's just like the original minus the pot/wiper - 100k in parallel to 47k gives 31.97k, plus the 1k from BB schematic ~ 32.97k, so 33k is pretty close :)
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Re: Mesa Flux Drive [traced]

Postby EddieTavares » 07 Jul 2016, 15:08

I know that they 99% the same but I guess the Flux sounds more organic (less compressed), because of the clipping diodes the mesa has more gain with less clipping distortion and maybe a little more volume available.
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