Mesa Flux Drive [traced]

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zoetrop
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Post by zoetrop »

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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EddieTavares
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Post by EddieTavares »

BB-preamp clone? Who is the older?

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zoetrop
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Post by zoetrop »

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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EddieTavares
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Post by EddieTavares »

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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Post by alltrax »

I built this pedal on vero according to this layout :
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https://tagboardeffects.blogspot.com/se ... flux+drive
I believe it follows the schematic posted here in the 1st post.

Everything works well and I like it very much, but the output level is low, barely unity volume with level pot full CW.
I tried to bypass the output buffer with my probe thinking the issue could be there but it's the same.
Anybody built it, any idea ?
Thanks

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deltafred
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Post by deltafred »

Can you post a schematic as well, a vero layout doesn't tell us much.
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Post by alltrax »

deltafred wrote: 08 Oct 2020, 14:27 Can you post a schematic as well, a vero layout doesn't tell us much.
You have the link to the pdf just below the pics in the opening post

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Post by deltafred »

alltrax wrote: 08 Oct 2020, 15:32
deltafred wrote: 08 Oct 2020, 14:27 Can you post a schematic as well, a vero layout doesn't tell us much.
You have the link to the pdf just below the pics in the opening post
Yea but if I can have a quick look at the schematic and and see if there is anything that springs to mind I am far more likely to offer help than if I have to download the schematic and open it in another window.
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Post by alltrax »

Ok, there you are, thanks
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The G
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Post by The G »

Please don't pollute analysis threads with troubleshooting requests. I created a Mesa Flux Drive (vero) low output thread, do continue there.

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