Mesa Triaxis analysis

[stephanovitch]

Hi,

Is somebody able to say wich is the value for this big white square resistor in Triaxis V2?:
http://9giga.sfr.fr/n/50-17/share/LNK1128525a4bf97db06/


Thanks

[psychedelicfish]

There's some schematics here, though not for the power supply, where I'm pretty sure that resistor is to be found. One of the mod info things on the link I gave says if you have any questions to call MESA and ask for Dan Van Riezen and then (what I assume is a phone number) 707 778 7282. Perhaps you should give that a try.

[stephanovitch]

It's a good idea but I'm french and my american language is not the best!

I search info about triaxis V2 because I have a V1.

I have redraw a part of TX4D board schematic and I know this resistor power supply is switched (parallel to another) to modify
high voltage on some stages in the preamp.
If someone can read the value on it, he will help me to progress in my schematic.

[jymaze]

I would say the slight modification of the high voltage is really a detail. It should not change the tone much, if at all. Try the other mods first!

[stephanovitch]

https://www.dropbox.com/s/y0mlqsougby1s27/Triaxis_PCB_view.jpg

[stephanovitch]

This is the first part of my schematics of TX4 D:
https://www.dropbox.com/s/js1cqwt3ljrdlls/TX4D_board_Triaxis_.pdf

[stephanovitch]

Now switching matrix of the TX4 board:
https://www.dropbox.com/s/2mmenrk4asdthxp/TX4D_switching_control.pdf

[MetalGuy]

What I see on this picture is a 10k/5W resistor:

[stephanovitch]

Thank you MetalGuy.

I have draw the diodes added/modded on the switching schematics:
https://www.dropbox.com/s/dy0685ewhvf05nt/Recto_switching_mods.pdf

The list of opto elements activated in each mods:
https://www.dropbox.com/s/4aip4mt1bahl2r1/Triaxis_logic_switching.pdf

[MetalGuy]

Your links seem to be broken.
As for the LDR controlling circuit it's per their patent, now thanks to you we know the values as well.
I've built these "LDR pots" in the past (with my own DIY 4 pin LDRs), they work well however add some coloration to the sound.

[anti-idiot]

What did you use to control 'em? laso, define "coloration". I'm very interested in those LDR Pots as well

[stephanovitch]

Links repaired!

Detailled mods of switching diodes:
- https://www.dropbox.com/s/vk9vfgnv5n44be4/diode_adds_mainboard.jpg

- https://www.dropbox.com/s/7klovtoydoowec0/Diode_1.JPG
- https://www.dropbox.com/s/1mjsqydp69saa6p/Diode_2.JPG
- https://www.dropbox.com/s/kjypsl80z85ctom/Diode_3.JPG

[MetalGuy]

stephanovitch: cograts for daring to digg into this mess called Triaxis and thanks for the job done!

What did you use to control 'em? laso, define "coloration". I'm very interested in those LDR Pots as well

I have a DIY tube preamp with digital pots so I used the Mesa circuit and one of the digital pots to control the LDR pot.
I did A/B tests between the LDR pot and a regular one and to my ears the sound of of the LDR pot is somewhat "flat" and "metallic" compared to the analog pot.
However note that this applies only to the specific photocells I used. I can't comment on different types or in general. The difference was more audible with clean to crunch sounds.