Arche Boost - do they need to be 1N747A diodes?

H

HamishR

Well-known member
Looking at the schematic for the Arche Boost I see that it requires two 1N747A zener diodes. Do they really need to be specifically those 3.6V zeners? They are the only part I don't have right now... I have other Zeners - I know I have 5.1V amongst others.

Thanks!
 
I'd say it's just for the protection from the inversion of the polarity power supply.
I guess you could totally excluded it or use another diode: a common 1N4148 or a 1N4001 is used in other circuits.
We can wait other opinions, but I'm pretty quite about the rule of this component.
 
I afraid I confuse the pedal. The Arche Boost is based on ThorpyFX Heavy Water! :oops:

Those diodes are sort of clipping, thought the orientation is unusual.
 
Yep, they're somewhat important. You could use another voltage zener (the dirty side uses germanium diodes instead of 1N747A) but it will change the clipping threshold.
 
Elijah-Baley said:
I afraid I confuse the pedal. The Arche Boost is based on ThorpyFX Heavy Water! :oops:

Those diodes are sort of clipping, thought the orientation is unusual.
Click to expand...
That's the normal configuration when using zeners for clipping because they conduct in both directions.

1N747A is 3.6V. A pair of blue or white LEDs will get you in the ballpark, but they have to be connected back-to-back so it's not exactly plug 'n' play.
1N5227 is a good sub for 1N747A. Or just go naked until you get the right zeners.

I have some 1N747A's I can mail to you. I should be able to disguise them as a letter so I don't pay $10 for postage or duty.
 
The Build Docs says we can sub D3 & D4 with Germanium diodes to obtain a dirty boost. If we do that, are they supposed to be connected in series like the zeners? I think not, they would have to be hay-wired in in parallel. Leakage is an issue, particularly with the Russian D9x diodes because they are so leaky that they will reduce the gain in a substantial and unpredictable manner.
 
The 1n747 back to back will clip at a voltage of 3.6v + 0.6v. So they clip at +/- 4.2v. Basically you want them to clip just before you would get op amp clipping for massive headroom, therefore a nice low gain overdrive.

I used similar back to back zeners on the first gain stage of the Special Overdrive (Dumble style) board
 
At the low currents present in the Arche's feedback loop, the zener's reverse breakdown voltage will be lower, which is a good thing because the OPA2134 running at 9V can barely swing 7.5Vp-p. The 1N747A's 3.6V rating is at a test current of 20mA, more than 40x the peak zener current available in the Arche. High output pickups or a boost in front of the Arche can easily drive the 2nd opamp to saturation.
 
Thanks guys - I have some 1N747As coming shortly so everything is ok! Quite curious about this boost. It sounds a bit like a more sophisticated Red Rooster.
 
HamishR said:
Thanks guys - I have some 1N747As coming shortly so everything is ok! Quite curious about this boost. It sounds a bit like a more sophisticated Red Rooster.
Click to expand...
I found 1N747's locally in Perth but they are 3.6v - 400mw, 1N747A's are 3.6v - 500mw.???
 
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