Vox - SATCHURATOR pedal  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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bajaman
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Post by bajaman »

2SC4617 ;-)
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Post by xenrelic »

How about Q5?

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bajaman
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Post by bajaman »

the same as Q9 :wink:
quite a common transistor to blow in these pedals - usually open base emitter junction - I use a BC547 (or similar) and carefully bend the legs to fit in place of the smd shit part.
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mdd0127
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Post by mdd0127 »

Hi,

First post here on the forum and my first SMD pedal repair issue. This is probably something easy and stupid but I've been suffering from chronic severe headaches for the last couple of years and for some reason, this pedal is really kicking my butt. I'm hoping that I'm just over thinking things.

I'm trying to tie up some loose ends up here in Camp Verde so I can get down there to Phoenix, AZ USA to help a friend who's house just burned down. I've had this pedal for a month and need to get it back to it's owner before I leave town again.

I'm wondering if any of you have any insight so I can get this thing done, delivered, and get down there.

The pedal is a Vox Satchurator distortion pedal and when I got it from the customer/friend, a tiny SMD transistor in the Q5 position was burnt out. I've searched all over for replacements and haven't been able to find one. I've identified the part as one of these.
2PB709AQ Phi N SC-59 PNP 45V 0.1A hfe 160-260 Datasheet: http://akizukidenshi.com/download/2PB709AR.pdf
Alternate part numbers that I also haven't been able to find locally or in low quantities: 2SC4617 and BC547

The fet was toast and my head hurts too bad to make sense of the circuit by following the traces. When there is nothing where the fet should be, the pedal doesn't come on at all. When I put a zener diode across what would be the base and emitter, with the stripe on the diode toward the emitter side, the pedal comes on and works but the "more" button is able to be activated even when the pedal is off, causing no change in sound instead of the gain boost it would normally provide. I've never seen one of these pedals working so I don't know if that's normal or not.

I tried to replace the fet with a 2N3906 in a TO-92 package Datasheet:http://www.fairchildsemi.com/ds/2N/2N3906.pdf but it didn't work. I'm hesitant to leave the diode permanently connected as these pedals run from a 9v battery and I don't want to cause a constant battery drain or other unseen issues.

Here are some links that might give you further insight:
Thread with general info: https://www.freestompboxes.org/viewtopic.php?f=1&t=2223

Mods I'll be performing in addition to the fet repair:
http://www.chewingoncrayons.com/2009/01 ... s-mod.html
http://www.chewingoncrayons.com/2009/01 ... e-mod.html

Pics of the board(halfway down-photobucket links):
http://www.jemsite.com/forums/f21/satch ... 14222.html


Schematic:
https://s592.photobucket.com/user/anders ... 2.jpg.html This is the biggest one I can find and I'm not enough of a computer guru to get it cleaned up enough to see the part labels. "Q5" is the burnt transistor that I'm dealing with though.

Anyway, sorry to type your eyes out. I'm probably over thinking this whole deal. As soon as I get this pedal back together and delivered, I can go down and help Mike with security, storage shed construction, and just being there for him. I'd love to hear your thoughts!

Thanks,
Danny

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mdd0127
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Post by mdd0127 »

Nevermind! I figured it out. A little probing with the meter showed me that there's no way there should be a PNP in there. I put a 2N3904 NPN in instead and it works perfectly. It's crazy how one wrong post on the internet can twist someone's head around. I'll have to find the post that called for the PNP and correct it on another day. For now, it's time to run a couple of errands and go help my friend!

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ataro
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Post by ataro »

I bought a non-working Satchurator the other day.
Red and yellow leds lid but the pedal was always on bypass. I found that Test Point TP1 was showing 3v instead of 9v, so I suspected Q5 ( 2SC4617 NPN transistor) or its bias circuit. Replaced Q5 with MPSA18, and the pedal seemed to work just fine. Can I leave the mpsa18 in there without any issues?

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Robhd147
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Post by Robhd147 »

Hey all I'm in the same boat with a broken Vox satchurator I'm wondering if anyone knows what Q10 is looks to be cracked along with Q5 is visibly blown thanks

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Post by Robhd147 »

I also need help from the Vox satchurator gurus trying to find out information on Q10 please and thank you greatly appreciated

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Post by mbender »

Hi,
i was looking for a long time, did not find the schematic. Only some fragments, not good readable.
So, I have traced mine completely. Some SMD parts I could not identify. Some values not absolutely sure, see foot note in the schematic.

Cheers, Markus
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VoxSatchurator.pdf
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McColson
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Post by McColson »

Hello, nice job ! thks for sharing this ! :worship:

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FeVeR2112
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Post by FeVeR2112 »

I saw somewhere that changing the C3 cap to a lower value will aid in getting better mids. The original is 47n and the mod is 39n (or lower).

Also an overall volume mod is out there using an opamp between the tone and Volume pots.

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Post by mbender »

Sorry, I realized a mistake. During moving around components on the schematic, the bypass branch slipped to a wrong connection. Attached is the corrected schematic.
Best,
Markus
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Lord Ashram
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Post by Lord Ashram »

Hi everyone!
Thanks a lot for the schematic of this pedal and of course for tracing it!

Can someone here explain to me what the "More"-Switch does? At the moment I don´t see a booster being engaged but maybe I´m wrong? I see the DS-1-configuration but I don´t see how I could modify a DS-1 to have that "More-kindofthing".
I own the pedal and I am quite happy with it, I really like how it reacts to the volume-pedal. I usually keep the more-switch on all of the time, that is why I´m asking. - I would like to build a DS1-pedal and integrate all the necessary mods to make it the Satch "with more". Would save me a lot of space on my board.
...and a bit more mids and added volume would be nice as well... ;-)

Cheers and Thanks in advance!
Tobias

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Nocentelli
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Post by Nocentelli »

Lord Ashram wrote: 08 Jul 2021, 13:59 Can someone here explain to me what the "More"-Switch does? At the moment I don´t see a booster being engaged but maybe I´m wrong? I see the DS-1-configuration but I don´t see how I could modify a DS-1 to have that "More-kindofthing"........

........ I would like to build a DS1-pedal and integrate all the necessary mods to make it the Satch "with more".
It looks like the DS-1 has a single opamp stage with the gain pot in the feedback loop followed by the clipping-diodes-to-vref:
_20210709_073022.JPG
The satchurator uses two parallel opamps in this position with the same gain pot arrangement as the DS-1, but only has that large (2u2) electrolytic cap connected from inverting input to ground in "normal" mode:
_20210709_073050.JPG
The "more" switch causes Q12 FET to start to conduct from drain to source, shorting the 1M resistor and adding a 22k-1u cap direct path to ground from both opamps' inverting inputs (in addition to the normal-mode's 100k + 2u2) thus boosting the gain of the two opamps.

So you would just need to omit the FET and associated switching circuitry and just have that 22k resistor and 1u cap permanently connected.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by Frank_NH »

I was intrigued by the use of parallel op amps. Did they do this to reduce noise? It would be interesting to experiment with this on my breadboard...

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