Arion - SCH-Z Stereo Chorus  [schematic]

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

I posted a detailled description with tons of images of some of the mods described here on:

http://forum.musikding.de/vb/forum/diy- ... chorus-mod

(I dont know, how to post pdf's here, so you will have to follow that link). There are some other mods in that document as well.

It would be great, if someone had an idea on how to use the remaining jack (output 2) to connect a standard expression pedal to control the rate of the pedal (leslie expression pedal). The pot in the pedal is 100k(B?), standard expression pedals have like 10 k, I think...

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mfunky
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Post by mfunky »

The pdf in the other forum did not work, so here is a direct download link: https://infotomb.com/u0idr.pdf

Have fun and let me know what you think!

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Dirk_Hendrik
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Post by Dirk_Hendrik »

Nice.

What I miss in the story is the the SCH-Z is not a current version of the SCH-1 but is based on the SFC-1 (the Fat Chorus). Main differende is the use of FET's instead op BJT's for the buffer transistors.

And "a black battery cover is much nicer"? :| naaah :mrgreen:
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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mfunky
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Post by mfunky »

Thanks a lot, Dirk. I did not know that (I never owned a SCH-1 or SFC-1 or validated the schematics against the SCH-Z). Skipping the "vintage" talk, I seriously can only say, that this is a fantastic chorus (I owned a CE-1, this one is different, but has similar magic for 10% of the price) - Your mods make it outstanding! My only intend of the documentation was to make it easier to find the components on the PCB and give some simple sound samples .

And of course, colour is a matter of taste :D .

Thanks again for this great thread!

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Post by JohnDodo »

hi everybody (my first post at these forums),

this thread has been very helpful to me, thanks guys. I'll try my hand at modding my Z in the easter holidays.

I just have a suggestion/question about the unity gain issues, chorus being louder than vibrato etc.
As I'm definitely no electronics pro, I thought I'd better ask your opinion first.

What I'm thinking about is, since were losing the stereo function anyway, why not use a different op-amp (U2a and U2b) for vibrato and chorus each? Their gain could then be adjusted individually, by replacing both feedback resistors (R30 for U2a, R 37 for U2b) with trim pots. (I think most of us will be able to afford the extra trim pot...)

The steps necessary for that would be (starting from an umodded SCH-Z):
- Cut R28, so U2a does not get any dry signal; it will be the vibrato op-amp. U2b will do the chorus.
- Disconnect SW2's upper (bypass) lug from C5 and R39 (since we're going for true bypass anyway)
- Connect that same lug to the junction of R31/R32. Disconnect OUT 1.
- Probably R31 – the 1k resistor right before OUT1 – will have to be bypassed, since R40 already performs that function for OUT2.
- Replace R30 and R37 with trim pots. (shouldn't 50k be enough, since less R in the feedback resistor means less gain?)
OUT2 is now the standard output.

And the true bypass:
bypass Q4 and Q7, as before;
FXin between IN and R2, as before;
but FXout now between OUT2 and R40.

So, what do you think?

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Post by FloPoeKo »

Dirk_Hendrik wrote:And so, one night and a morning later,
A SCH-Z is (almost) the same as a SFC. The Fat Chorus that is.
Component numbering is the same, I expect the PCB layout to be the same too, based on the fact that R44 (0 ohm) is still there. Difference is that all transistors with exception of Q5 are replaced by FET's.
Dirk, do you recall which FET´s were used in the SFC? Cheers Florian

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Post by FloPoeKo »

FloPoeKo wrote:
Dirk_Hendrik wrote:And so, one night and a morning later,
A SCH-Z is (almost) the same as a SFC. The Fat Chorus that is.
Component numbering is the same, I expect the PCB layout to be the same too, based on the fact that R44 (0 ohm) is still there. Difference is that all transistors with exception of Q5 are replaced by FET's.
Dirk, do you recall which FET´s were used in the SFC? Cheers Florian
Or did you mean: All BJT´s in the SFC were replaced by FET´s in the SCH-Z?

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Post by rocket512 »

I think the 2 mosfets 2SK512 are wrong. Those are TO3 power mosfets.

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Post by FloPoeKo »

rocket512 wrote:I think the 2 mosfets 2SK512 are wrong. Those are TO3 power mosfets.
They have a double code in two rows. The first said K512, the second below sais 2SC3198 which makes them NPN Bipolar Transistors with the same pinout as 2SC2458/2SC1815... How about a big new Arion Chorus Version/Component Thread? I have the SCH-Z (MIS), SCH-1 (MIJ), SCH-1 (MIS), SCF (MIS) here and wanted to start a component/version-comparison with gut shots. Searching for someone to post an SFC-1 (MIJ) w/gutshots.

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Post by FloPoeKo »

Has anyone ever meddled with the differences in the pre-/de-emphasis sections between the SCH-1 and SCH-Z?

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Post by FloPoeKo »

carranen wrote:old post but may be usefull!
Who came up with the SCH-Z to SCh-1 Mod originally?

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Post by hotguit »

Hi
I'm sorry but i can not understand how to do the TB mod.
I bought an arions schz but i really can not understand the TB mod; how do i have to wire the 3pdt?
Please help
Thank you
hot

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