Arion SCH-1 Questions

[BF84]

Been quite a while since I've been on this forum.... forgive me if this has been asked 100 times. I just came across a SCH-1 Chorus I forgot I had.
I am looking for info on a "true bypass" circ. and a schematic for this unit and for that matter any mod info.
Anyone able to point me in the right direction?
Thanks

[Mark Hammer]

Ever since the boo-teek biz started flouting true-bypass as the be-all and end-all (hence desirable), people have been asking how to true bypass this thing and that thing. The question I respond with is generally always the same: WHY do you want to do it?

That doesn't mean you're a fool for wanting to TB the pedal, but the advantages of TB only apply in certain contexts, and if your context is not one of them, why bugger up a perfectly good pedal?

Note the following:
1) Unless you are skillful, all the input and output buffers that are normally blamed for tonesucking will still be present in the signal path. Not if you apply TB in a certain way, mind you, but they will be there when the chorus is engaged.
2) Due to the typical manner in which FET-switched choruses, flangers, echoes, and phasers are switched (one single FET to connect the time-modulated signal to the mixing stage), you can't easily mod the pedal for vibrato (delay-only) unless you have a full bypass around the entire circuit. If you have no need/affection for vibrato, there is no advantage to TB.
3) TB provides advantage when there is the risk of power loss to the pedal (e.g., battery dying). If you plan to power a pedalboard with an adaptor, rather than use a battery, then there is no strategic advantage to TB with respect to power reliability.
4) TB does reduce potential hiss when you have a half dozen or so pedals in series and the tiny amount of hiss from the buffers in each pedal accumulates. With only a few pedals in the signal path, negligible hiss is added and little tone is lost. Even when there ARE 6-8 pedals in series, an easier tactic is to make/buy a loop selector pedal so that groups of pedals can be true bypassed easily without having to modify any single one of them.

[BF84]

Thanks

Mark,

Points well taken, appreciate for all the info.
My main reasoning for considering TB for this pedal is "tonesucking" aspect.
Though I have been giving serious thought to building a loop selector pedal as you mentioned in point #4, which is making more sense for the set-up I will probably be using.

I guess I was hoping to find a schematic for reference..... My searches have come up short.

Thanks

[Mark Hammer]

I posted a schematic I have on Photobucket: http://img.photobucket.com/albums/v4...ereoChorus.gif

I don't know if it is the identical model as yours, but it ought to be pretty close. Making it amenable to TB would involve shunting/bridging the drain and source pins of Q4 and Q9 up in the right hand corner of the schem. The schem doesn't tell me what type of FET those are so I couldn't tell you what numerical pins that involves but you can work your way forward from the 39k resistors and backwards from the IC input pins to identify them. Once the delay outputs are hardwired to be always on, you can then wire up a stompswitch to go from the input and output pads of the circuit board.

Is that enough info?

[BF84]

Just What I was looking for..

Big thanks again Mark!

The PCB for my unit is marked 'PCSCH10B' the same as the schematic and from everything I have seen has been dead on. The JFET's are 2SK772 and I have data sheets on them..... The package pin out's match up with the info you gave.

Plenty of info!

[novoros]

True bypass and Vibe mode

Hi Mark,
Thanks for Great info. I'm ready to mod my Arion SCH-1 with true BP but would like to ask if you can provide the ifo how to do Vibe mod also, I don't need stereo out and can use the SW1 for the mode. On my pedal to to bridge the Q4 and Q9 I had bridged the side pins of each FET's. I'll be rehousing my SCH-1 also and would like to have your opinion what kind of case to use and if I need new potentiometers for the pedal. Many thanks in advance for your time.
iouri