[sdiy] Substitute for IMF-3958 ARP 4015 S/H SubModule

[Dave Manley]

Ebay item: 160161196684

The guard isn't so much a plane, as a copper trace that surrounds the 
indicated pins.  If you look at page 3 of the Arp-Tech PDF you can just 
barely see it (the quality of the image is poor).  In the circuit, the 
guard ring surrounds the high-impedance node where the charge is held. 
If you do any repairs in this area make sure to clean the board of any 
residue which might form a leakage path and cause the S/H output voltage 
to droop over time.

-Dave

Jay Schwichtenberg wrote:
> Csaba,
> 
> It's a ground plane on the circuit board to isolate the sensitive sections
> of the circuit from outside interference. High impedance on the op-amp input
> can pick up noise or unwanted signals very easily. Also you want the signal
> path between the switch (FET), cap and op-amp input to be as short as
> possible.
> 
> Jay S.
> 
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Csaba Zvekan
> Sent: Wednesday, May 28, 2008 4:56 AM
> To: Synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Substitute for IMF-3958 ARP 4015 S/H SubModule
> 
> 
> Hi everybody,
> 
> I am looking for the IMF-3958 or 2N3958 N-Channel J-FET for a ARP 4015
> S/H Submodule (ARP2600). Is there a good substitute ?
> Also looking at the schematics from ARP-TECH's site. I don't
> understand what the "GUARD" means coming from the Source of the 2N4392
> to the two Gates of the 2N3958.
> 
> 
> Thanks
> 
> Csaba