FW: [sdiy] Keyboard controller question

[Needham, Alan]

OOPS - wrong address !
				try again ...

-----Original Message-----
From: Needham, Alan 
Sent: 23 May 2007 1:30 PM
To: 'synth-diy-bounces at dropmix.xs4all.nl'
Subject: RE: [sdiy] Keyboard controller question


Gustav, hi,

I wondered if this was a S-H fault, kind-of agreeing with Anthony, but ...
IF the S-H circuit is leaky, there will be a 'glissando'? to one end of the range when you release a key, probably quite slow.

If the S-H gate stays open just a fraction too long after you release the key, the key bus ramps from the current key voltage down to about -12v at a rate determined by R10 and C1 (1M and 5nF). If the gate is still open then this ramp will be seen by the S-H, causing a fairly constant drop in VCO pitch (some semitones) regardless of what key is pressed.
If the above is true then as long as you hold a note the above problem will be hidden - only on key release will it be seen.
I guess the actual fault will be in the pulse-shaping section (circuit diagram page 2).

Does the trigger out behave properly ?
is the trig out signal a quick pulse on key press?
is the Gate out active all the time a key is pressed?

	Alan

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Gustav
Andersson
Sent: 23 May 2007 8:38 AM
To: Synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Keyboard controller question


Thanks for the tip, however I think the S&H is actually working as it 
should since the output voltage remains the same as long as I hold at 
least one key down. At least for a minute or so.

/gustav


Anthony Rolando wrote:
> There was a good discussion about S&H circuits last week... check the 
> archives because it sounds like you have some sort of leakage (wrong 
> cap type) or DC input offset problem (wrong op-amp type). Just a thought.
>
> T
>
>

_____________________________________________________________________
The information contained in or attached to this email is intended only for the use of the individual or entity to which it is addressed. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. It may contain information which is confidential and/or covered by legal professional or other privilege (or other rules or laws with similar effect in jurisdictions outside England and Wales).
The views expressed in this email are not necessarily the views of Centrica plc, and the company, its directors, officers or employees make no representation or accept any liability for its accuracy or completeness unless expressly stated to the contrary.

Centrica plc

Registered office: Millstream, Maidenhead Road, Windsor, Berkshire SL4 5GD

Registered in England and Wales No 3033654