[sdiy] Re: Source of 2N5459 FETs

[Oren Leavitt]

Hi Steven,

Referring to:

http://www.arptech.synth.net/pdf/4035.pdf

Remove Q1, Q2, R20 and R21 from the circuit.
Using a dual JFET input op amp, such as the TL072 (8pin DIP),
connect pin 8(V+) to +15Vand pin 4(V-) to -15V
connect pins 1(-in1) & 2(out1) together and connect these to C7 +
connect pin 3(+in1) to where Q1's gate (G) went - pins 10 & 14 of Z4
connect pins 6(-in2) & 7(out2) together and connect these to C6 +
connect pin 5(+in2) to where Q2's gate (G) went - pins 7 & 5 of Z4

That should do it!

Oren

Steven Downhill wrote:

>Hi Oren,
>
>  
>
>>Hi Steven and all,
>>    
>>
>
>  
>
>>You can probably ditch the JFETs all together and use JFET input op amps 
>>as non-inverting buffers, too.
>>This would have been an expensive luxury back in 1974.
>>    
>>
>
>  
>
>>HTH,
>>Oren
>>    
>>
>
>You've lost me with this comment! (my electronics knowledge is limited at
>the moment).
>How would you go about doing this?.
>
>Regards
>Steven
>
>-----Original Message-----
>From: Oren Leavitt [mailto:oleavitt at ix.netcom.com] 
>Sent: 19 March 2004 04:33
>To: Synth DIY (synth-diy at dropmix.xs4all.nl)
>Subject: Re: [sdiy] Re: Source of 2N5459 FETs
>
>
>Hi Steven and all,
>
>You can probably ditch the JFETs all together and use JFET input op amps 
>as non-inverting buffers, too.
>This would have been an expensive luxury back in 1974.
>
>HTH,
>Oren
>
>Steven Downhill wrote:
>
>  
>
>>>Hi,
>>>The FET's in that circuit are the selected ( orange) ones. 2n5459's have a
>>>   
>>>
>>>      
>>>
>>wide
>> 
>>
>>    
>>
>>>spec on pinch-off voltage. The orange ones are selected for a pinch-off of
>>>   
>>>
>>>      
>>>
>>5V or
>> 
>>
>>    
>>
>>>less, the yellow coded ones are the rejects. the 2n4392's will work well
>>>      
>>>
>in
>  
>
>>>   
>>>
>>>      
>>>
>>the
>> 
>>
>>    
>>
>>>4035 circuit as their pinch-off voltage is always less than 5V.
>>>   
>>>
>>>      
>>>
>>Thanks for the additional info.
>>Now that I know the above I've decided to go with the 2N4392s (I can get
>>these immediately for half the price of the 2N5459s and use them in some
>>other projects).
>>
>> 
>>
>>    
>>
>>>The VCO I am referring to is the standard 4027-1 circuit used in 2600's .
>>>   
>>>
>>>      
>>>
>>Same
>> 
>>
>>    
>>
>>>circuit was used in Axxe and later Ody's.
>>>   
>>>
>>>      
>>>
>>I've looked at this schematic before and always wondered what the FETs were
>>as they're just labelled with (I assume) ARP's own part number.
>>
>>I would love to be able to build my own ARP Odyssey or 2600 at some point
>>    
>>
>in
>  
>
>>the future.
>>Do you think that this could be done using the schematics / service manuals
>>    
>>
>>from the Net and finding equivalent semiconductors to those which are now
>  
>
>>obsolete?.
>>
>>Regards
>>Steven
>>
>>-----Original Message-----
>>From: Dana Scott [mailto:danas at egosys.com] 
>>Sent: 18 March 2004 11:50
>>To: Steven Downhill
>>Cc: synth-diy at dropmix.xs4all.nl
>>Subject: Re: [sdiy] Re: Source of 2N5459 FETs
>>
>>
>>Hi,
>>The FET's in that circuit are the selected ( orange) ones. 2n5459's have a
>>wide
>>spec on pinch-off voltage. The orange ones are selected for a pinch-off of
>>5V or
>>less, the yellow coded ones are the rejects. the 2n4392's will work well in
>>the
>>4035 circuit as their pinch-off voltage is always less than 5V.
>>The VCO I am referring to is the standard 4027-1 circuit used in 2600's .
>>Same
>>circuit was used in Axxe and later Ody's.
>>-Dana
>>
>>----- Original Message ----- 
>>From: "Steven Downhill" <Steven.Downhill at brother.co.uk>
>>To: "'Dana Scott'" <
>>Cc: <synth-diy at dropmix.xs4all.nl>
>>Sent: Thursday, March 18, 2004 4:21 AM
>>Subject: RE: [sdiy] Re: Source of 2N5459 FETs
>>
>>
>> 
>>
>>    
>>
>>>Hi Dana,
>>>
>>>   
>>>
>>>      
>>>
>>>>What are you building? If you are building ARP VCO circuit, you will have
>>>>     
>>>>
>>>>        
>>>>
>>>better
>>>   
>>>
>>>      
>>>
>>>>luck using a 2n4392. It does come  in a metal can instead of a plastic,
>>>>     
>>>>
>>>>        
>>>>
>>>tho'.
>>>   
>>>
>>>      
>>>
>>>>-Dana
>>>>     
>>>>
>>>>        
>>>>
>>>The plan was to use them in the ARP 4035 VCF (assuming the below schematic
>>>is OK).
>>>
>>>http://www.arptech.synth.net/pdf/4035.pdf
>>>
>>>Thanks for the info on the ARP VCO.
>>>Which version of it are you referring to?.
>>>
>>>Regards
>>>Steven
>>>
>>>-----Original Message-----
>>>From: Dana Scott
>>>Sent: 17 March 2004 17:45
>>>To: Steven Downhill; synth-diy at dropmix.xs4all.nl
>>>Subject: Re: [sdiy] Re: Source of 2N5459 FETs
>>>
>>>
>>>What are you building? If you are building ARP VCO circuit, you will have
>>>better
>>>luck using a 2n4392. It does come  in a metal can instead of a plastic,
>>>tho'.
>>>-Dana
>>>
>>>----- Original Message ----- 
>>>From: "Steven Downhill" <Steven.Downhill at brother.co.uk>
>>>To: <synth-diy at dropmix.xs4all.nl>
>>>Sent: Wednesday, March 17, 2004 9:31 AM
>>>Subject: [sdiy] Re: Source of 2N5459 FETs
>>>
>>>
>>>   
>>>
>>>      
>>>
>>>>Hi All,
>>>>
>>>>Does anybody know of a company in the UK with the exception of RS that I
>>>>     
>>>>
>>>>        
>>>>
>>>can
>>>   
>>>
>>>      
>>>
>>>>obtain 2N5459 FETs from?.
>>>>(RS seem the only company to have this part and they'll be out of stock
>>>>     
>>>>
>>>>        
>>>>
>>>for
>>>   
>>>
>>>      
>>>
>>>>the next 10 weeks!).
>>>>
>>>>Equivalent part suggestions are also welcome.
>>>>
>>>>Thanks.
>>>>
>>>>Regards
>>>>Steven
>>>>     
>>>>
>>>>        
>>>>
>>
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>>    
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>
>  
>

-- 
Oren Leavitt
oleavitt at ix.netcom.com