[sdiy] Moog ladder theory questions

[Jim Patchell]

Assuming that beta in infinite is just a way of making analysis easier 
in some cases.  Depends on the circuit, alot, but generally anything 
over 20->50 is pretty close to infinity ;^)....

When designing transistor circuits, a lot of effort goes into making the 
circuit perform the same no matter what the beta is, since beta can vary 
quite a bit from unit to unit.

-Jim

cheater cheater wrote:
> Ah sure, but the document I'm reading assumes beta is +infinity, so
> I'm wondering what it is in reality.
> What transistors do you guys use for moog filters normally?
> 
> What transistors were used in the originals?
> 
> Cheers
> Damian
> 
> On Wed, Jan 14, 2009 at 4:37 PM, Tim Ressel <madhun2001 at yahoo.com> wrote:
>> Dear cheater^2,
>>
>> If you are talking about the transistors in the ladder itself, I don't think the beta is critical. The transistors are being used not for their amplification quality but for their ability to change AC impedance in relation to their collector current. I believe other transistor qualities, like noise, are much more important. I'm toying with the idea of making an ARP ladder phasor which uses 28 transistors in a ladder configuration similar to the Moog ladder filter. The MAT04 transistor quad is looking attractive for its low noise. With 28 transistors, noise is a real issue.
>>
>> Of course, the sonic quality of the filter is affected bt transistor choice as well. But you cannot determine that from a data sheet. BTW the choice of capacitor type will affect sound quality as much as transistor choice.
>>
>> --Tim (had $0.02 to spare) Ressel
>>
>> --- On Wed, 1/14/09, cheater cheater <cheater00 at gmail.com> wrote:
>>
>>> From: cheater cheater <cheater00 at gmail.com>
>>> Subject: [sdiy] Moog ladder theory questions
>>> To: synth-diy at dropmix.xs4all.nl
>>> Date: Wednesday, January 14, 2009, 3:29 AM
>>> Hi guys,
>>> I'm reading up on the moog ladder.
>>> What beta do the transistors used in the moog vcf normally
>>> have?
>>> I bet there's a difference between the case of
>>> 'original instruments
>>> of lore' and 'nowadays', so let's consider
>>> both options.
>>>
>>> Cheers
>>> Damian
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 
> 

-- 
----------------------------------------------
Visit http://www.noniandjim.com
SDIY: http://www.noniandjim.com/Jim/index.html
----------------------------------------------