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Filtrex II part question
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Filtrex II part question
terjewinther
I am building the Filtrex II, and there are some parts details that are not in the docs:

- In the photo of the Filtrex II on the Oakleysound web site, it seems to be some very special caps used in the ladder filter. What are these, and are there any specific suggestions for caps in this filter?

- Speaking of the ladder filter: since there are matched transistors (inside ICs) on the top and bottom of the ladder, are there any advantages in matching the rest of the transistors? I know that modern transistors usually are close, but would you be able to hear any difference if you do match the transistors?

- In the photo on the web site, there are two transistors roughly in the middle of the board that are held together with wire straps. Should these be matched too? I guess the wire strap is for thermal coupling?
bcitral
How far are you through the build terje?

I noticed the ladder caps too but had some surplus caps and used those.

Ill be interested to hear what they sound like.

B
thumbs up
terjewinther
I am just starting out, gathering parts.
bcitral
Its a really nice sounding build, enjoy.
Synthbuilder
terjewinther wrote:
In the photo of the Filtrex II on the Oakleysound web site, it seems to be some very special caps used in the ladder filter. What are these, and are there any specific suggestions for caps in this filter?

Those four caps were taken from an old Korg Polysix voice board. They were the only ones I could find in my workshop of the right value. They are just really old so they look different. They are radial polyester types of unknown tolerance.

There is no specific requirement on the ladder capacitors but I would fit either polyester, polystyrene or polypropylene in there.

terjewinther wrote:
are there any advantages in matching the rest of the transistors?

Not to my ears.

terjewinther wrote:
In the photo on the web site, there are two transistors roughly in the middle of the board that are held together with wire straps. Should these be matched too? I guess the wire strap is for thermal coupling?

Yes, they can be strapped together for thermal coupling and matched for Vbe. But really it's not necessary as the drift in cut-off frequency incurred by any mismatch would be not noticeable unless the Filtrex was being used as an oscillator.

Tony
terjewinther
OK, thanks a lot!
On to gathering parts, then.
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