Pearl transistor choice for Cascode

Hi there,

I am building the Pearl and noted that the Ono uses different cascode transistors. Since the pinout is different, I have checked out what Zetex has which might be more appropriate and come to the following conclusions which I would like to have verified:

1. I am not quite sure whether the ZTX450 is optimal in cascode position -- I guess it would be optimal to go with a lower current unit. Should I also consider going for a high Hfe unit such as the ZTX692B? ( (The unit used in the Pass Ono is 2SC1844)

(((2. The capacitance multiplier circuit benefits from high beta transistor. I am going with a high Hfe Zetex unit (ZTX692B) of that I am certain)))

Your insight into would be valued.

pearl cascode

You might want to try a Zetex ZTX3310 mosfet! An increasing number of designers are turning to all fet designs. I have been doing cascodes on amplifier front ends with it and it sounds great. You might want to put a 1k gate resistor connected directly to the gate. I note that the votage dividers are not real close to the ZTX450 cascode transistor in the pearl layout. I also wonder if bypassing the bottom resistor with a small cap might not be worth doing as I have seen it done in many bipolar cascodes. The Zetex are pretty nice transistors in my experience.



2001-03-06 3:07 pm
yeh yeh.....but anyway....why not use tubes...that would be waaay cooler hmm or maybe not... ;-)

but then with 20 000 fets that not a hel of a lot of logic circuits...but then it was a smal computer..hmmm when i come to think about might be fun after all......once i builded a extreamly small computer of logic cicuits in school...

Perhaps he's building a simple digital signal processer using emitter-coupled logic*. I wonder if a ECL buffer could be used to "clean up" digital signals for audio...


* ECL is the class-A of digital circuits. Basically, it involves using differntial BJTs in biased so that they never shut off (hence, class-A). A simple exmaple would be using an LTP as an inverter. Because they never shut off, they can be "switched" exceedingly fast. The original Cray used them.

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
No point to point. I'm not totally crazy.

The bulk of the devices ae going into a small amount of
memory. I haven't finalized it yet, but probably about
128 bytes.

Processors themselves don't consume nearly as many
devices, and that's how they managed tubed computers -
the memory was in mercury delay lines or on wire spinning
on bicycle hubs. I'm not that sophisticated, though, and
I'm simply building transistorized registers.
CPU diversion

So...... You really don't want to tell us how they sound in a Clever diversion! Maybe we have stumbled on to something......

Maybe it makes sense that you build a computer as hobby since you build amps for a living. I guess since I built digital telephony equipment for a living I can build audio for a hobby.....