Goldmund Mods, Improvements, Stability

Jamanese it is!

Hi Jay,

Mr.Curl uses Toshiba mosfets for drivers. You don.t have to bias the mosfets that high usually 80 to 100 mls. is good (and that is pushing it)

Rule of thumb is that mosfets can sound very good in output stages as well but the have to be biased higher and you you have to compensate for the Vgs drop which can be pretty high for vertical devices. You owe it to yourself to listen to a Pass design to hear what can be done with mosfets.

Jam
 
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You merely asked how designers come up with such a decision, not the exact same choice.

(i think i have an amp here that looks a bit like that prototype, but i call it Jamanese. :clown: )

Here is my words:
"Just wondering... how can some of you designers come up with such a decision to put IRFP240/9240 in that position (driving the output BJT)???"

IRFP240/9240 is big VFET. Enough to drive a loudspeaker. Even smaller one I disagree. But the Toshiba seems to be the best option.

Jam,

I know Pass DIY amplifiers. I started from the very first Zens. That's how I know about these mosfet sound.
 
Jay,

Have you listened to one the X or XA amplifers they sound quite different to the Zen's and Aleph's.

What I am trying to say is sometimes the application can be more important than the type of device used.

Jam

Yes, only the smaller one. It could be his best amp.

I agree that the application can be more important, but I think I would prefer to start with the device then try to find a good application for that device. Because there are devices with special characteristics in certain area that needs to be realized while thinking how to overcome the negative characteristics.

I have a few devices that I keep for it's characteristics, waiting for someday when I have no option but learn to design my own amplifiers.

JLH used certain mosfet as a driver/VAS in his amplifier. Holton and Alex Nikitin also. But they aren't IRF610/9610. Put IRF610/9610 in that design, and they become different design soundwise.
 
OS, what about your Darlington LTP VAS? How does it compare to cascoding? Cob is much less important now. This looks pretty useful to me if we want to keep the MPSA VAS.

- keantoken


I noticed on the MPSA VAS that the darlington barely brought the loop gain up to 48db. Without it the MPSA's could barely muster 42DB.This reflects the low beta of these devices as I tried both my MPSA and KSP42/92 models.

The KSA/C-1381/3503's do 53db in the same situation , in a darlington arrangement they do 75db+.. they have 4 X the gain. My mistake was running my BJT OPS in the simulations. By itself , the darlington VAS (CX2) has even lower distortion than the blameless or pioneer M-90 with the goodness of H2 dominant THD and super low high order components.

I am just glad all this hype "triggered" me to dig up the old CX (supersym) and give it it's "makeover".
OS
 
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Let's see, JFET, MosFET and BJT we will need to have a least one germanium diode and some Vacuum Glass device to round out this 5 Blind Men feeling the elephant symposium.

It's bound to sound like a straight wire with gain feeding your eardrum directly.

It is truly fascinating to watch this come together.