Cascoded ZV7

[Fuling]

The heatsink for the mosfets (Needs some cleaning...)

[Fuling]

...and the actual circuitry, except ccs´s and resistors:

(There must be some way to attach more than one picture in every post...)

[carpenter]

Nice job, fuling. BTW, those heatsinks of yours are just amazing!

Regarding the choke load, I noticed that in my ZV7-T an air-core choke draws quite a bit of the load--which seems to remove stress from the rest of the circuit. This leaves more capacity for the heatsinks, and you could cascode with less rail voltage. I only loose 5.5 volts across the chokes.

Just something to gnaw on,

John

[Fuling]

Thanks!

I DO like choke loading, but since I don´t have any suitable centertapped chokes nor any equipment to measure distortion the ZV7-T is not of any particular interest for me.
Both when I´m working with tubes and transistors I have a preference for "pure" SE topologies and thus airgapped iron wares.
A friend once came to this conclusion: "The sound is in the airgap"
Considering what happens with an iron cored choke or transformer when you put an airgap in the core there might be some truth in his statement, the inductance decreases but also gets more linear. There is also theories about the benefits of moving away from the "zero flux point" or whatever it´s called, I guess the magnetization curves could be compared with the bias current in an amplifier.

The greatly improved efficiency is another great thing about inductive loading, I once made an SE amp that delivered over 2x30W with only 75W losses per channel.
If I ever need more than, say, 20W class A I´ll definitely use inductive loading. The idea of using bifilar output transformers to get rid of the output caps has also crossed my mind.

[Fuling]

I tested the Xsoz in my system for the first time last night, unfortunately there was some hum which might have come from from my "10 minutes preamp" made of a volume pot, two IRF9610 and four resistors (a ZV4 buffer actually).

When I connected the amp (open inputs) to a pair of speakers with 87dB sensivity there was absolutely no hum to be heard, but with 94dB speakers and the preamp connected there was some hum that could be heard up to about two feet away from the speakers.
Not much, but enough to be a bit annoying.

I won´t say anything about the sound until I´ve heard the amp with a proper balanced preamp, the CCS is adjusted for balanced input and I suspect that it doesn´t work very well with SE input signal.
Not that there was anything wrong with the sound, but I´m expecting severe improvements with a decent preamp.
Nothing wrong with the ZV4 buffer, but the PSU I used and my hardwiring work left a lot to wish for

[carpenter]

Interesting news, fuling. I'm anxious to read a review of your amp with a balanced input.

I'm at the point where I get to fire up my second ZV7-T--today, is my goal. It, too, has the ZV4 buffered input. I'm hoping it performs well. I did match the ZVP3310 mosfets, so there should be some noise cancellation. Also, with the loop feedback routed to the buffer input, there should be even greater distortion reduction--that's assuming I have implemented my design with a proper understand of Nelson's reasoning.

I think the ZV7 version of the SOZ is an amazing sounding amp. It's nice to see someone else working along a similar line.

John

[Fuling]

The ZV4 buffer is a very clever way to implement a buffer with a single rail voltage and input at ground level, very useful!

As far as I can see there is no reason not to use a CCS in the tail of any SoZ-version instead of the power resistors, the efficiency goes up and so does the performance!

[Fuling]

"The Beast" is finished!!
Right now it´s warming up for a listening session later today, and the hum went away when I got the bright idea ( ) to put jumpers between -in and ground in the XLR inputs. I forgot that at the first listening session, hence the hum that I blamed on the external buffer.