Swordfishy/ASPEN FETZILLA power amp

[keantoken]

Thanks for the info Hugh.

If you look at current mirrors operating with large signals, you'll see that the nonlinear Re of the transistors causes a derivative spike in the capacitive currents of the transistors, at the negative peak when the falling conductance causes a fast risetime across the B-E junction. This is even worse for advanced current mirrors such as the Wilson and so on. So it makes sense linearizing Re is a good idea.

But I don't understand this "bridging ratio" you talk about. I did a Google search and found nothing (whoah...). Can you please tell me what this means?

[keantoken]

Also it should be mentioned that thermal drift and generation is an instantaneous mechanism in the silicon die. So by modifying the transistor's thermal profile you are actually affecting it's immediate response and transfer curve. I don't know to what degree though.

[AKSA]

Hi Kean,

From wikipaedia:

When the output (output impedance) Zout of a device (the source, ZS in illustration) is connected to the input (input impedance) Zin of another device (the load, ZL in the illustration), it is a bridging connection if the second device does not appreciably load the previous device.

Essentially no power is transferred. The second device is sensitive to the output voltage of the first device, and this is maximized when loading is minimized. All good line level audio connections are bridging, to ensure the high fidelity transfer of a voltage signal from one device in the chain to the next. If the bridging criterion is not satisfied, there may be distortion, altered frequency response or both.

A connection is commonly said to be bridged if the load impedance is at least ten times the source impedance.

So there you have it...... ten times is the magic number!

Hugh

[ajst2duk]

Not far away - one set of GB2 fetzillas waiting for the final couple of caps. Had some tricky bits with the fuse holders and the end diode bridges whos legs seemed too big for the PCB holes. Nothing worthwhile comes without challenges however, nothing 5 minutes with a dremel didn't sort out. I went for a pretty standard build with the Auricaps, was going to try some Mundorf supreme silver/gold and some V-caps TFTF I have but both were too big to not cause issues. I'm trialling a set of Atohm GT1.0's here at the moment and they are stunning with both my Plinius amps and a recent chip amp build - keen to see how Fetzilla steps up. Give me another week and I'll be posting some listening sessions. - AJ

[AKSA]

Looking very swish, Andrew!

'ats off, Sire.....

Hugh

[keantoken]

Thanks for the explanation AKSA. Now what if we could use diodes creatively to implement a log-law (or square law? not sure which one is right) Vce so that the dissipation would be perfectly flat, instead of monotonic with a canceled fundamental.

[AKSA]

Then, surely Kean, you would eliminate all distortion?

Be careful what you wish for!!

Hugh

[keantoken]

Well maybe it's a job for the square-law class A guys, I'll bet Ed Stuart could throw something interesting together.

I just got done re-fitting my Fetzilla with the proper parts! Ah, after all this time... I will check it over and if everything seems fine, set it on fire. (destroyed a prototype of my own a week ago, degen resistors on fire!)

[ajst2duk]

She's alive - all assembled - tested fine - only had time to listen to one song as I was running out the door sounded stupendous straight up. I'll post a review and some pics later. Many thanks to Hugh and the designers for an awesome piece of kit. - AJ

[ajst2duk]

Some pics - in the stack the Fetzilla is sitiing on top of an Oppo BDP83SE and a Plinius CD-LAD pre. Tried with my Lenehan ML1+ speakers yesterday, today I'm running Atohm GT1.0's