Swordfishy/ASPEN FETZILLA power amp

[wlewis]

Originally Posted by AKSA

NO more orders at this stage please guys.
GB #3 is now fully subscribed, but if interest continues to mount I will open GB #4 in a few months.

hi hugh.. as i would not rather not wait a few months to start building this amp can you get me the schematic this pcb is based on? I checked out lineup's fetzilla thread and can't tell which fetzilla version this is.

Great work btw.. two terms come to mind: prolific and persistence.

[Woody1911a1]

Originally Posted by wlewis

hi hugh.. as i would not rather not wait a few months to start building this amp can you get me the schematic this pcb is based on? I checked out lineup's fetzilla thread and can't tell which fetzilla version this is.

Great work btw.. two terms come to mind: prolific and persistence.

lets see if this works


cheers Woody

[AKSA]

Woody,

Many thanks!

WLewis,

That's the one, Woody has it nailed. This is it. You will find ALL documentation in the thread, I think it's Post #59.

Hugh

[AndrewT]

Aksa,
can you add Woodies links to post1?

[Woody1911a1]

Ya know Andrew , i was intending to suggest the same thing last nite , but after scrounging those up and uploading , I forgot to say something .

i just posted a new thread with all the documentation that i've collected . maybe sticky it .

cheers Woody

[taniknight]

Hi All,

I have yet to start collecting parts for this amp, but I am working on chassis possibilities and I was wondering if there is any reason why 2 Fetzilla amps couldn't be used in balanced mode.

Can someone shed some light on this for me please?

Many thanks,
Tani.

[AKSA]

Tani,

Do you mean balanced input, or bridged output?

If the former, you would need either additional input stage electronics OR a balanced line transformer, the best option.

If the latter, you would need to double the output stage count, two pairs of latfets rather than one, so that the bridged amp could handle the doubled current flow and to avoid degradation of the output impedance, important to damping.

Hope this answers your question,

Hugh

[taniknight]

Hi Hugh,

I'm probably using the wrong terminology, but I meant feeding each phase of a balanced input into separated amps, driving either end of the load - as a bridged output would. I thought that this was referred to as balanced operation.

Do the amps each see a more difficult load if this approach is used?

Thanks for the help.

[syklab]

Hi Hugh,
My first incompleted build on one channge first, I will start adding the transistors, the mosfet and the C1 during the weekend. I will post my BOM for the parts that I have selected.



Best regards

[AKSA]

Hi Syklab,

Nice build, neat and tidy, like the output source resistors!!

You are wisely leaving the 2SK170 and DN2530 until last....... good man!

Tani,

Balanced is where you have a three wire input, a Cannon XLR plug, where the two 'hot' inputs are in antiphase, and the third wire is a ground. This is widely used in proaudio because it's highly immune to noise, but only occasionally in domestic hifi. Your application is called 'bridged', but it does indeed produce a balanced, viz 'antiphase', output, which then drives from opposite ends of the speaker driver.

Bridged means that each amp sees half the load; so an amp designed here for 8R operation becomes two amps that each see 4R. This is the reason the output stage must be beefed up. It also means that even order distortion from each amp is 'balanced', that is, cancelled, and this in turn means the distortion spectrum is reduced, good for THD, but those distortions left are predominantly ODD order, which sound quite different to the FetZilla acting as a single amp.

I do not endorse this approach, because it undoes much of the careful distortion profiling designed into this amplifier, changing its sound drastically, in my opinion for the worse.

Cheers to you both!!

Hugh