I say it is not critical to use that special cap.
I would use a polypropylene cap of suitable value.
Polypropylene has low distortion when used in the signal path.
This is why it is very suitable for audio
I didn't use an Auricap for my first fetZilla for my brothers FetZilla I've used one from Intertechnics a QS a normal MKP cap.When you use an Auricap you can mount it horizontal cause they aren't big.I've mount mine and my brothers vertical cause of the size.You can use every good speaker crossover cap.Personaly I never use Wimas as input cap for a good amp.
I won't say too much here now, but thank you for the comments.
The FetZilla was designed on an idea that a fully fet amp was possible, and should work well. Paul and I felt that the weakness was the voltage amplifier; a mosfet works well, and is very easy to compensate, but it seemed to hold back the imaging performance. I don't recall Greg/Lineout/Mike thoughts on the VAS issue, however.
As Otto has explained, this forum is more suited to my non-commercial amps. Obviously my time (and noting that the FetZilla was completed two years ago and and is now the fifth group buy) is somewhat reduced since my health crisis last year. I need to dedicate my efforts to my commercial products at the Aspen forum.
Cheers,
Hugh
The FetZilla was designed on an idea that a fully fet amp was possible, and should work well. Paul and I felt that the weakness was the voltage amplifier; a mosfet works well, and is very easy to compensate, but it seemed to hold back the imaging performance. I don't recall Greg/Lineout/Mike thoughts on the VAS issue, however.
As Otto has explained, this forum is more suited to my non-commercial amps. Obviously my time (and noting that the FetZilla was completed two years ago and and is now the fifth group buy) is somewhat reduced since my health crisis last year. I need to dedicate my efforts to my commercial products at the Aspen forum.
Cheers,
Hugh
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This is now the fifth groupsbuy of the FetZilla.I don't think the FetZilla has to prove itself,for me this is a good sounding amp.There always will be better amps but when I fire up a fetZilla a tought comes up of what a good sounding amp.I build a lot of amps or planning to but they are all sold in favour of the FetZilla.Just build it if you don't like just sell it again.
Thanks Patrick,
That was what I wondered. Nothing more. I have quite a stack of amps building up. Too many to for me to get use out of. It would be good to get some in the hands of someone who would appreciate a quality amp. I'll have to look into the swap threads. Maybe I can pass some along.
Blessings, Terry
That was what I wondered. Nothing more. I have quite a stack of amps building up. Too many to for me to get use out of. It would be good to get some in the hands of someone who would appreciate a quality amp. I'll have to look into the swap threads. Maybe I can pass some along.
Blessings, Terry
Part list says 33pF schematic 15pF
I used this one see link http://www.diyaudio.com/forums/aksa/198170-group-buy-2-fetzilla.html
I used this one see link http://www.diyaudio.com/forums/aksa/198170-group-buy-2-fetzilla.html
I just put 22pf in there figuring I can add 10pf more if there is a problem. I have both channels completed and have set the biases and offset. All looks right so I will be passing a sinewave through them shortly and see what it looks through the scope. It should be playing music this morning some time. I built it without the PSU portion as I plan to run it from an SMPS. I didn't cut the boards so I can try the on board PSU later. I may even try using the PSU on one board and the SMPS on the other and see if I can see or hear a difference but I don't have a small transformer right now.
Blessings, Terry
Blessings, Terry
Test your compensation value.
Adjust the input filter to much higher than the usual 100kHz to 200kHz.
Try 1MHz.
Then apply a 500mVpp 10kHz squarewave that gets filtered by the input filter.
Read what the output does.
If you have significant overshoot or it takes forever to reach the flat top then adjust the compensation value.
Revert to your original RF input filter.
Adjust the input filter to much higher than the usual 100kHz to 200kHz.
Try 1MHz.
Then apply a 500mVpp 10kHz squarewave that gets filtered by the input filter.
Read what the output does.
If you have significant overshoot or it takes forever to reach the flat top then adjust the compensation value.
Revert to your original RF input filter.
Yes, I was starting a Fetzilla build back at the first group buy and realized AKSA carried out a few changes to his taste for his PCB/parts kit group buys. We exchanged emails on it and I have a schematic showing 15pF with another tiny tweak cap in there too.
That Fetzilla design is not quite the same as the Swordfishy (GregH) one, which was still under development in this forum at the time. Perhaps there is a mix-up of who's design became Fetzilla and the compensation he and the other guys contributing to the project wound up with, what compensation they decided on etc. Maybe I dunno either!
Hi Andrew,
I'm not sure what you mean by "adjust the input filter". How are they adjustable?
Thanks for the explanation Ian.
I have had the amp playing for a couple hours. I'm using a Connex SMPS set to +-38V rails. It sound very nice. Slightly less detailed than the VSSA. Very similar to my SKA GB150. It has good gain as I am just playing a CD player through a 15K pot and it gets plenty loud.
I used a Solen 1uF input cap. It fits nicely.
Blessings, Terry
Attachments
Thanks Christian,
Not a lot of parts in one of these. I paid for the boards back in December so I have had the components in a bag for over a month waiting on the boards so I really only took a couple hours to solder everything in place. Only two holes to drill and tap for mounting the boards. Can't get much easier than this. My only complaint is the way the input is set up. It's designed for two pins but I like using euro style terminals. I had to drill a couple holes. I may take the blocks off and solder direct once I'm ready to install it in a case so I can go lower profile. With the terminal block hanging off the side like that it is over 3" wide. I guess if you use a smaller input cap you could get away with a vertical mount block.
Adjusting everything is pretty straight forward. The VAS bias stays put once it is set. The main bias starts out high and reduces as the amp warms up and the offset is affected by temperature too. It wanders a little with temperature but stays reasonable. At 360mA bias the heatsink runs fairly warm. You need a good size heatsink from what I can tell. The sound I quite nice. This one will get a case soon.
Blessings, Terry
Not a lot of parts in one of these. I paid for the boards back in December so I have had the components in a bag for over a month waiting on the boards so I really only took a couple hours to solder everything in place. Only two holes to drill and tap for mounting the boards. Can't get much easier than this. My only complaint is the way the input is set up. It's designed for two pins but I like using euro style terminals. I had to drill a couple holes. I may take the blocks off and solder direct once I'm ready to install it in a case so I can go lower profile. With the terminal block hanging off the side like that it is over 3" wide. I guess if you use a smaller input cap you could get away with a vertical mount block.
Adjusting everything is pretty straight forward. The VAS bias stays put once it is set. The main bias starts out high and reduces as the amp warms up and the offset is affected by temperature too. It wanders a little with temperature but stays reasonable. At 360mA bias the heatsink runs fairly warm. You need a good size heatsink from what I can tell. The sound I quite nice. This one will get a case soon.
Blessings, Terry
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