First of all, I'm not trying to "change" anything. I just found out about the FetZilla. I see that it has reached a point of boredom for you so I understand your lack of zeal and/or interest in dealing with anything "new" folks are trying to do with it. The use of an SMPS is interesting to me since I have been hearing about them for a while now and just as I found this thread, Patrick was talking about using one. He actually built it. Then I see Paul suggest hooking it up differently than Patrick so I asked if he tried it.
As for as getting me moving, well Patrick hasn't even ordered the boards yet so at this point, all I can do is gather information so I can begin to accumulate parts. Who knows when I will actually have boards to build?
Hi Patrick,
Looking forward hearing your assessment.
Blessings, Terry
Is there a ltspice sim of the fetzy kicking around anywhere? I had a quick look about and hadn't found one as yet. I'd like to have a play around with subbing in a bf862 for the k170 (I have about 100 of them here, but I do have a couple of lsk170's just in case) and checking the dissipation there and throwing a bit of switching noise into the psu rails to see how well the filters work too. Cheers!
Why not ask Paul Bysouth through PM - he did this, but you will need some of his good models.
Hi ASV,
The LTSpice file is useful for figuring dissipation, but it gives limited information about the sound quality, although the harmonic profile was pretty good, mostly H2, H3, H4 and H5 not much more beyond. Loop gain was IIRC 50dB....... but the sonic signature of the VAS mosfet was very evident to me during listening tests.
GG,
For low power amps, I personally don't believe protection is needed. Some don't, of course, and it's your choice. On my Proaudio amp I have a DC protection system with a relay. Rail fuses are used on the FetZilla and we have not heard issues with serious mishaps with speakers.
Hugh
Hi ASV,
The LTSpice file is useful for figuring dissipation, but it gives limited information about the sound quality, although the harmonic profile was pretty good, mostly H2, H3, H4 and H5 not much more beyond. Loop gain was IIRC 50dB....... but the sonic signature of the VAS mosfet was very evident to me during listening tests.
GG,
For low power amps, I personally don't believe protection is needed. Some don't, of course, and it's your choice. On my Proaudio amp I have a DC protection system with a relay. Rail fuses are used on the FetZilla and we have not heard issues with serious mishaps with speakers.
Hugh
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Will do - and thank you for the model attached. I really approach this hobby as a 'what can I learn' exercise, and the amount of documentation and discussion around the fetzy is excellent for my wants and needs. Perhaps I may even aspire to contribute something with a smps build?
Anyway thanks for the ongoing support here. I hope everyone appreciates the hours of effort that must go into supporting such a project after the design stage - I certainly do!
Cheers.
Anyway thanks for the ongoing support here. I hope everyone appreciates the hours of effort that must go into supporting such a project after the design stage - I certainly do!
Cheers.
Hi all
While Hugh had a pivotal role in the amp, almost like a father,
as it is not "an Aksa amp", and
it could be of interest to a range of solid staters, some who might miss it here
Some of whom would eg know of further local goods parts suppliers, and/ or possibly contribute to experiments or refinements
and the group buy has progressed slowly ~
To reenergise the amps development and promotion
I suggest that future discussion be in a new thread in the SS forum, maybe called Fetzilla Part 2
Cheers
While Hugh had a pivotal role in the amp, almost like a father,
as it is not "an Aksa amp", and
it could be of interest to a range of solid staters, some who might miss it here
Some of whom would eg know of further local goods parts suppliers, and/ or possibly contribute to experiments or refinements
and the group buy has progressed slowly ~
To reenergise the amps development and promotion
I suggest that future discussion be in a new thread in the SS forum, maybe called Fetzilla Part 2
Cheers
In your opinion, what is worse for sonics, (non "hifi-tuning") fuses or the inevitable relay that comes with a DC protect?
Personally i used to think audiophile fuses were a bunch of balloney, but after realizing the amount of money i'm about to sink into my fetzilla build, tuning fuses are starting to look pretty good...
Are you by any chance referring to
http://www.diyaudio.com/forums/solid-state/247407-building-fetzilla-questions-answers.html
The latest snazzy thread? IMHO, each thread has a different flavor and some threads are read by various people who were in on it at the very beginning, these people seldom have time to read the more junior threads.
Frankly, the more threads there are the better. Exposure for the involved authors and Aspen can only be a good thing, right?
Yes
[/QUOTE] IMHO, each thread has a different flavor [/QUOTE]
I haven't noticed much difference - they're basically on the same topic
[/QUOTE] and some threads are read by various people who were in on it at the very beginning, these people seldom have time to read the more junior threads.
Frankly, the more threads there are the better. [/QUOTE]
Not if they duplicate the subject. Better all in one place - easier to search
[/QUOTE] Exposure for the involved authors and Aspen can only be a good thing, right?[/QUOTE]
Yes - especially if it is in the most widely read relevant forum - the Solid State
What do others think?
Cheers
Add links in the new thread in the Solidstate forum to all of the original threads so newcomers can know where they can go to search. According to Hugh, the FetZilla is not actually an ASKA amp. Personally, I didn't even know there was an ASKA forum until I saw the FetZilla boards offered in the Group buy forum. I think it is a good idea keeping the thread alive in the SS forum. The more folks hear about it, the more interest it will gather.
HI Terry,
Great idea! I have used this AKSA forum since the guys in DIYaudio offered it to me about five years back...... very nice for my commercial offers.
The FetZilla was done with four other guys as an open source design, and I laid out the pcb. I then offered pcbs and some active device for three group buys, and then passed it over to Patrick in Belgium. The idea was to offer something to DIY builders at low cost, just the price of the pcb, rather than selling as Aspen products at retail product, fully built.
Cheers,
Hugh
Great idea! I have used this AKSA forum since the guys in DIYaudio offered it to me about five years back...... very nice for my commercial offers.
The FetZilla was done with four other guys as an open source design, and I laid out the pcb. I then offered pcbs and some active device for three group buys, and then passed it over to Patrick in Belgium. The idea was to offer something to DIY builders at low cost, just the price of the pcb, rather than selling as Aspen products at retail product, fully built.
Cheers,
Hugh
After all these years I finally installed the FETzilla in a case. I gave up on the idea of using an SMPS. I am using a 600VA 28/0/28VDC transformer and a Mr Evil cap multiplier for the PSU. It is outputting +-36VDC. I'm running it at 330mA bias. The heatsinks are running about 40c playing loud so I think I am ok even though they are maybe a little smallish.
The amp doesn't look great on a scope but it sounds quite nice actually. The offset is all over the place. I have been chasing it for two hours and it wanders quite a lot. If I zero it, a half hour later it will be at +-80mV. I know that won't hurt anything but it's just weird. I'm going to stop chasing it and just let it wander.
The amp doesn't look great on a scope but it sounds quite nice actually. The offset is all over the place. I have been chasing it for two hours and it wanders quite a lot. If I zero it, a half hour later it will be at +-80mV. I know that won't hurt anything but it's just weird. I'm going to stop chasing it and just let it wander.
Attachments
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I'm not sure. I didn't stick a finger on it. I'll check for that tomorrow. It's only dropping about 1.5V. It's been so long now I don't remember how many amps it's good for. I'll have to look that up.
I looked it up and the Cap multiplier is rated for 5A so it should be fine but I will check the heat.
Finished capacitance multiplier
Finished capacitance multiplier
Hi Terry,
If the cap multiplier is fitted to the FetZilla and the quiescent is only 350mA, then two channels would draw about 720mA at idle and bounce up from there with music signals. I would not expect much heat from the cap multiplier because the total idle dissipation would be 0.72 x 1.5 = 1.08W, almost nothing for a large series pass transistor, maybe an average of about 3W passing heavy music.
Very different to a Class A like the Alpha Nirvana which will be passing and average of 1.7A and up to 4.5V across it. That is 7.65W and you'd really notice that.
The offset issue is a nuisance but based on past experiences with singletons and bipolars, it seems to be caused by the heavy tempco of the jfet input device and mosfet VAS device. Small temp changes there will cause big changes on the offset, and its origin is first and second stages, not the output stage. Understandably this could be improved; but to do it, and improve the depth of image as well, the best way would be replace the mosfet VAS with a bipolar, like a KSA1381. I believe a bipolar is far better for the VAS role; it has much more transconducance and therefore more accuracy than a small mosfet.
Thanks for keeping the thread moving........
Hugh
If the cap multiplier is fitted to the FetZilla and the quiescent is only 350mA, then two channels would draw about 720mA at idle and bounce up from there with music signals. I would not expect much heat from the cap multiplier because the total idle dissipation would be 0.72 x 1.5 = 1.08W, almost nothing for a large series pass transistor, maybe an average of about 3W passing heavy music.
Very different to a Class A like the Alpha Nirvana which will be passing and average of 1.7A and up to 4.5V across it. That is 7.65W and you'd really notice that.
The offset issue is a nuisance but based on past experiences with singletons and bipolars, it seems to be caused by the heavy tempco of the jfet input device and mosfet VAS device. Small temp changes there will cause big changes on the offset, and its origin is first and second stages, not the output stage. Understandably this could be improved; but to do it, and improve the depth of image as well, the best way would be replace the mosfet VAS with a bipolar, like a KSA1381. I believe a bipolar is far better for the VAS role; it has much more transconducance and therefore more accuracy than a small mosfet.
Thanks for keeping the thread moving........
Hugh
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