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Swordfishy/ASPEN FETZILLA power amp

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PaulBysouth

Member
Joined 2008
Meanman,
D1 and D2 are to protect the amplifier if a fuse blows. When one fuse blows, the amplifier will most likely try and drag all the circuit voltages off to the opposite rail. D1 and D2 stop the rails from going negative, and hence reverse biasing parts of the circuit.

NCC (re post 1057),
The FETzilla has an input earth lift circuit (D7, D8 and R26 in the attached diagram). This circuit is what is usually used and works most of the time. However some preamplifiers do their grounding differently, and sometimes the D7,D8,R26 circuit doesn't work. Remove resistor R26 (10ohms). I have a Audiolab 8200cdq which caused hum in my FETzilla amp, removing R26 fixed the problem.

I also have a Naksa80, which has the same type of input earth lift circuit and I have no hum issues at all (in fact it is so quiet that I only know that it is on by the big blue front panel LED). Why is is so I have no idea.

Paul Bysouth
 

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AKSA

AKSA

Member
Joined 2001
aksaonline.com
This confuses me, MM. Are you sure you are using a 0.15 ohm resistor, not something rated to 15R or 150R? Clearly a heavy ground current is flowing, but not a rail current......

Check that the two secondaries are completely separate - THERE IS NO CENTRE TAP ON THE TRAFO. Secondary #1 goes to the left of the schemat, and Secondary #2 goes to the right. Both pairs, quite separate.

Cheers,

Hugh
 
meanman1964

meanman1964

Member
Joined 2006
Hugh,I had the same prob with my FetZilla did happen only once by first start up.My rail voltage is on both negative and positive sides 35,26 Vdc.What does happen when D1 or D2 are shorted?

From HD: Yes, reversed D1 and D2 will take rails straight to ground, blowing BOTH 0.15R resistors on each side.

Hope this is the problem.......

Cheers,

Hugh
 
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N

ncc

Member
Joined 2006
meanman1964 said:
Wouldn't your pre amp causing the problems can you test without one?
Click to expand...
Hi Meanman,
I don't think the preamp causing the hum because I also tried to connect my DAC directly to Fetzilla bypassing the preamp but the problem is still there.

PaulBysouth said:
NCC (re post 1057),
The FETzilla has an input earth lift circuit (D7, D8 and R26 in the attached diagram). This circuit is what is usually used and works most of the time. However some preamplifiers do their grounding differently, and sometimes the D7,D8,R26 circuit doesn't work. Remove resistor R26 (10ohms). I have a Audiolab 8200cdq which caused hum in my FETzilla amp, removing R26 fixed the problem.

I also have a Naksa80, which has the same type of input earth lift circuit and I have no hum issues at all (in fact it is so quiet that I only know that it is on by the big blue front panel LED). Why is is so I have no idea.
Paul Bysouth
Click to expand...

Hi Paul,
I'm not sure if removing R26 will cure the problem since my amp chassis is not connected to earth ground. I've tried to connect both amp boards earth connecting points to a point in chassis but the hum does not change. I'll remove R26 to see if it'll cure the problem or not.
 
meanman1964

meanman1964

Member
Joined 2006
AKSA said:
MM,

I suspect that the two secondaries are connected; that is, the trafo has a centre tap.

Check power off that there is an ohmic connection between the two secondaries.

And yes, check that the diodes are OK; in fact, remove one lead on each of them.

This will take out the ground resistors.

Cheers,

Hugh
Click to expand...
Hugh ,
The toroid has 2 seperate windings red-yellow and black-white.Will test the diodes to see if they are OK.
 
L

Love Hz

Member
Joined 2013
Hi all,

This is my first post on diyAudio. A big thanks to the FetZilla developers and all who have contributed to this great thread. I’ve been looking for a power amp project but only for a short time and I realise I’m a bit late to the party but I would love to purchase a pair of PCBs for the FetZilla amp if at all possible. Are there any still available? Or is anyone considering another group buy (I believe there been four already?!).

This would be my first amplifier build (though by no means my first electronics project). I have decent soldering skills and a provisional plan for a case/heatsinks and just about all of the BOM (with the possible exception of T1, the 2SK170GR JFETs – some help sourcing those would be much appreciated if I can get my hands on the PCBs).

Thanks very much,

Chris
 
K

kannan_s

Member
Joined 2009
hi
I bought the pcb stereo set (two PCBs) in the first GB, still available as I had not used ithem. If you need please PM me asap
thanks
Kannan

Love Hz said:
Hi all,

This is my first post on diyAudio. A big thanks to the FetZilla developers and all who have contributed to this great thread. I’ve been looking for a power amp project but only for a short time and I realise I’m a bit late to the party but I would love to purchase a pair of PCBs for the FetZilla amp if at all possible. Are there any still available? Or is anyone considering another group buy (I believe there been four already?!).

This would be my first amplifier build (though by no means my first electronics project). I have decent soldering skills and a provisional plan for a case/heatsinks and just about all of the BOM (with the possible exception of T1, the 2SK170GR JFETs – some help sourcing those would be much appreciated if I can get my hands on the PCBs).

Thanks very much,

Chris
Click to expand...
 
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