Hugh,thanks for all these kind words.Terry,this amp want disappoint you at all,off course there will be people saying otherwise.Not everone has the same hearing and taste but I'm shure will grap you in a positive way. Build it and if you or other has questions regarding the building just ask.
Aksa did not agree that the layout was causing any avoidable noise.
He suggested a couple of solutions, but none worked for me.
It is still the noisiest Amp I have built. I reported this a long while back.
Looks like you have not read from the beginning.
I am trying to get through all the posts, there is a lot to read. I only have so much time for reading and I am still working out issues with some other amps.
Looking forward to it. Any idea when you will be ordering the boards?
Thanks, Terry
Funny - mine has an extremely quiet noise floor - as in nothing. I have to put my ear right next to the speaker (87db efficient) to hear it and we leave the amp on 24/7
On
Has Patrick been the only person to use an SMPS to power one of these? I am planning to go that route and have one on order. However, if you guys think the sound will be better with transformers and the on-board supply I would like to know. Looks like I have time to gather those before I get the boards.
Thanks, Terry
Thanks, Terry
by "gut the board both side", do you mean when using a SMPS, and Cut the board on the white line to leave the PS off?
Thanks
A number of people have raised some questions re the FETzilla, so I'll attempt to give my view on all of these:
1 - If you want to use a SMPS, then I'd attach it as shown in the attached drawing. I wouldn't cut off the rectifier and capacitor section of the FETzilla PCB, but just reduce the size of the on board capacitors. As most SMPS have a common ground wire, this will need to be connected to the speaker ground connector, and resistors R22 and R24 shorted out. If the rectifier diodes are not fitted and diodes D1a and D2a are just linked across, then the SMPS can be connected to ONE of the AC spade connectors. Some SMPS will not start if they are connected to a large capacitor, so C15 .. C18 may need to be reduced in size, perhaps 220uF to 1000uF. Keeping C15 .. C18 provides some high frequency filtering between the SMPS and the two amplifier channels, so they are worth keeping.
2 - My FETzilla is extremely quiet. However I did have a hum issue at first due to the earthing arrangement on the FETzilla not being compatible with my Audiolab 8200cdq CD/DAC player. Removing R26 fixed this.
3 - The FETzilla has a soft turn on `thump' which should not alter if a SMPS is used. The turn on behaviour is an initial positive step (about 200mV, and not audible) and then a very low frequency pulse up to about +3 volts and slowly back to zero. This pulse occurs at about 8 hertz and so is not audible. This behaviour is determined by the ratio of C3 (22uF) and C7 (470uF) and to some extent by C1. A lot of careful modelling was carried out to get this behaviour, so don't alter these values.
4 - The FETzilla is a small simple amplifier. It is very good up to about 30 watts, but from 30 watts to 50 watts it starts to struggle. By 50 watts the high order distortion products start to rise. Don't try to get more than 50 watts out of it.
5 - The FETzilla was designed as a bit of an experiment, so a lot of things are adjustable. The VAS current (set by P3) can be set to the minimum 12 mA value. So P3 could be replaced by a 200 ohm resistor. I initially ran my FETzilla at an output bias of 405 mA, but last summer I dropped it back to about 300mA. I don't think much is gained by running it much above 300mA. So P1 (which controls the output bias) could be replaced by a 10 .. 30 ohm resistor.
6 - I reduced the gain of my FETzilla to 18 by increasing R10 to 56 ohms (from 47 ohms).
7 - My FETzilla struggles to drive Quad esl68 electrostatics, so I wouldn't recommend a FETzilla for any electrostatic speakers.
Regards,
Paul Bysouth
1 - If you want to use a SMPS, then I'd attach it as shown in the attached drawing. I wouldn't cut off the rectifier and capacitor section of the FETzilla PCB, but just reduce the size of the on board capacitors. As most SMPS have a common ground wire, this will need to be connected to the speaker ground connector, and resistors R22 and R24 shorted out. If the rectifier diodes are not fitted and diodes D1a and D2a are just linked across, then the SMPS can be connected to ONE of the AC spade connectors. Some SMPS will not start if they are connected to a large capacitor, so C15 .. C18 may need to be reduced in size, perhaps 220uF to 1000uF. Keeping C15 .. C18 provides some high frequency filtering between the SMPS and the two amplifier channels, so they are worth keeping.
2 - My FETzilla is extremely quiet. However I did have a hum issue at first due to the earthing arrangement on the FETzilla not being compatible with my Audiolab 8200cdq CD/DAC player. Removing R26 fixed this.
3 - The FETzilla has a soft turn on `thump' which should not alter if a SMPS is used. The turn on behaviour is an initial positive step (about 200mV, and not audible) and then a very low frequency pulse up to about +3 volts and slowly back to zero. This pulse occurs at about 8 hertz and so is not audible. This behaviour is determined by the ratio of C3 (22uF) and C7 (470uF) and to some extent by C1. A lot of careful modelling was carried out to get this behaviour, so don't alter these values.
4 - The FETzilla is a small simple amplifier. It is very good up to about 30 watts, but from 30 watts to 50 watts it starts to struggle. By 50 watts the high order distortion products start to rise. Don't try to get more than 50 watts out of it.
5 - The FETzilla was designed as a bit of an experiment, so a lot of things are adjustable. The VAS current (set by P3) can be set to the minimum 12 mA value. So P3 could be replaced by a 200 ohm resistor. I initially ran my FETzilla at an output bias of 405 mA, but last summer I dropped it back to about 300mA. I don't think much is gained by running it much above 300mA. So P1 (which controls the output bias) could be replaced by a 10 .. 30 ohm resistor.
6 - I reduced the gain of my FETzilla to 18 by increasing R10 to 56 ohms (from 47 ohms).
7 - My FETzilla struggles to drive Quad esl68 electrostatics, so I wouldn't recommend a FETzilla for any electrostatic speakers.
Regards,
Paul Bysouth
Attachments
Paul,very helpfull regarding the use of a SMPS.I did run my first FetZilla build with Magnepan speakers with no problem.When I tested my FetZilla it was pushed very hard high volume,low efficiency speaker it keeps going without any limits;
Hi Paul,
Have you actually tried using an SMPS with your FetZilla or are you making assumptions?
Thanks, Terry
And he's a nice studio
No. He has not built it with Patrick's smps, he used a linear supply, BUT, he's 110% experienced and has done a good schematic. Take a risk, my friend, I spend thousands each year taking risks and it's been a lot of fun, most of them work out well! OTOH, we can guarantee that it will work very well........
Ciao,
Hugh
Ciao,
Hugh
Why does if feel like I've just been shushed? I'm just trying to learn here. If it is improper to ask questions in this forum than this is not the right amp for me.
Terry,
Paul, Patrick and me are trying to help. But you have bite the bullet, and if you change the FetZilla design to a smps there are no guarantees sonically unless you have built and had a listen yourself. Some people might not like a smps. I assessed that after good answers short of actually listening to a particular smps with the FetZilla - neither me nor Paul, hell I don't even have a FetZilla these days as I concentrate on my NAKSAs - it was time to move away from discussion and build it and test it.
Wherever there is the interpretation of a negative meaning in forum posts, invariably the OP assume the worst interpretation. In fact the meaning is much softer than your interpretation, and there was no intention to 'shush' you. Get you moving, yes, but not censure you.
Cheers,
Hugh
Paul, Patrick and me are trying to help. But you have bite the bullet, and if you change the FetZilla design to a smps there are no guarantees sonically unless you have built and had a listen yourself. Some people might not like a smps. I assessed that after good answers short of actually listening to a particular smps with the FetZilla - neither me nor Paul, hell I don't even have a FetZilla these days as I concentrate on my NAKSAs - it was time to move away from discussion and build it and test it.
Wherever there is the interpretation of a negative meaning in forum posts, invariably the OP assume the worst interpretation. In fact the meaning is much softer than your interpretation, and there was no intention to 'shush' you. Get you moving, yes, but not censure you.
Cheers,
Hugh
Terry,
You may ask questions I do it all the time too.This way I want to learn.
Regarding the SMPS I will perform a test my way and Pauls way.
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