he was posting initial schematic several posts before... Actually the differences are
- no output coil
- different mosfet in VAS (but very similar to ZVPxxx)
- 33pF compensation in feedback
- IRFs in the output instead of lateral mosfets...
The THD is not higher than 0.02% at rated power (45W) and it is almost only 2nd harmonic, IMD do not exceed 0.006%...
AFAIR he was posting in original FETZilla thread...
- no output coil
- different mosfet in VAS (but very similar to ZVPxxx)
- 33pF compensation in feedback
- IRFs in the output instead of lateral mosfets...
The THD is not higher than 0.02% at rated power (45W) and it is almost only 2nd harmonic, IMD do not exceed 0.006%...
AFAIR he was posting in original FETZilla thread...
Transformer wiring question
Hi everyone,
In hunting down transformers for this project, I found some 200VA, 0-12V x2, toroidals at a clearance price and was considering using 2 per channel wired as shown in the attachment (I'll of course switch and fuse it in practice). The 4 required for a stereo amp are still cheaper than any single 300VA 0-25V x2 transformer I can find, and much cheaper that two 160VA.
Within my limited knowledge of electrical wiring I can't see a problem, unless I must make sure the AC phase is the same at either end... but past the bridge its all one-sided anyway, right?
Does anyone care to comment on this scheme for the FETZilla? Is 24V AC an acceptable voltage to have. Also on sale are 300VA 30-0-30V... if this is not too high it would be cheaper again for me to use 1 per channel.
Many thanks,
Tani.
Hi everyone,
In hunting down transformers for this project, I found some 200VA, 0-12V x2, toroidals at a clearance price and was considering using 2 per channel wired as shown in the attachment (I'll of course switch and fuse it in practice). The 4 required for a stereo amp are still cheaper than any single 300VA 0-25V x2 transformer I can find, and much cheaper that two 160VA.
Within my limited knowledge of electrical wiring I can't see a problem, unless I must make sure the AC phase is the same at either end... but past the bridge its all one-sided anyway, right?
Does anyone care to comment on this scheme for the FETZilla? Is 24V AC an acceptable voltage to have. Also on sale are 300VA 30-0-30V... if this is not too high it would be cheaper again for me to use 1 per channel.
Many thanks,
Tani.
Attachments
Hi Tani,
That will work very well, no problem at all. You could in fact use each transformer to power the positive supply of EACH module, in fact. That way you'd only need to buy two of them, giving a combined 400VA anyways, more than enough. Separate bridges would ensure galvanic separation and give good results. Just be sure to have one trafo for the positive rails, and the other trafo for the negative rails, otherwise earthing may conflict.
A 30V secondary will give you 42V, which is too much for this design.
Did you visit Laurie at Safety Beach and listen to the VSonics?
Cheers,
Hugh
That will work very well, no problem at all. You could in fact use each transformer to power the positive supply of EACH module, in fact. That way you'd only need to buy two of them, giving a combined 400VA anyways, more than enough. Separate bridges would ensure galvanic separation and give good results. Just be sure to have one trafo for the positive rails, and the other trafo for the negative rails, otherwise earthing may conflict.
A 30V secondary will give you 42V, which is too much for this design.
Did you visit Laurie at Safety Beach and listen to the VSonics?
Cheers,
Hugh
Last edited:
Thanks Hugh,
I'll snap them up. I was sure that 30V was too high, but always worth asking I guess. I think I'll buy a couple of the 300VA anyway, just to have... they're $27! Aussie built with resetting thermal protection.
Yes I met Laurie on Thursday evening... turned out we had quite a bit in common and we were listening and chatting for quite a while... I learnt a lot. I had a good listening session with the VSonics, across wide and varied style of music.
Not wanting to go into details on this thread (I'll write up soon on your website) I'll simply say that the VSonics were outstanding. Furthermore, Laurie believed that the VSonics paired fanatically with the FETZilla, so I would be in for a treat if I ended up with the combination.
Having just bought a house though, I'll need to be putting my pennies aside before I purchase anything in the region of the VSonics. When I'm ready to, hopefully in a few months, I'd have to say that Laurie's design would likely be my choice.
Cheers,
Tani.
I'll snap them up. I was sure that 30V was too high, but always worth asking I guess. I think I'll buy a couple of the 300VA anyway, just to have... they're $27! Aussie built with resetting thermal protection.
Yes I met Laurie on Thursday evening... turned out we had quite a bit in common and we were listening and chatting for quite a while... I learnt a lot. I had a good listening session with the VSonics, across wide and varied style of music.
Not wanting to go into details on this thread (I'll write up soon on your website) I'll simply say that the VSonics were outstanding. Furthermore, Laurie believed that the VSonics paired fanatically with the FETZilla, so I would be in for a treat if I ended up with the combination.
Having just bought a house though, I'll need to be putting my pennies aside before I purchase anything in the region of the VSonics. When I'm ready to, hopefully in a few months, I'd have to say that Laurie's design would likely be my choice.
Cheers,
Tani.
Hmmmm.
Paired fantastically with the FETZilla.
Sorry about that. Serves me right for blindly accepting the first offer by the spell checker.
Tani.
Hi
Couple of questions :
1. How you connect the PCB to the radiator ( I don't see 4 standard holes for bolts)
2. amp has 30db gain , it's way to much , because I use 15dB preamp - JFET-DISPRE disgned by PMA, so the question is
- Can I reduce the gain without loosing some other aspect of the amp quality
or
- what max 6dB gain preamp you could recomend (better the standard B1 or JCurl jfet follower) which would make a good pair wih FetZilla ( it should be fet for sure
)
3. what kind of 3D soundstage reproduction I can expect from this amp
I'm talking about some sharp separation of single instruments during reproduction of some classic symphonies
(from my expierience a lot of amps in range of 1000 USD suffers on this field;
with big orchestrals the instrument separation starts to be not so clear )
Couple of questions :
1. How you connect the PCB to the radiator ( I don't see 4 standard holes for bolts)
2. amp has 30db gain , it's way to much , because I use 15dB preamp - JFET-DISPRE disgned by PMA, so the question is
- Can I reduce the gain without loosing some other aspect of the amp quality
or
- what max 6dB gain preamp you could recomend (better the standard B1 or JCurl jfet follower) which would make a good pair wih FetZilla ( it should be fet for sure
)3. what kind of 3D soundstage reproduction I can expect from this amp
I'm talking about some sharp separation of single instruments during reproduction of some classic symphonies
(from my expierience a lot of amps in range of 1000 USD suffers on this field;
with big orchestrals the instrument separation starts to be not so clear )
Hi Dodo,
#1 Amp pcb is connected to the heatsink via two (2) M3 16mm long bolts which thread through the board, the two output devices, into the heatsink. Large 9mm diameter washers are used between pcb and output devices which give some robustness to the pcb mount. It's quite strong.
#2 This is a global feedback amplifier and changes to gain will affect stability and sound quality and are therefore verbotten. Gain is in fact (1K + 47R)/47R = 22.28, or 27dB. This is about right for a 50W amplifier; most amps are very close to this and in fact the THX standard is presently 29dB. Your preamp has very high gain, however. Typically a line level preamp, designed to operate from CD/DVD players, has a gain between 6 and 12 dB. Eric Juaneda has an excellent ground base preamp for line level that I would recommend here.
#3 The FetZilla has an extremely wide, generous sound field with good, though not vast, depth. It's very good on orchestral works and good at layering. As mentioned elsewhere, it is definitely a high end amp and compares well with some of my finer commercial amplifiers.
Hope this is helpful,
Hugh
#1 Amp pcb is connected to the heatsink via two (2) M3 16mm long bolts which thread through the board, the two output devices, into the heatsink. Large 9mm diameter washers are used between pcb and output devices which give some robustness to the pcb mount. It's quite strong.
#2 This is a global feedback amplifier and changes to gain will affect stability and sound quality and are therefore verbotten. Gain is in fact (1K + 47R)/47R = 22.28, or 27dB. This is about right for a 50W amplifier; most amps are very close to this and in fact the THX standard is presently 29dB. Your preamp has very high gain, however. Typically a line level preamp, designed to operate from CD/DVD players, has a gain between 6 and 12 dB. Eric Juaneda has an excellent ground base preamp for line level that I would recommend here.
#3 The FetZilla has an extremely wide, generous sound field with good, though not vast, depth. It's very good on orchestral works and good at layering. As mentioned elsewhere, it is definitely a high end amp and compares well with some of my finer commercial amplifiers.
Hope this is helpful,
Hugh
Do,
Not important at all.
You do not need to match the lateral fets, in fact, you'd have a problem doing it as they all differ considerably in their transconductance... remember, there are only two, one p type and one n type!!
Some asymmetry in the output stage is nearly always a good thing. Why?
Because asymmetry leads to asymmetrical distortion, which defines EVEN order artefacts, which are musical. Matching knocks out the evens, leaving only the ODDs, and this is BAD, BAD, BAD..... in the words of Michael Jackson.
Hugh
Not important at all.
You do not need to match the lateral fets, in fact, you'd have a problem doing it as they all differ considerably in their transconductance... remember, there are only two, one p type and one n type!!
Some asymmetry in the output stage is nearly always a good thing. Why?
Because asymmetry leads to asymmetrical distortion, which defines EVEN order artefacts, which are musical. Matching knocks out the evens, leaving only the ODDs, and this is BAD, BAD, BAD..... in the words of Michael Jackson.
Hugh
Hugh, It looks like you guys really had fun here. I read the whole thread a few moments ago and I am sorry I forgot that you have your own forum and would appreciate a reminder when you decide to tackle a new project. I have always had a deep appreciation for what you do and accomplish. I apologize for not visiting your forum as of late.
Nico,
I just did the board. The design here was Greg Peters, with only minor input from me. As it happens, the amps is very, very good, with a marvellous, wide sound field I really like for classical and electronic music.
As you know, this is a laughably simple circuit, no bells or whistles at all, yet it manages to sound sensational on a good speaker. Because the power supplies are on the board, it's straightforward to get going. Most of the work went into honing the sound with careful dimensioning, of course. Most amps really benefit from that step.
I will certainly let you know of future projects, Nico, many thanks for your post! And BTW, the feeling is entirely reciprocated.....
Hugh
I just did the board. The design here was Greg Peters, with only minor input from me. As it happens, the amps is very, very good, with a marvellous, wide sound field I really like for classical and electronic music.
As you know, this is a laughably simple circuit, no bells or whistles at all, yet it manages to sound sensational on a good speaker. Because the power supplies are on the board, it's straightforward to get going. Most of the work went into honing the sound with careful dimensioning, of course. Most amps really benefit from that step.
I will certainly let you know of future projects, Nico, many thanks for your post! And BTW, the feeling is entirely reciprocated.....
Hugh
On Dispre jfet preamp, you can reduce gain by changing input resistors voltage divider. For Fetzilla I suggest to use 6dB or 2x gain.
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