amp under development
Hi Quazi,
I should have somewhere an article written in mid or later 1990s on quasi complementary amp design. It was in Electronics World. If you would like to get it send me email and I'll scan it and send to you as an attachement to the reply.
I have one quick question for you - where one could buy good quality toroidal transformers (quiet enough to be used in audio) for power amplifiers nowadays? I need 625V 2x40V toroids and these are not typical for the main suppliers such as Altronics, Jaycar, Wiltronics etc. I had a nice supplier of custom made toroids in Adelaide but I am afraid his business went down. The only one I know is Harbuch. Are toroids from Harbuch good enough?
When it comes to components I mentioned these are not so esoteric and usually cheaper than standard quality parts in Australia. The only drawback is that shipment costs are relatively high but with a larger order still it is often cheaper.
Cheers,
Janusz
Hi Quazi,
I should have somewhere an article written in mid or later 1990s on quasi complementary amp design. It was in Electronics World. If you would like to get it send me email and I'll scan it and send to you as an attachement to the reply.
I have one quick question for you - where one could buy good quality toroidal transformers (quiet enough to be used in audio) for power amplifiers nowadays? I need 625V 2x40V toroids and these are not typical for the main suppliers such as Altronics, Jaycar, Wiltronics etc. I had a nice supplier of custom made toroids in Adelaide but I am afraid his business went down. The only one I know is Harbuch. Are toroids from Harbuch good enough?
When it comes to components I mentioned these are not so esoteric and usually cheaper than standard quality parts in Australia. The only drawback is that shipment costs are relatively high but with a larger order still it is often cheaper.
Cheers,
Janusz
Hayayayay...amp_man_1 and janusz;
Hey it's Quasi not Qauzi !!!! sheeeesh.
Thanks amp_man_1; Yep thanks for the info and Iget everything except ...Umm....I still don't get it regarding the positive rail drive (it's ok....I'm not that smart). Without the collector of Q7 tied to the +70 volt rail how can it deliver sufficient voltage to the positive rail FETS if the collector is tied only to the 60 volt rail. This means that Q7 can only deliver a max of 60 volts relative to gnd to the gate of the FETS. Problem is, the drain near clipping is almost at 60 volts with repsect to gnd and then the gate needs to be around 67 volts (with load connected) to achieve a 7 volt drive between the gate and source.
Ok...or are you saying that it receives the extra voltage through the base emitter junction of Q7 straight from the Q4? In this case Q7 is basically a diode so do I need Q7 at all?
Or are you saying that I should not worry about the assymetric clipping because the whole thing isn't linear here anyway.
Please try and explain it one more time ...just the relationship of the voltages from Q4 to Q7 and the gates of the FETS. Sorry but I really want to understand this.
Cheers
Hey it's Quasi not Qauzi !!!! sheeeesh.
Thanks amp_man_1; Yep thanks for the info and Iget everything except ...Umm....I still don't get it regarding the positive rail drive (it's ok....I'm not that smart). Without the collector of Q7 tied to the +70 volt rail how can it deliver sufficient voltage to the positive rail FETS if the collector is tied only to the 60 volt rail. This means that Q7 can only deliver a max of 60 volts relative to gnd to the gate of the FETS. Problem is, the drain near clipping is almost at 60 volts with repsect to gnd and then the gate needs to be around 67 volts (with load connected) to achieve a 7 volt drive between the gate and source.
Ok...or are you saying that it receives the extra voltage through the base emitter junction of Q7 straight from the Q4? In this case Q7 is basically a diode so do I need Q7 at all?
Or are you saying that I should not worry about the assymetric clipping because the whole thing isn't linear here anyway.
Please try and explain it one more time ...just the relationship of the voltages from Q4 to Q7 and the gates of the FETS. Sorry but I really want to understand this.
Cheers
Hey Janusz
What a coincidence. I currently run 2x Harbuch 625va torroids in my PA amp. These are 60 0 60. I've had these for 10+ years and they seem good in every way.
But you know what? A friend of mine bought an old variac with 3 1kva torroids in it from a metal recyclers. Pulled one apart and indulated the winding (now a primary) then overwound the secondaries. Total price including (secondary windings) about $20 Aus. each with excellent results.
Yes please, I would like to see that article on the quasi amp. Email on the way.
Cheers
What a coincidence. I currently run 2x Harbuch 625va torroids in my PA amp. These are 60 0 60. I've had these for 10+ years and they seem good in every way.
But you know what? A friend of mine bought an old variac with 3 1kva torroids in it from a metal recyclers. Pulled one apart and indulated the winding (now a primary) then overwound the secondaries. Total price including (secondary windings) about $20 Aus. each with excellent results.
Yes please, I would like to see that article on the quasi amp. Email on the way.
Cheers
Hi Quasi,
You are right, the driver needs a higher voltage than the Fet output. Again you are right with the latest schematic, the quasi output Fet must share the -Vrail with the driver. You could add a regulated negative rail to the pre driver stages but you would not gain much by raising its voltage. I asked in another thread about the distortion advantage to swinging the VAS stage over a shorter range between the supply rails but got no response. Your layout gives a higher +Vpk than -Vpk but quasi topology forces this on you.
regards Andrew T.
You are right, the driver needs a higher voltage than the Fet output. Again you are right with the latest schematic, the quasi output Fet must share the -Vrail with the driver. You could add a regulated negative rail to the pre driver stages but you would not gain much by raising its voltage. I asked in another thread about the distortion advantage to swinging the VAS stage over a shorter range between the supply rails but got no response. Your layout gives a higher +Vpk than -Vpk but quasi topology forces this on you.
regards Andrew T.
Commentable thoughts
ok ...ok......Quasi not Quazi
U r rite in this respect, but There must be a phenomena for Asymmetric Clipping occuring at output.
Secondly In full drive conditions The symmetry must be maintained at any cost or u wont hear at output what u have fed at input. There is also a margin of preclipping which also insures that the mosfets aren't subjected to full saturation.
Regards
Workhorse Technologies.
ok ...ok......Quasi not Quazi
U r rite in this respect, but There must be a phenomena for Asymmetric Clipping occuring at output.
Secondly In full drive conditions The symmetry must be maintained at any cost or u wont hear at output what u have fed at input. There is also a margin of preclipping which also insures that the mosfets aren't subjected to full saturation.
Regards
Workhorse Technologies.
Antrim toroids
Thanks Aksa and Quasi
for the info on Antrim toroids.
I made an enquiry with HARBUCH asking if their toroids were good for audio PS and Peter replied that they do not guarantee acoustical silence and that I might need a special design. So I told him that in that case I would take one toroid first and if I am happy with it I'd order another one and asked him how should I pay for the order and since then he got quiet!!! I asked him again and ... silence. Is that guy over sensitive or what? Looks that he is not much interested in selling his toroids to every one. What should I do - especially now that you recommend Antrim toroids as really good ones.
Janusz
Thanks Aksa and Quasi
for the info on Antrim toroids.
I made an enquiry with HARBUCH asking if their toroids were good for audio PS and Peter replied that they do not guarantee acoustical silence and that I might need a special design. So I told him that in that case I would take one toroid first and if I am happy with it I'd order another one and asked him how should I pay for the order and since then he got quiet!!! I asked him again and ... silence. Is that guy over sensitive or what? Looks that he is not much interested in selling his toroids to every one. What should I do - especially now that you recommend Antrim toroids as really good ones.
Janusz
Janusz,
You have just discovered that many component manufacturers are unwilling to deal with audiophiles because they ask too many questions, take up a lot of time, buy tiny numbers, and generally make unreasonable demands.
Peter is in fact an honest man, but he is not noted for his refined customer skills. I know where he is coming from; he doesn't care to whom he sells his products but he won't be involved in a design discussion because his time is valuable.
His are the best made toroids in Australia in my opinion. You really can't go wrong.
Cheers,
Hugh
You have just discovered that many component manufacturers are unwilling to deal with audiophiles because they ask too many questions, take up a lot of time, buy tiny numbers, and generally make unreasonable demands.
Peter is in fact an honest man, but he is not noted for his refined customer skills. I know where he is coming from; he doesn't care to whom he sells his products but he won't be involved in a design discussion because his time is valuable.
His are the best made toroids in Australia in my opinion. You really can't go wrong.
Cheers,
Hugh
Hi janusz,
I can recommend the standard Antrim transformers from HARBUCH. I've used many of them and never had a problem. All my amps are dead quiet. They have hundreds in stock and a great selection. For example there is 3 25-0-25 160VA to choose from.
There are options to have a SAFETY SCREEN and/or ELECTROSTATIC SCREEN at extra cost and are a custom wind but I've only been tempted and haven't seen the need to worry. I think that's what his "special" design may be.
I visit them in person and do get a "funny" feeling each time I visit, must be because I only get 2 or 3 at a time. I've asked to have a look around and was given an unenthusiastic brief tour. They are good quality and cheap and I have gotten a discount a couple of times.
You have to remember they probably only make <$15 per toriod so having to pack, post and do the paper work for two separately would be a PITA.
Just in case you haven't seen their web site.
http://ourworld.compuserve.com/homepages/harbuch/harbuch.htm
Yeah, the folks at Harbuch are nearly the exact opposite to Hugh. Maybe Hugh should sell them?
BTW: The only toriod I have that hums is one I got from Jaycar. At the time I thought that was normal.
Thanks
I can recommend the standard Antrim transformers from HARBUCH. I've used many of them and never had a problem. All my amps are dead quiet. They have hundreds in stock and a great selection. For example there is 3 25-0-25 160VA to choose from.
There are options to have a SAFETY SCREEN and/or ELECTROSTATIC SCREEN at extra cost and are a custom wind but I've only been tempted and haven't seen the need to worry. I think that's what his "special" design may be.
I visit them in person and do get a "funny" feeling each time I visit, must be because I only get 2 or 3 at a time. I've asked to have a look around and was given an unenthusiastic brief tour. They are good quality and cheap and I have gotten a discount a couple of times.
You have to remember they probably only make <$15 per toriod so having to pack, post and do the paper work for two separately would be a PITA.
Just in case you haven't seen their web site.
http://ourworld.compuserve.com/homepages/harbuch/harbuch.htm
Yeah, the folks at Harbuch are nearly the exact opposite to Hugh. Maybe Hugh should sell them?
BTW: The only toriod I have that hums is one I got from Jaycar. At the time I thought that was normal.
Thanks
These toroids
Hey Janusz
The harcbuch toroids sit quite closely to my PA amp modules and I don't have a problem with noise.
I think the placement of the secondaries in the case is probably more important. Under heavy current draw they generate a bit of a field themselves.
Anyway I remember when I bought mine (ages ago) they didn't really know what to do with me because I walked in and asked them what they had (I hadn't really decided on the exact volts or VA then). But I walked out with the two 625VA's put them in my luggage and flew home (Adelaide). I think the airline staff were surprised how much small luggage could weigh.
It probably makes a difference if your there in person, you can just take them with you without fuss.
The only mod I made was overwind extra secondaries for my +/- 15 volts for other circuitry.
Cheers
PS. The board design for this amp is in the error checking stage.
Hey Janusz
The harcbuch toroids sit quite closely to my PA amp modules and I don't have a problem with noise.
I think the placement of the secondaries in the case is probably more important. Under heavy current draw they generate a bit of a field themselves.
Anyway I remember when I bought mine (ages ago) they didn't really know what to do with me because I walked in and asked them what they had (I hadn't really decided on the exact volts or VA then). But I walked out with the two 625VA's put them in my luggage and flew home (Adelaide). I think the airline staff were surprised how much small luggage could weigh.
It probably makes a difference if your there in person, you can just take them with you without fuss.
The only mod I made was overwind extra secondaries for my +/- 15 volts for other circuitry.
Cheers
PS. The board design for this amp is in the error checking stage.
HARBUCH toroids
Thanks Grege, Aksa and Quasi for your comments.
Consequently, I have decided to take two toroids as was my original intention. I think I have ordered these toroids (yesterday, I provided Peter with my card details, address etc) but as you have explained to me it looks I have to wait for the heavenly decison. It would have been much easier if I lived close by and could pop in and get them over the counter. Sometimes I feel as if Perth was located at the end of the world - and at the wrong end for that matter.
Thanks Grege, Aksa and Quasi for your comments.
Consequently, I have decided to take two toroids as was my original intention. I think I have ordered these toroids (yesterday, I provided Peter with my card details, address etc) but as you have explained to me it looks I have to wait for the heavenly decison. It would have been much easier if I lived close by and could pop in and get them over the counter. Sometimes I feel as if Perth was located at the end of the world - and at the wrong end for that matter.
I have had a similar experience with Antrim but I would be reluctant to use a large VA model (with loss losses) in an amplifier to be dead silent.
The last special they did for me of 1KVA that groaned like an old lady in my Pass Aleph 2 and I had to get rid of it. I called them about it and was fed a pile of crap about my mains quality to getv rid of me denying a problem with the design.(all my other transformers from them make no noise). The design was specified specifically for audio and I got quite the opposite.
I then called them back a week later under an assumed name and was told they don't make transformers specifically for audio.
It would appear they are mass market and won't enter the risk of making silent transformers like Pilitron (as used with hi end manufacturers in the USA like Passlabs).
The problem is the core size and the amount of copper. For low noise you need to use a much larger core size which costs money.
Ian
The last special they did for me of 1KVA that groaned like an old lady in my Pass Aleph 2 and I had to get rid of it. I called them about it and was fed a pile of crap about my mains quality to getv rid of me denying a problem with the design.(all my other transformers from them make no noise). The design was specified specifically for audio and I got quite the opposite.
I then called them back a week later under an assumed name and was told they don't make transformers specifically for audio.
It would appear they are mass market and won't enter the risk of making silent transformers like Pilitron (as used with hi end manufacturers in the USA like Passlabs).
The problem is the core size and the amount of copper. For low noise you need to use a much larger core size which costs money.
Ian
The making of the board part 1 - Exposing
A pair of layouts is exposed onto pre-sensitized board. I use a spray-on positive photoresist called POSITIV 20. Friends of mine in Germany bought some for me and sent it to Australia. I couldn't find it here ...but it's great stuff. Made by CRC industries.
cheers
A pair of layouts is exposed onto pre-sensitized board. I use a spray-on positive photoresist called POSITIV 20. Friends of mine in Germany bought some for me and sent it to Australia. I couldn't find it here ...but it's great stuff. Made by CRC industries.
cheers
