@Wayne
You have right,but I¡¦m not so much newbie.This isn¡¦t my first project.I have build some other projects ,too.This is my 4th amp.
The problem is that the other are all ready to build schematics.An EL34 UL P-P from Elector book, a simple 2A3 SE amp and a VOX AC30 with Fender preamp for my guitar practice.Some other projects ,too.Like speakers ,preamps ,e.t.c..
But I haven¡¦t build sth designed by me and I¡¦m not very good in theory.When I build my first amp (the EL34 one) I didn¡¦t know exactly what a phase splitter is!?! Now I know more!
And I¡¦d like to go more deeper in theory .I know what phase splitter , P-P ,ultra linear ,FB ,e.t.c. is and how they work. I know??? This is my problem! That¡¦s why I¡¦m asking about everything.What is this?
How exactly this works?Why you are doing this and not this?To be sure about my thoughts .
I¡¦m not an expert.I haven¡¦t built a lot of amps ,preamps and I¡¦m not very sure on what I¡¦m doing ¡¥cause in theory I¡¦m not very good. An other problem is that there are a lot of tubes out there!
You suggest 6FQ7.When I saw it in your schem I didn¡¦t know that this is noval or electrical same with 6SN7 or e.t.c. But now I know it. ƒº
Ok ,over here you will say ¡§ and why you are going to build a P-P CFB amp?
The idea gave it to me a local winder ,and they¡¦re not so much expensive OPTs. And it¡¦s an interesting idea .He sells to me the normal P-P OPTs (with UL taps ) from 60 to 100 euros /each .And for CFB taps a little bit more or the same.I don¡¦t know ,yet .I¡¦ll ask him the price and I¡¦ll tell you.
Also,I can experiment on these OPTs. Triode ,UL or pentode P-P mode or CFB!Only with some changes in primary.
What do you say?I like very much to have your help and from other experts out there like arnoldc , fdgrove,SY ,Kuei ,e.t.c..
You have right,but I¡¦m not so much newbie.This isn¡¦t my first project.I have build some other projects ,too.This is my 4th amp.
The problem is that the other are all ready to build schematics.An EL34 UL P-P from Elector book, a simple 2A3 SE amp and a VOX AC30 with Fender preamp for my guitar practice.Some other projects ,too.Like speakers ,preamps ,e.t.c..
But I haven¡¦t build sth designed by me and I¡¦m not very good in theory.When I build my first amp (the EL34 one) I didn¡¦t know exactly what a phase splitter is!?! Now I know more!
And I¡¦d like to go more deeper in theory .I know what phase splitter , P-P ,ultra linear ,FB ,e.t.c. is and how they work. I know??? This is my problem! That¡¦s why I¡¦m asking about everything.What is this?
How exactly this works?Why you are doing this and not this?To be sure about my thoughts .
I¡¦m not an expert.I haven¡¦t built a lot of amps ,preamps and I¡¦m not very sure on what I¡¦m doing ¡¥cause in theory I¡¦m not very good. An other problem is that there are a lot of tubes out there!
You suggest 6FQ7.When I saw it in your schem I didn¡¦t know that this is noval or electrical same with 6SN7 or e.t.c. But now I know it. ƒº
Ok ,over here you will say ¡§ and why you are going to build a P-P CFB amp?
The idea gave it to me a local winder ,and they¡¦re not so much expensive OPTs. And it¡¦s an interesting idea .He sells to me the normal P-P OPTs (with UL taps ) from 60 to 100 euros /each .And for CFB taps a little bit more or the same.I don¡¦t know ,yet .I¡¦ll ask him the price and I¡¦ll tell you.
Also,I can experiment on these OPTs. Triode ,UL or pentode P-P mode or CFB!Only with some changes in primary.
What do you say?I like very much to have your help and from other experts out there like arnoldc , fdgrove,SY ,Kuei ,e.t.c..
Res, two important things to consider with CFB. First, the phasing- it's difficult for me to tell from your drawing how you've connected the windings, but you need set the relative phase between plate and cathode windings to provide negative feedback.
Second, make sure you've got enough swing capability in the driver stage to accomodate the fed-back signal in addition to the normal grid swing. IME, diff amps with a high supply voltage are the best solution. Macintosh used a cleverish bootstrapping solution, but that can be a real tricky thing to implement and stabilize.
If you get a copy of the schematic for the old Luxman 3045, you'll find it quite educational.
Second, make sure you've got enough swing capability in the driver stage to accomodate the fed-back signal in addition to the normal grid swing. IME, diff amps with a high supply voltage are the best solution. Macintosh used a cleverish bootstrapping solution, but that can be a real tricky thing to implement and stabilize.
If you get a copy of the schematic for the old Luxman 3045, you'll find it quite educational.
hi resident, i am sorry to disappoint you, but as much as i would like to be, i am nowhere an expert.resident said:
expert in asking, i am 😀
Hi,
While I really like CFB PP amps for their musicality (another audio illusion?) I'm certainly no expert at designing them.
One reason so few people build anything around this IMO is the lack of availability of the proper OPTs to do this and the need for good drive for the outputstage.
There are workarounds as far as the xformers go, the most commmon one being the use of the 16 Ohm tap of the secondary winding of the OPT to provide for the NFB to the cathodes.
If you want to go down this road and want to develop you're own, you best come equipped with the necessary measuring gear.
If you're confident your OPT winder is capable of winding what you want_ very few of them are interested in audio_or you can at the very least present it on paper with the proper calculus, you'll probably do fine.
If it may help convince you to pursue this project, some wellknown amps are/were using this topology:
Quad II (Peter Walker being the first to implement this in a commercial amp), Jadis, Audiomat (a reliable "Jadis" with extended FR but without the pricetag and legendary status) and McIntosh are the better known makes.
All of them have one particular treat in common :they're"musical".
This may well be a coincidence, nonetheless I think most people would agree.
As SY pointed out, the MacIntosh has some clever tricks but to my ears this is certainly not the best of the lot and the crosscoupled stage is definetely its achilles heel, it operates in class B too which has "sonic" problems of its own.
Since information on the web is rather scarce, I thought I'd share this link:
STEPHEN W. MOORE
BTW, the Luxman MB3045 was designed by Tim de Paravicini, one of the most reputed tube circuit designers of the past decades.
Cheers,😉
While I really like CFB PP amps for their musicality (another audio illusion?) I'm certainly no expert at designing them.
One reason so few people build anything around this IMO is the lack of availability of the proper OPTs to do this and the need for good drive for the outputstage.
There are workarounds as far as the xformers go, the most commmon one being the use of the 16 Ohm tap of the secondary winding of the OPT to provide for the NFB to the cathodes.
If you want to go down this road and want to develop you're own, you best come equipped with the necessary measuring gear.
If you're confident your OPT winder is capable of winding what you want_ very few of them are interested in audio_or you can at the very least present it on paper with the proper calculus, you'll probably do fine.
If it may help convince you to pursue this project, some wellknown amps are/were using this topology:
Quad II (Peter Walker being the first to implement this in a commercial amp), Jadis, Audiomat (a reliable "Jadis" with extended FR but without the pricetag and legendary status) and McIntosh are the better known makes.
All of them have one particular treat in common :they're"musical".
This may well be a coincidence, nonetheless I think most people would agree.
As SY pointed out, the MacIntosh has some clever tricks but to my ears this is certainly not the best of the lot and the crosscoupled stage is definetely its achilles heel, it operates in class B too which has "sonic" problems of its own.
Since information on the web is rather scarce, I thought I'd share this link:
STEPHEN W. MOORE
BTW, the Luxman MB3045 was designed by Tim de Paravicini, one of the most reputed tube circuit designers of the past decades.
Cheers,😉
Have you (or anyone else on this forum) tried to configure the multiple secondaries on a Lundahl OPT for a separate cathode feedback winding (in addition to normal voice coil winding)?
John
Plitron has some CFB transformers in their "specialist" range. They also have good article on how to implement them (along with an amp schematic) in the news section, near the bottom. The article is titled "New Push-Pull Amplifiers".
www.plitron.com
🙂
www.plitron.com
🙂
Luhndal makes a version of the 1620 OPT with a pair of the primary windings split for CFB use. Check their data sheets on lundahl.se.
Tamura has CFB windings in their F series PP transformers.
Also James Transformers has the option of CFB windings on thier transfromers.
I am working on a design with 807s, a 6L6 variant, using CFB right now; and am getting the parts together.
For more insperation look at the Fi Primer by J.C. Morrison a web version is at http://tinpan.fortunecity.com/saints/668/primer/. There is 807 PP amp there that uses the 16 ohm tap of the secondary trick.
I am not a fan of this trick and prefer actual CFB windings. The changing load of the speaker will affect the feedback circuit, and you also have bypassed the isolation of the B+ from the speakers.
Tamura has CFB windings in their F series PP transformers.
Also James Transformers has the option of CFB windings on thier transfromers.
I am working on a design with 807s, a 6L6 variant, using CFB right now; and am getting the parts together.
For more insperation look at the Fi Primer by J.C. Morrison a web version is at http://tinpan.fortunecity.com/saints/668/primer/. There is 807 PP amp there that uses the 16 ohm tap of the secondary trick.
I am not a fan of this trick and prefer actual CFB windings. The changing load of the speaker will affect the feedback circuit, and you also have bypassed the isolation of the B+ from the speakers.
Sorry but I have problems with my PC. Virus or sth like this.
Hope until Monday I will fix it.
My local winder says that he can wind everything I want (with a reasonable price).
The time he wants to wind a P-P , UL or CFB OPT is about the same. The different is the taps.
My problem is,if I go CFB , I will take the same power? The 30W I want?
And how can I know how much grid-to grid voltage I need?
Hope until Monday I will fix it.
My local winder says that he can wind everything I want (with a reasonable price).
The time he wants to wind a P-P , UL or CFB OPT is about the same. The different is the taps.
My problem is,if I go CFB , I will take the same power? The 30W I want?
And how can I know how much grid-to grid voltage I need?
@ Phooka
Your design is with normal CFB windings?Can you share your design with us?
@BHD
Nice source! I have forgotten Plitron's site.The joke is that I have the book,too.That, explains the new P-P amps.
Your design is with normal CFB windings?Can you share your design with us?
@BHD
Nice source! I have forgotten Plitron's site.The joke is that I have the book,too.That, explains the new P-P amps.
Does anyone have Luxman 3045 schem??
🙁
Any comments on Van der Veen's schem??(page4)
http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf
🙁
Any comments on Van der Veen's schem??(page4)
http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf
I have not checked through everything well enough to post yet. I don't want to post somthing that I am not prepared to build myself. I may not have time to finish it up this week. Though I will be glad to post as soon as I have the design checked out better.
@phooka
What's going on with your amp?
I'm ordering the parts right now.I'll use SV6L6 at 450V and an OPT with CFB windings.
I'll try different driver stages so at the end I'll choose the best .
With what kind of driver stage you are starting with?
I'm thinking to go with 6SL7 or 6SN7 direct coupled to 6SN7 LTP .
I find out that 6SL7 has higher mu than 6SN7 (70 versus 20 ).So,the gain with 6SL7 dc to 6SN7 LTP will be too high.
What's going on with your amp?
I'm ordering the parts right now.I'll use SV6L6 at 450V and an OPT with CFB windings.
I'll try different driver stages so at the end I'll choose the best .
With what kind of driver stage you are starting with?
I'm thinking to go with 6SL7 or 6SN7 direct coupled to 6SN7 LTP .
I find out that 6SL7 has higher mu than 6SN7 (70 versus 20 ).So,the gain with 6SL7 dc to 6SN7 LTP will be too high.
Hmmm….
I give up with the CFB amp!!! 🙁
Too much theory that I don’t know!
I read a lot of interesting things,though. 🙂
But maybe I’ll try it when I’ll be an expert on standard P-P amps.
I’m going UL P-P. Please have a look at my schem .Any comments?
First question – fixed bias or self bias?
I’m planning to use SV6L6 svetlana and coqsnsoq's driver stage (as it is in post 19 ) .But with sovtek 6SN7.
6SN7 direct coupled to 6SN7 LTP.
If 6FQ7 is the same with 6SN7 I can use the schem exactly as it is,right?
I give up with the CFB amp!!! 🙁
Too much theory that I don’t know!
I read a lot of interesting things,though. 🙂
But maybe I’ll try it when I’ll be an expert on standard P-P amps.
I’m going UL P-P. Please have a look at my schem .Any comments?
First question – fixed bias or self bias?
I’m planning to use SV6L6 svetlana and coqsnsoq's driver stage (as it is in post 19 ) .But with sovtek 6SN7.
6SN7 direct coupled to 6SN7 LTP.
If 6FQ7 is the same with 6SN7 I can use the schem exactly as it is,right?
Attachments
Don't give up! Keep working at it!
Menno Van DerVeen's book is pretty good, the article on the plitron site is a bit updated, though. The guys here are waaaay cool. You'll get help - keep at it!
Menno Van DerVeen's book is pretty good, the article on the plitron site is a bit updated, though. The guys here are waaaay cool. You'll get help - keep at it!
Don't give up on the CFB amp!
Right now I'm working on an SE 300B amp, mainly because I've never heard one and want to know what the big deal is about, but ever since I bought Menno's book I've wondered what a PP KT88 amp would sound like with his CFB transformers - I'd like to parallel about four of 'em and run 'em pure class A in triode mode. Run 'em hot the way he says they sound best.
That's about it, I guess. It'll happen, it's right after I build a 2A3 PP amp.
Does that clear it up for you a bit?
BHD
Right now I'm working on an SE 300B amp, mainly because I've never heard one and want to know what the big deal is about, but ever since I bought Menno's book I've wondered what a PP KT88 amp would sound like with his CFB transformers - I'd like to parallel about four of 'em and run 'em pure class A in triode mode. Run 'em hot the way he says they sound best.
That's about it, I guess. It'll happen, it's right after I build a 2A3 PP amp.
Does that clear it up for you a bit?
BHD
Hi,
Indeed, you can.
In general amplifiers are developed back to front: you first decide how much power you require, pick the tubes for that, class of operation if not class A and decide on drive requirements, type of phase splitter, dB of NFB etc, etc.
Just don't expect to be able to design everything yourself from the word go, this takes time, lots of time.
IME the easiest amps to design are the ones running in pure class A.
Incidentally they're often the best sounding as well but they're just not efficient.
The reason I'm telling you all this is that it can turn out to be disappointing to just take a stage here, another there, tack it all together hoping it will all miraculously fit together as Lego building blocks.
Hope this helps, 😉
Indeed, you can.
In general amplifiers are developed back to front: you first decide how much power you require, pick the tubes for that, class of operation if not class A and decide on drive requirements, type of phase splitter, dB of NFB etc, etc.
Just don't expect to be able to design everything yourself from the word go, this takes time, lots of time.
IME the easiest amps to design are the ones running in pure class A.
Incidentally they're often the best sounding as well but they're just not efficient.
The reason I'm telling you all this is that it can turn out to be disappointing to just take a stage here, another there, tack it all together hoping it will all miraculously fit together as Lego building blocks.
Hope this helps, 😉
Ok I’m going CFB! 🙂
Thanks BHD for the courage!
My new approach is attached!
I’m planning to use Va=480V and Ia=70-75mA.
If my maths are correct I need about 150Vp-p at each grid!!! to have about 30W .
Wayne’s driver doesn’t suits to drive this.But I’m thinking to change the first 6SN7 to 6SL7.The gain with 6SN7 is about 40dB.With the 6SL7 and without changing the values of the components,the gain increases to 55dB.Too much headroom!!!!
Have my thoughts any sense?????
Thanks BHD for the courage!
My new approach is attached!
I’m planning to use Va=480V and Ia=70-75mA.
If my maths are correct I need about 150Vp-p at each grid!!! to have about 30W .
Wayne’s driver doesn’t suits to drive this.But I’m thinking to change the first 6SN7 to 6SL7.The gain with 6SN7 is about 40dB.With the 6SL7 and without changing the values of the components,the gain increases to 55dB.Too much headroom!!!!
Have my thoughts any sense?????
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