50 VOLT RAILS?
I thought this was a preamp not a power amp.... Why in the world would you need 50 volt rails? And why inverted cascodes?
I am not trying to make trouble, I am really curious.
I thought this was a preamp not a power amp.... Why in the world would you need 50 volt rails? And why inverted cascodes?
I am not trying to make trouble, I am really curious.
With a dc servo, we could remove the caps in the signal path.
Add a current sink/source to the diff input pair.
No feedback removes any problems with oscillation due to small phase margin.
I have nothing against FET's
Jfet in the diff pair and mosfet in the class A single ended output. Maybe BJT in the folded cacode?
High rail to get loose from stray capacitance. okay with me
Sonny
Add a current sink/source to the diff input pair.
No feedback removes any problems with oscillation due to small phase margin.
I have nothing against FET's
Jfet in the diff pair and mosfet in the class A single ended output. Maybe BJT in the folded cacode?
High rail to get loose from stray capacitance. okay with me
Sonny
True. Just pointing out that it might be a good alternative.
Still like the orignal idea based on the Borbely.
Jam😉
Still like the orignal idea based on the Borbely.
Jam😉
Jfet cascode
I really don't like the jfets as cascode devices for the reasons I outlined before. Has everyone read the jfet articles at?
http://www.borbelyaudio.com/index15.htm
Non gratuitous image.
I really don't like the jfets as cascode devices for the reasons I outlined before. Has everyone read the jfet articles at?
http://www.borbelyaudio.com/index15.htm
Non gratuitous image.
Attachments
i'm not about to give up yet. i'm not going to give all the nay-sayers the pleasure.
however, you are right, this thread has been stuck in first gear or even reverse at times. we are not accomplishing a whole lot.
let me tell you why i had the nerve (i.e. stupidity) to start this thing in the first place. a while back, i started some threads asking for opinions on buffer and IC opamp circuits. i got a slew of fantastic suggestions from different people (all of whom i haven't seen in a while here), including full-blown schematics, device recommendations, etc. most importantly, all these people had actually BUILT and LISTENED to their stuff, so they were actually in a position to say what worked or not. granted, ICs are much easier to work with, but it was still extremely constructive. i got so much great advice, i told them i would like to eventually put up a web page with there ideas on it so we could have a common resource. the web page never got done due to my laziness, but everyone was very enthusiastic and supportive.
i thought i could get the same sort of constructive discussion here. perhaps the question i posed was simply too broad. but i am willing to work a step at a time. what seems to be happening is people are posting either to only criticize something that was said, or to make everyone build what they want to build. i've also noticed that in the past, threads that some of these people participate in (i won't name names, you probably know who you are) eventually die out into narrow debates between the aformentioned members, drowning out others who eventually lose interest. you are right jam, a lot of it seems boils down to ego at times.
up to this point, i have tried to encourage open debate by being as diplomatic as possible, but there's no point when other people don't have the same courtesy. so i will take you up on your challenge, i will try my best to grab this thing by the horns and get things under control.
i am enforcing a new requirement. tweaks and theoretical analysis of designs others have suggested are still welcome, but i will only be seriously considering topologies from people who have built them, or at least some fundamental version of them. the only truly helpful advice i've gotten is from those who can say something to the effect of "i built this [insert favorite circuit here] for my [DAC, preamp, whatever] using [some technique here] and it sounds great." that is the whole point of me asking questions in the first place. i am trying to draw on people's experience. if you don't even have that experience than i'd have to assume your comments are pure conjecture, and not all that helpful. in this respect, the IC people have actually been the most constructive. you can trash-talk ICs all you want but at least these people spend more time building than talking about their stuff, and i have no doubt some of their circuits sound quite good. a lot of that is by virtue of the simplicitly of IC implementations, but it doesn't matter. again, commenting on other people's suggested circuits is great, but throwing whole circuits out there that you have not tried is not so useful to me. i'm looking for real solutions here, not idle debate.
having said all that, i see we're getting back on track with the boberly circuit. 🙂 yay.
cheers,
marc
however, you are right, this thread has been stuck in first gear or even reverse at times. we are not accomplishing a whole lot.
let me tell you why i had the nerve (i.e. stupidity) to start this thing in the first place. a while back, i started some threads asking for opinions on buffer and IC opamp circuits. i got a slew of fantastic suggestions from different people (all of whom i haven't seen in a while here), including full-blown schematics, device recommendations, etc. most importantly, all these people had actually BUILT and LISTENED to their stuff, so they were actually in a position to say what worked or not. granted, ICs are much easier to work with, but it was still extremely constructive. i got so much great advice, i told them i would like to eventually put up a web page with there ideas on it so we could have a common resource. the web page never got done due to my laziness, but everyone was very enthusiastic and supportive.
i thought i could get the same sort of constructive discussion here. perhaps the question i posed was simply too broad. but i am willing to work a step at a time. what seems to be happening is people are posting either to only criticize something that was said, or to make everyone build what they want to build. i've also noticed that in the past, threads that some of these people participate in (i won't name names, you probably know who you are) eventually die out into narrow debates between the aformentioned members, drowning out others who eventually lose interest. you are right jam, a lot of it seems boils down to ego at times.
up to this point, i have tried to encourage open debate by being as diplomatic as possible, but there's no point when other people don't have the same courtesy. so i will take you up on your challenge, i will try my best to grab this thing by the horns and get things under control.
i am enforcing a new requirement. tweaks and theoretical analysis of designs others have suggested are still welcome, but i will only be seriously considering topologies from people who have built them, or at least some fundamental version of them. the only truly helpful advice i've gotten is from those who can say something to the effect of "i built this [insert favorite circuit here] for my [DAC, preamp, whatever] using [some technique here] and it sounds great." that is the whole point of me asking questions in the first place. i am trying to draw on people's experience. if you don't even have that experience than i'd have to assume your comments are pure conjecture, and not all that helpful. in this respect, the IC people have actually been the most constructive. you can trash-talk ICs all you want but at least these people spend more time building than talking about their stuff, and i have no doubt some of their circuits sound quite good. a lot of that is by virtue of the simplicitly of IC implementations, but it doesn't matter. again, commenting on other people's suggested circuits is great, but throwing whole circuits out there that you have not tried is not so useful to me. i'm looking for real solutions here, not idle debate.
having said all that, i see we're getting back on track with the boberly circuit. 🙂 yay.
cheers,
marc
I was refering to a current source in the power supply. (Harry knows what I'm talking about. Another saucerful of secrets.)
There is going to more than enough complicated stuff everywhere else in this thing the way it was proposed. Why make a parts farm of the gain block?
Jocko
There is going to more than enough complicated stuff everywhere else in this thing the way it was proposed. Why make a parts farm of the gain block?
Jocko
cool, methinks we are getting somewhere
jocko: in theory there is no distinction between "input trimming" and the volume control. there is only a single attenuator which must have the required precision for both main control and trimming. the fact that there is separate trimming and volume is simply a function of the software. remember that there is a microprocessor control unit, the actual preamp modules will be remote in theory.
AudioFreak: yeah, why 50V rails? i know Pass has 60V rails in BOSOZ but i never understood why you absolutely need that sort of voltage. i'm sure you can still optimize the design with lower rails. i'm thinking we'll want something more around +/-24V. if the maximum output level is 10V, then we could go even lower. this would be nice because we would be able to swap in IC opamp modules for comparison purposes, but most people prefer the extra headroom higher rails provide i guess.
sonnya: yes, i was wondering about DC servo. some people say they sound bad. i dunno how it sounds compared to a cap, cap is probably more "musical" but what do i know. i do know that i'd like to avoid the cap if possible, but only if it sounds better of course. i like the BJT folded cascode idea. i haven't seen many hybrid design suggestions and i'd like to investigate it... i like the sound of bipolars for current gain. voltage gain we can leave for the FETs.
oops, maybe i'm getting away from the boberly again...
cheers,
marc
jocko: in theory there is no distinction between "input trimming" and the volume control. there is only a single attenuator which must have the required precision for both main control and trimming. the fact that there is separate trimming and volume is simply a function of the software. remember that there is a microprocessor control unit, the actual preamp modules will be remote in theory.
AudioFreak: yeah, why 50V rails? i know Pass has 60V rails in BOSOZ but i never understood why you absolutely need that sort of voltage. i'm sure you can still optimize the design with lower rails. i'm thinking we'll want something more around +/-24V. if the maximum output level is 10V, then we could go even lower. this would be nice because we would be able to swap in IC opamp modules for comparison purposes, but most people prefer the extra headroom higher rails provide i guess.
sonnya: yes, i was wondering about DC servo. some people say they sound bad. i dunno how it sounds compared to a cap, cap is probably more "musical" but what do i know. i do know that i'd like to avoid the cap if possible, but only if it sounds better of course. i like the BJT folded cascode idea. i haven't seen many hybrid design suggestions and i'd like to investigate it... i like the sound of bipolars for current gain. voltage gain we can leave for the FETs.
oops, maybe i'm getting away from the boberly again...
cheers,
marc
agreed jocko.
it would be ideal to keep the gain stages as simple as possible, though i still want to meet some of the design objectives for flexibility reasons. e.g. low-impedance drive capability (5V @1k load w/low distortion), stability into capacitive loads, low noise, reasonable input impedance ( > 20k).
let's save the complexity for the other goodies like power supply and control circuitry. that's where most of the parts belong anyway. 😛
it would be ideal to keep the gain stages as simple as possible, though i still want to meet some of the design objectives for flexibility reasons. e.g. low-impedance drive capability (5V @1k load w/low distortion), stability into capacitive loads, low noise, reasonable input impedance ( > 20k).
let's save the complexity for the other goodies like power supply and control circuitry. that's where most of the parts belong anyway. 😛
Harry,
If you read my earlier post I was suggesting the use of mosfets for the entire amplifier and replacing the comp. buffer with a single-ended current sourced mosfet buffer. It is the topology I like not the devices. The use of a cascode (mosfet) could be optional.
I would probably bias the buffers at about 15mA and run the thing off 30V rails. The buffers can be tied to ground instead of the negative rail.
Jam
If you read my earlier post I was suggesting the use of mosfets for the entire amplifier and replacing the comp. buffer with a single-ended current sourced mosfet buffer. It is the topology I like not the devices. The use of a cascode (mosfet) could be optional.
I would probably bias the buffers at about 15mA and run the thing off 30V rails. The buffers can be tied to ground instead of the negative rail.
Jam
I guess Borberly did. That's what he's saying: "The SE Balanced ALL-JFET lineamp is very musical amplifier. The output caps must be of highest quality in order to preserve the outstanding sound quality of this simple circuit". I think we could trust him.😉
Yeah, I know that the two attenuators is merely a function of software. It will be easier implement if you break it up in two pieces. (Did it ever occur to you that I may have been down this road many times before, hmmmmm?)
Harry informs me that the Borbely circuit has too low of a voltage across the gain transistor. Ermo should know better. Stiil, it is a simple enough idea that you should be able to get a concensus.
You don't need 10 volts out, or even 5 volts......it will clip any amp except a follower.
The FET/BJT folded cascode works great, but is not necessary. Just don't tell all the people I've sold them to.
Jocko
Harry informs me that the Borbely circuit has too low of a voltage across the gain transistor. Ermo should know better. Stiil, it is a simple enough idea that you should be able to get a concensus.
You don't need 10 volts out, or even 5 volts......it will clip any amp except a follower.
The FET/BJT folded cascode works great, but is not necessary. Just don't tell all the people I've sold them to.
Jocko
yes jocko, i know you have done this stuff before. no need to get defensive.
i was looking at an attenuator scheme which did indeed use two separate stages... it had a 10dB increment stage and a 1dB increment stage. easier to implement the attenuators this way but i'll have to see if the final gain topology we use lends itself to this. it also requires 2 active stages to implement properly.
we never need 5V or 10V output, but i would like to keep that spec to be sure our design is "overdesigned." in my experience, output stages that are not capable of output voltages well in excess of what is strictly required tend to sound compressed dynamically. of course that could just be a reflection of other constraints in the design...
i was looking at an attenuator scheme which did indeed use two separate stages... it had a 10dB increment stage and a 1dB increment stage. easier to implement the attenuators this way but i'll have to see if the final gain topology we use lends itself to this. it also requires 2 active stages to implement properly.
we never need 5V or 10V output, but i would like to keep that spec to be sure our design is "overdesigned." in my experience, output stages that are not capable of output voltages well in excess of what is strictly required tend to sound compressed dynamically. of course that could just be a reflection of other constraints in the design...
Jocko Homo said:
I can imagine what you are thinking of Jocko ... A current source and a shunt regulator .... Sounds like .. 😀
Sonny
The problem with the Borberley SE amp as i see it is :
1) that you are working your amplifying JFET in the Ohmic area.
2) The stray capacitance is also higher this way
3) The offset on the output because of the SE design... You need the caps which you can remove to some level by making an folded cacode.
Sonny
1) that you are working your amplifying JFET in the Ohmic area.
2) The stray capacitance is also higher this way
3) The offset on the output because of the SE design... You need the caps which you can remove to some level by making an folded cacode.
Sonny
Borberley SE amp
Ah somebody is doing some thinking..... I don't know that I would go for DC coupling due to the added complexity of DC servos and the possibility of DC at the output in a fault condition. Folded cascodes can be a little more complicated than a regular cascode also. Let's see some schematics from the commitee......
Ah somebody is doing some thinking..... I don't know that I would go for DC coupling due to the added complexity of DC servos and the possibility of DC at the output in a fault condition. Folded cascodes can be a little more complicated than a regular cascode also. Let's see some schematics from the commitee......
Don't forget that a full blown preamp will have 12 channels. High quality coupling caps might be quite expensive.
I can't understand the preoccupation with servos. Several manufacturers that used don't anymore because of the problems Harry mentioned.
Jam
Jam
I have been folllowing this thread with great interest since I got back from a short vacation last sunday...
A lot of people is following this thread, but somehow it takes off in all directions, exactly as prophetized initially....
Whether it should be cascodes or not, DC or AC,- and so on and so forth... it remains to be seen if an agreementcan be made at all.
In my opinion, one of the things we really need, is a decent control module ( read:input selections and volume control), preferrably remote controlled, that can be used with different amplifying modules. I think most of us prefer to tinker with the amplifiers, and some of us left uP programming in the past and others never got there at all.
I do agree that it would be neat to have everything on one or two PCBs, but that will also freeze the design to one amplifying topology and subsequently somewhat prohibit further experiments. If one can get around to a common control module, everyone can use the line amp of their own choice and coupling...
A lot of people is following this thread, but somehow it takes off in all directions, exactly as prophetized initially....
Whether it should be cascodes or not, DC or AC,- and so on and so forth... it remains to be seen if an agreementcan be made at all.
In my opinion, one of the things we really need, is a decent control module ( read:input selections and volume control), preferrably remote controlled, that can be used with different amplifying modules. I think most of us prefer to tinker with the amplifiers, and some of us left uP programming in the past and others never got there at all.
I do agree that it would be neat to have everything on one or two PCBs, but that will also freeze the design to one amplifying topology and subsequently somewhat prohibit further experiments. If one can get around to a common control module, everyone can use the line amp of their own choice and coupling...
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