Now, I just want to say "Thank You" very much to Mr. Pass. I know you have many people thanks you so much, but I want to say it one more time. Maybe you dont realize it, but articles you made so far (for public to see) has teach me alot-lot-lot-lot in making good sounding amp. I never get tired of reading those, reread, reread, reread. Always found something new. Handbooks like Doug Self or Randy Slone helps you in basic audio electronics, theory/calculation. Like they say, audio amp has two sides. One is perspective from electronic theory (resulting in complex amps, low THD, perfect measurement), and the other is the perspective of ear acceptance(just listen to it). You have to know both of them, but stressed on which?
Maybe some people looks at your article (like SOZ) "Whats so hi-tech about it?", they do not dig it further, and looks for far more complicated designs--->"Wow, this is Hi-tech, just what I need".
The lessons that I've learn from you have much-much simpler words, simpler schematics, simpler calculation, just simpler. BUT, I learn alot-lot-lot-lot from them. More basic things than the handbooks, but thats where the more important lessons are.
If you are a teacher, maybe you tought me not by giving lessons for examination, but you give lessons by telling stories. For me this has more impact, because I automaticly wonders "Why is this, why is that?".
For example, now I take differential more seriously. Some people say that the most important part in audio power amp is the VAS, because here the whole voltage swing happens. I think differential has more to dig. It only consist of 2 transistor facing each other, so what's so strange about them? What can be learned from them? He..he..he.. I found out how really an audio amp works from these 2 transistors facing each other. Maybe like "Crazy people", while others are looking at current mirror+cascodes+etc+etc, I still looking at this 2 transistors tied together. But, yes you have to understand it if you want to learn about more complex thing. No other way, no way you can jump over it.
Mr. Pass, you have made your big contribution in audio world (at least for DIYers). My son or my grandson will always can read what you have wrote. Why other "Gurus" don't like to write? Maybe their own grandson dont know what he has achieve?
Maybe some people looks at your article (like SOZ) "Whats so hi-tech about it?", they do not dig it further, and looks for far more complicated designs--->"Wow, this is Hi-tech, just what I need".
The lessons that I've learn from you have much-much simpler words, simpler schematics, simpler calculation, just simpler. BUT, I learn alot-lot-lot-lot from them. More basic things than the handbooks, but thats where the more important lessons are.
If you are a teacher, maybe you tought me not by giving lessons for examination, but you give lessons by telling stories. For me this has more impact, because I automaticly wonders "Why is this, why is that?".
For example, now I take differential more seriously. Some people say that the most important part in audio power amp is the VAS, because here the whole voltage swing happens. I think differential has more to dig. It only consist of 2 transistor facing each other, so what's so strange about them? What can be learned from them? He..he..he.. I found out how really an audio amp works from these 2 transistors facing each other. Maybe like "Crazy people", while others are looking at current mirror+cascodes+etc+etc, I still looking at this 2 transistors tied together. But, yes you have to understand it if you want to learn about more complex thing. No other way, no way you can jump over it.
Mr. Pass, you have made your big contribution in audio world (at least for DIYers). My son or my grandson will always can read what you have wrote. Why other "Gurus" don't like to write? Maybe their own grandson dont know what he has achieve?
Using a resistor to bias the front end differential won't hurt a thing. What you will notice is that the amp can no longer be driven single-ended. For a differential to work as a phase splitter it needs to see lots of resistance/impedance underneath. Something low--in the hundreds of ohms--won't create a strong anti-phase signal out of the back side of the differential. It'll be there, mind you, but it'll be 10 or 20 dB down from the output of the front side. If you're willing to drive the amp with a balanced signal, you can use a resistor to bias the differential.
I suspect the "X" distortion reduction would also be reduced somewhat, but haven't put it to the test. Given that an Aleph-X without the X is just two Alephs back-to-back, the resulting tonal properties might be just what the doctor ordered. I kinda like the way Alephs sound, myself. For solid state amps, they manage to sound damned good. Actually, given what I'm hunting for tonally at the moment, I may give it a whirl.
*****
A brief digression which may or may not be of interest to those who believe that current sources are the be-all, end-all.
I was in the R&D stages of my tube amps. The circuit itself isn't really all that radical (although I could change one connection and make them X, which would make them more "exotic" in some peoples' eyes). The basic idea is that the first stage is a single 6SN7 run as a differential. I chose to handle the phase splitting right up front. Well, as mentioned above, it takes a lot of resistance under a differential (some 10s of k) to make it work efficiently as a phase splitter, and though I could have run a -100V rail or so and used a really big resistor to bias the differential, I chose to use a current source. A solid state one, in fact. Fair enough. On to the second stage--what solid state folks would call the VAS, although that's not true in tube-land, since both the first and second stages contribute to the voltage amplification. The second stage consists of two more 6SN7s connected as differentials in parallel in order to drive the outputs (6550s) more easily. Those who want to start arguments about parallel devices not sounding as good can leave by the same door they used to enter the room--this is neither the time, nor the place for that discussion. So there. Anyway, it was a no-brainer to use another current source, right? The prototype was on the bench, it was getting late, and I wanted to listen to the thing before going to bed. It was easier to use a resistor to bias the thing rather than take the time to whip up a CCS. Sounded glorious. Hot diggity dawg. Off to bed. Next day, I took the time to stick a current source under the second stage. Listened. Sounded like crap, and I mean the smelly kind when the neighbor's dog has left you an unwelcome present on the front walk. What the hell? Well, obviously, my impressions the night before had been wrong. Right? Obviously. Fiddled. Fiddled some more. Then fiddled some more. Thing still sounded awful. High end, image, detail...you name it. All bad. Tried three or four different CCS topologies. Varying flavors of crap. I sat and thunk 'till my thunker was sore. Well, back to square one. Put back the stupid resistor.
You can guess what happened.
There's an expression that sometimes the right man for the job is a woman. Well, let me tell you here and now that sometimes the right CCS for the job is a plain ol' resistor. Don't believe those who tell you that "obviously" you'll need a CCS at some point in the circuit.
Hogfeathers.
As a sort of sideways proof of this, there's a schematic floating around that claims to represent the old Krell KSA 100. Whether it's accurate or not, I'm not in a position to say. Never owned a piece of Krell. But that amp and the 50W had good reputations. Some say they're the best sounding things Krell ever did, and that D'Agostino should reconsider his current fancy-pants "smart" designs. The schematic shows double differentials in the front end, one N, one P.
Yup, you guessed it. Each is biased by a resistor...not a current source. What? You think current sources hadn't been invented yet, or that Krell hadn't heard of them?
Just something to think about.
*****
So what's the "official" schematic of the Aleph-X at this point in time? In my opinion, it's the one posted on Page #1, Post #1, but with the addition of Ian's resistors from the ouputs to the node between the CCS and the Sources of the two MOSFETs in the front end differential. I've got a few changes in mind, but nothing so radical that it'll knock you on your butt.
Grey
I suspect the "X" distortion reduction would also be reduced somewhat, but haven't put it to the test. Given that an Aleph-X without the X is just two Alephs back-to-back, the resulting tonal properties might be just what the doctor ordered. I kinda like the way Alephs sound, myself. For solid state amps, they manage to sound damned good. Actually, given what I'm hunting for tonally at the moment, I may give it a whirl.
*****
A brief digression which may or may not be of interest to those who believe that current sources are the be-all, end-all.
I was in the R&D stages of my tube amps. The circuit itself isn't really all that radical (although I could change one connection and make them X, which would make them more "exotic" in some peoples' eyes). The basic idea is that the first stage is a single 6SN7 run as a differential. I chose to handle the phase splitting right up front. Well, as mentioned above, it takes a lot of resistance under a differential (some 10s of k) to make it work efficiently as a phase splitter, and though I could have run a -100V rail or so and used a really big resistor to bias the differential, I chose to use a current source. A solid state one, in fact. Fair enough. On to the second stage--what solid state folks would call the VAS, although that's not true in tube-land, since both the first and second stages contribute to the voltage amplification. The second stage consists of two more 6SN7s connected as differentials in parallel in order to drive the outputs (6550s) more easily. Those who want to start arguments about parallel devices not sounding as good can leave by the same door they used to enter the room--this is neither the time, nor the place for that discussion. So there. Anyway, it was a no-brainer to use another current source, right? The prototype was on the bench, it was getting late, and I wanted to listen to the thing before going to bed. It was easier to use a resistor to bias the thing rather than take the time to whip up a CCS. Sounded glorious. Hot diggity dawg. Off to bed. Next day, I took the time to stick a current source under the second stage. Listened. Sounded like crap, and I mean the smelly kind when the neighbor's dog has left you an unwelcome present on the front walk. What the hell? Well, obviously, my impressions the night before had been wrong. Right? Obviously. Fiddled. Fiddled some more. Then fiddled some more. Thing still sounded awful. High end, image, detail...you name it. All bad. Tried three or four different CCS topologies. Varying flavors of crap. I sat and thunk 'till my thunker was sore. Well, back to square one. Put back the stupid resistor.
You can guess what happened.
There's an expression that sometimes the right man for the job is a woman. Well, let me tell you here and now that sometimes the right CCS for the job is a plain ol' resistor. Don't believe those who tell you that "obviously" you'll need a CCS at some point in the circuit.
Hogfeathers.
As a sort of sideways proof of this, there's a schematic floating around that claims to represent the old Krell KSA 100. Whether it's accurate or not, I'm not in a position to say. Never owned a piece of Krell. But that amp and the 50W had good reputations. Some say they're the best sounding things Krell ever did, and that D'Agostino should reconsider his current fancy-pants "smart" designs. The schematic shows double differentials in the front end, one N, one P.
Yup, you guessed it. Each is biased by a resistor...not a current source. What? You think current sources hadn't been invented yet, or that Krell hadn't heard of them?
Just something to think about.
*****
So what's the "official" schematic of the Aleph-X at this point in time? In my opinion, it's the one posted on Page #1, Post #1, but with the addition of Ian's resistors from the ouputs to the node between the CCS and the Sources of the two MOSFETs in the front end differential. I've got a few changes in mind, but nothing so radical that it'll knock you on your butt.
Grey
GRollins said:
I can say that the schematics are accurate, and it would be
innapropriate for me to comment further. 😎
Since I'm not in the position that you are--i.e. competitor--I can say things plainly. However, I scrupulously adhere to the principle that I don't comment on things I haven't heard, and heard under good conditions. I've only heard Krell stuff a handful of times in my life due to the fact that there's no dealer in the area. The most recent time I heard anything was in Santa Fe about three years ago or so. A shop out there had those monstrous 600W jobbies, but they were hooked up to these rinky-tink little speakers and an el-cheapo CD player (don't remember what preamp), so as it happens I can't really comment on the sound of that one, either. All I can say with authority is that the sucker was big. Well, duh, you can tell that from the pictures. Prior to that, the last time I heard Krell was sometime in the mid '80s back when Excalibur was still in business in Washington DC. Come to think of it, I heard a preamp in the same system in which I heard the Genesis 1.1s, but absolutely nothing was familiar to me in that system, and there were some setup-related things that had not been attended to, so I'll refrain from comment on that also.
As I noted (clearly, I hope), the KSA had a decent reputation regarding sound quality, but I have not heard one myself, so I can neither confirm nor deny, as the expression goes. One thing's for sure. That schematic shows a fairly minimalist circuit and their current product is anything but. To the extent that sound quality and parts count are inversely related...
Well, let's just say that I'm not planning a road trip to go listen to Krell any time in the near future.
Grey
EDIT: I went and scrounged up a copy of that KSA schematic. Just in passing, I'll note that it shows 10k resistors under the tails of the differentials...I think...the thing's so blurred that I can't really be certain. That's just as an indication that it takes a fair number of ohms to get decent action out of a differential. They're not using the front end as a phase splitter, either, so the only thing left to worry about is how efficient the differentials are at error correction when the feedback comes in the back end. Given that there's a decent amount of resistance, I'd expect that it would do a fair job. That gets more into the subtleties of voicing the amp and how much of what harmonic is left. If I had the right sort of parts on hand, I'd build one just to see what it sounded like, but that's not possible at the moment. Might get around to that next decade...too many other things in the queue this decade.
For what it's worth, the NFB re-entry point on my tube amps is the first stage--the one with the current source.
As I noted (clearly, I hope), the KSA had a decent reputation regarding sound quality, but I have not heard one myself, so I can neither confirm nor deny, as the expression goes. One thing's for sure. That schematic shows a fairly minimalist circuit and their current product is anything but. To the extent that sound quality and parts count are inversely related...
Well, let's just say that I'm not planning a road trip to go listen to Krell any time in the near future.
Grey
EDIT: I went and scrounged up a copy of that KSA schematic. Just in passing, I'll note that it shows 10k resistors under the tails of the differentials...I think...the thing's so blurred that I can't really be certain. That's just as an indication that it takes a fair number of ohms to get decent action out of a differential. They're not using the front end as a phase splitter, either, so the only thing left to worry about is how efficient the differentials are at error correction when the feedback comes in the back end. Given that there's a decent amount of resistance, I'd expect that it would do a fair job. That gets more into the subtleties of voicing the amp and how much of what harmonic is left. If I had the right sort of parts on hand, I'd build one just to see what it sounded like, but that's not possible at the moment. Might get around to that next decade...too many other things in the queue this decade.
For what it's worth, the NFB re-entry point on my tube amps is the first stage--the one with the current source.
More Science Fiction fron Grey?
Grey,
Please explain this
Using a resistor to bias the front end differential won't hurt a thing. What you will notice is that the amp can no longer be driven single-ended. For a differential to work as a phase splitter it needs to see lots of resistance/impedance underneath. Something low--in the hundreds of ohms--won't create a strong anti-phase signal out of the back side of the differential. It'll be there, mind you, but it'll be 10 or 20 dB down from the output of the front side. If you're willing to drive the amp with a balanced signal, you can use a resistor to bias the differential.
I suspect the "X" distortion reduction would also be reduced somewhat, but haven't put it to the test. Given that an Aleph-X without the X is just two Alephs back-to-back, the resulting tonal properties might be just what the doctor ordered. I kinda like the way Alephs sound, myself. For solid state amps, they manage to sound damned good. Actually, given what I'm hunting
and this,
EDIT: I went and scrounged up a copy of that KSA schematic. Just in passing, I'll note that it shows 10k resistors under the tails of the differentials...I think...the thing's so blurred that I can't really be certain. That's just as an indication that it takes a fair number of ohms to get decent action out of a differential. They're not using the front end as a phase splitter, either, so the only thing left to worry about is how efficient the differentials are at error correction when the feedback comes in the back end. Given that there's a decent amount of resistance, I'd expect that it would do a fair job. That gets more into the subtleties of voicing the amp and how much of what harmonic is left.
You have me totally baffled.😀
Regards,
Jam
Grey,
Please explain this
Using a resistor to bias the front end differential won't hurt a thing. What you will notice is that the amp can no longer be driven single-ended. For a differential to work as a phase splitter it needs to see lots of resistance/impedance underneath. Something low--in the hundreds of ohms--won't create a strong anti-phase signal out of the back side of the differential. It'll be there, mind you, but it'll be 10 or 20 dB down from the output of the front side. If you're willing to drive the amp with a balanced signal, you can use a resistor to bias the differential.
I suspect the "X" distortion reduction would also be reduced somewhat, but haven't put it to the test. Given that an Aleph-X without the X is just two Alephs back-to-back, the resulting tonal properties might be just what the doctor ordered. I kinda like the way Alephs sound, myself. For solid state amps, they manage to sound damned good. Actually, given what I'm hunting
and this,
EDIT: I went and scrounged up a copy of that KSA schematic. Just in passing, I'll note that it shows 10k resistors under the tails of the differentials...I think...the thing's so blurred that I can't really be certain. That's just as an indication that it takes a fair number of ohms to get decent action out of a differential. They're not using the front end as a phase splitter, either, so the only thing left to worry about is how efficient the differentials are at error correction when the feedback comes in the back end. Given that there's a decent amount of resistance, I'd expect that it would do a fair job. That gets more into the subtleties of voicing the amp and how much of what harmonic is left.
You have me totally baffled.😀
Regards,
Jam
Jam,
And the reason you're baffled is...?
Lots of resistance makes a differential work better as a phase splitter. No surprise there. (Not to me, anyway, and hopefully not to you.) But not all differentials are used as phase splitters. Some just serve as feedback entry points. Some serve as both. How lower resistance under a differential effects the distortion spectrum, I'm not in a position to say. Don't have a spectrum analyzer. I suspect, perhaps wrongly, that it would not be as effective at nulling out distortion.
But that doesn't mean that the Aleph-X wouldn't work with a resistor biasing the front end differential. Just drive it with a balanced input and enjoy.
The worst case scenario is that you would get no distortion cancellation at all. This is a crisis? Not likely, given the interest that people have shown in zero feedback amps. Add to that the fact that the Aleph output stage is single-ended, meaning heavy on the second harmonic, and a zero feedback Aleph might be the cat's meow for some people. Yes, there's some inherent feedback in the Aleph circuit itself, but I mean the global feedback coming back to the front end.
Interestingly, earlier this evening I scribbled a note to myself to try a reduced feedback (about 13dB rather than the usual 20dB) Aleph.
The only people who would be mystified by what I said are members of the numbers-are-everything club, who would automatically assume that the amp is 'broken' if the distortion increases. I'm glad to say I quit paying dues to that group years ago. About the only thing I subscribe to now is the idea of wide bandwidth, something that makes folks in RF prone areas cringe. Here in the hinterlands, it's not so much of a problem. Once the cavemen next door discover TV, I may be in trouble, but so far the only time I've had a problem is when I tried to run a high impedance line for six feet without decent shielding. Hmmm. Signals from Mars, there, time to hit the junkbox and see what I can cobble together.
Incidentally, that's one area where I differ from Nelson. He builds in an upper limit of around 100-150kHz. I shoot for 250-400kHz, aware that I'm dancing on thin ice if I ever move to a civilized part of the world. Just a choice I make. Others are welcome to adjust things according to their local conditions.
Uh, sorry, got sidetracked...
Anyway, so which part do you not understand, other than the fact that you like current sources somewhat more than I do? That's not news, either. We hit that particular difference in our preferences ages ago. Big deal. Yawn. Next topic.
Grey
And the reason you're baffled is...?
Lots of resistance makes a differential work better as a phase splitter. No surprise there. (Not to me, anyway, and hopefully not to you.) But not all differentials are used as phase splitters. Some just serve as feedback entry points. Some serve as both. How lower resistance under a differential effects the distortion spectrum, I'm not in a position to say. Don't have a spectrum analyzer. I suspect, perhaps wrongly, that it would not be as effective at nulling out distortion.
But that doesn't mean that the Aleph-X wouldn't work with a resistor biasing the front end differential. Just drive it with a balanced input and enjoy.
The worst case scenario is that you would get no distortion cancellation at all. This is a crisis? Not likely, given the interest that people have shown in zero feedback amps. Add to that the fact that the Aleph output stage is single-ended, meaning heavy on the second harmonic, and a zero feedback Aleph might be the cat's meow for some people. Yes, there's some inherent feedback in the Aleph circuit itself, but I mean the global feedback coming back to the front end.
Interestingly, earlier this evening I scribbled a note to myself to try a reduced feedback (about 13dB rather than the usual 20dB) Aleph.
The only people who would be mystified by what I said are members of the numbers-are-everything club, who would automatically assume that the amp is 'broken' if the distortion increases. I'm glad to say I quit paying dues to that group years ago. About the only thing I subscribe to now is the idea of wide bandwidth, something that makes folks in RF prone areas cringe. Here in the hinterlands, it's not so much of a problem. Once the cavemen next door discover TV, I may be in trouble, but so far the only time I've had a problem is when I tried to run a high impedance line for six feet without decent shielding. Hmmm. Signals from Mars, there, time to hit the junkbox and see what I can cobble together.
Incidentally, that's one area where I differ from Nelson. He builds in an upper limit of around 100-150kHz. I shoot for 250-400kHz, aware that I'm dancing on thin ice if I ever move to a civilized part of the world. Just a choice I make. Others are welcome to adjust things according to their local conditions.
Uh, sorry, got sidetracked...
Anyway, so which part do you not understand, other than the fact that you like current sources somewhat more than I do? That's not news, either. We hit that particular difference in our preferences ages ago. Big deal. Yawn. Next topic.
Grey
Hi, Grey,
So, you have noticed the same thing to. In my experiment I also found out that biasing the differential with plain R sounds better (to me).
Since that, I've always wanted to post this question. But I'm afraid.
Looking at the evolution of Mr.Pass' designs, he certainly have use it in the old days (eg. Citation-Mosfet 12). But now he has leave it, he always use CCS, no matter how much bias, no matter rail voltages, always CCS. (the later versions of ZEN also uses CCS). There must be a strong reason why.
I'm afraid that if I post this question, it might challanges people like Mr.Pass, while I know nothing about audio power amp.
Now that you have make a way, I dare to write this.
So R for differential has sound advantage, but have limits, like values (10s of Ks) and rail voltage (maybe good for more than 25V, but not for 15V like AlephX, accept if drive it with balanced like you said).
What other setback and advantage if using R for the place of CCS, in anywhere in anystage of audio power amp?
(In Mr.Pass patent on SuSy, I also suspects that the upper 2 CCS for folded cascode is no CCS at all, just plain R)
So, you have noticed the same thing to. In my experiment I also found out that biasing the differential with plain R sounds better (to me).
Since that, I've always wanted to post this question. But I'm afraid.
Looking at the evolution of Mr.Pass' designs, he certainly have use it in the old days (eg. Citation-Mosfet 12). But now he has leave it, he always use CCS, no matter how much bias, no matter rail voltages, always CCS. (the later versions of ZEN also uses CCS). There must be a strong reason why.
I'm afraid that if I post this question, it might challanges people like Mr.Pass, while I know nothing about audio power amp.
Now that you have make a way, I dare to write this.
So R for differential has sound advantage, but have limits, like values (10s of Ks) and rail voltage (maybe good for more than 25V, but not for 15V like AlephX, accept if drive it with balanced like you said).
What other setback and advantage if using R for the place of CCS, in anywhere in anystage of audio power amp?
(In Mr.Pass patent on SuSy, I also suspects that the upper 2 CCS for folded cascode is no CCS at all, just plain R)
That's me...always saying weird and unpopular things.
I'm not saying that resistors always sound better. They may or they may not. But I have found cases where they do sound better than current sources.
In the case of the first stage of my tube circuit, the bias voltage (note to solid state folks, tube people often talk in terms of voltage instead of current for bias) is somewhere on the order of 1.75-2 volts. Given that I wanted a good anti-phase signal, I used a current source. The second stage bias is more on the order of 4 volts or so. If anything, there's more room there to slide in a CCS. But the resistor sounded better. I'm not advancing any explanations because, frankly, I don't have any. I suppose you could make a case that there's local degenerative feedback based on imbalances between the two sides of the tube. Dunno. I just made a decision based on what I heard, not on theory. In the case of the second stage, the incoming signal was already balanced (from the phase splitter in the first stage), so I didn't need the differential to play that role, and it's not a feedback entry point, so I don't have to lie awake at night staring at the ceiling wondering about what effect it has on distortion. CMRR sucks, I'm sure, but since I used individually regulated rails for both first and second stages, I don't have to worry about that. Incidentally, the value of the resistor under the cathodes in the second stage is really low, something like 390 ohms, so it's not as though I'm using a 10k resistor.
I think I'm on safe ground in saying that Nelson won't bite you if you want to experiment with resistors instead of current sources. For all I know, he listened to resistors and current sources for each design and concluded that--for that design--the CCS sounded better. Just remain aware that resistors may have a downside if you're expecting the differential to function as a phase splitter...and possibly as a feedback entry point.
Look at it this way, it's a cheap experiment. One of those 1% Vishay/Dale resistors from Mouser costs, what, 15-20 cents depending on quantity. There are few experiments you will come across in audio that are that inexpensive to try. If it doesn't suit you, feel free to use a current source. As long as you get the current right, all will be well.
Grey
EDIT: A little birdy tells me that the circuit for the X-600 and 1000 is pretty much as shown in the patent. No resistors masquerading as current sources.
I'm not saying that resistors always sound better. They may or they may not. But I have found cases where they do sound better than current sources.
In the case of the first stage of my tube circuit, the bias voltage (note to solid state folks, tube people often talk in terms of voltage instead of current for bias) is somewhere on the order of 1.75-2 volts. Given that I wanted a good anti-phase signal, I used a current source. The second stage bias is more on the order of 4 volts or so. If anything, there's more room there to slide in a CCS. But the resistor sounded better. I'm not advancing any explanations because, frankly, I don't have any. I suppose you could make a case that there's local degenerative feedback based on imbalances between the two sides of the tube. Dunno. I just made a decision based on what I heard, not on theory. In the case of the second stage, the incoming signal was already balanced (from the phase splitter in the first stage), so I didn't need the differential to play that role, and it's not a feedback entry point, so I don't have to lie awake at night staring at the ceiling wondering about what effect it has on distortion. CMRR sucks, I'm sure, but since I used individually regulated rails for both first and second stages, I don't have to worry about that. Incidentally, the value of the resistor under the cathodes in the second stage is really low, something like 390 ohms, so it's not as though I'm using a 10k resistor.
I think I'm on safe ground in saying that Nelson won't bite you if you want to experiment with resistors instead of current sources. For all I know, he listened to resistors and current sources for each design and concluded that--for that design--the CCS sounded better. Just remain aware that resistors may have a downside if you're expecting the differential to function as a phase splitter...and possibly as a feedback entry point.
Look at it this way, it's a cheap experiment. One of those 1% Vishay/Dale resistors from Mouser costs, what, 15-20 cents depending on quantity. There are few experiments you will come across in audio that are that inexpensive to try. If it doesn't suit you, feel free to use a current source. As long as you get the current right, all will be well.
Grey
EDIT: A little birdy tells me that the circuit for the X-600 and 1000 is pretty much as shown in the patent. No resistors masquerading as current sources.
lumanauw said:
I always try a resistor before I put in something else. In the
case of the folded cascode CCS, the performance is not good
if replaced by a resistor - too much impedance in the Source
of the cascoding device. You can improve this by using a high
value resistor, but soon your power supply voltage needs get
out of hand, as quite a large voltage must drop across the
resistor at a fairly high current.
All these techniques are just tools, to be used where they
do the job best.
😎
Actually, I never aim at that figure, it's just where it always seems
to land.
I learned many years ago that a manufacturer will generally
regret giving consumers 500 KHz bandwidths (like we did with
early Threshold) because too many consumers have ungrounded
volume controls, cable shields, and what not, and any
ungrounded piece of metal with a capacitive relationship to
the input cable of a preamp is an antenna. The result is that
at some arbitrarily high frequency enough of the the output of
the amplifier makes it back to the input of the preamp and you
have a very nice oscillator. If you limit the frequency response
to 100 KHz, you never see this, at but 500 KHz you get at least
a call a week. There are just too many crappy preamps, cables,
and careless/ignorant consumers out there.
Surely the truth. If I were making gear commercially, I'd have to rein in my wide-bandwidth impulses or else be very, very careful about shielding and other such matters. Or, like at least one manufacturer, specify (and sell [profitable strategy, that]) matching cables to go with my stuff.
If I ever move, I may have to go back through my system in a big hurry, dropping a prophylactic pF or two here and there just to keep the RF gremlins at bay.
My current rethink of the Xenover is running somewhere around 500kHz for the basic circuit. Enough to make even me wary.
On the other hand, I might be the one to receive signals from Aleph Centauri and prove the existence of single-ended little green men, thus stealing thunder from the SETI gang.
Who needs Arecibo, anyway?
Grey
If I ever move, I may have to go back through my system in a big hurry, dropping a prophylactic pF or two here and there just to keep the RF gremlins at bay.
My current rethink of the Xenover is running somewhere around 500kHz for the basic circuit. Enough to make even me wary.
On the other hand, I might be the one to receive signals from Aleph Centauri and prove the existence of single-ended little green men, thus stealing thunder from the SETI gang.
Who needs Arecibo, anyway?
Grey
Grey,
I have a question about the "official" AlephX in post#1.
How do you determine the value of R19-R29 (=68K1).
Like Mr.Pass said, the AlephX cct might have difficulty in DC offset, so the whole cct should have R19-R29-R1-R4-R44-R45 (+magic resistor).
Lower is better for reference. How low can we make this R19-R29? 10K? If too low will it form a voltage divider that lower the gain?
I have a question about the "official" AlephX in post#1.
How do you determine the value of R19-R29 (=68K1).
Like Mr.Pass said, the AlephX cct might have difficulty in DC offset, so the whole cct should have R19-R29-R1-R4-R44-R45 (+magic resistor).
Lower is better for reference. How low can we make this R19-R29? 10K? If too low will it form a voltage divider that lower the gain?
GRollins said:
I don't rein in the bandwidth though. If I wanted faster, I would
have to add some parts or sacrifice some other parameter.
I choose to do neither.
😎
It's not that you pull things in...it's that I go rumaging around looking for ways to extend bandwidth without having to resort to feedback. I'm loath to change my evil ways.
Grey
Grey
Balanced volume control
I'm inspired by the type of control as used in the Aleph 1.7 with relay's to change the attenuation.
Lay'd my hands on a bunch of relay's driven by an Eprom that contains the look-up table for lineair attenuation. The address pionter is controlled by a 6 bit binary counter. The counter can be driven by either up/down buttons or a rotary encoder.
I have plans to use a PIC to drive the relay's and also use RC5 remote control decoding to allow remote control. I just have no clou how PIC's work and have to find out. 😕 😕
Anybody out there having the same thoughts and have more experience with PIC's?
Marcel
I'm inspired by the type of control as used in the Aleph 1.7 with relay's to change the attenuation.
Lay'd my hands on a bunch of relay's driven by an Eprom that contains the look-up table for lineair attenuation. The address pionter is controlled by a 6 bit binary counter. The counter can be driven by either up/down buttons or a rotary encoder.
I have plans to use a PIC to drive the relay's and also use RC5 remote control decoding to allow remote control. I just have no clou how PIC's work and have to find out. 😕 😕
Anybody out there having the same thoughts and have more experience with PIC's?
Marcel
lumanauw,
The whole input array was ported over from the Volksamp Alephs.
Feel free to experiment with various values. Report back. That part of the circuit isn't so much science as it is art. You're not locked into 68.1k. Paint the picture with colors that look good to you. Yes, at some point the amp will require more from the preamp, but you're not going to get that extreme, are you?
I tend to go for higher input impedances for two reasons: one is that I'm used to thinking in terms of tube circuits where values from 100k to 1M are common, the other is that the higher the Zin, the smaller the cap I have to use in order to make a 6dB/oct high pass filter right at the input. Smaller caps are cheaper, easier to find, and can be tighter tolerance with higher quality. (Remember that for me this is a tweeter amp in a quad-amped system, though I'm thinking about whipping up an extra-bias Aleph 3 out of spare parts and trying that.) The more devices I can get rid of, the happier I am, and sticking a cap into the front of an amp simplifies things greatly. The downsides are that you have a somewhat increased potential for DC offset, and perhaps a little more high end rolloff with reactive interconnects. The choice is yours.
Grey
The whole input array was ported over from the Volksamp Alephs.
Feel free to experiment with various values. Report back. That part of the circuit isn't so much science as it is art. You're not locked into 68.1k. Paint the picture with colors that look good to you. Yes, at some point the amp will require more from the preamp, but you're not going to get that extreme, are you?
I tend to go for higher input impedances for two reasons: one is that I'm used to thinking in terms of tube circuits where values from 100k to 1M are common, the other is that the higher the Zin, the smaller the cap I have to use in order to make a 6dB/oct high pass filter right at the input. Smaller caps are cheaper, easier to find, and can be tighter tolerance with higher quality. (Remember that for me this is a tweeter amp in a quad-amped system, though I'm thinking about whipping up an extra-bias Aleph 3 out of spare parts and trying that.) The more devices I can get rid of, the happier I am, and sticking a cap into the front of an amp simplifies things greatly. The downsides are that you have a somewhat increased potential for DC offset, and perhaps a little more high end rolloff with reactive interconnects. The choice is yours.
Grey
Actual pcb
I have become very interesting in building an Aleoph-X. Having missed all the groupbuys, I went digging in this huge thread for a picture of the actual pcb so I could make a photoprint. I havn’t succeeded and I know that there a different variations of GRollins original diagram, but surely there be must be some somewhere. Could anyone point me in the right direction?
I have become very interesting in building an Aleoph-X. Having missed all the groupbuys, I went digging in this huge thread for a picture of the actual pcb so I could make a photoprint. I havn’t succeeded and I know that there a different variations of GRollins original diagram, but surely there be must be some somewhere. Could anyone point me in the right direction?