...apples and pears...
Joel,
Your lovely 71-a amp driver has 0.9mA standing current against a slewrate calculated current requirement of 1.7mA i.e. 53% of calculated current requirement. Your amp starts to slew limit at above 10khz and full amplitude signals...You won't often hit it....
Dimitrys amp has about 1.25mA against a required 6mA i.e 20% of calculated current requirement - so his starts to slew linit above 4khz...right where the ear is most sensitive...
This assumes the driver can double it's current drive +ve or swing to zero current -ve without introducing other distortions...
As Brett said this is basic engineering....
Yours is in the grey zone and, as previously remarked, you may have synergy occuring...
ciao
James
Joel,
Your lovely 71-a amp driver has 0.9mA standing current against a slewrate calculated current requirement of 1.7mA i.e. 53% of calculated current requirement. Your amp starts to slew limit at above 10khz and full amplitude signals...You won't often hit it....
Dimitrys amp has about 1.25mA against a required 6mA i.e 20% of calculated current requirement - so his starts to slew linit above 4khz...right where the ear is most sensitive...
This assumes the driver can double it's current drive +ve or swing to zero current -ve without introducing other distortions...
As Brett said this is basic engineering....
Yours is in the grey zone and, as previously remarked, you may have synergy occuring...
ciao
James
...Are you inadequate???
Just maybe its why so many of them have a reputation for having a restricted range of music they are good playing .... and also why they start to 'break down' when pushed hard.
You been shouting about wanting figures...I've given figures that show why yours is in the grey area - it's not a special case - you just engineered close enough to optimum for to perform well almost all of the time... Dimitry hasn't and doesn't like good advice judging from his response to Brett...
Another point is one of 'judgement' - not everyone hears slew rate limiting starting and recognises it..so they think their amp is great and it is for them...but it could be better with just a little more application of basic engineering - you know, that thing that gives us our lifestyles... the appliance of science...
ciao
James
Just maybe its why so many of them have a reputation for having a restricted range of music they are good playing .... and also why they start to 'break down' when pushed hard.
You been shouting about wanting figures...I've given figures that show why yours is in the grey area - it's not a special case - you just engineered close enough to optimum for to perform well almost all of the time... Dimitry hasn't and doesn't like good advice judging from his response to Brett...
Another point is one of 'judgement' - not everyone hears slew rate limiting starting and recognises it..so they think their amp is great and it is for them...but it could be better with just a little more application of basic engineering - you know, that thing that gives us our lifestyles... the appliance of science...
ciao
James
James, I'm not saying I don't believe you - but as I posted on another thread, it's often a question of "does it matter?"...
I wanted, specifically, to know what the rolloff due to the driver limitations was in the audio range. How much down at 20kHz.
Or is it increased distortion at HF? I'm not sure I understood your post.
I wanted, specifically, to know what the rolloff due to the driver limitations was in the audio range. How much down at 20kHz.
Or is it increased distortion at HF? I'm not sure I understood your post.
Joel, from the curves at the chosen operating point, I find that the 6SL7 stage has an output resistance of 56k.
Again from the curves, the 2A3 has so much cathode feedback that its ra is approximately 6k! Rather bigger than the load. Still, this reduces Miller capacitance, and the input capacitance is 47pF.
Allow 10pF for strays, and we have -3dB at 50kHz, or -1dB at 25kHz. Now, 1dB down at 25kHz would be considered acceptable if it was an entire system, but not when it is due to one cause within an amplifier.
Worse, the stunningly high ra of the unbypassed 2A3 means that it its gain is so low that the 6SL7 will need to swing 100VRMS for full power. It cannot possibly do this from a 300V supply. If we remove the cathode feedback from the 2A3 to reduce this savage voltage driving requirement, the input capacitance rises to 90pF, forcing the -1dB point down to 16kHz.
A 6SL7 just isn't the right valve to drive a 2A3...
And yes, in time, you can see my SET amplifier design...
Again from the curves, the 2A3 has so much cathode feedback that its ra is approximately 6k! Rather bigger than the load. Still, this reduces Miller capacitance, and the input capacitance is 47pF.
Allow 10pF for strays, and we have -3dB at 50kHz, or -1dB at 25kHz. Now, 1dB down at 25kHz would be considered acceptable if it was an entire system, but not when it is due to one cause within an amplifier.
Worse, the stunningly high ra of the unbypassed 2A3 means that it its gain is so low that the 6SL7 will need to swing 100VRMS for full power. It cannot possibly do this from a 300V supply. If we remove the cathode feedback from the 2A3 to reduce this savage voltage driving requirement, the input capacitance rises to 90pF, forcing the -1dB point down to 16kHz.
A 6SL7 just isn't the right valve to drive a 2A3...
And yes, in time, you can see my SET amplifier design...
lifeless 6sl7
I found this thread very informative.
I myself have a limited experience, but I can say I never made a classic 6sn7/300B amp that was satisfactory.
Therefore I went to the paralelled 6sl7 for my new LL1660/KT88 se-amp. And again not satisfactory. It is going to be a long journey but one day I will reach the nirvana
Till now my simple cap coupled 6N1P-EL84 se amp has not been beaten measured by the fun and umpfh factor.
So I made a test amp with a 6B4G and tested different drivers with the LL1660/10 mA as interstage. If it drives a DHT, it will also drive the KT88.
The 6n1p was o.k. but the best till now was the 5842 with about 10mA and in the same league was a paralelled 2C51. I suppose the 6C45 could do better but my LL1660 has his current limits.
My guess for drivers is that the best results can be obtained with high currents and low Rp's. If this is true it is obvious why you should not take a 6SL7. By the way, it is not sensible to re-invent wheels. There are decades of experience with the 2A3. I remember only the Morrison amp with parallel 6SL7. I would say just built the "free lunch" 2A3 (I suppose anything with a cap is worse than this one) or take an interstage.
Comments ?
Suggestions for a better driver for my LL1660 ?
I found this thread very informative.
I myself have a limited experience, but I can say I never made a classic 6sn7/300B amp that was satisfactory.
Therefore I went to the paralelled 6sl7 for my new LL1660/KT88 se-amp. And again not satisfactory. It is going to be a long journey but one day I will reach the nirvana
Till now my simple cap coupled 6N1P-EL84 se amp has not been beaten measured by the fun and umpfh factor.
So I made a test amp with a 6B4G and tested different drivers with the LL1660/10 mA as interstage. If it drives a DHT, it will also drive the KT88.
The 6n1p was o.k. but the best till now was the 5842 with about 10mA and in the same league was a paralelled 2C51. I suppose the 6C45 could do better but my LL1660 has his current limits.
My guess for drivers is that the best results can be obtained with high currents and low Rp's. If this is true it is obvious why you should not take a 6SL7. By the way, it is not sensible to re-invent wheels. There are decades of experience with the 2A3. I remember only the Morrison amp with parallel 6SL7. I would say just built the "free lunch" 2A3 (I suppose anything with a cap is worse than this one) or take an interstage.
Comments ?
Suggestions for a better driver for my LL1660 ?
Re: Re: Re: ...Are you inadequate???
I put in the link because it defined my language explicitely, rather than simply taking a shot. Most of the thread has been about the clear lack of understanding of the subject by some posters, ie ignorance, and in some cases an unwillingness to see beyond a present level of understanding (ignorance is bliss), even when specifically asked for. I'm commenting on knowledge/understanding, whereas you made a personal attack. Now that's rude.
Jeff, funny post. Sad, but funny.jeff mai said:
I put in the link because it defined my language explicitely, rather than simply taking a shot. Most of the thread has been about the clear lack of understanding of the subject by some posters, ie ignorance, and in some cases an unwillingness to see beyond a present level of understanding (ignorance is bliss), even when specifically asked for. I'm commenting on knowledge/understanding, whereas you made a personal attack. Now that's rude.
Re: Re: Re: Re: ...Are you inadequate???
Try again Brett. I asked for the roll off point at 20kHz. How that is seen as a desire to "remain ignorant" is beyond me.
Besides, what does a subjectivist like you care about somebody elses specs? Who cares where my roll off points are, as long as I like the sound, right? Isn't that what you said about swapping out passive components?
Brett said:
Try again Brett. I asked for the roll off point at 20kHz. How that is seen as a desire to "remain ignorant" is beyond me.
Besides, what does a subjectivist like you care about somebody elses specs? Who cares where my roll off points are, as long as I like the sound, right? Isn't that what you said about swapping out passive components?
Re: Re: Re: Re: Re: ...Are you inadequate???
Is that all you see is involved?Joel said:
What a lot of disingenuous crap. You have totally misrepresented me, but I would expect no less from someone who really is ignorant.Besides, what does a subjectivist like you care about somebody elses specs? Who cares where my roll off points are, as long as I like the sound, right? Isn't that what you said about swapping out passive components?
Sailing into the wind....
Actually, Dmitri's post has provoked some interesting technical points.
Not all of us need to be told many, but for everyone there is something.
For me it was the extraordinarly large change of Miller capacitance between bypassed and unbypassed cathode resistor.
Of course I could have looked it up, or calculated it, but the point is:I hadn't. And it surprised me.
Also, Dmitri, argued his design, and didn't just accept the first advice given. I like that, even when wrong
Cheers,
Actually, Dmitri's post has provoked some interesting technical points.
Not all of us need to be told many, but for everyone there is something.
For me it was the extraordinarly large change of Miller capacitance between bypassed and unbypassed cathode resistor.
Of course I could have looked it up, or calculated it, but the point is:I hadn't. And it surprised me.
Also, Dmitri, argued his design, and didn't just accept the first advice given. I like that, even when wrong
Cheers,
same one, hehe. 6C33C's are in mind for later. but for this im going to use russian 2A3's aka 2C4C. as for james and brett, how do i figure the roll of curves? is there somewhere i can get charts to help me out (aka reactance charts)? and as for the whole argument about not having enough current from the driver, if u could please refer to my post earlier on how there isnt any current goin to the output grid due to the coupling capacitor, etc..
more please
Brett - (yawn)
James - Slew rate distortion is manifested via the input signal's slew, is it not? So, making a blanket statement like "...starts to slew limit at above 10kHz..." is rather meaningless except in the context of a specific amplitude. In other words, you don't have a dramatic voltage rate of change as a product of time for a lazy 1 volt pk-pk 500Hz sine wave. Tell me if I'm wrong.
So, it follows that the greater the frequency, or the more square the waveform, the greater the change in voltage per unit of time?
Now, when you say "slew limit", you mean the amplitude of the output waveform no longer increases to spite an increase in the input signal's amplitude, correct? Thus a form of distortion? I'm not clear why, if the power supply can deliver the juice, why this would be. Can you explain that further?
Thanks.
James D. said:
Brett - (yawn)
James - Slew rate distortion is manifested via the input signal's slew, is it not? So, making a blanket statement like "...starts to slew limit at above 10kHz..." is rather meaningless except in the context of a specific amplitude. In other words, you don't have a dramatic voltage rate of change as a product of time for a lazy 1 volt pk-pk 500Hz sine wave. Tell me if I'm wrong.
So, it follows that the greater the frequency, or the more square the waveform, the greater the change in voltage per unit of time?
Now, when you say "slew limit", you mean the amplitude of the output waveform no longer increases to spite an increase in the input signal's amplitude, correct? Thus a form of distortion? I'm not clear why, if the power supply can deliver the juice, why this would be. Can you explain that further?
Thanks.
Re: Re: Re: Re: ...Are you inadequate???
Labelling someone rude is no more or less of a personal attack than labelling someone ignorant. Perhaps I should have said "And some ignorant in the ways of winning friends and influencing people." Does that make it sound like less of a personal attack?
There was no need for you to criticise the original circuit in order for you to present your ideas.
Brett said:
Labelling someone rude is no more or less of a personal attack than labelling someone ignorant. Perhaps I should have said "And some ignorant in the ways of winning friends and influencing people." Does that make it sound like less of a personal attack?
There was no need for you to criticise the original circuit in order for you to present your ideas.
Re: Re: Re: Re: Re: ...Are you inadequate???
The original post said <i>free to critique</i>, and I did, based both on my knowledge as an engineer, and my experience experimenting with circuits, having built, listened to, and measured a lot of amps over the years. There are a number of fundamental faults in the original circuit, so should I have just said "fine" and let it be, or critique it <i>as I was asked to</i>?
LOL. Are you serious?jeff mai said:
The original post said <i>free to critique</i>, and I did, based both on my knowledge as an engineer, and my experience experimenting with circuits, having built, listened to, and measured a lot of amps over the years. There are a number of fundamental faults in the original circuit, so should I have just said "fine" and let it be, or critique it <i>as I was asked to</i>?
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