As drawn its unity gain, with a output impedance pf about 175R, if the cathode R is bipassed that drops to about 55R. It a cool circuit shape, the gain can be higher or lower than unity, just by the ratio of the resistors.
D3a linestage
#1 D3a linestage
As I am using a pair of monoblock amps at the moment (6c33c), running log leads from the attenuator can't be helping. So I built my first line stage. Based on this http://www.tubecad.com/october99/page8.html, I built this:
As drawn its unity gain, with a output impedance pf about 175R, if the cathode R is bipassed that drops to about 55R. It a cool circuit shape, the gain can be higher or lower than unity, just by the ratio of the resistors.
As drawn its unity gain, with a output impedance pf about 175R, if the cathode R is bipassed that drops to about 55R. It a cool circuit shape, the gain can be higher or lower than unity, just by the ratio of the resistors.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#2
Hi Nick,
What's the freq limit of the sig gen you have?
It would be really interesting to see where this circuit starts to roll off in real life and if it matches the predicted 3db point of 100k into Miller Cap of D3a triode.
Theory says it should be well out of audible range, of course.
cheers,
-- Andrew
What's the freq limit of the sig gen you have?
It would be really interesting to see where this circuit starts to roll off in real life and if it matches the predicted 3db point of 100k into Miller Cap of D3a triode.
Theory says it should be well out of audible range, of course.
cheers,
-- Andrew
#3
When I tried it was about 2dB down at 300k where my sig gen stops.
I would think that feedback would counter the loss of gain due to miller.
I will measure it again tonight and make sure I am not going mad.
I would think that feedback would counter the loss of gain due to miller.
I will measure it again tonight and make sure I am not going mad.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#4
When I looked at this circuit, I thought nah it will never work, but then I looked up the Miller cap of the D3A and then added a bit for safety and got about 180kHz or something with a quick/rough calculation.
Now, that suprised me, there you go I thought, always worth thinking about these things.
Now, that suprised me, there you go I thought, always worth thinking about these things.
#5 Re: D3a linestage
sorry, couldn't resist(another pun)...don't log leads make the sound a bit grainy????Nick wrote:As I am using a pair of monoblock amps at the moment (6c33c), running log leads from the attenuator can't be helping.
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pre65
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#6
Hi-woodentit make a treemendous difference ?
But who am i to bough to your soupearior knowledge.
Perhaps i should branch out with some twiglets,or turn over a new leaf.
I dare say old DTB could add to this sillyness !
But who am i to bough to your soupearior knowledge.
Perhaps i should branch out with some twiglets,or turn over a new leaf.
I dare say old DTB could add to this sillyness !
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#7
Sigh.
You know, log leads, the ones that you measure using a slide rule.
I though any fule knew that.
You know, log leads, the ones that you measure using a slide rule.
I though any fule knew that.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Dave the bass
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#8
Yew must be Oakingpre65 wrote:
I dare say old DTB could add to this sillyness !
DTB
"The fat bourgeois and his doppelganger"
#9
Anyway.
Back to the frewquency response. I think miller is going to be very low, as its only unity gain. I measured it again, and its -3dB point is above 300kHz.
Just for fun (sorry about the poor pics) here is the result of a 1kHz square wave (in and out):
and the same at 100kHz:
Back to the frewquency response. I think miller is going to be very low, as its only unity gain. I measured it again, and its -3dB point is above 300kHz.
Just for fun (sorry about the poor pics) here is the result of a 1kHz square wave (in and out):
and the same at 100kHz:
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#11
Don't know, I should build one and see.how does it sonically compare to the old Cathode Follower?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Dave the bass
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#12
Thats pretty impressive at 100K innit, still very square. Is that 180 degree phase shift intentional Nick?
Was the o/p loaded too?
DTB
Was the o/p loaded too?
DTB
"The fat bourgeois and his doppelganger"
#13
Yes, unlike the CF the AF inverts. That actually is a good thing, as far as I can see, if you needed gain, and used the same valve before the AF, as a normal common cathode amp, with the same cathode and anode resistors, the current through the two stages would cancel, removing (in theory) power supply interaction.Is that 180 degree phase shift intentional
No, not in that case, I should try the same with a load attached.Was the o/p loaded too
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#14
The interesting thing about this line stage, apart from the fact it does exactly what it says on the tin, is that it is quiet as a mouse even when AC heated.
I'll let Nick go into the details as its his project, but it made me realize that non gain stages, such as Cathode Followers, and the above Anode Follower as Nick has it configured are fine with AC heating as they do not amplify, so can/will not amplify noise.
So, where is this leading, well Simon and myself have both had our share of trials trying to DC heat phonos with Aikido outputs using 6N6P/5687/6N30 valves - these suckers needs nearly an amp to heat them. Now, assuming you can mix AC-DC heaters that are all lifted, which shouldn't be a problem (I'm thinking a cap to ground on the lift), then the DC reg has less work to do and can do a better job. This leaves only the gain valves on DC (about 1.3A total) and let AC simply do the job on the output drivers.
So if you can AC heat without noise then why not make your life easier, thanks Nick.
cheers,
-- Andrew
I'll let Nick go into the details as its his project, but it made me realize that non gain stages, such as Cathode Followers, and the above Anode Follower as Nick has it configured are fine with AC heating as they do not amplify, so can/will not amplify noise.
So, where is this leading, well Simon and myself have both had our share of trials trying to DC heat phonos with Aikido outputs using 6N6P/5687/6N30 valves - these suckers needs nearly an amp to heat them. Now, assuming you can mix AC-DC heaters that are all lifted, which shouldn't be a problem (I'm thinking a cap to ground on the lift), then the DC reg has less work to do and can do a better job. This leaves only the gain valves on DC (about 1.3A total) and let AC simply do the job on the output drivers.
So if you can AC heat without noise then why not make your life easier, thanks Nick.
cheers,
-- Andrew
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andrew Ivimey
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#15
erm hello boys,
have you looked at the pre-amp section of izzy wizzy.com, given the fun we were having with phonos, too, it just struck me, as Dwayne Alman and Dicky Betts stretch out that last chord, that there are some relevant points here.
I have heard (a few times) an implementation and extension of this sort of line stage / phono business a few times and I am vey impressed indeed.
(Maybe this is 'old hat', is it?) but coupled to the Lynne Olsen stuff out there I can't help but feel impelled down this way.
!rrelevant to the above but augmenting my musical enjoyment no end, whatever else is cooking out there, VT4c a la Ongaku really does sound quite good.
have you looked at the pre-amp section of izzy wizzy.com, given the fun we were having with phonos, too, it just struck me, as Dwayne Alman and Dicky Betts stretch out that last chord, that there are some relevant points here.
I have heard (a few times) an implementation and extension of this sort of line stage / phono business a few times and I am vey impressed indeed.
(Maybe this is 'old hat', is it?) but coupled to the Lynne Olsen stuff out there I can't help but feel impelled down this way.
!rrelevant to the above but augmenting my musical enjoyment no end, whatever else is cooking out there, VT4c a la Ongaku really does sound quite good.