Hi,
Can't seem to find the corrected drawing I sent back but here's the one I had in mind in its original state:
http://www.diyaudio.com/forums/tubes-valves/253325-lamm-ll2-1-dc-offset-problem-5.html
PS is a FW valve rectified B+ ~250VDC, heaters a SS rectified and regulated.
Hope this helps, 😉
Can't seem to find the corrected drawing I sent back but here's the one I had in mind in its original state:
http://www.diyaudio.com/forums/tubes-valves/253325-lamm-ll2-1-dc-offset-problem-5.html
PS is a FW valve rectified B+ ~250VDC, heaters a SS rectified and regulated.
Hope this helps, 😉
That's no schematic, that's a farce.
Another farce is the use of things like 22k6 and others, as if the values have to be that exact (one tube to another are much more different). In my adaption, some posts back, there are more "normal" values.
Mona
Another farce is the use of things like 22k6 and others, as if the values have to be that exact (one tube to another are much more different). In my adaption, some posts back, there are more "normal" values.
Mona
;
That's not the schematic from the other threat.This one can function, but R10 should at least be decoupled. And still useless percise values, 22,1k 1,21k 81Ω.What is wrong with more "normal" values like 22k 1k2 or 82Ω ? 😉
Mona
The first schematic looks right. I know that Mr. Shushurin is a "solid state guy", later converted to vacuum tubes, it looks in his style. The resistor in anode of SRPP is to "increase symmetry". I saw it in other (amateur, though) Russian design, it is kind of a fashion.
The overall thingy provides gain about 12, and should work pretty clean.
The overall thingy provides gain about 12, and should work pretty clean.
An SRPP is a symmetrical circuit, that resistor spoils not only that but also the low output impedance.
Mona
Mona
Firstly, a SRPP stage is only symmetrical at a specific load. Considering that this a generic preamp which would see a variety of loads, that condition will be false in most cases. However, the minimum load impedance without anything connected to the output of the second stage is quite low already (determined roughly by R5 + R4) and it's possibly operating symmetrical without load. In this case, connecting a load of e.g. 50K would disturb that symmetry only slightly.
Secondly, the output impedance of that circuit is largely determined by the global feedback.
The intended functionality of R10 is unclear to me. What it does:
- Reduce bandwidth due to the miller effect
- Increase distortion of the second stage due to a much larger fluctuation of the anode-cathode voltage of the upper half
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""""""Secondly, the output impedance of that circuit is largely determined by the global feedback.
The intended functionality of R10 is unclear to me. What it does:
The intended functionality of R10 is unclear to me. What it does:
- Reduce bandwidth due to the miller effect
- Increase distortion of the second stage due to a much larger fluctuation of the anode-cathode voltage of the upper half """""'
"""" I suggest you familiarise yourself with how SRPP circuits work.""""
Well ! , I am familiar with how an SRPP works , I thought you might need some more explanations ! 😀 .
Well ! , I am familiar with how an SRPP works , I thought you might need some more explanations ! 😀 .
I just simulated the output stage with an assumed B+ of 300V and a load of 47K (which is basically parallel to the feedback resistors, R4+R5). Below are the currents through the bottom valve (green) and the top (yellow):
An externally hosted image should be here but it was not working when we last tested it.
The AC currents are opposite which to me constitutes push-pull operation and therefore calling it SRPP is valid even though the absolute value of the ac currents is not equal.
The same thing will happen if you try to look at the upper triode as a current source , but you seem to confuse it with a constant current source ( if you read well my previous post well you will see that I wrote current source and not CCS ) , so try to see it as a controled current source that will increase it's impedance in function with the lower triode ! .
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I did not suggest that it makes it more symmetrical. I just read such an explanation when I asked "Why?"
Somebody invented this fashion, similarly to "UL" output
Somebody invented this fashion, similarly to "UL" output
By the way, this is what happens to the currents when R10 is blocked with a large cap:
It looks almost like a perfect SRPP. This makes me suspect that the schematic is wrong.
An externally hosted image should be here but it was not working when we last tested it.
It looks almost like a perfect SRPP. This makes me suspect that the schematic is wrong.
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