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Old 22nd July 2011, 10:23 PM   #1
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Default Aikido LV improved psu

Hi all,
I am working on an low voltage aikido preheadamp, which is know to have good PSRR. Voltage is 24v, and i am currently using the standard lt1084 regulated psu, with limited capacitance. This psu powers both the heaters and the triodes. I am thinking about some options, and would like your opinions on the best path to take.

- do nothing, as psrr of the aikido is very good an improved psu will not make a big difference
- CLC unregulated
- shunt regulator, eg salas shunt
- separate heaters from tubes (in combination with any ofthr above)
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Old 23rd July 2011, 12:25 AM   #2
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Hello,
I have built several Aikido line stages, not the LV.
My $0.02 worth.
Use 2 different transformers. Use a solid choke in the CLC B+ Pi filter. The heaters draw the most current and create the biggest current, voltage peaks and biggest source of diode switching noise in a single transformer. If the heaters can be separated that is a good thing. The B+ Pi filter will have less work to do with the heaters supplied by a separate source.
If you have a O’scope use it to tune the voltage splitter that controls the noise canceling grid of the bottom tube in the output section (cathode follower) of the Aikido. The calculation that John provides is a scientific wild A** guess. Careful tuning can add another 20db (PSRR) of insertion loss.
DT
All just for fun!
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Old 23rd July 2011, 08:48 AM   #3
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Quote:
Originally Posted by DualTriode View Post
If you have a O’scope use it to tune the voltage splitter that controls the noise canceling grid of the bottom tube in the output section (cathode follower) of the Aikido. The calculation that John provides is a scientific wild A** guess. Careful tuning can add another 20db (PSRR) of insertion loss.
DT
All just for fun!
Thanks!
Can you elaborate on the bit above? You mean correcting for differences in both tubes?
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Old 23rd July 2011, 10:28 AM   #4
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My vote is for Salas shunt reg. Improves just everything quite a lot in my experience.
Run heaters from AC with common mode choke LC filter (two 100nF from L to ground).
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Old 23rd July 2011, 03:39 PM   #5
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Smile SWAG

Quote:
Originally Posted by studiostevus View Post
Thanks!
Can you elaborate on the bit above? You mean correcting for differences in both tubes?
Hello,
For grins take a look at the pdf manuals for both the LV and ACF. The ACF is only the cathode follower (buffer) output stage of the Aikido. For the ACF resistors R8 and R9 set the level of input to the buffer stage bottom triode grid input. For the LV resistors R15 and R16 set the level of input to the buffer stage bottom triode grid input. Notice the formulas in the pdf manuals for selecting the voltage divider resistor values are different. The difference is the full 2 stage Aikido the injection of B+ noise at the bottom triode grid in the output buffer works to cancel noise from both the input and output stages. For the full Aikido the different tube types, brands or just manufacture variation in performance characteristics between input and output stages the degree of noise cancelation will vary. The provided calculations are sort of close in theory. In the real world there is room for improvement in the noise cancellation (PSRR) by adjusting the voltage divider under test as mentioned in the previous post.
DT
All just for fun!
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Old 23rd July 2011, 04:32 PM   #6
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Yes, it is possible to make PSRR better with tuning the power supply noise injection divider. But you would then have to make it for each new tube. What I mean is, that it is possible, when you adjust for specific tube for best PSRR, you can have setting which can have with another tube worse PSRR than the calculated values listed in Aikido manual PDF. Basically it can happen when those two tubes have very big tolerances in specs. On measurement scale one tube is max to left other max to right. The golden middle way is what I choose, unless you want to adjust all the time when you change one tube. Machines should work for us, not we for them :-).

Last edited by kacernator; 23rd July 2011 at 04:35 PM.
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Old 24th July 2011, 11:12 PM   #7
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Hello,
Start rolling tubes in the Aikido LV for that matter any Aikido and you leave that golden middle as you call it, if there was one. A screw driver adjustable resistor may be a good idea.
A thought; we never see any sound performance claims or data at tubecad.com.
If you use a shunt regulator that will make the injection of 180 degree out of phase B+ noise belt and suspenders.
DT
All just for fun!

Last edited by DualTriode; 24th July 2011 at 11:40 PM.
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Old 25th July 2011, 05:53 AM   #8
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I dont quite understand you. You say that regulators inverts phase of AC noise, right? And then the aikido wouldn´t remove this noise? I think it still would remove the noise because, said simplified - the first and second tube will still see the noise from B+ in anti-phase. Or am I missing something?

Last edited by kacernator; 25th July 2011 at 06:03 AM.
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Old 25th July 2011, 03:34 PM   #9
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Quote:
Originally Posted by kacernator View Post
I dont quite understand you. You say that regulators inverts phase of AC noise, right? And then the aikido wouldn´t remove this noise? I think it still would remove the noise because, said simplified - the first and second tube will still see the noise from B+ in anti-phase. Or am I missing something?
Hello,
The B+ noise at the plate of the top tubes is whatever the power supply including the regulator if any puts out. A regulator is good at reducing the noise it makes the precise adjustment of the voltage divider less critical to the overall noise performance of the amplifier.
A CLC Pi filtered power supply works well with the Aikido. Tuning the voltage divider can improve the result.
DT
All just for fun!
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Old 25th July 2011, 04:12 PM   #10
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Quote:
Originally Posted by DualTriode View Post
If you use a shunt regulator that will make the injection of 180 degree out of phase B+ noise belt and suspenders.
DT
All just for fun!
DT,
Still dont understand this comment regarding out of phase noise.
1. Does a salas shunt reg indeed create this?
2. This would be cancelled by the differential setup of the aikido topology, wouldnt it?
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