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Old 9th October 2007, 03:31 PM   #1
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Default Aikido problems!!!

Have built Aikido on old National chassis before using the circuit board version. Hooked it up and lots of noise. Looked at it on scope and it is power supply 120HZ. The power supply is 270vdc with 1.6vac rms ripple. I thought that the Aikido had excellent PSRR. I am measureing 150mv ac at the output. Looked at voltages that I could find on Tubecad and they look ok as far as plate voltages being 1/2 of supply and cathode's being a few volts. I did this pretty quickly and did not use shielded cable on input wiring from input through volume to input of tube 1st stage. Looking at the voltage coming from 1st stage out i can see the 120hz at about a 1/3 rd of the level of ripple at the B+ connection at that tube. Any ideas. Tempted to just go ahead and build the board, but would like to understand first. Have noticed some typos on resister values on instruction sheet , does anyone know if the website has the latest values updated.

P.S. I am using AC heater voltage but this would be 60hz.

RG
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Old 9th October 2007, 04:40 PM   #2
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You're breaking into the ripple loop in your power supply. A photo or two showing layout details would be useful. The collective wisdom here is usually sufficient to uncover the hum demons and exorcise them.
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Old 10th October 2007, 03:07 AM   #3
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Not sure exactly what you mean by "breaking into ripple loop" but your still talking of PS noise injected into circuit. The point is that the Aikido is touted as having excellent power supply rejection. Broskie claimed 30db with no tweaking on his first try at it. If I correct 30db should be about 1000 times less and i'm only getting about 10db. I've also noticed other posts commenting on hum issues with Aikido. I figure that there has to be alot of other people that have built this pre and can comment.

RG
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Old 10th October 2007, 03:37 AM   #4
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All the power supply rejection in the world won't overcome a grounding problem.

30dB as a voltage ratio is 31 times, not a thousand; that's a more realistic number and almost certainly what JB meant.

FWIW, I've built two Aikidos using JB's boards and they were as quiet as any line stage I've used.
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Old 10th October 2007, 08:37 AM   #5
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Sounds like I struck a nerve. I'm not disagreeing with you just trying to understand the problem. I originally thought it was 32 times and then confused myself by reading the explanation on wikipedia!! If the problem were related to grounding issues i.e. ground loops then it would manifest as a 60hz problem. It being 120hz means after the full wave rectification. Correct??? BTW this is a P2P wiring project wired to the sockets directly for most of the project. I was going to try it before I wired the board. Maybe that would be the best thing to proceed with the board. The ones you have built, did they use SS power supply or tube rectifiers? Thanks for the insight.
RG
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Old 10th October 2007, 08:47 AM   #6
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Grounding can manifest as high frequency oscillation - which in turn can modulate mains/supply hum directly into the tube.
Hum in an Aikido is most likely a grounding/layout issue. The design takes very good care of supply based noise by itself.

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Old 10th October 2007, 11:29 AM   #7
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There's a big 120Hz source in your preamp, just waiting for you to slip up so that it can bite. In fact, there are probably two of them, the HV and heater supplies. And in those supplies are all kinds of ripple currents which try to find their way into your circuit, usually via innocent-looking grounds.

The Aikidos that I built used solid state rectification and regulation.
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Old 10th October 2007, 11:52 AM   #8
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Quote:
The Aikidos that I built used solid state rectification and regulation
Cheater!

No, just kidding!

The Aikido's I built used tube rectification and have no hum.

Extreme caution must be given to eliminate any of those nasty ground loops.
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Old 10th October 2007, 01:35 PM   #9
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This thread is effectively dead until you can show us a photo and give us some details (ie what valves, what power supply, etc)

Shoog
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Old 10th October 2007, 05:51 PM   #10
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I think that i will probably just build the circuit board version. This thread has at least convinced me that I need to build a power supply with less ripple and better grounding config. Thanks everybody!!
RG
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