Aikido Phono Stage with Step-up Transformers - diyAudio
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Old 15th September 2009, 08:37 PM   #1
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Default Aikido Phono Stage with Step-up Transformers

Hello all, I have built John Broskie's Aikido phono amplifier. Everything works as designed. I am using 12ax7's in the gain portions and 12at7's in the cathode follower portion of the 2 stages.

I have received the Lundahl 9206 step up transformers and will use them at a 1:10 ratio. I'm wondering if there is any modifications to the circuit that needs to be done to accept this transformer on the front end. It will be used with a Denon DL-103.

Also I'd like to balance the outputs of the phono stage to better interface with my pro recording setup. I'm not sure what impedence I'd need to use for this. I'll be using edcor transformers in this case since my budget is limited. Any help is appreciated.
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Old 16th September 2009, 12:54 PM   #2
MarkER is offline MarkER  United States
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Default Lundahl/Aikido Combo Works Well

I am using the Aikido phono stage with the same configuration and it works great with the Lundahl 9206 as is (as well as the Lundahl 1681) with a ZYX moving coil cartridge with similar output to the DL-103. No modifications needed, just plug and play.
Can't help you with the balanced output question.
Good luck.
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Old 16th September 2009, 08:36 PM   #3
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Marker,
Good to hear. Could you tell me a little more about your setup? Caps for passive filter/tubes used etc?
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Old 16th September 2009, 10:35 PM   #4
SY is offline SY  United States
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One thing to double-check is that the transient response of the transformer has not been degraded by the rather high Miller capacitance of the 12AX7 input tube. A few minutes with a scope, square wave generator and an attenuator will be worthwhile. You may be fine, but if you see ringing, fixing that will audibly improve things. The Miller capacitance in that circuit will be roughly 150pF.

For the attenuator, you want to show the transformer the same source impedance as the cartridge, as well as stepping down the generator output. Let's say your cartridge source Z is 10R (I don't know what yours actually is). You want to feed the transformer with something like 0.1mV. So if you have a 100k resistor in series with the generator output and a 10R resistor from the "far" end of the 100k to ground, then connect the transformer input to each end of the 10R, you'll be in the ballpark. Put 150pF across the secondary, attach your scope probe, and you're off to the races.

In the case of my MC step-up (a Sowter) and the load capacitance of my input stage, I found that there was indeed some ringing, which cleared up almost entirely when I paralleled the secondary with a 6k8 resistor.
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Old 17th September 2009, 01:26 AM   #5
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Default Two replies

The easy one:
I built both the Aikido pre and phono stage as kits from John Broskie. They use a common power supply (as he suggested they could) which is a Hammond 270 CX to a 6X5 to a CLCRCR supply to provide 300V B+ to both stages. The phono is the 12AX7/12AT7 combo and the line stage is 6CG7; the tubes are Electroharomix. Heaters are DC for the phono stage and AC for the pre; both are referenced to 1/4 B+ as suggested by JB. I used paper in oil capacitors, both as offered by John and others as I had in my spare parts. They are all Russian NOS. The phono stage is hard wired into the pre stage. You can see more at my Audio Asylum profile under MarkER:

The hard one:
Sy-I will try to make the measurements as you indicate. I have the equipment but have never done it and have been meaning to take the plunge. This is as good a time as any.

Last edited by MarkER; 17th September 2009 at 01:35 AM.
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Old 20th January 2010, 12:01 AM   #6
alexg is offline alexg  Philippines
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Hi,

How did the LL9206 sound with your aikido phono?

I just bought a pair of LL9206 to be used on my 12at7/12au7 phonostage, and a Denon 103R MC cartridge.

Thanks.
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Old 20th January 2010, 01:12 AM   #7
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Default Lundahl 9206 w Aikido Phono

I think the Lundahl step ups sound great. If your phono is using 12AT7/12AU7 you probably want to wire it for maximum gain given the low output of the Denon. Of course it depends on how much gain you are getting from your preamp and amp. Good luck and happy listening.
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Old 20th January 2010, 08:20 AM   #8
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Sorry, I haven't checked this forum in a while. I love the sound of the Lundahl's. I first tried it at 20:1 then at 10:1, and can't tell much of a difference. It's truely a pretty transparent little passive gain unit.

After a while though, from switching between the 20:1 into a 12AT7 and 10:1 and a 12AX7, I think I prefer the latter. Seems to have more "oomph" and "punch" to it.
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Old 21st January 2010, 06:00 AM   #9
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I got home around 7:00 pm last night, finished my chassis at around 8:30pm, my Lundahl 9602 was singing around 9:30pm, excellent sound with my aikido phono (12at7 input, 12au7 output) into an aikido preamp (12sl7 input, 12sn7 output). The combination of using the 9206 at 1:10, the 12at7 aikido phono and the 12sl7 aikido preamp, have just enough gain for my 2a3 SE amp.

Sounds excellent and promising with my Denon 103R
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Old 21st January 2010, 06:21 PM   #10
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Very good Alex! Glad to hear your vinyl bliss has begun. How do you like your SL/SN aikido preamp? Seems like that would have quite a bit of gain with the SL in the first (gain) stage of the Aikido.

I also was using a DL103 until my bro tried to play a record while I wasn't home and wound up snapping off the cantilever!!!! It's ok though, he's agreed to pay 75% of what a new cartridge would cost. I'll take that money and add a little more and go ahead and upgrade to a AT33PTG. I've heard much good praise about this cartridge and I'm a detail freak when it comes to music presentation, so it should hopefully satisfy that craving.

Again, congrats on your newly completed setup. I hope it gives you many pleasurable years of music enjoyment.

Joe
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