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    Building, troubleshooting and testing of these amplifiers should only be
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Aikido LV 6N27P SMPS completed

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Last night I finished my new Aikido LV preamp (Aikido LV).

The parts I used:

- Rubycon ZLH 2200uF reservoir cap
- Wima FKP2 0.22uF decoupling caps
- 0.1% matched metal film resistors (all 2W except 1Mohm)
- Ebay smd 100K stepped attenuator
- Russian K71 polystyrene 1uF input coupling caps (one of two inputs only, other one dc coupled)
- Shizuki polyprop in oil 8uF output coupling caps
- Russian 6N27P valves
- Astec LPS25 switch mode power supply (110KHz switching frequency)
- Lucent FLTR100V20 PSU filter

Very happy with the sound so far (many thanks to Mr Broskie!). I have some popping when I change volume, not something I've had with this type of attenuator before. Should be easy enough to fix.


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Solved the popping volume control. The input stage appears to be dc biased at about 60mV. With no source connected, the input rcas have this voltage from pin to ground when the pot is set to full volume, as the volume is decreased the voltage reduces to zero. I added a pair of 1uF russian polystyrene caps between the pot output and board input - no pops at all now.

Very happy with the preamp. Silky smooth but with bass definition and dynamics.


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Very nice project! I like the use of the cast chassis - top mounting the valves makes it look quite attractive.

Clever use of the 2 chassis attached to each other to help shield the SMPS from the circuit. Did you choose to do it this way for lack of an umbilical? Or just a neat way to get good shielding, and you did want it as one unit? Either way, it is a nice execution.

Are the oil output caps the only thing in the top chassis? (Other than the Jacks and switches?)

Again, congrats on a project completed! I wish I could come over and hear it!!
Hi 6L6,

You're right: I used the two aluminium enclosures bolted together to help screen the SMPS and also side-step the need for an umbilical power cable. Also, I can buy these enclosures locally for about £9, so it's a cheap way to go.

The oil output caps and polystyrene input coupling caps (line 2 to pot and pot to board) are all mounted in base of the top enclosure.

I only really use input 1 which is dc coupled to the pot, so the signal only goes through one set of coupling caps on the way in. All of my sources connect to a AK4393 dac with passive transformer outputs so one preamp input is fine.
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