[JoshK]

i thought i'd up a couple of snaps of the preamp i am working on.  this is a dry fit.  the face has been drilled and tapped but not finished so there is no real screws holding it together. 




the preamp consists of two six input stereo w/ ground seiden selector switches and a seiden volume control switch.  the vc switch will switch a pair of dave slagle autoformer volume controls, avc's.  the first selector switch will allow for 6 inputs, the second will select either volume control only via the avc's, vol plus aikido tube stage or one of two bypasses for home theater and squeezebox.  the volume control knob is on the right, the first selector on the left and second in the middle.

[JoshK]

for scale, the knobs are 2 inches in diameter. they are solid aluminum purchased off ebay.  the case is a parmetal case i bought from a fellow circler with the faceplate removed and the wood used in place. the wood is dark cherry with a lot of figuring.  it looks quite a bit different in the pictures than in person.  not quite sure how to correct for that.

oh, and i used extention shafts with the knobs so that all switches are at the back to keep the signal path shorter.  if i put the power supply for the aikido in this case it will be in the empty front with the ti shielding material creating a shielded box. 

[SET Man]

Hey!

   Nice! Looking good there Josh. Don't forget to take picture of the inside after it done. And maybe you could bring it to one of the upcoming Rave.

Take care,
Buddy

[Gordy]

Beautiful Josh!  I've been ponderin' a tube stage for my S&B's as well, Mike G. is, hopefully, going to post a circuit 'elsewhere' that he designed as an output stage for his eq.  The Aikido looks very interesting though, considering the ps noise cancellation etc!  What amount of gain / tubes are you going to be using? 

Thanks!

[JoshK]

i haven't put the guts in it yet, they are assembled outside and waiting to go in. 

[JoshK]

i built the all 6sn7 aikido, so gain is around 10x.  i don't think i really need the gain for most things, but if i use the sb's analog out, or build the mc phono stage i've been pondering, then having the choice of additional gain i thought might be nice.

[Audiovista]

Way to go Josh   Love the options and flexibility.
To better show texture of the front panel avoid on-camera flash and try side lighting.
Keep us posted!
Boris

[Gordy]

Sweet!  I'm thinking 6dB is all the gain I would be wanting.  Do you think 5751's in the first stage would get me there, still using the 6sn7's?

[JoshK]

Gordy,
6db takes a little bit of thought with tubes since most tubes provide much more than that as gain devices.  The aikido provides gain roughly half the mu of the tube.  5751, that is a 12au7?  If so, that would be close to 10x, or 20db as well.  5687 in first spot would give you ~7-8x.  There aren't many tubes that have a mu of 4, which is what you'd want for 6db.  Some power tubes have that, but wouldn't be ideal for aikido, the 6bx7 has a mu of 8 iirc, but also have pretty high distortion.  About the best bet would be the 12b4, but then you'd need to make your own aikido point to point as you'd need two valves for the first spot since this is a single triode tube.

What some guys do is use a line level output transformer with step down.  Things like LL1676 from Lundahl for example.  Then one can wire it for a 4:1 voltage stepdown.  This will yield some gain and turn the extra gain into current to drive the cables and input stage in the amp.  The Aikido can be modified to do this and do away with the cap coupling on the output, but requires a couple of PSU tricks with stack shunt regulators.  This is something I was thinking of doing, because even with the SB or MC input, I won't need that much.