My Aikido All-In-One Octal 6SN7 Preamp Build

DaveC113 · « **on:** 29 May 2012, 06:51 pm »

This is going to replace my Anthem Pre-1, a fairly highly regarded mu-follower tube preamp with a separate tube rectified power supply. One day the PT went out and started filling my living room with the smell of burning electronics. I was thinking about attempting to repair the unit, but partsconnexion offered me $275 for it with them covering shipping, so I took that deal since I wanted to build a preamp to match my Simple SE amp (in avatar).

I recently spent about $700 in parts and materials to build this preamp, a bit more than I wanted to spend, but it does include REL PCU copper foil output caps, 2 Hammond trafos, and high end passive parts throughout including Amtrans carbon film and Mills resistors. I bought 4 6H8C Russian tubes for the output and 4 Sylvania 6SN7GTA for the input tubes so I will have spares. I am using 2 mono stepped attenuators with prp 1/2W metal film resistors. These attenuators are a ladder/series hybrid with 66 steps of attenuation, one knob for coarse adjustment, one for fine... so my preamp will have 4 volume knobs and a selector switch, lol.

http://glass-ware.stores.yahoo.net/m1mostat.html

I am building it with dual outputs, the .47uF REL PCU caps for full range, and another set of outs with a 2uF Solen cap for subwoofer output, just in case my subwoofer's amp (now or in the future) has a low input impedance. The .47uF cap has a 4.2Hz corner frequency driving my tube amp, but the freq would be too high for a 10k input plate amp...

Here is a link to the user guide PDF, it's for the 9-pin but most all of the parts are the same for the 6CG7 build. I have the Octal guide, but it is more confusing and has more mistakes than the 9 pin guide.

http://tubecad.com/2009/03/13/Aikido%20All%20in%20One.pdf

Here is my BOM, please let me know if you have any comments or suggestions:

mjock3 · « **Reply #1 on:** 29 May 2012, 10:30 pm »

I too am planning on putting together an Aikido preamp in the near future. I was wondering why you are using 2 different tubes? The 6ns7's and the 6H8C for outputs. What does this do?

Thanks,

Mark

JohnR · « **Reply #2 on:** 30 May 2012, 01:35 am »

Are you using one of Broskie's boards? (Or point to point?)

mjock3 · « **Reply #3 on:** 30 May 2012, 02:06 am »

I have the Broskie dual mono boards. For Octal setup.

DaveC113 · « **Reply #4 on:** 30 May 2012, 02:48 am »

Quote from: mjock3 on 29 May 2012, 10:30 pm

I too am planning on putting together an Aikido preamp in the near future. I was wondering why you are using 2 different tubes? The 6ns7's and the 6H8C for outputs. What does this do?

Thanks,

Mark

Hi, 6H8C are the Russian 6SN7 equivalent. You can get them as cheap as $2 each for recent production (80's) or $5 each for 1960's tubes made in the Foton plant in Tashkent. The best are 1578 Melz tubes with metal base, they range from $80-150 a pair on ebay depending on the particulars... too rich for me. I went for the 60's Foton tubes, it was about $27 shipped from Russia for 4.

I am using the 6H8Cs as outputs, they won't affect the sound quality as much as the input tubes since the inputs are the ones doing the voltage amplification. The Sylvanias will hopefully be good input tubes, all 4 have near perfectly matched triode sections, and for $75 for the matched quad it wasn't too outrageously priced. I will be interested to see how the 6H8Cs compare to the Sylvanias in the input position too.

I selected tubes that were close to the gain I needed, actually the 6SN7s have more than I need but it's close enough. I was close to going 9 pin so I could use 12BH7 but everyone seems to agree the octals sound better.

I was considering a dual mono setup, but I'm spending enough as it is!

tull skull · « **Reply #5 on:** 30 May 2012, 03:11 am »

Dave,
Thanks for taking the time to include us in your journey. I will be watching with great interest. I am in the market for a preamp and have had repeated interest in the Aikido.

I noticed in your BOM that you purchased tube sockets, so are you using the Broskie board or???

If you could possible include your thought processes for your part selection and procedures; written at dufus level I would be most appreciative

DaveC113 · « **Reply #6 on:** 30 May 2012, 04:56 pm »

Quote from: tull skull on 30 May 2012, 03:11 am

Dave,
Thanks for taking the time to include us in your journey. I will be watching with great interest. I am in the market for a preamp and have had repeated interest in the Aikido.

I noticed in your BOM that you purchased tube sockets, so are you using the Broskie board or???

If you could possible include your thought processes for your part selection and procedures; written at dufus level I would be most appreciative

The tube sockets are PCB-mount, they will be soldered into the top of the PCB, everything else will be bottom mounted so the PCB attaches just below the top surface of the amp chassis and the tubes stick out the top. I am using the all-in-one PCB, I feel this is a great way to go, with a PCB the "wiring" is done for you and tested, chances are it is a better layout that what you can do yourself unless you are an expert in amp wiring and layout. Even then, there is a chance a PCB is going to be better, it depends a lot of different factors.

As for passive parts selection, definitely spend some time learning about the different types of resistors and capacitors used in tube amps, or just buy the PCB with the all the parts included from Broski. I used Mills wirewound non-inductive in the PS, they are the cleanest of resistor types. Carbon comp is best for grid stoppers (I used Allen Bradley), and I prefer a good carbon film directly in the signal path, which includes anode and cathode resistors. I used prp metal film for the attenuators because they aren't as expensive as Riken or Amtrans carbon film. There are higher end than these even, some Vishay bulk foil goes for $10-$15 each, but like the $100+ teflon v-caps they are out of my budget range. I went with REL PCU copper foil output caps mainly because they were on sale for $50 each, down from $100 and get spectacular reviews. For my tastes I think a copper foil cap will be great. I would read some reviews and choose your poison depending on your own tastes and wallet thickness. Price range is $5 to $500 each.

Tube selection should start with gain, decide what gain you need and narrow down your tube choices according to the specs. I have heard many opinions saying Octal is best for SQ, but tube choice is much more limited.

1MOR · « **Reply #7 on:** 31 May 2012, 08:36 pm »

Dave, thanks for putting this up for all to see. I have the Aikido all in one board, but will be using 12AU7/12BH7 tubes, had a bunch in the stash and will be closely following.

Russellc · « **Reply #8 on:** 4 Jun 2012, 05:19 pm »

Quote from: 1MOR on 31 May 2012, 08:36 pm

Dave, thanks for putting this up for all to see. I have the Aikido all in one board, but will be using 12AU7/12BH7 tubes, had a bunch in the stash and will be closely following.

1Mor!!! Snap out of it! These tubes are a sickness...get thee back to J-fet land!LOL

Russellc

poseidonsvoice · « **Reply #9 on:** 4 Jun 2012, 05:30 pm »

I've got some Octal Stereo boards around as well.

Dave, you should have a real good time with these and they are sensitive to passive parts selection so as you said...do your research!

Good luck and will look forward to your final build.

Anand.

1MOR · « **Reply #10 on:** 4 Jun 2012, 05:36 pm »

Quote from: Russellc on 4 Jun 2012, 05:19 pm

1Mor!!! Snap out of it! These tubes are a sickness...get thee back to J-fet land!LOL

Russellc

Just thought I would cross the tracks and sample the dark side! F5s like tubes I hear........

DaveC113 · « **Reply #11 on:** 8 Jun 2012, 06:16 pm »

Quote from: poseidonsvoice on 4 Jun 2012, 05:30 pm

I've got some Octal Stereo boards around as well.

Dave, you should have a real good time with these and they are sensitive to passive parts selection so as you said...do your research!

Good luck and will look forward to your final build.

Anand.

Thanks Anand and everyone following this thread.

I just got the PCBs in the mail and am going to start on soldering the parts I have onto the PCBs... I'm still waiting on the parts from partsconnexion, it took a week to get the trafos in, and I got notice it shipped a day or 2 ago via UPS so I expect to get the parts in a week or two. Hopefully UPS won't rape me on customs fees.

If anyone has suggestions/improvements/corrections for the parts I'm using now's the time!

DaveC113 · « **Reply #12 on:** 14 Jul 2012, 03:26 am »

Here's some pics of the progress, I hope to put it all together real soon...

poseidonsvoice · « **Reply #13 on:** 14 Jul 2012, 08:01 am »

Now that my friend is beautiful. Love the contrasting woods, super nice.

Best,
Anand.

mjock3 · « **Reply #14 on:** 14 Jul 2012, 12:24 pm »

Dave very nice,

Looking forward to a listening review.

DaveC113 · « **Reply #15 on:** 19 Jul 2012, 11:05 pm »

And it works! One of my cheap Russian 6H8Cs didn't make the trip from the Ukraine, so I started it up with 2 perfectly matched brand new Sylvania 6SN7GTAs in the input position (after verifying it didn't blow up with the HT trafo on w/o tubes). I was worried but had to try it out.

I'll post some pics of the complete preamp. So far it sounds great, no buzz/hum.

DaveC113 · « **Reply #16 on:** 20 Jul 2012, 01:53 am »

Here's some pics, it's driving my SimpleSE EL34 SET amp.

grubyhalo · « **Reply #17 on:** 20 Jul 2012, 10:14 am »

Beautiful!

richidoo · « **Reply #18 on:** 20 Jul 2012, 01:05 pm »

Boyz got talent! Nice work Dave!

I've had octal and nine pin PCBs for a few years, you are inspiring me to get moving!
Rich

DaveC113 · « **Reply #19 on:** 20 Jul 2012, 03:54 pm »

Thanks everyone!

mjock, sounds great overall, but I got a wrong resistor in the heater voltage regulator, it's running a little too high. I'm going to have to put it aside until I get it changed out, should be a few days or so... I'll wait to listen to it for a while before I report on it's sound quality, it was only playing for a few hours so far.

Been looking at that Schiit Bifrost DAC to replace those ancient Audio Alchemy DAC pieces in the pic, and my Trends USB>SPDIF converter...