VTA SP12 and PH12 Build Thread

After finishing my ST-70 rebuild, I figured that I needed to continue on and build a great preamp. After looking around and also being so impressed with the VTA board in my ST-70, I decided to bite the bullet and buy the best preamp and phono stage that Roy Mottram at Tubes4hifi.com had to offer.

I ordered the kits for the SP12 line stage pre and PH12 phono stage, along with the 16" chassis kit, tube rectifier option, and SE upgrades. The upgrades get you stepped attenuators for volume and gain controls, along with some higher quality caps and resistors. The whole setup sells for just short of $1000.

Hopefully folks on this great forum can get an idea of what it's like to build this kit and also provide me with some help when I solder myself into a corner.

I have been building for a few days, so I have some catching up to do on this thread, so here goes...

Thus far Roy has been great to deal with and very helpful.

Here is the box as I received it:



Here are some pics of unpacking and inventorying:
















That's all for tonight, it took me much longer to get these hosted and appropriately sized to use on this forum. As many of you know, the image posting here is a little goofy. I'll get the rest on tomorrow.

Best to all,
Ed

Appreciate you taking the time to share.

Thanks for posting the pictures. I'm anxious to see your progress.

Mike

The first thing that caught my attention as I got ready to begin this build was the very high quality of the PCB.




This thing is really thick and sturdy as well as double sided. It has plated through holes with pads on both sides and is beautifully printed. Because of the thickness and different sizes of the holes component leads it took me a few components to get the soldering iron temperature just right. At first it was too cool and after I got the solder to flow it was layering on the opposite side of the board.

I am typically an over-engineer-er and err on the maybe-too-much-solder end of the spectrum, and I had a real tough time (given my relative inexperience) having a consistent finished look on the opposite side of the board.


Here it is with resistors installed:



Although the instructions suggested soldering the components in from their top side, I chose to solder on the bottom, as I'd rather have the flux splashes and marks on the underside and out of sight.

I decided to install the resistors with the tolerance color band uniformly to the right and oriented the Dale/Vishay and PRP resistors so that the values were easily visible and facing the same direction. (Who knows when I might have to trouble shoot??? )

You'll notice that the resistors aren't installed in the top left High Voltage B+ area of the board. These are unnecessary because of the tube rectifier option that I will be using with this pre. (The diodes in that area are left out as well.)

R18 is not yet installed because a design change from Roy's PCB supplier created a need for two R18s in this circuit rather than one and I am waiting for the part to arrive.

On a totally dorky note, one of the resistor values is 909 ohm. This immediately got The Beatles singing "One After 909" in my head and that kept me haunted for the rest of the evening while I worked. (And typing about it has done it again...so great.)


Next went in the diodes and tube sockets:



I installed the diodes, being careful to orient them properly.

The quality ceramic tube sockets went in very easily, without any bending or adjusting and getting them level and aligned was almost effortless. I first soldered pin 5 on each socket, checked them for levelness and "twistedness," and soldered in pins 1 and 9. From there, I made sure that they were all exactly where I wanted them and then soldered in the rest of the pins.


I next installed the capacitors, starting with the lowest profile components and working to the tallest.



The white ones are the upgraded SoniCaps and I got so excited about getting them in that I had to go back and put in the little 1000pF guys that reside in the heater voltage section of the circuit back in the right hand corner...lest my anal mind do things out of order and eventually explode.

After I got the other axial caps installed I moved to the radials in the heater voltage section. (Brown ones.) Because this PCB can be used for several different circuits, there are two options for the orientation of C12 and C13. I studied the schematic and the PCB circuit and it looked to me like the orientation should be left to right. I confirmed with Roy and had myself a "I actually am learning something!" moment.


Here are the photos as I added the rest of the capacitors:






From there it was a simple matter of getting in the heater voltage regulator and heatsink:



It is easier to install the regulator and heatsink all as one piece and Roy sends it already together. I had to muscle the heatsink in there and it was a little scary, but it worked out fine. I soldered it in and there you have it!

After one last look to double check the symmetrical consistency, my next step will be to install the jumpers and the R18 resistors and then get started on the phono stage.

My future posts won't be this long as I built more than I posted but am now caught up, so I promise not to be so tedious on your brain from here on out.

BUT one more thing...
Roy has the chassis made to order, so the cool thing about it was I got to choose if I wanted a tape loop and mute switch. Roy sent me pics and we talked about my needs and then off the chassis went to be drilled and printed. I thought that was the bee's knees, man! (I always wanted to say that.) It should be ready sometime this week and am really jacked to get it.

So thanks for following along and feel free to comment and suggest, I'm in this to learn, have fun, and listen to great music.

Cheers,
Ed

My SP8 has yet to be dusted for the first time, and already I'm wondering about my NEXT pre amp: an SP12?

I must . . . resist . . . asking Roy . . . for a .. . comparative .. . analysis.

HI
I asked roy about a crossover in one of the preamps roy said. (Do you have the circuit for the crossover?
no problem adding the circuit if you've got it - otherwise it's something I can't do,
it would take dozens of hours to design something like that, it would have to be an active electronic circuits most likely using ICs and lots of filters).I don't but maybe one of you know a easier way. This is what i was looking for it would be great for small satellite speakers with a powered sub or for biamping your mains(with a stereo sub out).Maybe if there is enough request for something like this it would make it cost effective to have as a option.



https://picasaweb.google.com/118085165278786462832/DropBox?authkey=Gv1sRgCMvek-vKr_zHDg#5579569311173317202

there are several commercially made preamps that have that type of crossover system, although typically something like that comes as part of an expensive subwoofer system. A preamp having those features is usually going to be in the $3000++ price range, and so I thought MAYBE you might have one and wanted to extract it and put it into one of my preamps, which would be a relatively simple thing to do. But as I mentioned, something like that designed with tubes would be extremely expensive. I know Audio Research used to have something like that about 25-30 years ago, it cost more than a new car would. Using a couple of ICs on the other hand, something like that could probably be made for about $100, if someone wanted to spend hours researching the net and/or manufacturers catalogs of analogue IC circuis.

OK people, now here is someone that obviously knows how to put together an electronic project !!
See, it is NOT so hard! Commmon sense! Resistors and diodes first, leads neatly bent and fitted to the right length to fit into the holes (which were designed to fit the parts, so why do so many poeple screw that up?)
then the larger parts, and YES, soldering ONE leg of each tube socket and then making sure they are flush and level and not twisted or cockeyed, then the larger caps. Proper amount of heat and solder. Too cold, solder doesn't melt within 1 or 2 seconds, doesn't flow. Not enough solder, doesn't fill pad. Not enough heat, or for not long enough, solder doesn't flow thru hole as it should. Not soldered long enough, leaves a dull finish and a DOME shaped to the solder. Proper heat, solder iron on BOTH the PCB and on the part, solder melts in about 1-2 seconds, leave iron on about 2-3 seconds more, adding enough solder to let it flow around pad and thru hole, then remove solder but leave iron on for another 1/2 second, and you wind up with a nice shiny solder connection that just covers the pad, leaves a convex? slope, not a rounded dome. Not rocket science, just a little bit of practice!!
If my words don't cover it, I've found at least a dozen videos of how to solder properly on YOU-TUBE.
GREAT JOB Ed !!!

Wow, thanks Roy! I appreciate the support. I'm having a great time building this thing.

Now onward!

I haven't had too much time to build this week, with the little one starting soccer and all, but I did finish the line stage and inventory the parts for the PH12 phono stage.


Here is the SP12 with R18 and jumpers in place:



Adding the R18 resistors was no biggie and I checked the schematic and verified with Roy that jumpers 1, 3, 4, and 6 are used in this application. The jumpers route the current to the heater filaments of the tubes, (valves for the North Americanally challenged) and that needs to be correct.


Here are the parts for the PH12 organized and ready to go:



I should start building that either tonight or tomorrow and it should go together rather quickly. This PCB isn't the same stock as the SP12. The component numbers aren't printed on the board so I'll have to rely on the diagram, but no problem.

Roy has let me know that the chassis parts are complete and the kit is on its way to me, so hopefully I'll have it in hand for the weekend. If all goes well I'll be listening to this thing pretty soon.

I'll have to decide exactly how I'm going to work the grounding. Also, if anyone has any suggestions on some good shielded cable to use for the internal phono connections I'd love to hear them.

Good times to all,
Ed

Keep us posted on the progress! Thanks for taking the time to do so.

for phono cabling you can use RG174 or S-video cable, or buy a cheap stereo interconnect and cut the ends off, it's small and flexible and shielded. DO NOT use microphone cable!
You should be able to find shielded cable that is only about 1/8" in diameter, none of that huge 1/4" stuff !! I used to have 100' roll of S-video cable that worked fantastic for phono wiring but have finally used it all up and looking for something good that's not crazy expensive since alot of places only sell this stuff in 100' or more rolls.
Once I find a good source I will start supplying it again with the phono kits.

I haven't turned on the iron for a couple of days. Life's been getting in the way, but I have been thinking about it almost endlessly.

I've been trying to better understand the entire concept of grounding; different methods and theory, etc.

I sent Roy a a link forum post about it as I was further torturing him with questions, and he pointed out a link on that page. I thought some might be interested in it, so here it is. http://www.diyaudio.com/forums/diyaudio-com-articles/163575-audio-component-grounding-interconnection-2.html

It is pretty well written and informative.

As to the shielded cable, one fellow also suggested pilfering a tonearm cable from somewhere. Interesting idea, I thought.

The chassis and parts are on their way, so I've got to get this thing finished here pretty soon.

ed

OK. I finally got to work on the PH12. I put in some resistors...




This is a much more delicate build than the Aikido board. Much lower heat and much less solder. and much smaller parts... Dealing with the 1/4 watt resistors makes it more difficult to get things aligned perfectly. I'll hopefully get another dent in it tomorrow.


I got sidetracked today and breadboarded a VU meter using an EM80 magic eye tube and hooked it to one channel of my VTA ST-70. It was pretty cool, but I'm wondering if my original transformer can handle the burden of two more 6.3V filaments. But that is an entirely different thread!

Anyway thanks for reading.

Ed

Got another dozen resistors in tonight. Resistance is not a futile as was once believed.




You'll notice the asymmetrical resistors in there... That little swap seems to be the only non-symmetrical instance in the entire preamp. Just enough to plant the seed in my mind that may ultimately be my undoing.

I am building for a MM setup on this one and don't plan on switching, but it is possible to configure this stage to switch between MM and MC with the addition of an additional header and jumper.

Finally, be sure to close your eyes for that brief moment when you snip off the extra lead length after soldering. 'Nuff said.

ed

Thanks for giving us such an easy to follow "tutorial" on building an SP-12. You have inspired me to order my own SP-12 kit(after a fashion). I am hoping to be able to count on you to show pictures of completed unit before you close it up.

I didn't want to hijack your thread, but I wanted to post my experience ordering from Roy. I hope anyone on the fence considering dealing with Tubes4HiFi will read my post here. https://dynacotubeaudio.forumotion.com/t694-my-new-sp-12

Tonight I finished up the resistors and started in on the much needed capacitance.

Here's what she looks like right now:




Things are coming together very nicely. As I mentioned earlier, I've got to be really careful and take my time to get everything just right. Even though these holes are plated through with pads on both sides, they don't seem to heat quite as uniformly as on the Aikido board, so I've really got to be patient. The fact that the leads are different for the various components (1/2 watt, 1/4 watt, 3 watt, Dale/Vishay, MF, and etc.) are of different thicknesses and possibly composition makes each solder point different from the last in many cases. There was a time in my life, not so long ago, when I would not have had the necessary patience to keep this a neat build. Oh, and those 1M Dales on the right hand side were a little tight because the holes were just a tad close. I had to bend the leads right up against the resistor and even then I had some reshaping to do.

Anyway, I'm stalling a little because it looks like my chassis and final parts won't arrive until Thursday and who knows what kind of trouble I'll get into if I have a night without anything to do...

You know that huge box of wires and connects and power adapters and hard drives and USB cables and network cables and coax and blah blah blah that most of us seem to have in our closet? Well I found a four foot long, double wire S-Video cable in there so I have eight feet of shielded cable to use for the internal wiring of the phono stage. Is it a good idea to use shielded cable on the tape loop internals as well?

Alright, I'm off to study all of the wiring diagrams that I have so that I can get a clear picture in my head of how I'm going to wire this thing into the chassis with tape loop, mute switch, and the three attenuators. Plus I've got to get B+ and filament voltage to the tube rectifier and both the SP12 and PH12.

later,
ed

I like Ed's internal monologue. I had the same thing going recently on my "Epperson" FM-3 project. Its DIY "therapy". Worked for me.
Talk it through then visualize it all, then do it, sometimes up to three times to make it perfect. I love my hobby.

So I finished the PH12 tonight.

I got the rest of the capacitors in, along with the JFETs and sockets.


Here is the finished product...



Everything went very easily, with only a couple of delicate moments. Below you can see the careful bending of the leads that needed to be done for this particular board. The capacitors will not need to be adjusted for future instances of this PCB, as Roy has made a design change for the next run. As for the JFETs, well...it is what it is.


Behold:




Here is everything ready to go into the chassis...



I resisted the temptation to get the twisted wire pairs in place. I decided it was a better idea to just wait until I have chassis in hand. Which, incidentally, will arrive tomorrow. I received the knobs today and FedEx is taking their own sweet time getting the chassis kit and transformer to me.

The knobs are very nice quality, solid aluminum and pretty substantial. I really like them and will include pics in my chassis post. Only problem is that the set screw on one of the knobs got free during shipping and scratched up the surface of one of them. I'm still trying to decide if it is an imperfection that I can live with...


Here's a goofy flyover shot of the line stage, just for fun.



Other than that, I'm excited to get the chassis tomorrow and get this thing finished. I'm already experiencing a little of the "end of build" depression. No matter how jacked I am to finish a project, I always have this little part that is sad it's over.

Happy ashy, lenten hump-day,
Ed

I got the chassis kit and associated parts today!!!

Everything looks pretty cool, but I didn't have much chance to build tonight. Here are some pics of all the unpacking joy. As many times as I looked at this thing online, I was still surprised at how big it is. I stuck a Pepsi in a couple of them to give a little perspective.


Here we have front and back panels.




Here's the ever exciting top:




From there, I direct you to the transformer view...




And the Pepsi Max front panel shot:




And also a likeness of the associated parts; attenuators, RCA jacks, switches, knobs and etc...



All I did tonight was to halfway install the right channel RCA jacks into the back panel. Here are the things that I learned. First, I think it would have been easier to tighten each jack down with its final tightening before moving on to the next one. I chose to put them all in there and hand tighten them and then come back through and torque them down. I will be doing them one at a time on the left channel; it gives you more freedom to position the wrenches when the jack isn't boxed in on both sides with other jacks. AND if I had to do it all again, I would do the left channel first, because the ground tabs from the right channel jacks are going to be in the way as I do the left. It is tricky enough to get everything aligned the way that you want it without having to deal with self-imposed obstructions.


Here they are from the outside:



I'll get an inside photo up when I get them all in and aligned.

I was confident that I had thought the chassis wiring stage through, but now having everything in front of me has raised a few questions. I need to decide where I'm going to ground the magnetic shield wire from the transformer. I've also got to figure out how to have the tape loop work along with having "tape" on the selector knob. The stepped attenuator volume is a pretty unique creature and I've got some figuring to do on how that guy is wired in there, too.

As for that end of project depression? Well, I'm suddenly a bit overwhelmed with how much work there is to do on this final stage...so everything is back to normal.

ed

If you have access to a set of deep socket wrenches, it will make the RCA jack installation much easier.

Best Regards,
Charlie

this is the latest and greatest version of the SP12 preamp (with PH12 added), lucky Byron H. get's this one.
Frank S. is the next lucky guy, then I'm done for the month, and off on vacation for a couple of weeks . . .
need a break, can't keep up . . . . apologies for any delays . . .
latest SP12-SE preamp

OK, moving right along...I've been building more than I've been posting so this will be a larger post. Please feel free to make suggestions or observations, as I'm in to learn as much as I can.


Here is the back panel with RCAs complete...kind of.



I am going to readjust the ground tabs so that I can use one ground bus in the middle instead of two. That process is a bit meticulous. I'll add a pic after that change.




After that I added the fuse and IEC AC input, and ground screw.





From there I put the resistors into the balance attenuators.





To build these, I started by putting in the resistor bridging posts 1 and 2, and 2 and 3 in first. Then I soldered the shared post (2). Here is a pic that I stole from Roy since I forgot to take a pic of the process.




From there I went counterclockwise, alternating the placement of the next resistor lead over or under the previous one. That created the two layer effect that you see in my second picture. (Only slightly higher so you get a two layer effect with a little path running down the middle. Ni!) I gave the leads that share the post a little twist to hold them in place and then soldered. I left the resistor leads from posts one and twelve unsoldered so I'll only have to solder that joint once when I wire. Mine ended up a little closer to the attenuator posts than Roy's handy work.


Next, I installed all the hardware on the front panel which includes three stepped attenuators, three toggle switches, one selector switch, and the LED. (I'm looking for a blue LED to replace this one cuz I think that blue LEDs are cool.)






Then I put on the rubber feet.



I put a washer under the screw on the outside and used kep nuts on the inside.


After that, I temporarily attached the front and back panels so that I can mock-up what I want the inside to look like before I drill.






From here, I drill the chassis bottom and get started on wiring. I'm having a great time and can't wait to hear this thing.

Ed

fantastic job Ed, I should have you building more of these for me, maybe between the two of us I can keep up with orders.
Nice job on the attenuators too, and I didn't even give you instructions on how to do that!!

I had a day where I could get some work done and progress was made.


Today I twisted wire pairs:





I had the expert help of my five year old son, who is a certified power drill operator.

After that, I needed to get the holes in the bottom of the chassis drilled in order to mount the PCBs. I didn't have a template, so I mocked-up how I wanted it set up and devised an original plan. I used my son's dinosaur rubber stamping kit to "stamp" the location of the spacers onto a piece of paper. I then center punched each hole and dotted the chassis with drill marks using the ever popular Sharpie marker.






Then I drilled...




I then went back and adjusted the ground tabs on the RCAs and prepared for bussing:



A true test of my patience, it was. Trying too hard to make it all perfect supplies my demise more often than not. Eventually serenity prevailed over calamity and I finished with only minor scrapes to the panel.


Then I bussed:



You'll notice that the points get cleaner as you move to the left. Stupid learning curve.

I surmise that Roy is right handed because I do everything in the opposite direction than him with my lefthandedness.

Things are flying along now...the way I figure it though, I'll finish just in time to leave for the weekend trip we have planned with my family. So while I'm sleeping on the ground in the woods, my new toy will not be burning in new tubes.

Anyway, THANKS ROY! and more tomorrow.

Give peas a chance,
ed

Welcome to the next installment of this preamp project.

I spent some good building time last night and tonight. My plan of attack from here was to first complete as much as possible on the front and back panels before permanently attaching them to the chassis.

I started by wiring the AC input and fuse and affixing the ground wire.




Pretty simple. I then figured out where to put the terminal strip that will get juice to the transformer. The toroid transformer is set up to wire the primary coils for either 115vac or 230vac depending on whether you wire them in parallel or a series, so a terminal strip is used for the input wiring. You can see the white and black coiled pair.




At this point I applied power to the transformer so that I could test the output voltages. There are two windings for HV 250vac and two filament windings at 6.3vac each. You can see where I wired the filament taps in series to get the necessary 12V...just haven't shrink tubed it yet. Turns out this puppy was putting out 13.5vac, which is ok for the regulated tubes on the stages, but a bit too much for the 12X4 rectifier tube. I will have to add a resistor to drop the voltage on its way to the rectifier.

I took on the front panel next, wiring everything that I could while still leaving out the input to selector switch wiring.


First the attenuators:



The volume stepped attenuator was pretty much brain surgery for me. A lot of detail work packed into a small area. Sometimes soldering is like caulking the trim in your house. I eventually had to scream at myself; DON'T GO BACK AND TRY TO MAKE IT LOOK BETTER! You'll only make it worse.







I bumped and scorched the PVC on a couple of wires and had to re-do. But overall it turned out OK!

I will be using my reel to reel in this new setup, so I am wiring in the tape loop with a monitor switch.


Here's the signal path from the selector switch through the tape monitor switch and into the attenuators...




And finally the completed front panel.



From here I will get the interconnecting PCB wiring completed as much as possible, and finally move to the signal wiring.

I'm off to camp in the desert for the weekend, so my project will have to get along without me until either Monday night or possibly Tuesday. I hope to be having my first listen in about a week. (and not my first troubleshooting.)

Thanks for following along and feel free to chime in on anything.
Ed