VTA SP12 and PH12 Build Thread

Thought this was interesting.

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If you guys could go back in time and buy one of these preamps again... Would you?

Sorry, not trying to stir up trouble. I've been looking at Pre-amp options for my ST-120 Amp for a while now... I was thinking of doing one from www.tubes4hifi.com but this thread has me wondering..

mantha3 wrote:If you guys could go back in time and buy one of these preamps again... Would you?

Sorry, not trying to stir up trouble. I've been looking at Pre-amp options for my ST-120 Amp for a while now... I was thinking of doing one from www.tubes4hifi.com but this thread has me wondering..

Yup, me too. Bottlehead or Audio Note may be a better choice for me even if the overall quality or design is not as good.

edgobb wrote:
I do, however have a concern about the extra transformer. I'm not sure what kind of current rating I'll need to power this up and test it. The Antek has two 250V taps @ .2A. They are in wired in parallel to my rectifier tube input. The extra transformer is 250V @ .1A. Is this unit going to draw too much current? (I think that peak plate current of a 12X4 is 245mA, so if I'm just testing it without any source input it should be fine? I'm sure that someone much wiser will school me if I'm confused.)

My unit draws roughly 37mA, so you should be okay with that transformer. Make sure you have enough heater current though - far more current demand there.

If you are getting interference from the toroid, you may want to try tweaking your layout. I positioned my boards such that the audio circuitry is far away from the trafo:



Ignore the extra (ground loop forming) ground lines on the SP12 and PH12 mounting holes - an experiment that didn't pan out.


Regards,
JP

WntrMute2 wrote:

mantha3 wrote:If you guys could go back in time and buy one of these preamps again... Would you?

Sorry, not trying to stir up trouble. I've been looking at Pre-amp options for my ST-120 Amp for a while now... I was thinking of doing one from www.tubes4hifi.com but this thread has me wondering..

Yup, me too. Bottlehead or Audio Note may be a better choice for me even if the overall quality or design is not as good.

I would.

I attribute half my issue to some cold solder joints. I heard Heathkit and Dynaco used to say 99% of the issues with their kits were related to cold solder joints. The PS ripple could be a special circumstance - I do have over 50 lighting dimmers, 20 switching power supplies, etc. in my house, and to top that off my AC waveform is clipped. I'd attach a pic from the oscope but I'm in Beijing at the moment. Also keep in mind Roy added a regulated B+ supply to the SP12 - ours are the previous, unregulated design.

Ground loops could happen with any kit - they're a system issue, and there is no end-all, be-all solution.

Really, you should discuss your concerns with Roy. I've no doubt he'll address all your questions and concerns thoroughly and honestly.


Regards,
JP

If you guys could go back in time and buy one of these preamps again... Would you?


I can't speak for Josh, but I know that for me the timing of everything is working against me right now.

I am by no means an expert, and I am sure that a 15 minute phone conversation with Roy would arm me with a whole list of things to experiment with. HOWEVER, the completion of my project just happened to fall in line with Roy's vacation. I've been documenting my experiments with getting the hum stopped in the spirit of continuing this thread. Had Roy been around for the last 18 days I'm sure that my luck would have been better.

Thus far, Roy has been a great help and I am sure that he will continue to be when he returns and gets caught up with the stuffed email box that is awaiting him.

I, at this point, do not know. Until the saga plays out and I get the problem fixed I can't say for sure.

I would suggest that folks resist the temptation to have have a knee-jerk reaction to my experience thus far. Chances are that I did something elementary and stupid that my novice eyes overlook again and again.


FWIW,
Ed

edgobb wrote:If you guys could go back in time and buy one of these preamps again... Would you?


I would suggest that folks resist the temptation to have have a knee-jerk reaction to my experience thus far. Chances are that I did something elementary and stupid that my novice eyes overlook again and again.


FWIW,
Ed

Here, Here, well said. This is the nature of DIY and I for one thank you for your dedication to document your trials and tribulations through to the end, I'm sure you will find a solution. Smooth seas do not make skillful sailors.

Hi Ed and others,
I'm back from vacation.
The hum isn't from the transformer, I've been using these for about 5 years now and they are alot quieter than other types.
John, thanks for your input and photo. Ed and John both bought their SP12 kits at the same time, John got his together in about a week but then spend a month tracking down the noise and rewiring it.
Most likely the hum is 120 Hz power supply noise, but it could also be a ground loop.
Impossible to say without seeing the preamp and listening to it.
There never seems to be a "magic cure". I've build 3 of these SP12's myself (along with about 30 SP8 preamps) and only had one or two (of the 30+) that ever had noise issues. Finding the cure is always difficult, and almost always turns out to be something incredibly simple that was overlooked.
Anyway, Ed, as I mentioned before, try running the SP12 board just by itself, with an MP3 player (battery powered) as input. That will eliminate a possible source ground loop, and any extra load on the filament supply. The SP12 should be absolutely total dead quiet by itself.
The PH12 phono circuit has about 50db of gain, and so of course that will add hum and noise for sure, but the last one I built a month ago was quiet enough that I couldn't hear it unless I had the volume more than halfway up with no input, and my ear within 1 foot of the speaker.

Sorry if I offended anyone with my "would you do it again" question... I am honestly in the market for either a passive/line Stage/preamp... I've been watching this thread and enjoying watching the build. It looked like you were putting on a clinic on how to do it right. I'm sure you will get this worked out with time.

JP,
You mentioned the "50 lighting dimmers, 20 switching power supplies". You could try putting your speakers or some smaller booke shelf speakers (assuming these have the hum) if you have em, your amp and the new preamp in the back of an SUV and run to a buddies place to see if the hum happens... Maybe work... Perhaps just have this in the back of the suv with a power strip and then run the cord into a garage outlet... Just so you don't have to pull all the stuff out of the ride. Just run a quick test.

Good luck and keep us posted.

mantha3 wrote:
JP,
You mentioned the "50 lighting dimmers, 20 switching power supplies". You could try putting your speakers or some smaller booke shelf speakers (assuming these have the hum) if you have em, your amp and the new preamp in the back of an SUV and run to a buddies place to see if the hum happens... Maybe work... Perhaps just have this in the back of the suv with a power strip and then run the cord into a garage outlet... Just so you don't have to pull all the stuff out of the ride. Just run a quick test.

Good luck and keep us posted.

Thanks, but I'm all good. I added additional filtering with Roy's help as I mentioned in post 73 - my SP12 and PH12 are dead quiet, and sound wonderful.


Regards,
JP

Whoops.. What I said I think I directed to the wrong person. I meant that for jjones3318. Good to hear you got your preamp worked out and it is performing. Good to hear you are happy and that Roy got you on to a fix.

I have also been thinking about this pre and have been following the posts. I do not see any posts about adding additional caps for filtering. What did you actually do to stop the hum?
Thanks

Apologies - it was post 74, not 73:

jjones3318 wrote:
I eventually figured out that my hum was not 60Hz; it was 120Hz, which I read was probably power supply ripple. I strongly suggest you search the net for an online signal generator or sound files you can download of 60Hz and 120Hz sine waves to compare to the hum from your preamp - it's very helpful to know what frequency the hum is.

From there the game was improving PSU filtering so I put a choke in the place of R17 (Hammond 155J) which eliminated the hum from the SP12, and significantly reduced it from the PH12. To get rid of the rest of the hum from the PH12 I put another choke (Hammond 156G) in series from where I took the B+ from the center of the AIKIDO board, followed by paralleled (2) .33uF Nichicon caps. That did the trick.

One of my hum/noise issues was due to some cold solder joints on the board. The other I isolated to being 120Hz, which was ripple on the B+. After adding the extra filtering noted above, I can't hear any noise at all from the AIKIDO, and only a little from the PH12 when I get to step 22 of 24 on the attenuator - this is with no input.

I'm very pleased with the SP12/PH12.


Regards,
JP

Thanks, I see that I had missed that post.

Mike

thanks for the extra comment John, this is just a reminder that tube preamps are alot more fussy and prone to problems than simple tube amplifiers, and that these are DIY projects. I know John and Ed have spent alot of time getting them done, but as John has mentioned,
he is very happy with the finished results. Also, combining the SP12 with the PH12 using the same power supply did add more current demands and thus more ripple which was cured by adding a choke and capacitor to the power supply.
The combination for a complete kit is about $800, for your own labor you wind up with a nice preamp that would have cost you at least
$2000 and possibly $3000 for comparible results.

Ed, have you made any progress?

OK. I've been traveling, but am back and determined to get this thing figured out.

Roy gave me some reference voltages to check at various resistance points in the circuit and everything seems within acceptable range.

Given people talking about B+ ripples and so forth, I realized that I again have a lot of studying to do. So off I went. I now feel like I have a decent grasp on the power concept.

I don't have a scope, but I read about a dirty way of reading a B+ ripple is to take the reading using a DVM and looking at both the DC and AC readings. So my B+ right off the rectifier board is 316vdc and 32.5VAC. So if I use some division, I learn that that is a little more than 10%. Now here I need a little education from the masses...That AC reading is an RMS value, correct? In order to identify the ripple do I need to convert it to P-P? If I do, that puts the percentage to 29.1%.

So being a guy who knows only enough to get in trouble, would we say that I need to filter my power? Is my hum a B+ ripple problem?

I'd love to hear your thoughts.
Ed

Is it 120Hz?

Ed,

I believe you are correct, if your meter doesnt read in RMS, multiply by 3 to get the aproximate value. As to what the value should be, based on some reading I've done, I would think less than 1% would be closer to the allowable ripple.

Ive found this interesting video for the folks who are not that versed in what power supply ripple is and how the various components interact. Kinda long but informative

Ed and Josh
I feel your frustration. I've been working one on of Roys creations. It has toroid, reg power supply, sp5 # sp6 boards and the same hum you are trying to figure out. Mine took a trip back to Roy ( super fellow) and I have tried shielded wire, different tubes, even hum isolator, made it much worse. I am running it with one of Roys st36 ltd 36 watt amps. Hi eff speakers. Put my old yamaha pre back in and all is dead quiet. I have asked the creator about chokes in mine. Hope someone gets this figured it out. Doug

John J,
I tried to find some of your old emails, but I wasn't sure if you were measuring AC on the outputs or AC on the B+ power supply,
I see you still had about 2vac when you were still trying to reduce the noise.
I don't currently have an SP12 myself (maybe I'll need to build another one next week, this week I've got to finish up an SP9 for a customer).
Maybe you could take some AC measurements on the B+ and let us know what you get.
I'm certain they should be under 100mv of AC.
Roy

I apologize for not posting in a while. In early march I bought a 25 year old BMW and it's been taking up my project time almost every week while the SP12/PH12 sits on the back burner. Compared to electronics, cars are EASY!

tubes4hifi wrote:John J,
I tried to find some of your old emails, but I wasn't sure if you were measuring AC on the outputs or AC on the B+ power supply,
I see you still had about 2vac when you were still trying to reduce the noise.
I don't currently have an SP12 myself (maybe I'll need to build another one next week, this week I've got to finish up an SP9 for a customer).
Maybe you could take some AC measurements on the B+ and let us know what you get.
I'm certain they should be under 100mv of AC.
Roy

I've 1.9vac right off the 12x4, and 12-15mv on the taps at the center of the board.

thanks much for the info John, so you and I have both built this preamp and it turned out "dead quiet"

John, I do believe that it is 120Hz. I think that I am ready to follow your previous instructions and get chokes in the circuit as you did.

ed