VTA SP12 and PH12 Build Thread

Ill second that Bob, this is everything good about the internet. Ed, wonderful job an inspiration for sure. I cant wait for your listening impressions on this build.

Nice work, Ed, and nice closeup shots. Makes me want to start on one.
Gord

OK. I'm back from the dirty desert and had a little time to get some wiring done.


First, here's a pic of my view when I woke up every morning on my trip.





And on with the build. My goal is to get as much of the wiring on the PCBs done before I install them for good.


I started by getting the wires on the rectifier board.



I kept the yellow and white wire colors for the HV, as those are the colors out of the transformer. There is a voltage dropping resistor going to the filament voltage, and I might take that one out and reinstall it with less lead showing but I'm not sure yet.


Next I ran the B+ and heater lines from the main PCB to the phono stage.



I also used the heater voltage to power the LED on the front panel. I'm using black and white wire pairs for all low voltage power lines.


Here's everything:



Next will be to wire the rectifier board to the line stage and get the signal input and output wires on the phono stage and the outputs on the line stage. From there I'll get the signal wires in there and put this sucker together. Getting close now.

Till tomorrow,
Ed

avi.inc wrote: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

This is what i came up with i was thinking about two of these do you think this would work?
The FULL RANGE output is designed for use with full-range speaker systems which do not contain a
woofer (below 100 Hz). The passband is 100 Hz to 30 kHz, with an equalization adjustment centered at 2
kHz. Through the application of a smile-curve providing up to 8 dB attenuation through midband audio
frequencies, the performance of the whole system may be significantly enhanced.
The WOOFER output is designed for use with woofers amplified independently of any full-range speakers.
The passband is 40 Hz to 165 Hz when set flat, with an equalization BOOST adjustment centered at 50
Hz.
For systems also incorporating subwoofers, the LOOP THRU output connects to an input of the RDL
ST-CX1S Subwoofer Crossover. The ST-CX2 features RDL’s SupplyFlex power input configuration for
operation directly from ground-referenced, floating or bipolar 24 Vdc power.

http://www.rackups.com/product.php?page=282
http://www.rackups.com/pdf/Data_Sheets/st-cx2.pdf

Avi,

I'm not sure why you are going this way -- are you getting/building a subwoofer, powering it separately with a different power amp?

Do you already have main speakers that you know need the extra -- well, everything that a sub woofer brings?

Unless I'm reading you wrong, it seems you're interested in full-range speakers, but concerned that there's a compromise in the lack of fullness of the full rangers that demands a sub.

If you're interested in single driver full-range speakers, there are some around that really aren't handicapped by any lack of bass.

I believe at least one member of this forum has a pair of Horn Shop horns.

http://www.thehornshoppe.com/

All I've ever heard about these speakers is that they are magnificent.

Alternately, if you have access to a table saw, you can slap a pair of these together with no woodworking experience:

http://www.diyaudio.com/forums/full-range/172605-frugel-horn-mk3.html

This'll be my next speaker build, I've decided.

Alternately, some of the bigger bad boys from the Frugal-Horn website:

http://www.frugal-horn.com/spawn.html

I built the Saburos with very satisfying results. If I wanted more bass, I' build the slightly wider Hiro. A member of the DIYAudio forum reported that his (even bigger)Sachikos were good, but he preferred the quicker sound of the smaller-driver version (Saburo) that he's also built.

30 hours work, about $500 total cost, some wood glue, 5 or 6 clamps and access to a table saw and Bob's yer uncle!

By the way, great pic of a fantastic view from your campsite!

Hi tube nube

I am looking to go this way because the system i have now is used as both a surround sound system and a two channel system. I am not using full range speakers because of small room size. The way i have it configured now is when i am in any mode other then stereo the denon receiver drives all speakers and the st-120 is auto switched off (power).There is a 600watt auto speaker switch that is controlled by the surround mode when in stereo mode the st-120 is powered on and the speaker switcher moves the mains left and right to the tube amp.My main speakers are sunfire crm-2's i like the ribbon drivers and there overall sound but there Frequency Response is 95Hz-40kHz so a sub is not a option.
I am looking to build a nice tube preamp but i need a high pass out of at least 100Hz the sub out could be full range sens the subs are powered

https://picasaweb.google.com/118085165278786462832/20010324#5587749947925959858

First, thanks to Bob and others for the kind comments. I have found threads like this very helpful to me in another hobby and am really enjoying authoring my own.

Second, did you ever have one of those work sessions where you seemed to wreck everything that you touched? This last one was like that for me. I kept bumping things with the iron and forgetting things for some reason. Was I smart enough to just step away and come back later??? Nope. I kept plugging for some reason... Very frustrating. Looking at the photos, it wasn't that bad but I would have liked to not make the mistakes in the first place.


I got the shielded phono inputs and paired outputs on the PH12.







BTW, The power lines to the phono came off the B+ and heater holes right in the center of the Aikido board.


From there the B+ from the rectifier tube was connected to the SP12.



The solder joint could have been prettier, but the more I tried to improve it the worse it got.


Here's the whole thing with the line outs on there.



From there it was just a matter of flipping it over and installing it into the chassis. Of course after getting it in there, I noticed that I forgot to add the wires for the mute switch. So off it came and I wrestled with that for way too long.


Then in it went for good.



I don't want to add a second terminal strip so I'll be splicing the HV wires as they go into the rectifier.

From here all that remains is signal wiring and input power to the PT. Then listen, listen, listen.

Good times,
Ed

Today I had some nice afternoon time to get some more wiring done.

The manufacturer states that the transformer is "specially designed to work on all standard 115V or 230V at 50Hz or 60Hz." This is plays into how the primaries are wired. In our Stateside case, they get mains voltage in parallel.


Here is the terminal strip that I used to get input voltage going.



This method is only used with the Aikido board. In Roy's new integrated design, he has the power situation included so the terminal strip is eliminated.


I then wired the power switch with the .01uF capacitor to curb the ugly popping sound on powering down.



My work's been prettier, but it will suffice.


From there the chassis ground and toroid purple shield wire went to AC ground.




And then the filament voltage to the stages and rectifier.



Note the dropping resistor on the rectifier board.


All that remains is to supply some juice to the LED and the power wiring is complete. This leaves the signal wiring and then listening!

I'm only days away.
Ed

I am building this exact same setup from Roy right now as well. Your posts, pictures, and descriptions have been invaluable as I am not as knowledgeable or experienced as you obviously are. I have Very Thankful indeed.

Can you tell me what value that resistor is where the filament voltage goes into the tube rectifier board? It is hard to see the color of the stripes in the photos.

Thanks!

Joshua

Joshua,

It is a 3.3 ohm 1W resistor. The rectifier tube pulls 300mA, so you can use Ohm's law to calculate. In my case the transformer was putting out about 13.54vac and the max for that 12X4 is around 12.6vac. I needed about a one volt drop.

V=IR filled in is:
1=.3R (1=Voltage Drop Desired, .3A = 300mA)
1/.3=R
3.3ohms = R

Wattage is W=V^2/R (There are a few incarnations of power equations, but this one works here.)
W=1.1^2/3.3 (I'm getting a little more than a volt drop, so 1.1 squared divided by the 3.3 ohm resistor.)
so W=.37

Now double the wattage to be safe in real life and we're up to .74W. Rounded up to a 1W resistor makes the world a happy place. (We don't want it to get too hot. Since energy can't be created or destroyed, the drop in voltage is reborn as heat.)

Hope this helps, just in case you wanted to know why. (I likes me all that geeky stuff.)
Ed

More pics coming later, I am done with everything except for the soldering on the RCA jacks but didn't post last night. Might finish tonite!

Awesome response, Ed. Very educational! They don't teach us that in Med School I'm glad I can learn this hobby stuff at a place like this thanks to folks like you, Roy Motram and Bob Latino and all the others that contribute on this forum!

Man, I'm just a hack but I'm glad to help. And by no means am I even in the same league as Roy and Bob. I'm just a sax player.
Ed

Alright. Close but no cigar. Maybe I'll do some more after I post, but I've only got the left channel signal wires to solder and then I'm listening.


So I got the mute switch wired and I connected power to the LED on the front panel.



The thing to remember is that DC power is polarized and the LED is rather particular about the direction of the electron flow that makes it go.


Then I got the wires on the selector switch.



I'll get it neatened up and get control of those ground wires when I connect to the RCA jacks. The outputs to the attenuators share space with the tape out twisted pairs. (The right channel is not complete in the photo because I have to twist another 16 inches of red and black. Missed it by 'that' much.)

I rotated the selector fully CCW and marked the position on the sides of the switch to give me a point of reference. (Roy's wisdom.) It helps when you're double and triple checking to make sure that you have the correct wires going to the correct inputs and outputs.


Here's a flyover with all of the signal wires in place but not soldered.




Tonight I soldered the right channel to the RCAs.




And closer.



I'm so close to finishing that it hurts, but need to be patient instead of tired and careless. And besides, if I finished tonight Roy would still be around for troubleshooting help if I need it. If I do it patiently, I'll finish the second Roy goes offline for vacation...that's how my life generally works.

Good night.
ed

hey Ed, it's looking great, I wish most of my other customers would think first and ask later like you have, you've got it all figured out with very little help. It's gonna work great too!
I shouldn't say this, but hey . . . . when I sell a kit, it's a DIY kit. I'm here to provide kits and parts.
I'm not really here to provide a 10 year education on tube electronics for newbies.
I don't mind helping, but hey, would you build a car or a house from scratch without doing a little research and education first??
I know at least a few people have heard of GOOGLE . . . .
I'm tired . . . hope I'm not p****ng off anyone. Vacation should help, then a week or two to play catch-up!!

Roy,

Yeah I'm one of those guys you're talking about. I would really have no business attempting to put your kit together. The advantage I have is a retired radio tech for a neighbor. He'd already offered to help before I ordered.
You have been very upfront about the level of expertise required in assembly. Anyone who complains just didn't read your description fully, or failed to heed.
I ordered your kit with the board assembled, not because I felt I couldn't put it together, but because I know I would have found it to be tedious. After looking at the parts I've received so far, it looks to be just enough of a puzzle to be interesting and fun.
With Ed's thread and my neighbor for backup I know I won't be scratching my head until it bleeds.

'Frank

P.S. Hey Ed, I'm pulling for your thread to set the forum record for views

Thanks, Frank, Roy.

Looks like I went and finished it.

I've got the soldering done and am ready to power this thing up and listen. I've still got to bind the wires and neaten things up...and put on the knobs, but the meat is finished.


Here's the back panel.




Here's a closeup of the shielded cable fro the phono input.



That was a real challenge. The S-Video cable that I used was very unhappy about the necessary heat to attach to the thick RCA jack. The insulator material melted a bit. I also had to expose quite a bit of the ground half of the wire because of the orientation of the ground tab on the jack.

Tomorrow finish the housekeeping aspects, but most importantly I listen. Can't wait, but now there must be sleep.

Ed

Awesome build, may have to consider purchase when they are in stock. Thanks for sharing.

Nubie Question:
You have a resistor between the two output RCA's, what is the value and why/what it's purpose?

Thanks

Ted

edgobb wrote:
That was a real challenge. The S-Video cable that I used was very unhappy about the necessary heat to attach to the thick RCA jack. The insulator material melted a bit. I also had to expose quite a bit of the ground half of the wire because of the orientation of the ground tab on the jack.


Ed

Ed,

TIP: The S-Video cable probably uses polyethylene insulation on the inner conductor which has a low melting point. Frankly just about any "plastic" insulation except teflon, can melt fairly easily when soldering. The best way I've found to circumvent this is to first strip the insulation back as normal, then before soldering, shrink a small piece of heatshrink tubing over the end of the stripped insulation. This usually seems to work for me.

Best Regards,
Charlie

Hello!

Ted, they are 1K, 1/2 watt resistors and they act as a buffer between the two outputs. From what I understand, they prevent a load on either output from affecting the other. (or making it insignificant.)

Charlie. Thanks for the tip. That makes good sense. I'm sure it will come in handy.


NOW...

I brought power up and I have a hum. Oh man. I'll take some time later to list the myriad things that I have tried so far and didn't work to fix it. Real life is in the way right now, so it will have to wait a bit.

I also have too much B+ voltage going to the phono stage, so a dropping resistor will have to go in there.

I really hope that the collective knowledge on this great forum will help me to solve the problem so that I can move on and get a real listening session in.

thanks!
Ed

OK. Here's the nature of my dilemma...

Hum is present as soon as I plug in the AC cord. It intensifies when I turn on the power. It is in both speakers, but is stronger in the right channel.

Here is a list of the things that I have done which have not made a change:
- Triple checked my work and connections.
- Moved the preamp to my SS home theater receiver. It is on a different power circuit altogether than my audio system.
- Unplugged everything else on the same outlet. (TT, CD Player, Light, Amp, etc...)
- I don't have a cheater plug adapter, but I do have an extra AC cord that I tore the ground prong out of.
- Reversed the polarity of the AC plug in the wall.
- Unhooked the AC ground connection to chassis.
- Took out ALL 7 tubes.
- Took all voltage readings where Roy suggested and all voltages are just what they should be, except the B+ to the phono stage is high.
- Tested the input source through all inputs at all combinations of volume and balance, including tape loop.
- Said the "F" word.

I do not have a scope so I can't tell you the nature of the hum or how clean my B+ is. I have a friend that I am getting together with on Monday who does and is a bench tech. He is going away for the weekend so I am seeing what I can accomplish this weekend with you all.

Here is what I have done that makes a difference in the hum:
- Unscrewed the Aikido PCB and picked it up by the heat sink. When I move it away from the transformer, it gets softer. When I move it closer, it gets louder.
- Unbolted the transformer from the chassis and moved it away from the PCB with the same results.
- When I place the palm of my hand on the transformer with my fingers between the PCB and the transformer, the hum substantially quiets.
- When performing any of the above and I touch the chassis with my other hand, there is a popping and I can physically feel the arc on my finger. (Maybe not the smartest thing that I've ever done. My heart still beats.)

It seems like EMI from the PT, but the toroid should not have that problem, especially with the grounded shield in this particular model.

So I'm at a loss in this age-old dilemma. Any suggestions might save the day and my sanity.

thanks,
Ed

All- long time listener, first time caller.

Ed,

First, thanks for the post. I too am building Aikido based SP12 and you have been a great help. As luck would have it you are ahead of me so we can not compare.
Issues at hand; I would try removing the input wires at the Aikido/SP12 PCB. Turn it back on ---no hum,then it should be in the "input wiring", pots etc. Do the same for the output wiring, one test at a time. If the hum is still there, I would guess that it is in the PS. Based on the "arc" you are getting, I would check chassis to ground for voltage both AC and DC ---might give you some insight. Also,try dumping the purple shield from the transformer. These things can be a real pain in the A$$, but hey if it was easy Girl Scouts could do it------got to go, there is a knock at the door. I am back--- just bought a $1000 bucks worth of cookies.

Regards, Mike

I finished mine last week before leaving town. I just got back this evening. I've done the same things as you and have the same results. I feel it is an AC hum because it happens even with the power off. Somehow AC is getting from the power cable into the output RCA jacks. It dissapears as soon as I disconnect the power cable. I have tried disconnecting inputs to the Aikido and output wires from the output RCA jacks with no change. I wonder if a shield needs to be fabricated to be placed between the transformer and PCBs. One way or another, one of us will figure something out. I'll keep messing with it.

Josh

Wow. You've got exactly the same issue? That's not really good to know, but it is good to know.

I was wondering if I had a defective transformer, but it would seem that I don't.

Maybe my friend and I tomorrow will figure something out.

Thanks for the info.
Ed

Roy mentioned that the transformer yellow/white wires could be wired for 500v in series in which case the resistors and diodes are not used on the rectifier board. I may try that to see if it makes a difference.

One mistake I found is that I had grounded both outputs instead of just one, so that may be adding additional hum to my other hum. I hope I don't have TOO many sources of hum!!

Good Luck!!

Joshua