diytube.com

So I decided to build my own version of the ST35. I really liked DIY Tube's use of the 12AX7 and 12AU7 and incorporated that. I also implemented Dave Gillespie's EFB mod.

I'm using a Shunguang 12AX7 I got for free, a nos RCA clear top 12AU7 and Valve Art EL84 power tubes.

Oh and for the record I had used the box previously as a preamp hence the holes in the front.

It was challenging integrating the circuits and coming up with a layout and ground scheme. Thankfully once I worked out my initial troubleshooting and missed connections it worked like a charm. Sounds pretty good too!

http://i576.photobucket.com/albums/ss20 ... d16aed.jpg

http://i576.photobucket.com/albums/ss20 ... d68d7c.jpg

http://i576.photobucket.com/albums/ss20 ... 42abad.jpg
Here I'm using my iPod Touch, Bottlehead Quickie Battery-Powered Tube Preamp with the new amp.

Thanks for giving me a challenge and for sharing all of your posts and experience. It's been a tough time recently and this project has helped me in many ways. I'm really happy with how it sounds and looks.

Very cool! Nice pics too. Love that tube glow

Cheers!

Proof again that this hobby helps us in ways we may not always immediately recognize. Congrats on a great project! Glad it's working well for you.

Dave

Great job, Corndog!

Now you can kick out some jams.

Shannon

http://i576.photobucket.com/albums/ss20 ... 7341c2.jpg

Here's a closer pic of the power supply board. I went a little overboard on some parts. Panasonic TS caps bypassed by Clarity Cap ESA .1uF caps that I had leftover from a speaker crossover experiment. Most of the resistors are 1% tolerance. I sourced parts from Digikey, Mouser, Partsconnexion, and Antique Electronic Supply.

I used a piece of 16awg solid core copper wire for my ground. It's in sort of a "u" shape under the board and can be seen protruding out the right side of the board. That allowed me to expose it for speaker connection grounds at the top, followed by another 16awg wire used to connect all of the amp board grounds as well as input grounds.

Next down the line: Red/Yellow lead from the PA-774, chassis ground, and ground lead coming off of the mounting tab of the LM337.

I was wondering about that last ground connection. In the orginal paper Dave wrote that the tab is internally connected to the input lead which is connected to ground. But I saw in at least 2 EFB installations shown on this forum that the mounting tab was connected to the chassis ground via a seperate wire. I'm thinking now that running that extra lead is redundant although I can't say the sound has suffered for it.

In the end my amp sounds very good! I've tried it with a few different speakers and all have sounded great. The bass I'm hearing is very impressive for such a low power amp! Good soundstage too with plenty of detail shining through. The best part is the whole project came in under $400.

Both the tab and the center pin of the regulator in the TO220 package are ground connections. So you can use either one that is convenient. It doesn't appear that the heat sink itself is grounded in your amplifier, so by grounding the center pin, you have grounded the heat sink in the process, assuming that you didn't use an insulating washer and spacer. I cannot tell from the photos, but if you did also attach a ground wire to the heat sink, it isn't necessary. However, it shouldn't cause any problems, either.

The heat sink is not grounded but there's no current going through it either.

Holy crap this thing sounds great!

It just gets better and better with time. It's especially favorable to playing rock music. It just has a speed to it that pulls you along for the ride.

Too much fun!

corndog71 wrote:this thing sounds great!

I'll agree, there is something about the Stereo 35 that just plain sounds good. I tend to rotate amps through a couple single ended designs, some Dynaco Mark III, and the Stereo 35. For some reason I'm always especially happy when the Stereo 35 comes into rotation. I sometimes think that if I could keep just one, the 35 might be it.

Slight change update. I basically copied the EFB power supply by Audioregenesis. Since it was designed for the SCA35 it had an extra RC in the high voltage supply. I thought about somehow integrating the preamp board of the SCA35 but finally conceded I would need to change the whole layout for that. So I took it out.

http://i576.photobucket.com/albums/ss20 ... 567011.jpg

Here's a close up of the main board which is the same as the DIY tube circuit minus the separate bias circuits.

http://i576.photobucket.com/albums/ss20 ... a3905c.jpg

I wanted to get a pic under the main board but it gets pretty crowded once it's fully wired. Here's a shot of it before finishing the grounds and connecting the power supply board so you can at least see how all of those caps and resistors are connected.

http://i576.photobucket.com/albums/ss20 ... b3f02d.jpg

Update: So while I still have a minor hum coming from the PT it's low enough that I only notice it when everything else is dead quiet. Short of spending a couple of grand or moving I just have to deal with it.

I really thought I was hitting the limits of my rig which was sounding great but still not at the level of the best gear I've heard. I recently changed the output caps of my Bottlehead Quickie preamp and have been utterly shocked by the improvement in resolution.

The more I thought about it the more I realized how great my little homemade ST35 turned out to be. It seems to me that a good chunk of resolution was being held up at the preamp and now that it's coming through I can't help but boggle at how fantastic this whole rig sounds! Some recordings fill my room with sound and others are fully exposed of all their warts. It's great and not so great at the same time. I've often read about ruthlessly revealing gear but never fully appreciated it until now.

The upside is that my rig is now so damn addictive to listen to I can't get enough of it! Dynamics are explosive, soundstage is wider and deeper, and I'm hearing tons of detail that was previously obscured. After a long time of almost becoming bored with music this has helped me fall in love with it again!

Since I built my ST35 in honor of my best friend who passed away last year I've decided not to cannabalize this amp for parts. But I really want to build another one. Do it a little different this time. I found some new caps I want to try in the power supply. I want to build a more traditional layout with tubes and trannys on top and keeping the guts inside. And I want to use the same caps I put in my Quickie for maximum resolution. Of course I will incorporate Dave's terrific EFB circuit. It seems silly not to considering the effect it has.

This will probably take me a few months to source the parts for a new amp but I don't mind. It's all about the journey, right?

edit: I forgot to add that I replaced the 12AU7 and 12AX7 with Gold Lion Genelex tubes each with matching triode sections and those too improved the resolution and over all sound of the amp.

Update!

I wanted to get another pic of the underside of the main circuit board with the grounds and heaters connected. I could've done better but I was trying not to break anything.

http://i576.photobucket.com/albums/ss20 ... 4b6a6c.jpg

I also got a well-broken in matched pair of .22uF V-Caps for a steal and thought I'd throw them in to see if I could hear a difference. I haven't gotten a second opinion yet but I detect a lower noise floor and blacker background. A little better focus but nothing dramatic.

Still sounds fantastic by the way and is still my favorite amp!

http://i576.photobucket.com/albums/ss20 ... 2f2515.jpg

So I ran into a problem the other night. The amp was playing fine one minute and then I started hearing some intermittent pops of distortion and then I lost a channel. The R12 (50 Ohm 5W) resistor suddenly started glowing and smoking. I hadn't made any changes to the circuit. It had been running fine for over a year.

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I pulled the board and couldn't find anything wrong. Every solder joint was solid. No shorts. As far as I can tell nothing else seems to be affected. When I power it on I measure 311VDC going into R12 and 296 after it.

Any thoughts on what could be wrong? Do resistors go bad like this? Could it be a bad power supply cap? Bad tube? I have replacement resistors but I have to dig for them.

That resistor is WOEFULLY underrated (I think deliberately, for fusing action). Check your tubes to see if they still have emission/grids and replace with a 5W cement resistor as they can handle heat better (and stand it off from the board by leaving the leads long, don't let the resistor touch the board).

Cheers!

Sorry about the recent problem you had with the resistor. Shouldn't be too hard to resolve. Congrats on a great build!

One thing I tried that improved my ST-35 a lot was to replace the 12AX7 with a 5751 (lower gain tube) and the 12AU7 with a 12BH7. This made a big difference in my amp. I never went back and am still using them.

Good luck with the amp! What fun this hobby is.