Building the SP8...

Greetings to the group, after a long absence.

I learned today from Roy that I missed the chance to snap up his demo SP8, so I'm thinking to build one. I'm impressed by Bob's review of that amplifier (should that review maybe be a sticky thread?).

I notice that at least one member of the forum has built an SP8.

I had no trouble building the ST 70, or the Transcendent pre amp and phono stage, though I'm a little nervous about the extra challenges of putting together the SP8.

I wonder if any would like to offer some encouraging words on jumping on in?

Also, how do you SP8 users like the amp?

Thanks in advance,

Brenton

Updating my own thread,

I've decided to pull the trigger and order Roy's pre-amp kit.

I believe the current, latest, greatest is the SP8 SE.

Since I already have a nice pre amp, the Transcendent Grounded Grid, I don't have to be in any hurry to build the SP8 right.

I also decided that to give this new amp it's best shot at being my #1 pre-amp, in my main system, I better not scrimp, so I've ordered all the various up-graded parts (caps, resistors, step-attenuators, toroidal transformers).

I'm quite excited about the opportunity to have a pre-amp designed by the very fellow so many of us appreciate for the VTA board he developed for the Dynaco power amps that Bob Latino offers.

I'll be happy to post a not-too-wordy commentary on the building process, if there is interest in it. So members know exactly what I'm working with, I've ordered everything from Roy, including case and all.

I won't have anything to add for a few weeks, when I'm ready to start building.
In the mean time, for reference, my back ground in building these kits goes back only a couple of years. My first kit was Bob's ST 70, then I built the Transcendent pre amp and phono, then I became addicted, upgrading my turntable (LP12) in steps, then built some speakers (zigmahornets), and, recently just finished a large pair of double mouthed, back loaded, folded horns utilizing a single full range driver. (No previous wood working skills).

Yes, clearly I got it bad -- but, like many on the forum, I am strictly an amateur, so I am hoping that my experiences will be of use to other amateurs around the forum.

here's an OLD online forum discussion about building the SP6 which is nearly identical to the SP8 without voltage regulators
http://forums.klipsch.com/forums/t/114302.aspx?PageIndex=1
also a note to readers - I've actually discontinued the single piece PC SP8 preamp kit,
so what I am supplying now are the same PCBs in a 3 piece set, phono, line, and power supply.
Plus working on new projects.
Roy www.tubes4hifi.com

Thanks for that link, Roy, I don't think I've seen that.

I'll read that thread carefully before I put solder to pc board.

Sorry I mis-identified the amp, there.

Thanks you for the post.
Hi guys, Im a newbie. Nice to join this forum.



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Greeting to you, newbie!

I'm sure you're going to find this forum both informative and friendly.

Of course, this is a dangerous combination, if you don't already have Dynaco / VTA related equipment on your shelf!

Brenton

Update:

Well, I've pulled the trigger on the decision to build the VTA pre amp.

I ordered up the complete kit from Roy. Because I was a little confused with all the options he provides, I emailed him, rather than opting for choose and click shopping on the website.

Just as we invariably find him here on the Dynaco forum, Roy got back to me right away with helpful clarifications, and answered all my questions.

Soon enough all my stuff was en route to Canada, arriving in two packages. First a small box with 3 circuit boards and various bits and pieces to complete them. Second, the custom amp enclosure, which was jam packed with all the rest of what I need to build the kit.

Posting was prompt, packaging was...(sorry, here's where the alliteration ends) exemplary. Sound and secure.

Here's how it looks after unwrapping the two packages, laid out and begging for some assembly:

http://www.flickr.com/photos/55410282@N04/5137605225/

Hi TubeNube,
thanks for the photo, but wow, it's just a tiny thumbnail and won't enlarge,
how about more like full size??

Hi Roy,

Thanks for pointing that out. I see what you mean.
Ok, I'll fix this up when I get back on my Mac, later this afternoon.


The next update I have to make follows completion of one of the three PC boards, the Power Supply board.
I've been taking my sweet time with this, not wanting to rush. With my leisurly pace in mind, it was about 2 hours work to complete the PS board.

I don't recall if the ST 70 has any diodes in it, but it's worth mentioning that before you touch soldering iron to diode, you want to clip on an aligator clip to act as a heat sink, preventing damage to the heat sensitive component. Same goes for the transistor and the other two 3-legged silicon-filled parts!

A word about the instructions. Roy warns us on his website that these kits are a bit more advanced to build than the ST 70, and I was certainly hesitant about this.

If you were able to follow Bob's Dynaco instructions, then that's good preparation for Roy's instructions. It's a bit less of a step-by-step, walk you through it instruction manual, but so far it's not hard.

Assembly is aided, I suspect, by the way he's now broken it up into three separate PC boards. There are relatively few parts per board so the lay out is easy to follow. There's good spacing between components giving you room to work if you don't have the nimble fingers of a seamstress.

A side benefit of the instructions being some what less step-by-step is that I'm learning to read schematics. Never bothered before--who can be bothered, right?! Well, it's a good way to cross reference that the right part is going in the right place.

And if you're still not sure, well, you can always call for help.

Now I don't want to cause Roy any grief should this create an expectation, but I emailed Roy a question I had yesterday afternoon (Sunday), and I had a reply from him by supper time!

Has anyone else noted before what great customer service both Roy and Bob give you? This isn't the first time. More like the 14th. It's always like this!

More to come...

Tube Nube wrote:

I don't recall if the ST 70 has any diodes in it,

An original one would not, but by now I hope any of you who have a Stereo 70 has replaced the old selenium rectifier with a modern silicon diode.

Alright lads,

I've placed a bigger photo in PhotoBucket, replacing the one above. Hopefully I've "rectified" the problem with it only opening up as a small thumbnail, yuk yuk yuk.

As to selenium rectifiers, GP, I haven't gone that route yet. In fact I was recently looking around for a Mullard rectifier tube. Must be my glass bottle fetish, but I kinda wish there were a vacuum tube that could take the place of that ugly tin can quad cap . . . then my ST 70 would be completely beautiful to my eye!

;-)

Seriously, though, I know some people say solid state rectification affects the sound in ways that are audible. I don't know enough to have an opinion about it, but I do have a bit of a tube fixation. I'd prefer to go with as much tube, and as little silicon as possible, unless there's a convincing advantage.

I dunno, must be something Freudian about it. I suspect that not only was I a bottle fed baby, but that they were glass bottles.
Following on, I do have fond memories of milk being delivered in glass bottles.

-Brenton

Edit:

Acturally, Photobucket won't give more than a thumbnail. I changed over from Photo Bucket to Flikr. That seems to give a bigger photo (in my post a few messages above).

Tube Nube wrote:
As to selenium rectifiers, GP, I haven't gone that route yet. In fact I was recently looking around for a Mullard rectifier tube.....I'd prefer to go with as much tube, and as little silicon as possible, unless there's a convincing advantage.

Brenton,

Just to clarify, the selenium rectifier is in the bias circuit, not the HV circuit of the power supply. It and the GZ34 rectifier tube perform different functions. Selenium is a heavy metal and is very toxic. That is why it should be replaced with a diode such as a IN4003 or IN4004.

Best Regards,
Charlie

Hey Charlie, Holy foot in mouth, Batman! Who's the "Luddite" now, hey?!

Thanks for that.

The REAL reason why the selenium rectifier should be replaced has nothing to do with toxicity. Selenium rectifiers go bad with age. The usual failure mode is high-resistive which decreases the amount of negative bias voltage available; if the internal resistance goes high enough, there won't be sufficient negative voltage on the grids of the output tubes to properly set the bias. Another failure mode is open-circuit. If that happens the output tubes will red-plate instantly and you may not be able to turn the amp off before they are destroyed.

Hi GP,

Thanks for that info. Geez, do I have such a rectifier in my Dynaco Kit, as procured from Bob?

Hi Bob,

Thanks for that info. I need not worry about my ST 70!

And now back to my VTA Pre-amp build . . .

Did you ever finish this pre-amp? I'm finishing up my ST-120 and am already looking around for more stuff to build

Hi Wntr!

I decided I couldn't finish it myself. Perahps if I plagued Roy with more questions, maybe a real-time video link via skype, and some hand holding sessions etc, and I'd be able to get through it. But Roy's already been more than generous with helping me out with my repeated needs for support. In the end, I decided it's more than I can handle, and more than I can fairly ask of him to try and get me through the last stages, so I packed it up and sent it to the master himself, today. I can now be confident that it'll be done right, and I'll feel better paying Roy for his time spent on the thing....

But I'm really eager to hear the thing play!