First hifi build

[Cliff Schecht]

I just finished testing my first hifi build. It's a SE triode-strapped 807 configuration using the pair of Stancor A3310 (5k SE 70mA xfrms) driven by a 12AT7 SRPP. The output stage is a cathode biased setup running on about 350V and 370 Ohms on the cathodes (about 17.5W plate dissipation). This was yet another build out of my scrap pile and, appropriately enough, is housed in the same chassis that I used for my first guitar amp build. I just flipped the chassis, the bottom now has a bunch of holes in it. While it may look pretty atrocious, it's got all of the modern safety features that one would want in an amp and is relatively safe. The mess of wires in the back looks goofy but I didn't want to cut up the transformer leads at all. These transformers are really meant for a 300B/2A3 type amplifier and I want to some day put them to use as such.

My initial impressions are that it sounds pretty darn good. It's not overly loud with the KEF bookshelf speakers I'm testing with but this is just a little boombox for my lab more than anything. I'm going to try them on the monster Fischer speakers I have tomorrow which sound great with the old Pioneer stereo receiver/PA I'm using now. I guess it's time to whip out all of the nicer audio sources I have shoved away in storage too.. Anywho, enjoy some pics!

[moj067]

That's great! Find some sort of efficiant folded horn design speakers and you'll be in buisiness. I used to see guys push Klipsch Horns w/ such amps and the results were great.

[Andy Le Blanc]

awesome...

Tubes rule, if you watch movies, a dvd player is a excellent audio source and
a great way to listen. Test it on soundtracks, great way to soften the misses
to tube geek infatuations.

Did you dress a simple srpp?, it can give you a high and a low impedance
output depending on where the output cap is attached.

Or did you try a Mu-follower?. Srpp can color, I found a mu-follower had greater
transparency and a deeper sound stage, especially in a small SE amp.

Make sure you try to use high efficiency speakers, make the most of the watts you have.

[Structo]

Sweet!:D
So this is just a power amp right?
What are you feeding it with for a preamp and what do you use for EQ?

I've wanted to build a tube setup and buy a turntable for years.

[Trout]

I have always been very fond of 807's. You can get NOS 807's really cheap and they sound fantastic.

I have built several of these over the past few years and just love them.
http://www.tubeaudio.8m.com/807/807.html
Only difference being the PT I use, otherwise the same.

I drive it with an old IBM think-pad laptop, loaded her up with a few thousand MP3's and use it in the garage.

[Cliff Schecht]

I went with the SRPP really just out of curiosity. If I can't stand the sound then I may start playing around with other topologies, but for now I have a few other amps to finish up (or start).

It's a preamp and power amp, albeit the preamp doesn't have much gain. I'll post a schematic soon so we can really discuss the design. One thing I wasn't sure about was the power amp cathode bypass cap, so I just shoved in something large (220uF). I'm afraid making this value too large has muddied up the bass of the amp.

I'm sure I'll be able to look back on this build in a year and laugh at some of the goofiness I came up with. Until then, this is all I got .

[Alexo]

Here's a quick and easy way to improve your bias scheme in a cathode-biased hifi amp, beware though, it uses SILICONE.

http://diyparadise.com/yhlmccs.html

I think it wants a bypass cap too. If you use a super-large bypass cap in a cathode biased amp, btw, like 1Kuf+ (available at rat shack) you will actually TIGHTEN up your bass.

[Structo]

Do you mean SILICON? As in diodes? Add the E to the end and it becomes the stuff you caulk with.


Do you guys have any links to good DIY Hi Fi sites that show SE amps?

[Alexo]

Woops! Was thinking silicon was the fake boobs!

This site has some good intro hifi stuff http://boozhoundlabs.com/

as does angela instruments http://angela.com/thehow-tosection.aspx.

[Cliff Schecht]

Do you mean SILICON? As in diodes? Add the E to the end and it becomes the stuff you caulk with.


Do you guys have any links to good DIY Hi Fi sites that show SE amps?

Pete Millett has lots of good info available on his website and also runs tubebooks.org which is a great resource for all things tube. For schematics and such, google is your friend. I went with an 807 triode setup but here was another build I was looking at that a guy used two 807's per channel (parallel) as pentodes. Here is a link to his stuff: http://sarris.info/main/807-single-ended-tube-amps

I've seen the silicon CCS cathode setups and may try them eventually. Again this was my first build so there was as much speculative design and experimenting as there was actual calculated design parameters. I'd love to put this on a distortion analyzer and fine tune the whole thing for the best performance but I'm not setup to do so right now. I'm going to try it out with my Fischer speaker system when I get home today in hopes that I get more (better) sound out of the amp. I can't be pushing more than a few watts as is..

[Cliff Schecht]

Not sure why but the amp sounded terrible with my Fischer speakers. Completely lacked mids and sounded somewhat distorted. I need to test this again tomorrow making sure the speaker wiring polarity is correct. I put the amp back on the KEF's with a scope on the speaker and didn't see anything goofy, but the sound is not right. As far as I can tell the amp is built right and not oscillating so I'm a bit puzzled right now. The only real unknown is the tubes I'm using are not "proven", although each channel sounds and acts alike (again as far as I can tell).

I ran a few simulations on the preamp and power amp stage separately and together and saw exactly what I wanted, a nice linear passband and nothing goofy. Hrmm..

[Cliff Schecht]

I'm pretty sure the power stage was oscillating. Just because I didn't see it on the scope (looking only at the secondary side) doesn't mean it wasn't there. I went ahead and added 110 Ohm 3W CC resistors wrapped in 10 turns of solid core 22 AWG wire. Seems to have cleared up the muddiness with the KEF's although they still lack in bass response. Will try them on the Fischer's tomorrow, I'm hoping for a bit better bass response out of the 15" LF drivers .

[Structo]

I was really surprised at some of the prices on some of those SE amp kits.

I wish I had a big bone pile to weed through to use used stuff.

Those old big bottle tubes sure look cool and I'm sure they sound wonderful.

I'm not certain what the sensitivity of my speakers are.
Probably not real high.

Oh well, someday maybe I'll build a stereo amp for a turntable.

[Cliff Schecht]

How many guitar amps have you built? I've only built maybe a dozen guitar amps by now and I've only been at it about a year. That number surely would have been higher if I wasn't in an apartment all summer with the "bare essentials" at my side. Funny enough, I still built my 2W guitar amp prototype using only my "essentials". My point is that if you've built a few guitar amps, hifi is by no means unobtainable even using scrap parts. Not to say that I don't have a LOT of scrap laying around .

The 807's are a 6L6, both in sound and in specs (6l6g = 20W, 807 = 25W, 6L6GC = 30W IIRC). It's just made with a plate cap for lower interelectrode capacitances (for higher frequency operation). 807's are relatively expensive now, people know what they are and charge accordingly. It's cousin, the 1625, is an 807 with a 6.3/12V heater config. They are very abundant and not well known which is rocks. I'm using some soon in a 5F6A style build because I can play this amp constantly and retube for cheap .

[Aurora]

There's plenty of really good hifi designs around, using 6L6s, EL34s, EL84s and a lot of other tubes, most of them being around 20-40W in PP, and the OTs don't necessearly very cost much more than a good OT for a guitar amp.
While I can see the fascination with SE designs, I don't concider SE a viable option for myself, - one reason being the sole fact that I live in northern Europe ( literally!) and have to pay blood in shipping costs for heavy irons. Little or mostly nothing is available in the local or national market, be it new or even used, in terms of transformers or high efficiency loudspeakers, and lot of Ebay sellers just don't bother shipping outside US.

One thing that gives tube hifi a bad rep is the fact that most modern hifi loudspeakers are so inefficient that you really need up to 100W or more, to find the proper "punch" often wanted , so modern HiFI loudspeakers and SE is really not a good match.