OT in a potential Hifi Build

[JoeTele]

I'm hoping there might be some hifi enthusiasts here who can give a newbie some advice. I'm toying with a tube stereo build, having done only guitar amps up to now. I would build a single-ended mono Mullard 3 tube-3 watter, which I would listen to at low to moderate volumes in my apartment through a decent bookshelf speaker (probably $100 or less used). Given these parameters, is there much value to be gained spending $150 for a 20-20k frequency hifi OT rather than $50 on a solid (Hammond) one that would do 100-15k? I'm not worried about the high end losses. Lows maybe, though my computer speakers have a subwoofer with its own volume control and always keep it all the way down. The project is really more to try something new and expand my tube horizons and not due to any inherent dissatisfaction with my powered computer speakers so I'd like to keep it as economical as possible.

Thanks as always!

JoeTele

[Leo_Gnardo]

I'm thinkin' it's going to depend a lot on the quality of the speaker you use, whether you're going to realize the lo frequency extension of an expensive hi fi single ended transformer. If you're looking for music at a background level, sorta mid-fi, you'll do OK with the cheap iron. It's not a whole lot more $$ to get larger OT's with better low frequency specs, but why bother unless your speaker can produce them? Another (small) comfort is, those frequency specs are generally given at the power limit of the transformer, and widen considerably with lower power levels, so you might be well impressed with the low frequency response - as long as you're listening at low volumes, without other masking noises in your listening environment.

"Bookshelf" speakers come with a wide range of efficiency ratings. If you select low efficiency, you'll always be limited to low volumes with your 3W amp. OTOH hi efficiency speakers can work magic with a couple of watts. I used to live in a student apartment, had a pair of big Altecs (no bookshelf model these!) with only a tiny GE suitcase-stereo amp to drive them, a single EL84 per channel. Got all the volume we could stand with that tiny amp.

In general, I'd be looking at some of the larger Hammond SE OT's, rated 8 or 10 or 15 watts even though your power goal is only 3W. They don't cost all that much more, likely will deliver a bit more oomph in the low end, and you can re-use them if you decide to build a more powerful amp.

[bluesfendermanblues]

+1

There are a lot of myths regarding OT's - youd be hard pressed to hear any frequency or quality difference at all.

Used to own a Fender Bassman Ri 59', that got 'upgraded' with an expensive Mercury Magnets OT. Couldn't hear any sonic difference what so ever.
Since then, I've used Hammond in all DIY amps. Fine quality. No worries.

Recently did a rebuild (guttet and got hardwired) of a friends Chinese "Dynavox" clone of a Hifi Dynaco ST70. OT's are cheap chinese stuff. Sounds great.

[JoeTele]

Great! I was actually thinking that going with the lower bandwidth version but upping the wattage a bit might be a good compromise and is sounds like that's the case.

[Phil_S]

Given the nature of this discussion, I want to suggest taking a look at what MPS offers for output transformers. If you tell Matt you are building a stereo, he should be willing to cull his stock for a matched pair. They are sold at an aggressive price point and have more than adequate frequency range.

The other thing is that, as you age, hearing acuity declines. I'm in my 60's and I can hear from about 20Hz to 11KHz, and that's considered very good. By the time a person reaches the mid 20's, I've been told by an audiologist that the upper end of hearing is closer to 15KHz. Ordinary speech cuts off around 8KHz. What I'm saying is that reproduction of extended high end probably won't produce meaningful audible results. This is the other reason you can probably pass on high end, high $$$$ output transformers.

[rp]

Best bet for a 3-3 is all Edcor - plenty good enough and the PT 2xOT will aesthetically match nicely.

In guitar good can be bad. Better iron is always good when it comes to hifi, more money is better, but everything from source to speakers must be worthy too. 128kbpsMP3s/youtube into it and Canal St. speakers out then go thrifty. I'd advise against 3w SE. In hifi it's all about clean and headroom, you do not want to hit the wall, which in guitar is when the good stuff starts. Honestly, build a 2xEL84/6V6 push pull, won't cost you much more, use the cheapest Chinese tubes and edcors, and it'll be able to drive real world desktop speakers cleanly. Not a lot of small desktop passive btw, most are powered these days. Not sure what you found to use. Do the Mullard 5-10, up the filtering for 2016. If you do the 5-10 there's the Dynaco ST35 OTs from Triode/ClassicTone as a sure thing too. In fact the ST35 clone is a terrific option.

Here's a little edcor vs little hammond SE:
http://tubelab.com/articles/component-t ... nsformers/

Transcender seems to have vanished sadly, no homepage, no ebay.

Check out One Electron at AES/CE Dist.

The Asians are crazy mad over this stuff, their passion might pay off in affordable quality (Chinese, not Japane$e). Best sift through DIYA forum for details on the Chinese brands. I think asian hifi guys have the needle in so deep that they must all be pretty good.

http://www.ebay.com/itm/Raphaelite-5K-8 ... SwuMFUiK00

Check out DIYA - Baby Huey, Pete Millet (website too), El Cheapo.

Last option - price out your little amp and maybe just get a pair of these, the A2 or A5 powered. Sound really good and price is honest, in the end maybe better sound than a 3-3 tube.

http://audioengineusa.com/Store/Powered-Speaker-Systems

Just noticed also they make a desk top passive - good mates for your little tube amp? BUT Sensitivity 88dB, again as above, you need some decent power. Small closed or ported hifi boxes, just like smaller guitar speakers, move less air, the sensitivity goes down. You can do desktops "mini horns" with fostex full range drivers cheap. curious myself on sound, these last might even work with the 3-3 amp. here's a start:

http://fostex.jp/
https://www.madisoundspeakerstore.com/2 ... -kit-pair/

[JoeTele]

Thanks to all! Will look at some of these OTs but FYI the stock 3-3 build is actually mono, which I don't mind, so I'll just need one OT. I might have used "stereo" generically in an earlier post to distinguish from instrument amplifier. Apologies for confusion.

JoeTele

[galtjunk]

I built a Decware Zen Triode amp.
It uses 2 6P15P-EV's and a 6n1p-ev.
It puts out 2 watt per channel.
These are bridgeable so you can build 2 and double you power.
I used an Edcor PT XPWR107-120 and 2 Edcor GXSE10-6-8K OT's.
You can use a 6Dj8 instead of the 6n1p.
You can sub el84's for 6P15P for more power but the 6P15P's sound better with the Hazen mod.
Schematics are available on Decware.com
Go to the DIY section and look at the Zkit1.
I wired mine PTP like the videos, minus the solid silver wire.
I built mine using a 5u4g instead of diodes.
The 6p15p-ev and 6n1p-ev are available on ebay and they are cheap, plus the ev rated tubes are good for about 5000 hours.

Build videos are available on Youtube. I think there are 11 of them.
https://www.youtube.com/watch?v=n1ENOdYN6iA

It really sounded remarkable connected to a pair of Klipsch Cornwalls.

You will need 96db or better speakers to get any volume.
I use Klipsch RB-61's with an spl of 95db.
I tried RB-15's but they were only 90db and didn't work very well for me.

Good luck with whatever you decide to build.

[rp]

Thanks to all! Will look at some of these OTs but FYI the stock 3-3 build is actually mono, which I don't mind, so I'll just need one OT. I might have used "stereo" generically in an earlier post to distinguish from instrument amplifier. Apologies for confusion. JoeTele

Mono? So now you must decide which side of the monitor to put the speaker? What will you put on the other side for feng-shui harmony? Book? Potted plant?

[rp]

Oh, and if it's mono then you have to build one single Fostex "full range" single driver like in the link. A mini-me desktop for 1952! Play Julie London. Talk about back to the future.

Here's some google pics - mad cute right!

[JoeTele]

rp,

Thanks for the tips on edcor and that fostex driver. If I can order just one (driver kit) that may be perfect! This 3-3 has been living in my head for quite awhile so I'm going to get it out of my system for the first "hifi" build, keep it basically stock, and rely on tube power/passive speaker, but I'll consider other options later, if I get the bug, like the Zen Tetrode, which landed on my radar as I was searching info. For the PT, I have a soon to be orphaned Weber Deluxe Reverb transformer with a 270-0-270 tap. Given that it would be under significantly less load in the 3-3 I'm thinking that would put it close enough to the 300-0-300 specified in the 3-3 plans that I can get it where it needs to by be slightly tweaking the value of the series resistor after the rectifier in that circuit (the plans also say that the value of that resistor depends on the mains).

So I guess a "full range driver" does not need a crossover? I see no mention of one in the kit.

Oh, and most important of all, the single speaker will get a central location in my living room, where my computer desk lives, so feng-shui harmony will be ok!

Joe

[rp]

I want my own TAG hifi subforum...

I've been long sitting on two Edcors GSXE 10-8-5K that I ordered for Champ types. I wanted to make a little tube hifi amp for a gift to a righteous pal here but could never figure what to run off 3Ws. You got me looking at it again. I can’t personally recommend the mini Fostex “full ranges”, just pointing them out to you. I have my suspicions - 3” full range - hah! Supposedly, it’ll do 80-20Khz but I doubt that too and I rechecked and the drivers are 86-88db hmm, but no cross-overs to eat up power and the stuffed ported box should be a very easy reflex load, the light wood box might intentionally resonate to enrich the vocal range, an old BBC speaker design trick. Reading up people out there speak of them working well with 3-3W - some are amazed, but half the people are the internet are dazzled about anything. I’d say for the low outlay of mono money go for it, maybe not for a house party but in your face on a desktop should work. Report back even if a year from now as I’m really curious, especially about the Fostex Kanspea.

For the rubberneckers here, here’s what we are talking about:

http://www.r-type.org/articles/art-003h.htm

Here’s some encouragement for you, some info I found now that you got me interested again. Mind you these tube geezers are gobsmacked. gobsmacked!

Mullard 3 watt amp - gobsmacked!
http://www.vintage-radio.net/forum/show ... hp?t=62423

Check out some 3-3 w/ slight variations mentioned above and relinked here plus a German one with some changed values:

Radio Constructor 1956 3-3
http://www.vintage-radio.net/forum/atta ... 1291407601

Phillips Hi-fi Amplifier Circuits 1960 3-3
http://www.vintage-radio.net/forum/atta ... 1291548491

http://www.audioelektronik-shop.de/ein_ ... _klon.html

For a stereo model this is a transformer made in heaven - extra tap for an EZ81:

http://www.tube-town.net/ttstore/Transf ... :5989.html

Note seems Mullard and a lot of builders swear by quality iron in this little sucker. Look at the orig Sterns 3-3 in google images, hulking Parmeko OT for 3Ws. I wouldn’t go lower quality than Edcor.

Also read up on DIYA about the input loading of the EF86. The 5-20 and it’s offspring like Eicos seem to overload when driven by modern sources like cd players and computers, supposedly there is some tweaking to the done to the EF86, it’s not just the grid loading but the whole starvation mode. A lot of manufactures gave up on the pentode which is why you see many variants with a 12AX7 in front.

Here's some Kanspea encourgaement:

http://diyaudioprojects.com/Forum/viewt ... =11&t=4516

Gobsmacking luck!

[JoeTele]

Good stuff. I found this fostex 4" full range driver that is 93db.

https://www.madisoundspeakerstore.com/a ... ull-range/

I also found that I can buy the box for the 4" Kanspea kit on ebay for around $50 so that may be my go-to speaker solution.

I'm liking the price to spec ratio on that Edcor so I'm basically sold in it. Thanks again for that tip as I was not familiar with the brand. Funny, before it occurred to me that I could use my DR PT, I was going to get a Weber Champ PT, as it has a 300-0-300 tap in addition to the 330..., which I knew because my first build was a tweed princeton kit I got from them.

Good to know about the 12ax7 mods. Will start stock, but tweak as necessary thereafter.

Thanks again!

Joe

[rp]

Careful that driver might require a bigger box than the Kanspea, double check your ebay. The recommended box is ~12" deep, maybe too much for a desk? Otherwise should be bigger better sound.

http://www.fostexinternational.com/docs ... E126En.pdf

Gotta love that cute mini-me 2' transmission line.

[Leo_Gnardo]

There's a lot good to be said about some of the "single point" speakers, and maybe some can be gobsmacked with a birdhouse size speaker. I saw you want to put your speaker in the same room as your computer rig, but does it need to fit right on your desk?

A couple years ago my ears got a treat, when I was running mono FM radio thru an old 10 watt Knight kit amp, into a single Altec 417 12" speaker. Sounded unbelievably good, very wide range, veddy high figh. Super clear high frequencies, satisfying bass, and everything between as nice as could be. Of course one of these needs a box bigger than a birdhouse. This one was in a cab just a little too big (20"w, 24"h, 15"d) to be described as "bookshelf", but if you're building your own, you can make it as large as you're comfortable with. And of course, the Altec makes a terrific guitar or bass speaker too. Altec's spec says 96 dB sensitivity 100-1KHz @ 1 watt, measured at 4 ft for the H version.