DIY Audio Projects Forum

Ok first impressions are ... interesting!
It's definitely a work in progress for me.

I'm operating from battery - I can see a separate power supply in it's future. Wall-warts bring too much hum. Haven't tried a regulated supply (as the one mentioned). It (and I mean my build) seems voltage sensitive - go above about 12.6 VDC and the sound goes oddly bad.

My sole substitution is 1.0uf instead of 2.2uf for C1 - all other parts are per schematic. Heh - I had all of it on-hand.

1. First - audio is quite good. As the article predicts, lows are great.
2. I can't get the trim-pots to go below about 9.7 volts - this is also dependent on which tube I have - I tried a variety of used 12AU7A's - some noisier than other - I have some NOS 12AU7A's coming this week, so I'm looking to try those. Swapping tubes brought the lowest to 11.2, 10.8... lowest I can reach is 9.7V.
3. Hissy - increasing volume masks it, but at least with my build, there's a good deal of constant background hiss.

I'm wondering if I have some 'baked' IRF510's, LM317's show about 1.25V on the output.
Or, perhaps a New- or New-Old-Stock tube will improve on it.

I managed to put it all in a stock Radio Shack enclosure - 270-1805 - fielding the LM317T's and IRF510's under the metal top. On top of that, I've attached an older stick-on VGA heat-sink. Seems to be holding temps down quite well; you can rest your hand on the top with no adverse effect. Did point-to-point wiring below the top; balance of the circuit including an added 'e3' delay on a perf-board in the bottom of the enclosure.

(edited) - interesting as the battery goes down in voltage, the HISS quiets down. This is an interesting little amplifier. It'll be fun tinkering with it.

Subtracting the hiss - there's no other adverse noise. Lows are VERY good as the highs are still very sharp.
Too late / too tired to upload some photos. Perhaps tomorrow.

Mike Y
Dallas, Texas

I was thinking and I happen to have a Mullard DCC90 twin triode (http://www.mif.pg.gda.pl/homepages/frank/sheets/030/d/DCC90.pdf) at hand so I was wondering if this might work with small mods to the circuit?

Regards
Ebbe

_________________
"I've done this a thousand times befo..." on not voltage testing before getting to work.
"I'm gonna take my time on the next amp....." on First tube project.

Photos in a folder here:

http://km5z.us/photo/One-Tube%20Amp/

I'm not happy with some of the photos - dropped down to my wife's older Canon PowerShot A75 - not so good on closeups (even with 'macro' on. I'm going back to my Digital Rebel (even though I have to resize 'em so they're not so large).

Listened for quite a while last night. As the battery voltage dropped, the hiss went away with no drop in audio quality or volume.
I marked the voltage at 12.52 volts, so next little project will be a heavily filtered, regulated power supply for about 12.5 volts!
Too bad there's not enough room in the enclosure - or there might be... Hate to open it up again.

http://km5z.us/photo/One-Tube%20Amp/test_run.jpg

And, who can resist putting a blue LED under the tube?? *sigh*, everyone but me, I guess...
My only three changes: I added the e12 delay relay; I only had a 1uf for C1 on hand; and I inserted a Schottky diode inline with power to prevent reverse voltages on the FETs and LM317s. Only a 0.120 voltage drop traded for safety.

I have a gainclone project on the shelf - just haven't finished it. Would like to put it in a nice, $30 Hammond enclosure - guess that's the hold up... Not sure about a preamp. Still learning the audio 'ropes'... but it seems you could drop the 'current' stage and use only the tube as a voltage preamp... Might be some impedance issues, though...

Mike Y
Dallas, Texas

Looks Great Mike i like the blue LED under the valve BTW

so the hiss went with the lower voltage glad to hear.

i was thinking of using a toroid or a SMPS and making a LM317 PSU as running off a battery its really not an option for me as my source is the X-Fi on the PC to a DAC and the stuff is on all the time.

heres a quick pic Mike of my LM3785 Gainclone testbed till i get round to a proper enclosure all of the circuits will fit in the U channel also it doubles as the heatsink (inspired by Peter Daniel)

http://homepage.ntlworld.com/ruperthirst/Recent%20DIY%20Projects/Audio%20Projects/GainClone/TestBed%20Chassis/Gainclone%203.jpg

Regards, Rupert

_________________
Homebuilthifi Projects
runawaybrainz.blogspot
Head Amp On 555 Delay all in one
NP-100v12 - 12AU7 / IRF510 HeadAmp

Mike,
I briefly looked over your images Looking good with the LED.
Just wondering if you insulated both sides of the MOSFET and LM317 mounting screws. Or with the power off, measure the center tab of the MOSFET (drain) and the LM to chassis. I see you have mica, but just in case.


Rogers

> i like the blue LED under the valve BTW

I do too - these usually wind up on my desk at work and it's always a conversation starter if I'm listening and working and someone drops by...

> so the hiss went with the lower voltage glad to hear.

Last night, I added two 1000uf caps across power at two places, along with a couple of .1uf at a couple of locations. Seems to quieted a bunch of hum (with lab supply) and hiss. Now not quite so twitchy on voltage - I can run it off of a Heathkit lab supply for 12V to about 13V, no issues. But, regarding a SMPS - ditto - I have a bucket full of (various brand) discarded laptop power supplies (all about 15 to 19 VDC, all at LEAST 1.5 amp, some to 3A), so yup, a nice filter / regulator is what I've already sketched out..

>heres a quick pic Mike of my LM3785 Gainclone testbed till i get round to a proper enclosure...

Oooooooo. Handmade / homebrew trumps fancy Hammond enclosure most anytime. I like it! It Just needs a lid.

> .(Rogers) ..Both sides of the MOSFET and LM317 ...

Nope - used four TO-220 mica insulators, with a sort-of nylon shoulder insulator for the bolt. Also some heatsink grease, for what it's worth - dunno if it'll transfer THAT MUCH more heat. Topside, just screw against metal. Due to some misalignment, the mica insulator actually bared a bit of metal to the tab, so I did have a short in initial testing, but after some realignment and fudging, it works fine now. I think I had a shard of drill debris hanging on.

Yup - always good to check that TAB if it's mounted on ground - and I grounded the lid just for convenience - I love the PC boards, but I'm always just using a perf-board and point-to-point wiring, so it's convenient (and sometimes necessary for RF applications) to have a nice, large ground-plane to tie to or to just 'be near-by'.

I will crank out the 'good' camera and shoot some good images later this week, I hope... if work doesn't kill me...

Mike Y

How'd you get the tube layout into Eagle? I can't find any parts in the libraries I have.

Hi,

CadSoft has a huge collection of libraries for all versions of Eagle Cad, uploaded by some kind users.
You'll find the libs (.lbr) on CADSoft's download section: http://www.cadsoft.de/download.htm

Or just DL them here:



Just unzip and copy them to your library directory...

Have fun

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Thanks, Tom!

Anybody care to double-check my schematic before I do the board layout? These tube parts didn't quite come out the way I expected them to, so I'm not sure if it's laid out right. I'm also not positive about the potentiometer, but I think I got that laid out correctly as well.

I ordered some IRF510's at a local electronics shop and they gave me NTE66 MOSFETS will these work?

Thanks,
Max