Vademeccum pre.

[Kit]

Hi folks.

Thought I share a tube pre I´ve been working on.

It´s a ef86-ecc82 thing.

For now just some pictures of my messy wiring.
Im working on uploading a schematic.

I havent actually had a chance to listen to it yet.
But it measures out fine on the scope.

It shouldnt suck to bad.

Gain/feedback is variable in 3dB steps on a 6 position rotary. 30 to 45dB.

And a 20dB pad on the input.

Gotta run.

www.munchenmotor.se/mickesbilder/IMG_5926.JPG

www.munchenmotor.se/mickesbilder/IMG_5928.JPG

 

[rafafredd]

nothing messy at all. Nice wiring, if you ask me.

 

[Kit]

Thanks rafa.


It was kinda done in a hurry. But its allright i guess.

Im gonna put two of these in a 2he 19" enclosure. But for now i thought ill just use this old two piece box i had lying around.

Stay tuned for schematics.

 

[AudioJunkie]

When I saw the title, I had visions of a Dyson hooked up to a G9. :green:

Daniel

 

[rotation]

[quote author="Kit"]Hi folks.

Thought I share a tube pre I´ve been working on.

It´s a ef86-ecc82 thing.

For now just some pictures of my messy wiring.
Im working on uploading a schematic.

I havent actually had a chance to listen to it yet.
But it measures out fine on the scope.

It shouldnt suck to bad.

Gain/feedback is variable in 3dB steps on a 6 position rotary. 30 to 45dB.

And a 20dB pad on the input.

Gotta run.

www.munchenmotor.se/mickesbilder/IMG_5926.JPG

www.munchenmotor.se/mickesbilder/IMG_5928.JPG[/quote]

Nice build, nothing messy inside...
Which design did you use? Is it IO Auido's #7 preamp? It has EF86 and ECC82, penthode/tiode switch and DI.
How does it sound?

 

[Kit]

Thanks rotation.

No, its not like #7 which is a zero feedback srpp thing, if his schematics still apply.

Here are the schematics;

www.munchenmotor.se/mickesbilder/ef86pre.jpg

Comments and critisism are most welcome.

Im thinking, maybe wiring up the ef86 as pentode for higher OLG.
Partition noise VS gain. Its always a trade-off.

Soundwise?

I really dont know yet.... :?

Hopefully i will get some time to try it out next weekend.

 

[ioaudio]

hi kit,

concrats to you build - doesnt really look "messy"!
your schematic reminds me of the redd47

note the 330k resistor in the signal path of the redd, the ef86 might have a hard time being loaded by the parallel triodes without it - at least when connected as a pentode.
in the #7 thing there´s local feedback around the ef86.

-max

 

[Kit]

concrats to you build - doesnt really look "messy"!

Thanks Max.

your schematic reminds me of the redd47

Sssshhhhhhh......

note the 330k resistor in the signal path of the redd,

Yeah, i think that local feedback loop is mostly there to keep the ecc88 within reasonable distortion limits as its hardly the most linear triode. But you have a point.

in the #7 thing there´s local feedback around the ef86.

Oh, sorry. I didnt see that.

 

[mikka]

I haven't seen a Redd.... but I doubt EMI would pass a signal through a 330k resistor. My experience is that a large resistor like that "chokes" the sound. I suspect the Redd schematic is "almost" true......

 

[Sorr]

I agree with Mikka, more like 3.3k as a grid stopper for ECC88.

 

[Kit]

Its function is not as a grid stopper. (Altough if its soldered close enough to the socket it serves that purpose too.)

Its main purpose is that it is part of the local inverting feedback loop around the ecc88.

Whether its suppose to be 3,3K, 33K or 330K, I cant be sure.....

 

[ioaudio]

winston himself confirms 330k in this thread (R11)
http://www.groupdiy.com/index.php?topic=17847

 

[Kit]

I did get a chance to listen to it yesterday.

Sounded good. Smooth.

Hopefully i will find the time to make some more serious recordings this weekend. Last night was just me speaking.

I dont think Ill bother to try the pentode approach. 45dB max gain will do just fine on loud rock and a roll.
:thumb:

So any other suggestion from you fellars?

Im thinking about B+ regulation..........neons, maybe.

 

[amorris]

For now just some pictures of my messy wiring.

huh? that's some pretty wiring dude. sah-wheat! (sweet)

 

[Kit]

Thanks, man. :thumb:

I wire stuff for a living (not mic pres!!)so I guess im a little biased.

 

[Kit]

BTW, do any of you guys know of a source for cheap power transformers for tubes?

I need a secondary winding around 280-300V with a 50V tap + a 6,3V heaterwinding.

Thanks.

 

[analag]

I have (2) custom made 500V@250ma, 50V@10ma, 6.3V@3A, 12.6@1A
I might not get around to using them so I would sell em.

 

[rotation]

[quote author="Kit"]BTW, do any of you guys know of a source for cheap power transformers for tubes?

I need a secondary winding around 280-300V with a 50V tap + a 6,3V heaterwinding.

Thanks.[/quote]

Can't you get cheap transformers in Sweden? It shouldn't be a problem.
Latelly i'm buying power transformers for my projects from small local company. I found out it is cheaper than Farnell or other big distributors, and they can do whatever i want, for cheap. I suggest you to try this way.
Have you got any particular reason, beside cooling, for mounitng tubes on the top of chasis? If it is to be used as a mic pre in the studio this is maybe not so good idea.
You could easily add a DI input to the grid of EF86. I tried several designes with DI into EF86 and all sounded very very good. I think Max (IOAudio) has same experiences.

 

[Kit]

Can't you get cheap transformers in Sweden? It shouldn't be a problem.

The only ones with a 50V tap i have found so far are hammonds and they aint cheap........

Have you got any particular reason, beside cooling, for mounitng tubes on the top of chasis? If it is to be used as a mic pre in the studio this is maybe not so good idea.

Its a prototype, i did this for overall ease of construction and wiring. The 19" version will have the tubes in the box.

You could easily add a DI input to the grid of EF86.

Yep, that too will be on the coming 19" version.

 

[keefaz]

I use this boutique for not expensive power transformers for tube :
http://die-wuestens.de/eindex.htm