One-Bottle Preamp

[solder_city]

rule number one: dont believe anything a tube dealer says.

i look at curves for 12at7 and 12av7 and theyre not the same tube at all.

12at7 is a terrible tube for a mic pre, its ok for guitar amps where you want distortion.

 

[Junction]

New to this thread, have checked out most of it and find most links broken, can someone post the schematic again with the 20dB pad corrected.

Thanks
Michael

 

[solder_city]

i just checked, the schematic on page 1 of this thread still shows up. the 20db pad looks correct to me.

 

[Junction]

Trying to find some 12AV7 for under $2, all seem to be around $4-5, even Antique Electronic Supply, any suggestions??
Michael[/quote]

 

[rotation]

[quote author="solder_city"]rule number one: dont believe anything a tube dealer says.

i look at curves for 12at7 and 12av7 and theyre not the same tube at all.

12at7 is a terrible tube for a mic pre, its ok for guitar amps where you want distortion.[/quote]

I don't belive them, that's why i posted here. Look at the prices too :roll:
What else would do here? ECC99? Should we find another design?

Miha

 

[ioaudio]

hey miha
did you ask btb elektronik? they seem to have 12av7´s in stock.
http://www.btb-elektronik.de/de/preise_lager_international.htm

i think you were trying to build my pre#7 - did you come around it ?

-max

 

[rotation]

Hi Max!

Yes, BTB have them in stock for 6,65 euro. Posting is 16,90, bank takes about 15 more. If i take in account price for like3 pieces because of selection, i end paying around 50 euros for one healthy tube...To get transformers(except for OEP), i have to repeat the exercise at much higher price. :roll:
I would like to get at least tubes from cheap local supplier. But he only has JJ/Tesla's, nothing else. That's why i'm trying to use another tube. And users from another forum want this too. Of course we sometimes find NOS from Ei Nis, or Russia, but stocks are limited to mostly ECC tubes (E180CC not included).

I end up using your #7 as a DI. That's because i could only get OEP for cheap at that time. We tried it, it was ok, but DI was much better, specially on bass. I think this kind of circuit is very nice if you want high gain. I can't talk much about the sound if it's mic pre, but i like it as a DI a lot, even if two tubes are not needed for it.
Btw, thanks for sharing and help :thumb:

This time i'm trying to get simple design with one tube to get mic pre (with DI) for dynamic mics. There are other people i mentioned before interested too.

How are G7s doing? Did you make any records with it, commented the sound? Any links?
Have you got any idea what to do about getting One Bottle pre from ECC tube?

Miha

 

[ioaudio]

yeah diy is not cheap - and it gets worse after some time :shock:

you didnt like the oep-input transformer - which one did you use? i made two pre#7, one with lundahl and the other one with oep, and the oep - equipped unit got more use...

building dave´s design with another tube will likely lead to a different-sounding preamp. he designed it around this particular tube, and since its a one-bottle, the kind of bottle is definately a big part of the system
you might try a one bottle with a ecc88.

-max

 

[rafafredd]

you didnt like the oep-input transformer

In a simple tube circuit like this one, it all depends on how you are terminating it. Any transformer can sound bad if badly implemented.

 

[rotation]

[quote author="ioaudio"]yeah diy is not cheap - and it gets worse after some time :shock:

you didnt like the oep-input transformer - which one did you use? i made two pre#7, one with lundahl and the other one with oep, and the oep - equipped unit got more use...

building dave´s design with another tube will likely lead to a different-sounding preamp. he designed it around this particular tube, and since its a one-bottle, the kind of bottle is definately a big part of the system
you might try a one bottle with a ecc88.

-max[/quote]

#7 didn't sound bad with OEP. Compared to Tube-Tech Mp1A they were not in same league, Tube Tech was better. But DI was better on #7, it had more details and warmth. So i finished #7 as a DI. I used transformer that you suggested.
I PM-ed Dave about tube replacement. I think it is better if he tells me what to do as One Bottle is his design.
@rafafredd
I didn't use new components, layout was not very well done, power transformer was noisy (got it from old radio), tubes were old...I built it to learn how to do a proper layout on veroboard.
It is not fair to judge #7 from my results, because it was not well built.

Miha

 

[3nity]

Hey guys, was wondering if 450V caps for filtering the PSU wouldn't be too small for a 225-0-225V CT hammond transformer??

I remember some one used once a bigger transformer 250-0-250v and the same cap values.

Merci Beaucoup.

 

[rotation]

They are ok. Caps need to be 1/3 bigger than maximum voltage.

Miha

 

[NewYorkDave]

Unfortunately, I'm not aware of any direct equivalent for the 12AV7. I've looked at the plate curves for the various European types that have been suggested here and don't really see a close match. I'll look some more if I have the time.

 

[rotation]

Ok, thanks. It would be interesting to find European substitute.

 

[ioaudio]

sorry for being off-topic

[quote author="rafafredd"]
In a simple tube circuit like this one, it all depends on how you are terminating it. Any transformer can sound bad if badly implemented.[/quote]

did you try my circuit?

 

[rotation]

It seems no one tried it for real. Would you give us some more info? Sound files, maybe layout, list of transformers...Lets go back to #7 thread, ok?

 

[rafafredd]

I thought you were talking about the nyd one bottle... :?

 

[Kingston]

I built a two-channel two-bottle and it's seen roughly a year of usage now. Most of the time it has sat as a kind of a pseudo line level amp that I've used to subtly color my DAW busses. The second common usage is for a RB500 ribbon mic, SM57 and some oktava MK-02's. All these tasks it handles like a dream. Sometimes the preamp has been left on for several weeks in a row.

Except it has one (lately major) problem: it keeps eating those 12AV7's. I've already gone through three pairs of them. The noise level steadily rises until I deem the pair broken. Initially the hum is nice a low, below -100dB (at 50hz). Then it'll slowly start rising in level with nasty harmonics creeping up with it. A pair of 12AV7 will be cooked and dead in around 2 months.

Oddly enough I'm still on the first pair of 5879 (as it's a two-bottle) and they haven't changed at all ever since I first fired it up.

With my lowly measuring equipment I can't detect any anomalies from the original design. Voltage levels seem to be in check, with no nasty ripples in sight. Nothing I could detect anyway. This two-bottle design is a very robust and flexible one and there's nothing there I could possibly blame for it.

I don't know quite where and how to troubleshoot this one. I positively doubt this isn't just plain bad luck with tube selection as both channels start to fail at roughly the same time.

Since 12AV7 is (still) cheap I guess I could just keep replacing them, but that's a band-aid, not a real fix.

 

[pstamler]

Are the tubes mounted vertically or horizontally? If horizontally, you may be getting filament sag.

Peace,
Paul

 

[Kingston]

horizontally. I had no idea filaments can sag but it certainly makes sense. thanks

does filament sag apply to tube storage as well by the way? or just hot units?

I'll flip the mounts. I've been meaning to tune up the insides of this thing anyway. Few other grave layout errors on this (my first bigger one) so I should get the noise level (on max gain) down 10dB or so further.