Vacuum Tube Valley 6SN7 preamp

[Elkaid]

Hi !

I was navigating across a member's website and found this interesting preamp :

http://ptsoundlab.free.fr/sectubes/p...tv6sn7line.htm

I would like to hear your comments about it. Should I bother building this one ? Which tube brand do you recommend ? My electronic parts supplier is able to provide me tubes for about 25$CAN each but he cannot tell me from which manufacturer they'll come from. This is of course inacceptable.

One final question : Would it be possible with some modifications to add output for headphones ? Schematics ?

Thanks for your help !

[PTSOUNDLAB]

Hello,

at this time, only Sovtek make very good 6SN7 (and for low price), I buy all my tubes in Germany www.tube-town.de (very good price and service, I recommend it, contact Dirk the boss of my share), the best shop for europeans.
For you it is certainly more easy to buy in USA http://store.yahoo.com/thetubestore/sovtek6sn7.html

Cordially.

Pascal.

[DougL]

Like everything else in life, the Circuit has its pluses and minuses.

Pluses:
6SN7 is a good sounding pre-amp tube.
The output Z is under 400 ohms
Power supply with CLCRC should be quiet
Tube rectifier will be quiet and slow turn on.
Very Conservative bias currents on tube sections
5 and 8 ma respectively. Tube life should be good.
DC filament supply.
Good Voltage swings of +-100v max.

Minuses.
Low Z in of about 100k may affect high frequency response at some pot settings.
Higher gain than I like in a line amp. About 24 db.
Bypassed cathode resistor adds unwanted gain and probably increases distortion.
Cathode followers do not have the best sonic reputation, especially at only 8 ma current.
For best sound, both tube sections should have about 15 ma current each. Running the grounded cathode at only 18% of its static dissipation and 25% of its current capability will increase distortion.
Will be very sensitive to parts quality.

IMHO, it should sound good.
Should you build one? That's for you to decide.
Will I build one. No. I think I could do better with the same tubes.

HTH

Doug

[Original Burnedfingers]

If you do a search you will find an excellent schematic for the 5692/6SN7 that Frank has done. I personally use this line stage and can attest to its sonic quality. I do recommend using VR tube regulation. I have had good luck with both the 6SN7 tubes and 5692 in this circuit.

I purchase both used 6SN7 tubes and 5692's off Ebay and have had excellent results. I am a firm believer in the sonic quality of the older tubes vers the current production. Just my .02

Joe

[Elkaid]

Thanks a lot !

I think I found Frank's preamp :
http://www.diyaudio.com/forums/showt...666#post235666
Is that right ?

However, I would like to use 5U4G rectifier in the Power Supply. Since I'm a completely noob in PSU (and audio gear) design, a little hand would be appreciated.

I tried to play a bit with Duncan'S PSUD II but I can't achieve nice results since I don't really know what I'm doing... Only trials and errors.

[Original Burnedfingers]

Looks like you found Frank's line stage all right. I'm not versed in using Duncans power supply progran so I can't help. There are others that are very well versed on the program that can help. A 5U4 will work but it seems kinda like overkill to me since the current required by this design is small. Personally I like the sound of a tube rectifier over the silicone rival. Once you get the power supply figured out you can rest easy knowing that this design is tried and true. With a good regulated supply it will easily surpass anything that you can buy in my opinion.


Joe

[fdegrove]

Hi,

I think I found Frank's preamp :

There actually is a mistake in that diagram, the value of the coupling cap between the two stages should be 0.33µF, not 0.033µF as stated.

Maybe this was corrected later on, I haven't checked.

However, I would like to use 5U4G rectifier in the Power Supply.

You can but as Joe says, it's a bit of a waste.

I'm not versed with PSUD either but it's not hard to build a basic PS as long as you have enough volts to start with...

Have you decided on the powerxformer yet or is that still open?

With a good regulated supply it will easily surpass anything that you can buy in my opinion.

No idea it was actually that good...Thanks, Joe.

What version did you actually build in the end?

Cheers,

[Original Burnedfingers]

Hi Frank

Actually I started out with a VR90 and VR150 for each channel and liked that. I ended up with a second version that included a regulated supply that you designed. Unfortunately I cannot find the link to it or I would post it.

Like I said earlier and I believe others have also mentioned a lot is to be gained sonically by a well designed power supply. I could be wrong but I seem to favor a larger transformer capable of higher voltage and amp rating.

I have build a number of line stages since I joined this group. I have build several 6sn7 designs as well as 5687's and 12B4's, #27's, #37's, and a humming #26. If i had to choose a favorite it would be between the 12B4 and the 6SN7/5692. The #26 holds promise but I seem to be lacking patience.

Sorry about rambling on...

Joe

[fdegrove]

Hi Joe,

Unfortunately I cannot find the link to it or I would post it.

I suppose this is the one you mean?

250VDC REG.

I could be wrong but I seem to favor a larger transformer capable of higher voltage and amp rating.

So do I in general...A well designed powerxformer is very important to me.

The #26 holds promise but I seem to be lacking patience.

It seems to rank among the favourites for linestage duties.
Triode Dick at http://www.vt52.com/ has even build a little gallery around it.
Look under Tubeinfo, UX226 gallery.

BTW, did you know that the 12B4A is a direct descendent of the 2A3?
That a trioded 6BQ5 is almost the same as a 12B4A (curveswise)?
That one of my favourite mini amps is the VTL 15/15 AKA Tiny Tott which uses 6BQ5s in triode mode?

Tubes are fun, aren't they?

Cheers,

[Elkaid]

Hi !

First of all, thank you for your comments !

Have you decided on the powerxformer yet or is that still open?

Everything concerning the PSU is still open as long as the parts are easily obtainable and not too expensive (i.e. Hammond)

I'm completely convinced about the preamp but the PSU is still giving me headache. I would really use the 5u4g for two reasons : I have some on hand and they're sooo nice. Even if it means an additional 3A 5V tranny.

Since I know next to nothing about PSU design, your experience would be greatly appreciated !

Have a nice day !