High gain noise.

[tonequester]

Greetings.

For once I have a short post. What are the usual culprits for causing excess noise on the high gain channel, when the clean channel is extremely quiet. I have this situation on my VHT Special 6 Ultra. I don't want much high gain caused distortion in the pre-amp, but DO want to have enough gain to overdrive the output tube. Any and all opinions are quite welcome !.................tonequester.

[VacuumVoodoo]

Gain=Noise. Can't break this law of physics. The guilty party in any amplifying system is always 1st gain stage having too low signal/noise ratio or too low gain and too high noise floor.
The rule is to design the very first gain stage with as high gain as possible and as low noise floor as possible. At the same time this gain stage should set the bandwidth limits for the system.
Paralleling gain elements i.e. triodes lowers noise, connecting 2 triodes in parallel for input stage and setiing them up for highest gain will result in lower noise floor than a single triode offers.

[xtian]

Practical advice is, try different tubes in V1 to find lower noise alternatives. Including lower gain tubes like 12AY7, 12AT7.

[tonequester]

Greetings VacuumVoodoo.

Thanks for the reply, and the good explanation. I think that I had mentioned that my tube vendor's tech recommended a 12AY7 in V1, but it made no difference. I spoke with him again concerning exactly what you recommended : low noise tube in V1. He recommended a couple of tubes for low noise, but he asked me to first try the 12AY7(Electro-Harmonix gold) in V2. I thought he was nutz, but I gave it a try. I can't yet believe it, but it nearly got rid of all high gain noise. The only problem is that i am still not getting output tube(6V6GT) overdrive/clipping. Since V2B is the driver for the 6V6GT(V3), I fear that there is not enough gain to overdrive V3.
I have to say that I don't understand why there is so much difference between running the 12AY7 in V1, and running it in V2. On top of the tube recommendations made by my vendor's tech, VHT finally emailed me, and informed me of "a little secret". They designed the amp so that one could use 12DW7's in either position(V1 and V2) !
It's starting to look like I am going into the tube collection business, or should I say hobby ? anyway, with the new developements, I would appreciate your thoughts on all of this, IF you find time.

Very Best of Regards VacuumVoodoo. Much Thanks.

[Leo_Gnardo]

use 12DW7's in either position(V1 and V2)

12DW7 AKA 7247 now made by JJ and called ECC 832, reasonably priced under $20.

[tonequester]

Thanks Leo_Gnardo.

I appreciate the info on the 12dw7. I'm going to order one, along with a 12at7, hopefully low noise versions, and see which works better. I'll post the results.

I really appreciate your time in posting. tonequester